View Full Version : Introduction To Loop Quantum Gravity
INTRODUCTION TO LOOP QUANTUM GRAVITY, everything you ever wanted to know...
In Loop Quantum Gravity, also referred to as LQG, the attempt is made to introduce the concept of quantum gravity. This is the unification of the General Theory of Relativity and the Quantummechanics. It is a very well established fact that gravitation and quantummechanics both have totally different foundations, which makes it very difficult to unify them at “first sight”. On the one hand position is uncertain in QM due to the Heisenberg-principle, while this is never the case in GTR. On the other hand, there is no metrical connection between space and time in QM, similar to the space-time-continuum of GTR. This leads to the fact that there is no curvature of space nor time in QM
In order to quantize the GTR we need gauge-fields, curved on a manifold just like in GTR. These gauge fields then need to be quantized just like other fermionic fields are quantized in QFT. When following this procedure, one needs to obey the following two laws at any point and time :
1) diffeomorfism invariance (this is the general covariance of GTR)
2) gauge invariance (like in QFT, invariance of gauge fields under local symmetries)
Basically these two laws ensure us that we have background independence so that we can choose any metric we want in order to describe the manifold. The different possible frames on that manifold must yield the same physical equations at any point on the manifold, that is the covariance (just like in GTR). These diffeomorfisms from one possible metric to another make sure that the physical laws remain the same when metrics are interchanged.
More specifically one needs to describe a manifold. Great mathematicians like Gauss and Riemann have taught us that this is done by the socalled connections. A metric describing a manifold is the most familiar example of a connection, i.e. the socalled metrical connection. There are other options though, like in GTR the connections are not metric-functions but they are gauge fields.
Next question is, how do we study some manifold ? What system can be followed in order to describe how objects behave on some chosen manifold ?
Well, we want background independence, so we must be able to chose any metric or connection we want in order to describe our manifold we are working on. In the early stages of LQG all possible metrics were used in order to implement this concept of back-ground-independence. A certain physical state was then represented as a probability-density containing all these metrics. This way of working was not very practical and in the mid-eighties it was even replaced by a description based upon the set of connections instead of all possible metrics.
Now, how does a connection work ? Well suppose you are on the manifold at a certain point A. Then you want to move in some direction on the manifold along a loop to that starts in A and comes back to A, like a circle. In order to describe this transition in mathematics, one uses the concept of parallel transport of tangent vectors. In order to be able to talk about such things as vectors, we need a reference frame that we can choose as we please because of the two laws mentioned above. Take a frame in A then make a very little step along the loop and look how this chosen frame has changed its position during the movement. Then complete the same procedure until you get back in A after completing the loop. Ofcourse it is not useful to look at the movement of the frame at every intermediate step along the loop. Actually one can integrate out the evolution of the frame over the entire trajectory that is followed from A to A.
When we start in A we actually take a tangent vector. This is an element of the tangent space of the manifold at point A. The transformation that is used to go from a point A on the manifold to the tangential space is called a projection. This tangent space can be turned into a socalled the Lie-Algebra, containing vectors written in terms of differentials, and provides the description for the movement from A to A along the loop. Now the operations that can be executed on the elements of a Lie-Algebra, like the identity or rotations, can be found in the Lie-Group.
As stated in the above paragraph it will be the intention to map elements from the Lie-Algebra to the Lie-Group. To be more specific : suppose we look at some vectors from the Lie-Algebra at A and we parallel transport them along the loop back to A. Now, we see for example that these vectors have rotated 45 degrees during their transport. This 45-degree-rotation is an element from the Lie-Group and the map between these two concepts gives us some idea on how vectors behave when replaced along some chosen loop on the manifold. Thus, yielding in a system to describe the manifold itself. It is proven that if you exponentiate Lie-Algebra-elements, you get the Lie-Group-elements.
More specifically, we take the frame around some loop and integrate all the differential motions of this frame during it’s transport. It is this integral that is exponentiated in order to get the corresponding group-element. In the Lie-Algebra, the group-element has a certain representation like a matrix. It is the trace if this matrix that is considered because the trace is a scalar and it will be the same for all reference frames. The map between the Lie-Algebra element and the Lie-Group element is called a Wilson Loop. Basically it “tries to feel” the metric by parallel transporting a Lie-Algebra element along a loop and “measuring” how this element changes it’s position with respect to the original position, after the loop is completed. Thus yielding a Lie-Group element.
The reason why we can ultimately speak about integrations and so on, is because initially everything is considered to be very very small. We work in terms of differential motions, which add up into the total motion between A and A. We use the Algebra’s in order to talk in terms of differentials d. As we move the frame along some "d(loop)" it experiences some "d(rotation)."
Now, once we have established such a relation, we can calculate the total movement by exponentiating the two differentials of the Lie-Algebra. The d(loop) ofcourse yields a transformation that describes the trajectory of the loop, while the d(rotation) yields the total rotation that has been undergone by the transported vector.
The main consequence of Loop Quantum Gravity is the fact that our space-time-continuum is no longer infinitely divisible. In LQG space has a “granular” structure that represents the fact that space is divided into elementary space-quanta of which the dimensions can be measured in LQG. The main problem of QFT is the fact that it relies on the existence of some physical background. As stated one of the main postulates of LQG is the fact that we need background independence. The diffeomorfisms give us the possibility to go from one metric to another and the physical laws must remain the same. Basically some physical state in LQG is a superposition over all possible backgrounds or in other words a physical state is a wavefunction over all geometries.
In String Theory, the main “competitor” when it comes to quantumgravity starts from the fact that there must be some kind of fictitious background space, thus actually undoing the aspects of general relativity. All calculations can then be made with respect to this background field and in the end the background independence must “somehow” be recovered. LQG starts from a totally different approach, though. We start from the knowledge we have from General Relativity, thus no background field, and we then try to rewrite the entire Quantum Field Theory in a certain way that no background-field is needed.
How to implement this nice background-independence in QFT has already shortly been introduced, i.e. The Wilson Loop and more generally the spin networks :
The map between the Lie-Algebra element and the Lie-Group element is called a Wilson Loop. Basically it “tries to feel” the metric by parallel transporting a Lie-Algebra element along a loop and “measuring” how this element changes it’s position with respect to the original position, after the loop is completed. Thus yielding a Lie-Group element.
The strategy is as follows : in stead of working with one specific metric like in “ordinary” QFT, just sum up over all possible metrics. So QFT should be redefined into somekind of pathintegral over all possible geometries. A wavefunction is then expressed in terms of all these geometries and one can calculate the probability of one specific metric over another. This special LQG-adapted wavefunction must obey the Wheeler-DeWitt equation, which can be viewed at as some kind of Schrödinger-equation for the gravitational field. So just like the dynamics of the EM-field is described by the Maxwell-equations, they dynamics of the gravitational-field are dedeterminedy the above mentioned equation. Now how can we describe the motion of some object or particle in this gravitational field. Or in other words, knowing the Maxwell equations, what will be the variant of the Lorentz-force ???
This is where the loops come in. First questions one must ask is :
Why exactly them loops ?
Well, let’s steal some ideas from particle physics... In QFT we have fermionic matter-fields and bosonic force-fields. The quanta of these force-fields or the socalled force-carrier-particles that mediate forces between matter-particles. Sometimes force-carriers can also interact with eachother, like strong-force-mediating gluons for example. These force carriers also have wavelike properties and in this view they are looked as excitations of the bosonic-forcefields. For example some line in a field can start to vibrate (think of a guitar-string) and in QFT one then says that this vibration is a particle. This may sound strange but what is really meant is that the vibration has the properties of some particle with energy, speed, and so on, corresponding to that of the vibration. These lines are also known as Faraday’s lines of force. Photons are "generated" this way in QFT, where they are excitations of the EM-field. Normally these lines go from one matter-particle to another and in the absence of particles or charges they form closed lines, aka loops. Loop Quantum Gravity is the mathematical description of quantum gravity in terms of loops on a manifold. We have already shown how we can work with loops on a manifold and still be assured of background-independence and gauge-invariance for QFT. So we want to quantize the gravitational field by expressing it in terms of loops. These loops are quantum excitations of the Faraday-lines that live in the field and who represent the gravitational force. Gravitons or closed loops that arise as low-energy-excitations of the gravitational field and these particles mediate the gravitational force between objects.
It is important to realize that these loops do not live on some space-time-continuum, they are space-time !!! The loops arise as excitations of the gravitational field, which on itself constitutes “space”. Now the problem is how to incorporate the concept of space or to put it more accurately : “how do we define all these different geometries in order to be able to work with a wave function ?”
The Wheeler-DeWitt equation has solutions describing excitations of the gravitational field in terms of loops. A great step was taken when Abhay Ashtekar rewrote the General Theory of Relativity in a similar form as the Yang-Mills-Theory of QFT. The main gauge-field was not the gravitational field. No, the gravitational field was replaced by the socalled connection-field that will then be used to work with different metrics. In this model space must be regarded as some kind of fabric weaved together by loops. This fabric contains finite small space-parts that reflect the quantization of space. It is easy to see that there are no infinite small space regions, thus no space-continuum. Quantummechanics teaches us that in order to look at very small distance-scales, an very big amount of energy is needed. But since we also work in General Relativity we must take into account the fact that great amounts of energy concentrated at a very small scale gives rise to black holes that make the space-region disappear. By making the Schwardzschildradius equal to the Comptonradius we can get a number expressing the minimum size of such a space-region. The result is a number that is in the order of the Planck Length.
Now how is space constructed in LQG ? Well, the above mentioned minimal space-regions are denoted by spheres called the nodes. Nodes are connected to eachother by lines called the links.
By quantizing a physical theory, operators that calculate physical quantities will acquire a certain set of possible outcomes or values. It can be proven that in our case the area of the surface between two nodes is quantized and the corresponding quantumnumbers can be denoted along a link. These surfaces I am referring are drawn as purple triangles. In this way a three-dimensional space can be constructed.
One can also assign a quantumnumber which each node, that corresponds to the volume of the grain. Finally, a physical state is now represented as a superposition of such spin-networks.
regards
marlon, thanks to marcus for the necessary information and corrections of this text
REFERENCE : maestro Carlo Rovelli “Loop Quantum Gravity”
Physics World, November 2003
marlon,
congratulations on a great sticky thread!
though you are the primary author, I'm assuming it is OK
for others to contribute. So I would like to bring in some
bibliography----some more links to online reading, besides
the Rovelli article that you already have
I believe you plan on continuing your essay, when studies permit,
and hope that others' contributions don't interfere with
your writing future chapters.
best regards,
====
hi, I just saw your next message #3 that you posted. I will reply here to save space. That is a good point about keeping the level Introductory.
I will keep that in mind and concentrate on adding just a small amount of bibliography (unless you get around to it before I do) which is the
more accessible sort. Actually that makes sense for several reasons including the fact that more technical articles can have a shorter shelf life!
the technical methods can get old and be replaced while the basic intuitions
stay useful longer. hope your mainstream QFT studies are going well.
BTW this sticky is really nice to have. thanks again!
Marcus, thanks for the reply...
It can only be a good thing that others contribute but i am convinced that we need to keep the level basic enough in this sense that i wanna move up the "difficulty-scale" gradually. It would be a bad thing if we were to discuss high-level papers because i think most of us (including myself) will not be able to follow this up and we would get discouraged and drop the subject. I will continue this matter and i would suggest that we follow the content of Rovelli's book which is online at his website.You have given the reference to it...
regards
marlon
I will continue this matter and i would suggest that we follow the content of Rovelli's book which is online at his website.You have given the reference to it...
regards
marlon
I am very much looking forward to your continuing the essay, marlon!
I will restrain my tendency to talk too much, so as not to crowd.
BTW just yesterday in the mail was delivered the copy of Rovelli "Quantum Gravity" which I ordered from Amazon. I am very happy with the book and
have been reading it instead of being at computer.
I am only sad that it is so expensive----70 dollars. You have to be rich, or be willing to splurge. Or you have to be in graduate school and need it for a class, as textbook. In US the textbooks are all very expensive, so 70 dollars is fairly normal.
Anyway Rovelli is a good writer and Cambridge Press did a good job, with the editing and just the physical production----nice paper, nice binding, nice feel, and printing. So it is a pleasure to own: at least for me.
But to save money it certainly makes sense to print off the free draft copy at Rovelli site. Even just the first 3 or 4 chapters and some appendices---or whatever you find the most accessible parts and most relevant for you.
Marlon, why not give some online bibliography yourself? It would be a refreshing change (I am always doing the librarian work) and I would enjoy seeing your picks and how you organize it. (If you do not want to, I will not shirk the job, but maybe you would like to list intro-level links?)
yesterday in the mail was delivered the copy of Rovelli "Quantum Gravity"
I sincerely hope you enjoy your new book, which I know you will. I was leafing through it at the U of T bookstore. I want to point out two things carlo says in the introductory bit.
1) That any correct quantum gravity theory must be able to calculate amplitudes for graviton-graviton scattering, and that he hopes that lqg will one day lead to a theory that can.
2) That he knows that GR must almost certainly be an effective field theory that is modified at higher energies so that lqg can't be correct. Thus he says he views lqg basically as a laboratory for investigating certain fundamental issues in quantum gravity.
As far as your sticky goes, would you be bothered if I corrected it?
... I want to point out two things carlo says in the introductory bit.
1) That any correct quantum gravity theory must be able to calculate amplitudes for graviton-graviton scattering, and that he hopes that lqg will one day lead to a theory that can.
2) That he knows that GR must almost certainly be an effective field theory that is modified at higher energies so that lqg can't be correct. Thus he says he views lqg basically as a laboratory for investigating certain fundamental issues in quantum gravity.
...
I believe you are mistaken, jeff. Carlo does not say these things in the introductory bit.
At least I looked in the first part of the book, and used the index to search the rest, and could not find any statements of the kind.
It would be nice to have some page references, if you have any more would-be paraphrases from Rovelli----even sweller of you to provide actual quotes. Since a paraphrase can often mislead as to what was said in the original.
Thanks for your kind wish as to the book! Indeed it is surprising me. I was not expecting this much, since I had read much of the last year's draft version.
BTW if you pick up a copy either at library or store and can give me some actual page reference (whether or not in the first 50-or-so pages, anywhere in the book will do) where he says these things 1. and 2. that you state, that would be most helpful of you and I will be very interested to read the actual passages and think about it. If he does say something like that my eye somehow missed it.
I believe you are mistaken, jeff. Carlo does not say these things in the introductory bit.
We'll, I don't have the book on hand, but...
In rovelli's dec 30 2003 draft, he says on page ix entitled "PREFACE"
"What we need is not just a technique for computing, say, graviton-graviton scattering amplitudes (although we certainly want to be able to do so, eventually)"
On page 5 of the same draft,
"The einstein-hilbert action might very well be a low energy approximation of something else. But the modification of the notions of space and time has to do with the diffeomorphism invariance and the background independence of the action, not with it's specific form."
Be this as it may, jim bjorken in the forward of carlo's book states quite plainly that effective field theory has taught us that GR must be viewed as just an effective field theory, and it's difficult to believe that carlo would've allowed such a statement if it fundamentally contradicted his position.
Btw, did you notice that carlo writes (probably in the preface) that thiemann is publishing a book on the more mathematical aspects of lqg?
Oh I see.
I thought you were talking about the actual book. that you said you were browsing in the bookstore.
but you apparently meant the draft, from 2003, which is available online.
there's been considerable up-dating and revision. so one should be specific which
=============
Meanwhile, maybe readers of this thread would be interested in the Loop and String lineup of talks at the conference that just finished in Mexico (at the Quintana Roo beach resort in sight of the island of Cozumel)
A lot of the lectures were by top people both string and loop, and they were rather much introductory. The conference aimed at being a "school" to bring more people in. And to introduce stringies to loop research and viceversa.
I thought the lineup of who the organizers wanted to talk about the various hot topics was enlightening. So since it could be instructive, I will copy it here:
http://www.nuclecu.unam.mx/~gravit/EscuelaVI/courses.html
--quote--
COURSES AND INVITED TALKS
Courses:
A. Ashtekar (PSU, USA): Quantum Geometry
A. P. Balachandran (Syracuse, USA): Quantum Physics with Time-Space Noncommutativity
P. T. Chrusciel (Tours, France): Selected Problems in Classical Gravity
R. Kallosh (Stanford, USA): De Sitter Vacua in String Theory and the String Landscape
A. Peet (Toronto, Canada): Black Holes in String Theory
C. Rovelli (Marseille, France): Loop Quantum Gravity and Spinfoams
Plenary talks:
J. D. Barrow (Cambridge, UK): Cosmological Constants and Variations
M. Bojowald (AEI, Germany): Loop Quantum Cosmology
A. Corichi (ICN-UNAM, Mexico): Black Holes and Quantum Gravity
A. Linde (Stanford, USA): Inflation and String Theory
O. Obregon (U. Guanajuato, Mexico): Noncommutativity in Gravity, Topological Gravity and Cosmology
A. Perez (PSU, USA): Selected Topics on Spin Foams
L. Smolin (PITP, Canada): Loops and Strings
R. Wald (U. Chicago, USA): Topics on Quantum Field Theory
Short talks:
E. Caceres (CINVESTAV, Mexico): Wrapped D-branes and confining gauge theories
A. Guijosa (ICN-UNAM, Mexico): Far-from-Extremal Black Holes from Branes and Antibranes
H. Morales (UAM, Mexico): Semiclassical Aspects and Phenomenology of Loop Quantum Gravity
D. Sudarsky (ICN-UNAM, Mexico): Spacetime Granularity and Lorentz Invariance
L. Urrutia (ICN-UNAM, Mexico): Synchrotron Radiation in Lorentz-Violating Effective Electrodynamics
---endquote---
matthias
Nov29-04, 02:53 PM
marlon...got any extra info on LQG???
great introduction btw...
lola
Oh I see.
I thought you were talking about the actual book. that you said you were browsing in the bookstore.
but you apparently meant the draft, from 2003, which is available online.
there's been considerable up-dating and revision. so one should be specific which
You want to play games? Fine with me.
nightcleaner
Nov29-04, 08:17 PM
This is a project I've been working on, and I'd very much like to know what the participants on this thread think. Thanks, nc
Abstract and prospectus, Spacetime at the Planck Scale
This is an abstract and prospectus for additional research. The proposal would use computational techniques such as those described in Stephen Wolfram's New Kind of Science as an exploratory probe of events at the Planck scale. Authors are currently recruiting mathematicians and physicists to mentor and contribute to the work. We still need someone who can design the NKS experiments.
In this work in progress, we describe a mechanism by which four space-time dimensions are reduced to the classical view of three space-like dimensions arrayed in the customary orthagonal basis with one time-like dimension which can be thought of as permeating the space-like dimensions. The time-like dimension is shown to appear to be unique to a moving observer, and preserves the appearance of freedom of choice as one perspective in a structure which can also be viewed from other perspectives as competely deterministic.
The Einstein-Minkowski principle of space time equivalence taken in the strongest sense creates a powerful model for investigation of the relationship between general relitivity and quantum mechanics. We begin by defining the Planck Sphere (here named to be consistant with the Planck length and Planck time) as a three dimensional volume filled by a radient event at the speed of light in one Planck time. Thus the radius of the Planck Sphere is equal to one Planck length and is equal to one Planck time, making a three dimensional model which can be used in a perspective sense to portray events which occur at the Planck scale in four dimensions.
After describing the features of the model, we go on to propose that computational graphing techniques similar to those used by Stephan Wolfram in his book A New Kind Of Science be developed to explore the evolution of the Planck Sphere in Kepler dense packed space up to the scale of the fine structure constant, thereby showing the geometric origins of mass and charge. The first step in this process is to define a viable space-time lattice structure, which we believe we have done by defining the Planck Sphere as an element in a Kepler stack. The next step in this process is to develop a rational algorithem to simulate events on the Planck scale. This may be accomplished by applying what we know of cosmogeny and of physics near singularities. As a first approximation we advance the conjecture that expansion from the Planck scale will recapitulate cosmogeny. We carry through the first steps in this approximation to demonstrate a mechanism for early inflation in the burgeoning universe.
References:
[PDF] On quantum nature of black hole space-time: A Possible new source of intense radiation DV Ahluwalia - View as HTML - Cited by 11 ... spheres of fluctua- tions. The one that may be called a Schwarzschild sphere, and the other a Planck sphere. The sizes of these ... International Journal of Modern Physics D, 1999 - arxiv.org - ejournals.wspc.com.sg - arxiv.org - adsabs.harvard.edu
[PDF] The Quantum structure of space-time at the Planck scale and quantum fields S Doplicher, K Fredenhagen, JE Roberts, CM Phys - View as HTML - Cited by 242... In the classical limit where the Planck length goes to zero, our Quantum spacetime ...components are homeomorphic to the tangent bundle TS 2 of the 2–sphere. ... Communications in Mathematical Physics, 1995 - arxiv.org - arxiv.org - adsabs.harvard.edu
[PDF] Inflationary theory and alternative cosmology L Kofman, A Linde, V Mukhanov - Cited by 9 ... the large scale structure observed today were generated at an epoch when the energy
density of the hot universe was 10 95 times greater than the Planck density ... The Journal of High Energy Physics (JHEP) - iop.org - arxiv.org - physik.tu-muenchen.de - adsabs.harvard.edu - all 7 versions »
[PDF] Physics, Cosmology and the New Creationism VJ Stenger - View as HTML ... 10. -43 second time interval around t. = 0, if it was confined within a Planck sphere as big bang cosmology implies. The. universe ... colorado.edu
200411290100GTC
Richard T. Harbaugh
Program Director
Society for the Investigation of Prescience
luco_jash
Dec1-04, 06:00 PM
Hello Marlon
i will thank you for the nice clear introduction on loop quantum gravity. I am planning to do my thesis on this subject and i would like to keep in touch with all the specialists here in order to get more info. I am just starting to know this field...
bye...Luco
Rothiemurchus
Dec8-04, 12:29 PM
The challenge for string theorists and LQG theorists is to explain why the vacuum energy exists at 10^120 J/m^3 ( there is no reason to think there is anything wrong with the QM calculation) but does not curve space-time.How can
quantum gravity be proved if gravity is not understood on its own yet?
( there is no reason to think there is anything wrong with the QM calculation)
!
:bugeye:
gotta be something wrong with it
explain why the vacuum energy exists at 10^120 J/m^3 ...
beg your pardon Rothie but that is a crazy amount of energy
maybe QFT can come up with a mechanism that cancels all or most of it out, or find some reason to say that it doesnt really exist----maybe QFT already has.
but that density of energy, not canceled out and real enough to cause gravity, is simply incredible (at least to me). commonsense persuades me that there must be something wrong with any theory that predicts it
And there is some reason to be hopeful, because QFT is still formulated in an unrealistic way: using a fixed spacetime framework. Reformulating it in a background independent version might possibly get rid of that huge vacuum energy.
BTW just to have a basis for comparision, the astronomers' dark energy estimate is currently around 0.6 joule per cubic km. In joules per cubic meter (the units you were using) that comes to:
0.6 x 10-9 joule per cubic meter.
Rothiemurchus
Dec8-04, 02:41 PM
I am aware of the cosmological evidence.But the problem is this:
the energy that can be experimentally associated with the Casimir force
is greater than the cosmological observation (10^-6 Newtons/m^2 net force
at 10^-7 m plate separation - i think but i'm not sure,that this is at
least 10-7 J/m^3).So, the plates involved in
measurements of the Casimir force must somehow, switch on vacuum energy,locally.And what sort of effect would a galaxy have on the vacuum energy?
I am aware of the cosmological evidence.But the problem is this:
the energy that can be experimentally associated with the Casimir force
...
Rothie, I will try to respond---tell me if I am making a mistake. I do not believe that the experimental existence of the Cas. force proves that the
QFT calculation of a huge vacuum energy is correct.
what I think is true is that there is some normal vacuum energy density and that between two conducting plates it is LESS namely
\text{energy density betw. plates = usual vacuum energy density} -\frac{\hbar c \pi^2}{720 d^4}
the QFT calculation of the usual vacuum energy density is bad or dubious, but the Casimir effect does not depend on this, it depends on the fact that the energy density between plates is LESS by the amount shown, which QFT does calculate successfully!, and which depends on the inverse fourth power of the separation distance.
So I say that I believe the QFT calculation of the Casimir effect and I like the Casimir effect, and this is consistent with not believing the huge vacuum energy which QFT calculates, which is roughly 120 OOM wrong---or actually different people try to fix it different ways and say different things, but anyway wrong.
\text{energy density betw. plates = usual vacuum energy density} -\frac{\hbar c \pi^2}{720 d^4}
If I calculate right, this is what the energy density has to be in order that the force turn out
what one usually sees for the Casimir effect
\text{force divided by area} = -\frac{\hbar c \pi^2}{240 d^4}
http://www.physicsforums.com/journal.php?s=&journalid=13790&action=view#DUALITY%20:%20STRING%20THEORY%20PART%2 03
check out my journal if you are interested in an introductory text on string theory and dualities
regards
marlon, let me know your comments
http://www.physicsforums.com/journal.php?s=&journalid=13790&action=view
Check out my journal. I posted a link to the paper that John Baez will be using for his speech on monday on LQG...very nice introduction...
regards
marlon
http://www.physicsforums.com/journal.php?s=&journalid=13790&action=view
Check out my journal. I posted a link to the paper that John Baez will be using for his speech on monday on LQG...very nice introduction...
regards
marlon
marlon thanks for the link!
your journal has become a real trove of information!
I liked the Tensors-made-easy,
and the interesting historical bits
http://math.ucr.edu/home/baez/acm/
http://math.ucr.edu/home/baez/acm/acm.pdf
the paper Marlon referred to is Baez 24January 2005 talk to the ACM symposium on discrete algorithms, essentially introducing spinfoam research to Computer Science people.
However the talk is titled "Loop Quantum Gravity"
this points out an everpresent knotty semantics problem: LQG is used in two senses
A. Restricted sense of LQG proper (program set out in early 1990s) which does not include spinfoams approach and some other allied developments
B. Inclusive sense to mean Loop-and-allied QG approaches, in which case spinfoams is included.
These are mostly approaches which have grown out of the LQG of the 1990s.
I dont know the statistics but I believe that most LQG people actually do their work in spinfoam-related areas: the thrust of the research is towards a path-integral treatment of spacetime geometry.
(path-integral didnt figure in the original LQG program of the early 1990s AFAIK but it obviously is a major part of things now)
Judging from his talk Baez believes in including spinfoams under the LQG rubric because in his talk to the ComputerScience people he titled it LQG and gave an 11 page thumbnail of LQG proper
and then on page 12, without even saying what he was doing, he shifted to talking about the Barrett-Crane (spinfoam) model and related computing problems!
Baez helped initiate the spinfoam approach and invented the term, so if he wants to include it under the LQG heading then I guess he has the right to.
By contrast, Hermann Nicolai had a sad case of talking at cross-purposes recently where he wrote this review paper about LQG (an outsider's view) and didnt even mention what most of the LQG people have been doing for 5 or 10 years! He didnt discuss spinfoams at all!
He took LQG in the narrow (circa 1995) sense and went thru the motions of reviewing it. Didnt even discuss Thomas Thiemann masterconstraint, which is the closest thing to directline development from 1995 strict interpretation LQG. Didnt discuss Loop Cosmology either. So his review looks kind of vacuous: a review of no one's current research.
Somehow we have to get the general classifications straight so that we include in our picture of LQG not just the LQG of 5 or 10 years ago but what LQG people actually do i.e. the models of spacetime and gravity that they actually investigate.
What I'm thinking about is our ADDING ON to this thread whatever it takes to make it more of an introduction to the general field of LQG (including allied approaches that have grown out of the LQG of the past)
Probably the key paper that one wants to prepare to understand is one the authors say they are working on but has not appeared yet!!! here is a chance to use various embarrassment smilies :blushing: :redface: :grumpy:
that's right it hasnt appeared yet.
Laurent Freidel and Artem Starodubtsev
Perturbative Gravity Via Spin Foam
this was cited in their January 2005 preprint
http://arxiv.org/hep-th/0501191
I want to better understand where the spinfoam approach comes from and how it fits together with the original or basic LQG approach. Sometimes it helps to go back to the beginnings of a research line which in this case is not only Baez papers but also this (which does not even use the term "spin foam":
http://arxiv.org/gr-qc/9612035
"Sum over Surfaces'' form of Loop Quantum Gravity
Michael P Reisenberger, Carlo Rovelli
Phys.Rev. D56 (1997) 3490-3508
"We derive a spacetime formulation of quantum general relativity from (hamiltonian) loop quantum gravity. In particular, we study the quantum propagator that evolves the 3-geometry in proper time. We show that the perturbation expansion of this operator is finite and computable order by order. By giving a graphical representation á la Feynman of this expansion, we find that the theory can be expressed as a sum over topologically inequivalent (branched, colored) 2d surfaces in 4d. The contribution of one surface to the sum is given by the product of one factor per branching point of the surface. Therefore branching points play the role of elementary vertices of the theory. Their value is determined by the matrix elements of the hamiltonian constraint, which are known. The formulation we obtain can be viewed as a continuum version of Reisenberger's simplicial quantum gravity. Also, it has the same structure as the Ooguri-Crane-Yetter 4d topological field theory, with a few key differences that illuminate the relation between quantum gravity and TQFT. Finally, we suggests that certain new terms should be added to the hamiltonian constraint in order to implement a "crossing'' symmetry related to 4d diffeomorphism invariance."
that says what spinfoam later came to mean: a branched colored surface in 4D, or an equivalence class of such.
In Baez talk to the ACM symposium which Marlon just flagged a couple of posts back he concludes:
"Moral for physicists: In a regime where analytical methods don’t work well (yet), we need computer simulations to test our models.
Moral for computer scientists: In loop quantum gravity, the geometry of space is built from qubits. Spacetime is like a parallel-processing quantum computer that constantly modifies its own topology. "
he is definitely talking about spinfoams here, and indeed has just been discussing his own and others' computer simulations of spinfoam models (Barrett-Crane in particular IIRC). the dynamics of a spinfoam is step by step modification of topology and there are amplitudes of each kind of "move"----to put it crudely and imprecisely, moves like inserting a vertex, removing a vertex, replacing one sort of edge by another, disconnecting things and reconnecting them differently, bit by bit. Maybe we could say it portrays space as a sort of glittering blur of never-certain and ever-shifting relationships.
anyway the point is that each elementary change or move, in the path that is a spinfoam, can have an amplitude number calculated for it.
the researchers want to integrate or average over lots and lots of paths (spinfoams are pathways that the geometry of space can take) from one shape of space to another. they need to calculate an amplitude for each, and sum.
I am going to try to get another piece of the jigsaw out of this February2005 paper of Freidel and Livine. For now I'll just get it out on the table.
http://arxiv.org/hep-th/0502106
"1 Introduction
Spin Foam models offer a rigorous framework implementing a path integral for quantum gravity [1]. They provide a definition of a quantum spacetime in purely algebraic and combinatorial terms and describe it as generalized two-dimensional Feynman diagrams with degrees of freedom propagating along surfaces. Since these models were introduced, the most pressing issue has been to understand their semi-classical limit, in order to check whether we effectively recover general relativity and quantum field theory as low energy regimes and in order to make physical and experimental predictions carrying a quantum gravity signature. A necessary ingredient of such an analysis is the inclusion of matter and particles in a setting which has been primarily constructed for pure gravity. On one hand, matter degrees of freedom allow to write physically relevant diffeomorphism invariant observables, which are needed to fully build and interpret the theory. On the other hand, ultimately, we would like to derive an effective theory describing the propagation of matter within a quantum geometry and extract quantum gravity corrections to scattering amplitudes and cross-sections..."
katelynndevere
Mar19-05, 07:19 PM
D'Oh! i just found your beautiful introduction, after I posted a thread asking if anyone had one. it's very close to being simple enough for me to understand it. I will persevere, dictionary at hand.....
D'Oh! i just found your beautiful introduction, after I posted a thread asking if anyone had one. it's very close to being simple enough for me to understand it. I will persevere, dictionary at hand.....
I think you must mean Marlon's introduction, which begins this thread. He will be very pleased that you are interested and finding it useful. For something that is very introductory, conceptual and non-math, I think a magazine article by Carlo Rovelli is pretty good. I will get a link or two.
Here is Rovelli's homepage:
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html
Here is the Rovelli magazine article:
http://cgpg.gravity.psu.edu/people/Ashtekar/articles/rovelli03.pdf
this is a general audience intro to LQG from Physics World November 2003 issue.
this link to Rovelli's article is actually at the website of Abhay Ashtekar at Penn State. Abhay has links to an interesting collection of other popular and semipopular articles, as well as to technical writings about LQG. Here is the main Ashtekar link
http://cgpg.gravity.psu.edu/people/Ashtekar/articles.html
and his home page
http://cgpg.gravity.psu.edu/people/Ashtekar/index.html
Ashtekar and Rovelli are two of the original pioneers of the LQG approach, so its worth checking out what they they think is a good introduction.
katelynndevere
Mar19-05, 08:28 PM
Thanks, Marcus!
The Rovelli article is superb; I can actually understand it! I really need to sort out my maths, though.
Thanks again,
Kate.
Tom McCurdy
Mar21-05, 10:33 PM
Yes kately marcus and marlon are the sources to go to for loopquantum questions and most other questions. I hope to get back to my studying of loop quantum gravity over the summer... I know I know.. I have been saying this for months but I am redesigning the site in my spare time to get ready for a relaunch....
omg... this is my 1,000 post... I have moved out of the triple digit range.
I hope to get back to my studying of loop quantum gravity over the summer... I know I know.. I have been saying this for months but
:rofl: :rofl: :rofl:
I can relate, really i can...i have not done any LQG related studies over the past months because i was too busy with applying and preparing for my phd...maybe in the future...
regards
marlon
ps : thanks for the nice complements, glad to see the intro to LQG is usefull
it isnt good to stay permanently with the naive, non-math story told of LQG in popular accounts, because it can lead to misconceptions.
the main reference cited in the first segment of this thread is a popular wide-audience presentation by Rovelli. It was published in "Physics World" November 2003 IIRC and it is very good for what it is: a non-math story. I have recommended it to beginners as a first exposure to LQG and it seems to work fine. But it is easy to get misled by popularizations and at some point you have to move on.
It came to my attention that there are seriously mistaken ideas going around that appear to come from the impressionistic verbal story (as told by Rovelli or Smolin or whoever) and need to be corrected, so it is probably time to start Part II of this introduction.
LQG is either used to refer to a specific definite approach to quantizing Gen Rel, or it is used to refer to a collection of allied approaches that many of the same people (the LQG people) work on.
there should be a recognized collective name like "Loop-and-allied Quantum Gravity", but there isnt yet. People just say LQG for the whole collection.
If we had a collective name for the field like "Loop-and-allied Quantum Gravity", then it would include LQG in the specialized restrictive sense and would also include spinfoam research and some related form-theories of gravity (modified topological field theories) and some allied path-integral approaches like dynamical triangulations. Although most of these approaches are what is called "nonperturbative" it would even include a recently initiated perturbative approach. In a growing field the terminology is necessarily loose and you cannot perfectly delineate things in advance.
BTW I am not an expert, i just watch QG, so I dont speak authoritatively. But I'm pretty sure of what I'm telling you. The field is dynamic and in flux.
It is a creative time in LQG.
So when there is a "LQG conference" people give papers on all these allied lines of research. Then LQG is used as a collective name to refer to a bunch of things. It is what "LQG people" do and it includes a lot of approaches to quantizing the theory of spacetime and its geometry----to quantizing Gen Rel. probabably some of these approaches are eventually going to change and converge and turn out to be connected or even equivalent. but we cant say which, in advance.
So keep in mind that sometimes LQG means a particular canonical nonperturbative approach to quantizing Gen Rel (an approach that Abhay Ashtekar, who helped invent it, likes to call "quantum geometry") and sometimes LQG means a bunch of related lines of investigation that LQG people are currently pursuing.
Rovelli's book Quantum Gravity (Cambridge 2004), also on-line 2003 draft free
Thiemann's Lecture Notes (Springer 2004?) also on-line free
Ashtekar Lewandowski Background Independent Quantum Gravity (2004) online
Rovelli's 1998 Living Reviews introduction online
Smolin 2004 Invitation to Loop Quantum Gravity online
The links to these things are in the surrogate sticky thread where we've been keeping LQG links. You can also get them with an arxiv search or google search using author's name. When time permits i will fetch them from the LQG links thread.
the diff manif is a key concept in mathematics and the main thing separating popular accounts from textbook level.
In Gen Rel, spacetime is represented by a geometry-less floppy limp shapeless thing called a differentiable manifold
this is sometimes called a "continuum"
it is basically a set with a collection of coordinate charts.
you have to realize that a diff-manif is harmless. the good thing about it is that it doesnt have any pre-committment to any particular geometry!
you can impose whatever geometry on a diff-manif by specifying a METRIC or distance function, that will then allow you to calculate areas and volumes and angles and define what corresponds to geodesics or "straight" lines.
the great thing about a diff-manif, before you choose a metric, is that it comes into the world without any preconceptions, innocent of bias in favor of this or that geometry.
Gen Rel has a version which uses a 3D differentiable manifold representing space. It does not always have to be constructed using a 4D diff-manif spacetime. But either way it is based on a limp diff-manif ON WHICH A METRIC IS LATER IMPOSED where the metric arises as a solution of the einstein equation.
you start out with a shapeless continuum and you set up some conditions (which can involve having some matter in the picture) and then you crank out what the geometry (as shown by the distance function) is going to be.
OK, now LQG is characterized by the fact that it tries to imitate Gen Rel very closely. So the first thing you get in textbook LQG is a shapeless differentiable manifold representing space.
This version of space is infinitely divisible and smooth and continuous like any differentiable manifold has to be. it is the same diff-manif model of space that you get in one of the versions of Gen Rel.
WHAT IS "QUANTUM" ABOUT LQG IS HOW YOU PUT THE GEOMETRY ON
the main feature of quantum mechanics is that it copes in an apparently realistic way with indeterminacy, uncertainty, the incomplete information that one system or observe has about another system.
in the real world everything depends, literally, on who is observing what.
and no who can ever know everything about any what.
it is not possible to have a realistic description of the world which fails to take this into account
"QUANTUM" IS NOT ABOUT DIVIDING SPACE UP INTO LITTLE BITS
quantum is not about dividing anything up into little bits
It can happen that discrete spectra come out of the mathematics, you quantize a system and you find that a certain measurement has a discrete range of possibilities, like the energy levels of a hydrogen atom
but this discreteness is a byproduct of what quantizing is really about, which is setting up a way to implement uncertainty and incomplete information-----call it fuzziness, call it probability.
the predominant mathematical machine that quantum theories use to hold the uncertainty and deal out the probabilities is called a hilbertspace
The possible states of a system are represented by the hilbertspace and measurements of the realworld system correspond to linear OPERATORS on the hilbertspace.
But if you dont know what a hilberspace is, or what operators on it are dont worry, someday some different language will be invented. What matters now is that
QUANTIZING A CLASSICAL THEORY IS NOT primarily about dividing some stuff into little bits. It is primarily about building a machine which can represent states of the system and measurements on the system but embodies uncertainty.
QUANTIZING GEN REL means to build a machine that can represent STATES OF GEOMETRY and MEASUREMENTS OF GEOMETRIC VARIABLES like area and volume and angle and so on, and which is also more realistic than classical Gen Rel because it implements the inherent uncertainties.
Gen Rel is an amazingly accurate theory of spacetime geometry whever it is applicable, where it doesnt break down and fail to compute.
Where it is applicable it predicts very fine differences in angles and times out to many decimal places. People have tried for decades to improve on it, or to test it and find it wrong out at the 6th decimal place. But they havent succeeded yet.
But Gen Rel famously has places where it blows up and predicts infinities, in other words it is flawed. It has singularities.
this has been the case with other classical theories and it has been found that if you can QUANTIZE a classical theory it will often extend the applicability and get rid of places where it breaks down.
So a big aim of quantizing Gen Rel is to get rid of the classical singularities. mainly the "bigbang" and "blackhole" singularities.
The main reason why LQG is so active these days is that it appears to have removed Gen Rel singularities. the main reason Martin Bojowald is a key LQG figure is that he has been in the forefront in this and has gathered a considerable group of people who are working on this.
the first break came in 2001 when MB removed the bigbang classical singularity in a certain case.
To get the history since then, just go to arxiv.org and get the list of all Bojowald papers since 2001. the people active in this field are the people who have co-authored papers with Bojowald, and you can click on their names and find all the papers they have published independently.
the blackhole singularity is being removed just now, starting at end 2004 and very much at the present. a bojo paper on that came out this month (March 2005)
When a classical singularity is removed then you can run the model THROUGH where it used to be. the machine no longer blows up or stalls at that point. So you can explore BEYOND the classical singularity and that is interesting. It is expected that one way to check LQG is to look for traces in the cosmic microwave background of what LQG predicts about the bigbang that is different from classical Gen Rel, different because of it having removed the singularity.
So that is a very important feature of LQG, the fact that it doesnt encounter these irritating singularities in Gen Rel that have bothered people so long.
If you want a non-math way to think about it, focus on the uncertainty of a quantum theory. For the universe or a black hole to collapse all the way to a point would just be too certain, wouldnt it? Too definite for real nature to allow :smile:. So it doesnt happen. At a certain indeterminate very high density there is a "bounce" according to the math (a time-evolution difference equation model) and contraction turns into expansion. And conditions for inflation are automatically generated.
recent papers
arxiv.org/gr-qc/0503020
Bojo
the early universe in Loop Quantum Cosmology
arxiv.org/gr-qc/0503041
Bojo, Goswami, Maartens, Singh
a black hole mass threshhold from non-singular quantum gravitational collapse
if you glance at these papers you will not see anything about thinking of space as divided up into little bits, or grains :smile:
because that is not what real LQG is about,
but you will get a taste of what is going on with the overcoming of the Gen Rel singularities at bigbang and blackhole.
We have to give an introduction to LQG that is reasonably faithful to the textbook version that researchers actually use----not just some possibly misleading verbal imagery. but it has to be understandable as an introduction.
that's hard. it will take several tries and the first ones will fail
It would be so great if people could just go and read a paper like
smolin "An Invitation to LQG" and have that suffice, but it somehow does not work. "Invitation" is too condensed for many people, or not explanatory enough.
Well I will try to get moving on this. I also want to keep those background points handy, from the previous 3 or 4 posts. So here, as a reminder, are the headings from post #31 onwards:
Introduction to LQG Part II
LQG can mean several things
There are textbook-level LQG sources
Textbook LQG is based on a differentiable manifold
QUANTUM" is a way of handling uncertainty and incomplete information realistically
Quantizing Gen Rel gets rid of singularities
selfAdjoint
Mar28-05, 03:41 PM
Can we get word definitions of some of the technical concepts? Nightcleaner's interest in BF theory suggests that we could show what the Ashtekar variables are, at some honest, non-confusing level. Then Wilson action, and why it takes values in the Lie Algebra of the group, for that matter how the group comes in (ation on the manifold, forget oll the bundle staff), and Circle functions and so on. I go up and down on this; I think it would be boring if it wasn't impossible, and then I think it's a duty to get this across to the bright, self-selected audiance we have here.
Differentiable manifold has 8 or 9 syllables and it is easier to say smooth set, which only has 2 syllables. And that is what one is. It is a set with a bunch of coordinate charts that work smoothly together.
Typically you cant get the whole set on one coordinate chart so you have several overlapping charts
that is like you cant get the whole earth on one square map, but you can plaster maps all over the earth so you have overlapping coverage.
On every patch of surface there is some map that is good at least on that local region.
the typical set used to represent space in LQG is the "3-sphere" where the surface of a balloon is a 2-sphere and you have to imagine going up one dimension. a local chart looks like regular 3-D graph paper or familiar euclidean 3-space
Only thing is we ignore the geometry you might have thought we had when I said 3-sphere. If we were thinking of the 2-sphere balloon as an analogy, the air is out of the balloon and it is crumpled up and thrown into your sock drawer. it has no shape. In the same way, by analogy, the 3-sphere has no shape. It is just a set of points, without a boundary, that has been equipped with an adequate bunch of coordinate maps
the "smooth" part is that whereever the charts overlap if you want to start on one map and find the corresponding point on the other map, and do a whole transference thing that remaps you from one to the other, well that
remapping (from one patch of 3-D graph paper to another) is smooth. that is to say differentiable, as in calculus, you can take the derivative as many times as you want. In other words the coordinate charts are COMPATIBLE with each other because whenever you remap between two that overlap you find you can DO CALCULUS at will on the function taking you from one to the other. this is an example of a technical condition that basically doesnt say very much except that we wont have nasty surprises when we get around to using the charts. The charts are smoothly compatible with each other.
The idea of a differentiable manifold was given us by George Riemann in 1854 when he was trying to get a job as lecturer at Göttingen and had to give a sample lecture, and it is actually SIMPLER than euclidean space because it does not have any geometry! Euclidean space has all kinds of rich structure immediately availabe, like you can say what a straight line is and you can measure the angle between two intersecting straight lines!
what we have here is a SHAPELESS SMOOTH SET and you cant do any of that. It has the absolute mininum of structure for something that can serve as a useful model of a CONTINUUM.
this is why it was a good idea of Riemann, because it is simpler and less structured than Euclidean space and so it is more able to adapt to the wonders of the universe. mathematics was changed very much in 1854.
George Riemann lived 1826 to 1866.
Here is his 1854 talk, in full:
http://www.ru.nl/w-en-s/gmfw/bronnen/riemann1.html
I think what he called a "stetige Mannigfaltigkeit" here in this talk we would call a smooth manifold. But thereafter the name "differenzierbare Mannigfaltigkeit" became prevalent and is what we call differentiable manifold.
selfAdjoint
Mar28-05, 04:27 PM
stetig Maniigfaltigkeit translates literally to continuous manyfoldedness. The manyfoldedness is the number of independent variables, which if you think of them geometrically, become dimensions. Our word manifold is the result of a long history of trying to express the idea of multiplicity of variables in English. The French of course say variete, with a grave accent I am too lazy to supply. Personally I like continuum, which did for Einstein, and which he compared, as to its smoothness, to a marble table top (Soooo nineteenth century!).
Can we get word definitions of some of the technical concepts? ...
I would consider it a favor if you stepped in and supplied some. I will not be going very fast so it will be possible to step in at pretty much any point and add or improve definitions. right now I think of this as "Introduction Mark II" and the aim is to get a preliminary description out there which is at least not too misleading. that means there will be topics to expand later in a "Introduction Mark III"
At some point some student of Ashtekar or Rovelli will probably write something that makes all this unnecessary. a real beginner textbook for Loop Gravity. but we cant afford to wait around for that because we dont know when it will happen
selfAdjoint
Mar28-05, 04:35 PM
I would consider it a favor if you stepped in and supplied some. I will not be going very fast so it will be possible to step in at pretty much any point and add or improve definitions. right now I think of this as "Introduction Mark II" and the aim is to get a preliminary description out there which is at least not too misleading. that means there will be topics to expand later in a "Introduction Mark III"
At some point some student of Ashtekar or Rovelli will probably write something that makes all this unnecessary. a real beginner textbook for Loop Gravity. but we cant afford to wait around for that because we dont know when it will happen
I am up for F, but the "densitized dual 2-form" B (or E) has me buffaloed. A dual 2-form maps a pair of vectors multilinearly into the ground field, either reals or complex numbers. Dentsitizing makes it integrable, so far so good, but B or E has values in the Lie Algebra just like F, rather than the ground field. Why?
It is suggestive that you mention Ashtekar variables, and also mention the variables of BF theory (which Freidel tries to reform us so that we write EF thinking that it makes better sense than BF). Let me tell you what my sense of direction tells me. I listened to a (January, Toronto?) recorded talk by Vafa and I heard something ring in his voice when he said "form theories of gravity"----and I went back and looked at the current paper Dijkgraaf, Gukov, Neitzke, Vafa just to make sure. there was a sense of relief. it represents a hopeful general idea for him.
from my perspective, Ashtekar variables and BF are foremostly examples of "form theories" and there could be modifications and other "form theories" we dont know about yet. there is a mental compass needle pointing in this general direction.
it we want to play the game of making verbal (non-math) definitions for an intelligent reader, then it is important the ORDER we define the concepts and also the GOAL or where we are going. I think the direction is that we want to get to where we can say what a "form defined on a manifold" is, or to be more official we should always say "differential form" defined on a "differentiable manifold". So we need to say what the "tangent vectors" are at a point in a manifold.
the obstacle here is that these concepts are unmotivated, have too many syllables if you try to speak correctly, and seem kind of arbitrary and technical.
So I am thinking like this. the thing about a tangent vectors and forms is that they are BACKGROUND INDEPENDENT. All that means, basically, is that you dont have to have a metric. A background independent approach to any kind of physics simply means in practice that you start with a manifold as usual (a "continuum" you say Einstein liked to say) and you refrain from giving yourself a metric.
Well, how can you do physics on a manifold that (at least for now at the beginning) has no metric? What kind of useful objects can you define without a metric? Well, you do have infinitesimal directions because you have coordinates and you can take the derivative at any point, so at a microscopic level you do have a vectorspace of directions-----call them TANGENTS. and on any vectorspace one can readily define the dual space of linear functionals of the vectors-----things that eat the vectors up and give a number. The dual space of the tangents is called the FORMS.
and also the forms dont have to be number-valued, they can be "matrix" valued, one form can eat a tangent vector and produce therefrom not simply one number but 3 numbers or 4 numbers, or a matrix of numbers, but that is not quite right let's say it eats the tangent vector and produces not a number but an element of some Lie algebra. then it is a ALGEBRA-VALUED form.
now this already seems disgustingly complicated so let's see why it might appeal to Cumrun Vafa arguably the world's top string theorist still functioning as such.
I think it appeals to Cumrun Vafa because it is a background independent way to do physics. that is essentially what "form theory of gravity" means.
And string theorists have been held up for two decades by not having a background independent approach. And it JUST HAPPENS that the Ashtekar variables are forms, and the B and F of BF theory are forms, and (no matter what detractors say) Loop has been making a lot of progress lately, and Vafa says "hey, this might be the way to get background independence" and he creates a new fashion called "topological Mtheory" which is a way of focussing on forms and linking up with "form theories of gravity".
So maybe the point is not that this or that particular approach is good or not, but simply that one should work with a manifold sans metric, and do physics with the restricted set of tools that can be defined without a metric. And that means that, painfully abstract as it sounds, nightcleaner has to understand 3 things:
1. the tangent space at a point of a manifold is a vectorspace
2. any vectorspace has a dual space (the things that eat the vectors) and that dual space IS ITSELF a vectorspace.
3. the dual of the tangentspace is the forms and you can do stuff with forms.
Like, you can multiply two forms together (the cute "wedge" symbol), and you can construct more complicate forms that eat two vectors at once or that produce something more jazzy, in place of a number.
The hardest thing in the world to accept is that this is not merely something that mathematicians have invented to do for fun, a genteel and slightly exasperating amusement. The hardest thing to accept is that nature wants us to consider these things because it is practically the only thing you can do with a manifold that doesnt require a metric!
So instead of talking about BF theory or Ashtekar variables in particular, my compass is telling me to wait for a while and see if anyone is interested in "forms on a manifold" that is to say in the clunky polysyllabic language "differential forms defined on the tangent space of a differentiable manifold" UGH.
Also, selfAdjoint, you mentioned the word "bundle". Bundles may be going too far but they are in this general area of discussion, and there is also "connection"
A "connection" is a type of form. So if you understand "form" then you can maybe understand connection.
there is also this extremely disastrous thing that "form" is a misleading term. In real English it means "shape" but a differential form is not a shape at all. Richard being a serious fan of words will insist that it means shape. But no. Some frenchman happened accidentally to call a machine that eats tangent vectors and spits out numbers by the name "form" and so that is what it is called, even tho it is in nowise a shape. It is more like an incometax form, than it is a shape-form. And it is not like an incometax form either.
And as a final ace in the hole we can always say that Gen Rel is an example of a physical theory defined on a manifold without a metric. The metric is a variable that you eventually solve the equation to get. you start without a metric and you do physics and you eventually get a metric.
If there is any useful sense to Kuhntalk then this is a "paradigm". and when Vafa has a good word to say about "form theories of gravity" then this might be the kind of softening that accompanies a shift in perspective.
Cinquero
Apr10-05, 05:38 AM
Could you please try to give an example of a calculation? I would like to get some feeling of how to handle all up to the mapping from a Lie algebra element to a Lie group element via parallel transport along a loop. Additionally, I'd like to see what a projection from the manifold into the tangent space looks like in practice.
Just to make things more clear: what exactly is the nature of this manifold you are talking of? Is there any physical interpretation?
Could you please try to give an example of a calculation? I would like to get some feeling of how to handle all up to the mapping from a Lie algebra element to a Lie group element via parallel transport along a loop. Additionally, I'd like to see what a projection from the manifold into the tangent space looks like in practice.
Just to make things more clear: what exactly is the nature of this manifold you are talking of? Is there any physical interpretation?
hello Cinquero, have you by any chance looked at the beginning treatment of LQG in Rovelli and Upadhya's paper? This was my introduction to the subject back in 2003. Several of us at Physics Forum were reading that paper back then.
It is short (on the order of 10 pages) and shows how a number of things are calculated. If you are interested in learning LQG, then I could review the paper myself, and read some of it with you.
If you do not already have Rovelli/Upadhya and would like the link, please let me know. the date at arxiv is about 1998.
meanwhile, a manifold is a topological space locally homeomorphic to Rd by mappings phi, psi,...which have the following differentiability property: where the domains of two maps overlap,
going from Rd to Rd by the composition of one with the inverse of the other is (either continuously differentiable a certain number of times or) infinitely differentiable.
LQG is usually developed in the d=3 case and the manifold that physically represents space is taken to be "smooth"----which means that the mappings from Rd to Rd which I just mentioned are infinitely differentiable.
LQG can be defined in any dimension d. It is not limited to the d = 3 case, and indeed has been studied in some other cases besides d = 3. But typically the manifold representing space is a compact smooth 3-manifold, a "continuum", denoted by the letter M.
You can get all this from any beginning treatment of LQG like, e.g. Rovelli/Upadhya, or Rovelli/Gaul. Again, if you need links, let me know.
All I have done to supplement the standard treatment that you find there is to define a differentiable manifold. I assume this is very familiar to you Cinquero but some other reader might conceivably want it defined.
As a background note, the classical "ADM" treatment of General Relativity has been posted on arxiv!
http://arxiv.org/gr-qc/0405109
this is a reprint of something published in 1962! You might say this is where the manifold M, that Cinquero is asking about, comes from:
the 1962 Arnowitt, Deser, Misner treatment of classical Gen Rel. Instead of a purely spacetime development, ADM looked at the metric restricted to an embedded 3-d spatial hypersurface.
Around 1986, two other people, Sen and Ashtekar, adapted the ADM approach by shifting attention to connections defined on the 3-d manifold. The connection then, rather than the metric, represented the variable geometry on space.
In the 1990s, when LQG started to develop, much of the context (concepts and notation) was already in place because of this prior work in classical Gen Rel. It was a matter of quantizing the ADM/Ashtekar version of Gen Rel, which had already been established for some time and was familiar to relativists. Here is some of that context (notation has not been fully standardized)
M smooth compact manifold represent space
A connections on M, representing the set of all geometries
K complex-valued functions on A, quantum states of geometry
K is too big and needs to be collapsed down (by applying constraints and equivalences) to a separable Hilbert space----the physical state space---of quantum states of geometry.
But already, with this bare minimum of concepts, one can begin to get oriented. K is a linear space of functions defined on A, the set of connections. One can think of A as the "configurations" and K as "wave functions" familiar from common QM. It is interesting to look for a BASIS of K----a minimal spanning set of complex-valued functions defined on connections.
Already, even with this abbreviated roadmap of the subject, I am touching on concepts that would be a lot of work to define and are better to read about. So if there is further interest I will get some links.
this little sketch is typed from memory, I havent reviewed the definitions and history for quite a while. And I'm not omniscient either! So suggestions and improvements, including links to articles that develop LQG formalism, are welcome.
hi Cinquero, I got the link for Rov/Upad in case you want it
http://arxiv.org/gr-qc/9806079
I checked and they are using notation L where I wrote K, but otherwise no change
BTW, I see you are a new member, welcome!
Cinquero
Apr13-05, 06:44 PM
Thx! That article is very helpful.
Question:
in II.B, the very first sentence: A is defined on M, right? But then, why does AV make sense? V maps from M to SU(2), but A is defined on M! What am I missing?
Thx! That article is very helpful.
Question:
in II.B, the very first sentence: A is defined on M, right? But then, why does AV make sense? V maps from M to SU(2), but A is defined on M! What am I missing?
Hi Cinquero, I just saw your post. Sorry for not replying earlier!
you remember on page 1, section II A, they say
"Let A be an SU(2) connection on M; that is, A is a smooth 1-form with values in su(2), the Lie algebra of SU(2)."
that means if you specify a point and a direction you get a matrix
(lets imagine that a basis has been chosen so that things are less abstract and all the SU(2) things and su(2) things are actually just 2x2 matrices :smile:)
but at every point of M, the function V also gives a matrix! so we can conjugate A by V and have
the new matrix V-1A V
what is meant by writing them together this way is just matrix multiplication
this is how to interpret the first sentence of II B, where the notation
AV is defined
==============
do I need to be more rigorous and formal, and spell this out in more detail?
or is this OK?
Cinquero
Apr15-05, 08:00 AM
do I need to be more rigorous and formal, and spell this out in more detail?
or is this OK?
No, it's ok. Thx!
Someone might be curious as to what "Introduction to LQG(Mark II)" is all about, what is the main direction, if one were to look ahead. Someone teaching a course for juniors/seniors in LQG might, by the end of the semester, want to be in sight of this body of work:
http://arxiv.org/find/grp_physics/1/au:+bojowald/0/1/0/all/0/1
and in particular within striking distance of this 2001 trailblazer
http://arxiv.org/abs/gr-qc/0102069
Absence of Singularity in Loop Quantum Cosmology
it is just 4 pages. the classical BB singularity is replaced by a bounce (from a prior gravitational collapse)
later it was discovered that conditions at the bounce automatically trigger a brief episode of inflation (without fine-tuning or elaborate "extras")
see for example http://arxiv.org/abs/gr-qc/0407069, "Genericness of Inflation in LQC" (also just 4 pages) and references thererin.
here are the papers which have cited this key paper:
http://arxiv.org/cits/gr-qc/0102069
there are currently about 75 papers which have cited it, and about half of these appeared after January 2004
One's approach to LQG, in an introduction, depends a lot on where one wants to be at the end of it and their are several equally valid goals that one could have. For me what stands out is that quantizing General Relativity gets rid of some important singularities where classical GR broke down and allows one to study in more detail what goes on there.
For example it might be good to aim for making contact not only with "Absence of Singularity in LQC" but also
http://arxiv.org/abs/gr-qc/0503041
which treats what emerges when the classical black hole singularity is removed by LQG.
marlon, so are you saying that there is some sort of ''ether'', a actual physical property to space that changes with the interaction of particles on particles? The space itself warps, changes value, and interacts with the particles themself - this being the gravity ?
It's common knowledge that the three people most responsible for initiating the LQG approach to quantizing General Relativity are Abhay Ashtekar, Carlo Rovelli, and Lee Smolin.
A good way to get a sense of what LQG is about is to keep an eye on major books and survey articles by these people, since they are like the "founding fathers" of the field.
From Smolin we have an excellent recent survey article "An Invitation to LQG" which gives useful information for the trained physicist considering getting into LQG research----main results, experimental tests, and a list of unsolved problems to work on.
From Rovelli we have his book Quantum Gravity which came out November 2004 published by Cambridge Press. the December 2003 draft is still online. He also has some earlier surveys and popular articles.
From Ashtekar there are several valuable surveys. Here are links to a couple of the more recent ones that might be useful.
http://arxiv.org/abs/gr-qc/0410054
http://arxiv.org/abs/gr-qc/0404018
But what is especially interesting right now is a book Ashtekar is preparing, to be published by World Scientific, called
A Hundred Years of Relativity.
this book has a broad scope including all of General Relativity, and it will show how Ashtekar sees LQG and other allied approaches to quantizing Gen Rel in their wider context.
Interestingly, several chapters of this book "100Y.of R." are already online as preprints!
I will get links for some preprint chapters.
Martin Bojowald
[he has contributed an article called "Loop Quantum Cosmology"
which I have not yet seen online]
Larry Ford
http://arxiv.org/abs/gr-qc/0504096
Rodolfo Gambini and Jorge Pullin
http://arxiv.org/abs/gr-qc/0505023
Hermann Nicolai
["Gravitational Billiards, Dualities and Hidden Symmetries" not yet online]
Thanu Padmanabhan
http://arxiv.org/abs/gr-qc/0503107
Alan Rendall
http://arxiv.org/abs/gr-qc/0503112
Clifford Will
http://arxiv.org/abs/gr-qc/0504086
Although Bojowald's article may not be available yet, see
http://edoc.mpg.de/display.epl?mode=people&fname=Martin&svir=0&name=Bojowald
and also
http://edoc.mpg.de/display.epl?mode=doc&id=213885&col=6&grp=84
More information has come in, so i will revise parts of the preceding post.
From Ashtekar there are several valuable surveys. Here are links to a couple of recent ones that might be useful.
http://arxiv.org/abs/gr-qc/0410054
Gravity and the Quantum
http://arxiv.org/abs/gr-qc/0404018
Background Independent Quantum Gravity: A Status Report
What is especially interesting right now is a book Ashtekar is preparing, to be published by World Scientific, called
A Hundred Years of Relativity.
This book has a broad scope covering all of General Relativity, including numerical GR and testing. It will show how Ashtekar sees LQG and allied approaches to quantizing Gen Rel in the wider context. Several chapters of this book are already online as preprints:
Martin Bojowald
http://arxiv.org/abs/gr-qc/0505057
Elements of Loop Quantum Cosmology
Larry Ford
http://arxiv.org/abs/gr-qc/0504096
Rodolfo Gambini and Jorge Pullin
http://arxiv.org/abs/gr-qc/0505023
Discrete space-time
Hermann Nicolai
["Gravitational Billiards, Dualities and Hidden Symmetries" not yet online]
Thanu Padmanabhan
http://arxiv.org/abs/gr-qc/0503107
Understanding Our Universe: Current Status and Open Issues
Alan Rendall
http://arxiv.org/abs/gr-qc/0503112
Clifford Will
http://arxiv.org/abs/gr-qc/0504086
Was Einstein Right? Testing Relativity at the Centenary
Because LQG contains some leading-edge lines of research it cannot be given a fixed definition. The practical definition is that it is what Loop people do-----and in practice that means the research lines that are featured in this year's major Loop conference(s).
So for an operational definition of Loop-and-allied approaches to Quantum Gravity, watch the Programme of the October 10-14 conference at Potsdam AEI. Here's the link and some available details:
http://loops05.aei.mpg.de/index_files/Home.html
http://loops05.aei.mpg.de/index_files/Programme.html
The topics of this conference will include:
Background Independent Algebraic QFT
Causal Sets
Dynamical Triangulations
Loop Quantum Gravity
Non-perturbative Path Integrals
String Theory
A detailed programme will be available in July.
Invited Speakers will include:
Abhay Ashtekar (USA)
John Baez (USA)
John Barrett (UK)
Alejandro Corichi (MEX)
Robbert Dijkgraaf (NL)
Fay Dowker (UK)
Laurent Freidel (FR and CA)
Karel Kuchar (USA)
Jurek Lewandowski (POL)
Renate Loll (NL)
Roy Martens (UK)
Hugo Morales Tecotl (MEX)
Alejandro Perez (FR)
Jorge Pullin (USA)
Martin Reuter (GER)
Carlo Rovelli (FR)
Lee Smolin (CA)
Rafael Sorkin (USA)
Stefan Theisen (GER)
Rainer Verch (GER)
-------------------------------
My comment: because these are fast developing areas of research, it makes sense not to nail down the TITLES of the invited speaker's talks until shortly before the conference (July is 3 months before, plenty of time) but it's nice to know WHO will be giving the plenary talks.
I would say that String and old-style LQG are no longer leading edge, and I dont have a big interest in Causal Sets. So I would narrow the exciting topics down to these:
Dynamical Triangulations
Background Independent Algebraic QFT
Non-perturbative Path Integrals
1. Notice that Renate Loll is on the invited list. She will talk about CDT, causal dynam. triang.
This is currently the deepest part of Loop-and-allied research. Anyone interested in LQG, or quantum gravity in general for that matter, should know about it.
2. What they mean by "Background Independent" QFT is basically that it is done on a (metric-less) differentiable manifold. the way you work on a shapeless continuum without first introducing a prior geometry is you use
DIFFERENTIAL FORMS and stuff like bundles and connections. Cumrun Vafa's term for one case of this is "form theories of gravity". A key invited speaker in this line would be Laurent Freidel.
I am not sure what Background Independent "Algebraic" QFT means. I think the papers of Rainer Verch (which I dont know) could touch on this.
the moment you posit a manifold you have already specified a dimension like D = 4 and you already have patches of coordinates but notice that the CDT of Renate Loll does not have a prior commitment to a dimension and it uses NO COORDINATES AT ALL. the brilliant Tullio Regge figured in 1950 how to do Einstein Gen Rel without coordinates. and, in CDT which is basically a child of Regge, the dimension emerges rather than being specified in advance and the dimension can vary with scale----it can be 4D at macro and run smoothly down to around 2D at micro-scale.
This is why I cannot escape concluding that CDT is deeper-probing. It may be WRONG we dont know about right or wrong. However it seems to have Gen Rel as its classical limit, and integrate out to a simple quantum cosmology associated with Hawking as a kind of semiclassical limit.
3. Non-perturbative Path Integrals might be an improved and more general term for what used to be called Spin Foams, but it also includes CDT because in CDT you get a path integral. Which, however, is evaluated barbarically using Monte Carlo runs on the computer.
This is going to be an interesting Loops 05 Conference and I guess it is the conference that defines the field (more than the other way round).
So we will see in Potsdam in October what LQG is.
in case anyone is interested in getting a tast of causal dynamical triangulations (CDT) here is a short reading list.
A new monograph "Reconstructing the Universe" is due to come out this month. It will replace the 2001 paper which I link to here. the 3 short papers from 2004 and 2005 give the highlights of recent research results.
It is better to first read the 3 short recent papers before getting into the details in the 2001 paper IMHO.
1.
http://arxiv.org/hep-th/0105267
Dynamically Triangulating Lorentzian Quantum Gravity
J. Ambjorn (NBI, Copenhagen), J. Jurkiewicz (U. Krakow), R. Loll (AEI, Golm)
41 pages, 14 figures
Nucl.Phys. B610 (2001) 347-382
"Fruitful ideas on how to quantize gravity are few and far between. In this paper, we give a complete description of a recently introduced non-perturbative gravitational path integral whose continuum limit has already been investigated extensively in d less than 4, with promising results. It is based on a simplicial regularization of Lorentzian space-times and, most importantly, possesses a well-defined, non-perturbative Wick rotation. We present a detailed analysis of the geometric and mathematical properties of the discretized model in d=3,4..."
2.
http://arxiv.org/abs/hep-th/0404156
Emergence of a 4D World from Causal Quantum Gravity
J. Ambjorn (1 and 3), J. Jurkiewicz (2), R. Loll (3) ((1) Niels Bohr Institute, Copenhagen, (2) Jagellonian University, Krakow, (3) Spinoza Institute, Utrecht)
11 pages, 3 figures; final version to appear in Phys. Rev. Lett
Phys.Rev.Lett. 93 (2004) 131301
"Causal Dynamical Triangulations in four dimensions provide a background-independent definition of the sum over geometries in nonperturbative quantum gravity, with a positive cosmological constant. We present evidence that a macroscopic four-dimensional world emerges from this theory dynamically."
3.
http://arxiv.org/abs/hep-th/0411152
Semiclassical Universe from First Principles
J. Ambjorn, J. Jurkiewicz, R. Loll
15 pages, 4 figures
Phys.Lett. B607 (2005) 205-213
"Causal Dynamical Triangulations in four dimensions provide a background-independent definition of the sum over space-time geometries in nonperturbative quantum gravity. We show that the macroscopic four-dimensional world which emerges in the Euclidean sector of this theory is a bounce which satisfies a semiclassical equation. After integrating out all degrees of freedom except for a global scale factor, we obtain the ground state wave function of the universe as a function of this scale factor."
4.
http://arxiv.org/abs/hep-th/0505113
Spectral Dimension of the Universe
J. Ambjorn (NBI Copenhagen and U. Utrecht), J. Jurkiewicz (U. Krakow), R. Loll (U. Utrecht)
10 pages, 1 figure
SPIN-05/05, ITP-UU-05/07
"We measure the spectral dimension of universes emerging from nonperturbative quantum gravity, defined through state sums of causal triangulated geometries. While four-dimensional on large scales, the quantum universe appears two-dimensional at short distances. We conclude that quantum gravity may be "self-renormalizing" at the Planck scale, by virtue of a mechanism of dynamical dimensional reduction."
AFAICS a breakthrough form of simplex path-integral gravity called causal dynamical triangulations (CDT) is the most important current development in Quantum Gravity going on. In case anyone is interested in getting a taste of CDT here is a short reading list.
this is an update of what I listed earlier:
1.
http://arxiv.org/hep-th/0105267
Dynamically Triangulating Lorentzian Quantum Gravity
J. Ambjorn (NBI, Copenhagen), J. Jurkiewicz (U. Krakow), R. Loll (AEI, Golm)
41 pages, 14 figures
Nucl.Phys. B610 (2001) 347-382
"Fruitful ideas on how to quantize gravity are few and far between. In this paper, we give a complete description of a recently introduced non-perturbative gravitational path integral whose continuum limit has already been investigated extensively in d less than 4, with promising results. It is based on a simplicial regularization of Lorentzian space-times and, most importantly, possesses a well-defined, non-perturbative Wick rotation. We present a detailed analysis of the geometric and mathematical properties of the discretized model in d=3,4..."
2.
http://arxiv.org/abs/hep-th/0404156
Emergence of a 4D World from Causal Quantum Gravity
J. Ambjorn (1 and 3), J. Jurkiewicz (2), R. Loll (3) ((1) Niels Bohr Institute, Copenhagen, (2) Jagellonian University, Krakow, (3) Spinoza Institute, Utrecht)
11 pages, 3 figures; final version to appear in Phys. Rev. Lett
Phys.Rev.Lett. 93 (2004) 131301
"Causal Dynamical Triangulations in four dimensions provide a background-independent definition of the sum over geometries in nonperturbative quantum gravity, with a positive cosmological constant. We present evidence that a macroscopic four-dimensional world emerges from this theory dynamically."
3.
http://arxiv.org/abs/hep-th/0411152
Semiclassical Universe from First Principles
J. Ambjorn, J. Jurkiewicz, R. Loll
15 pages, 4 figures
Phys.Lett. B607 (2005) 205-213
"Causal Dynamical Triangulations in four dimensions provide a background-independent definition of the sum over space-time geometries in nonperturbative quantum gravity. We show that the macroscopic four-dimensional world which emerges in the Euclidean sector of this theory is a bounce which satisfies a semiclassical equation. After integrating out all degrees of freedom except for a global scale factor, we obtain the ground state wave function of the universe as a function of this scale factor."
4.
http://arxiv.org/abs/hep-th/0505113
Spectral Dimension of the Universe
J. Ambjorn (NBI Copenhagen and U. Utrecht), J. Jurkiewicz (U. Krakow), R. Loll (U. Utrecht)
10 pages, 1 figure
SPIN-05/05, ITP-UU-05/07
"We measure the spectral dimension of universes emerging from nonperturbative quantum gravity, defined through state sums of causal triangulated geometries. While four-dimensional on large scales, the quantum universe appears two-dimensional at short distances. We conclude that quantum gravity may be "self-renormalizing" at the Planck scale, by virtue of a mechanism of dynamical dimensional reduction."
5.
http://arxiv.org/hep-th/0505154
Reconstructing the Universe
J. Ambjorn (NBI Copenhagen and U. Utrecht), J. Jurkiewicz (U. Krakow), R. Loll (U. Utrecht)
52 pages, 20 figures
Report-no: SPIN-05/14, ITP-UU-05/18
"We provide detailed evidence for the claim that nonperturbative quantum gravity, defined through state sums of causal triangulated geometries, possesses a large-scale limit in which the dimension of spacetime is four and the dynamics of the volume of the universe behaves semiclassically. This is a first step in reconstructing the universe from a dynamical principle at the Planck scale, and at the same time provides a nontrivial consistency check of the method of causal dynamical triangulations. A closer look at the quantum geometry reveals a number of highly nonclassical aspects, including a dynamical reduction of spacetime to two dimensions on short scales and a fractal structure of slices of constant time."
this is a landmark paper.
I have been looking also for a reader-friendly introductor paper. there is one that is lecture notes aimed at the graduate student level
6.
http://arxiv.org/hep-th/0212340
A discrete history of the Lorentzian path integral
R. Loll (U. Utrecht)
38 pages, 16 figures
SPIN-2002/40
Lect.Notes Phys. 631 (2003) 137-171
"In these lecture notes, I describe the motivation behind a recent formulation of a non-perturbative gravitational path integral for Lorentzian (instead of the usual Euclidean) space-times, and give a pedagogical introduction to its main features. At the regularized, discrete level this approach solves the problems of (i) having a well-defined Wick rotation, (ii) possessing a coordinate-invariant cutoff, and (iii) leading to_convergent_ sums over geometries. Although little is known as yet about the existence and nature of an underlying continuum theory of quantum gravity in four dimensions, there are already a number of beautiful results in d=2 and d=3 where continuum limits have been found. They include an explicit example of the inequivalence of the Euclidean and Lorentzian path integrals, a non-perturbative mechanism for the cancellation of the conformal factor, and the discovery that causality can act as an effective regulator of quantum geometry."
Loll wrote this as an introduction to CDT for Utrecht graduate students who might want to get into her line of research. It is a good beginning. It is already 2 years out of date so it does not have the latest headline results but that is OK.
Here is a reminder of the importance of background independence (no prior metric) and diffeomorphism invariance (general covariance) in the case where the spacetime model is a differential manifold.
these are principles are basic to LQG, and to all allied approaches to quantum gravity.
in fact these two features are basic to classical 1915 General Relativity! So any approach that really tries to quantize Gen Rel is going to exhibit these features or the equivalent
Anyway this is sometimes pointed out as one of the troubles with string theory---that it doesnt have background independence etc. And people debate this. I will not take a stand but simply point out that these principles are really important---and implementing them has shaped LQG and some related approaches---and that one can get into trouble if one does not.
this was illustrated by something posted a few minutes ago in "Third Road" sticky-thread,
http://arxiv.org/gr-qc/0505138
Fibered Manifolds, Natural Bundles, Structured Sets, G-Sets and all that: The Hole Story from Space Time to Elementary Particles
J. Stachel, M. Iftime
40 pages
The article had this in the conclusions (partly already quoted in "third road" thread, but we can use them too as emphasizing how crucial background independence is) :
<<...Perturbative string theory fails this test, since the background spacetime (of no matter how many dimensions) is only invariant under a finite parameter Lie subgroup of the group of all possible diffeomorphisms of its elements. This point now seems to be widely acknowledged in the string community. I quote from two recent review articles. Speaking of the original string theory Michael Green[19] notes: “This description of string theory is wedded to a semiclassical perturbative formulation in which the string is viewed as a particle moving through a fixed background geometry .... Although the series of superstring diagrams has an elegant description in terms of two-dimensional surfaces embedded in spacetime, this is only the perturbative approximation to some underlying structure that must include a description of the quantum geometry of the target space as well as the strings propagating through it ( p. A78). ... A conceptually complete theory of quantum gravity cannot be based on a background dependent perturbation theory ...."
"In ... a complete formulation the notion of string-like particles would arise only as an approximation, as would the whole notion of classical spacetime (p. A 86) ” Speaking of the more recent development of M-theory, Green says: “An even worse problem with the present formulation of the matrix model is that the formalism is manifestly background dependent. This may be adequate for understanding M theory in specific backgrounds but is obviously not the fundamental way of describing quantum gravity (p. A 96).”
And in a review of matrix theory, Thomas Banks comments: String theorists have long fantasized about a beautiful new physical principle which will replace Einsteins marriage of Riemannian geometry and gravitation. Matrix theory most emphatically does not provide us with such a principle. Gravity and geometry emerge in a rather awkward fashion, if at all. Surely this is the major defect of the current formulation, and we need to make a further conceptual step in order to overcome it (pp. 181-182). It is my hope that emphasis on the importance of the principle of dynamic individuation of the fundamental entities, with its corollary requirement of invariance of the theory under the entire permutation group acting on these entities, constitutes a small contribution to the taking of that further conceptual step. >>
[19] Green(1999) Superstrings, M-theory and quantum gravity, Classical and Quantum Gravity, 16, A77-A100
Michael Green and Thomas Banks are major figures in string/M research---originators----and speak with authority. They may be wrong (they are the experts on string, not me, so I cannot judge if they are right or not) but in any case these strong words help give adequate emphasis to the issues of background independence and invariance under diffeomorphic mappings.
somebody might wish to ask how Loll-style "Triangulations" gravity implements background independence and diffeo invariance (or reasonable substitute, since it doesnt have any diffeos)
the triangulations QG approach of Loll and coworkers looks like the most interesting, and perhaps promising, development being pursued by the people participating in this years "Loops 05" conference.
It is one of the broadly defined "Loop-and-allied" approaches that Loop people do----not narrowly defined core LQG. there are a bunch of approaches that deal with similar stuff but differ in details.
this thread can serve a useful purpose as an INTRODUCTION to more than just one of the Loop-and-allied approaches. Probably the most timely to consider at the moment is CDT-style Triangulations.
As a point of departure here is how the abstract of a recent landmark CDT paper starts off:
"We provide detailed evidence for the claim that nonperturbative quantum gravity, defined through state sums of causal triangulated geometries, possesses a large-scale limit in which the dimension of spacetime is four and the dynamics of the volume of the universe behaves semiclassically. This is a first step in reconstructing the universe from a dynamical principle at the Planck scale,..."
this is from
http://arxiv.org/hep-th/0505154
Reconstructing the Universe
J. Ambjorn (NBI Copenhagen and U. Utrecht), J. Jurkiewicz (U. Krakow), R. Loll (U. Utrecht)
52 pages, 20 figures
here is a short reading list
http://www.physicsforums.com/showpost.php?p=585294&postcount=59
Now what I want to do is describe the CDT "Triangulations" method as simply as I can.
First there is a kind of birdseye view illustrated by a talk that Renate Loll gave in 2002 called
"Quantum gravity IS counting geometries"
It is a possible approach---sometimes called "state sum" or "path integral"
Its roots go back to the Feynman path integral for a particle where you add up all the possible (approximate piecewise straight) paths the particle might take to get from here to there----with complex weights to make a kind of weighted average. It is a way to get probability amplitudes and calculate things about the quantum path the particle takes. This turns out to be 100 percent of the time very ROUGH, nowhere is it even differentiable, but nevertheless intuitively it kind of blurs or fuzzes out to resemble a smooth continuously differentiable classical path that you might expect from freshman calculus.
In the "state sum" approach to a particle's path the calculation is in effect counting lots of different (piecewise straight) paths. And adding them all together, with a system of weighting that embodies the microscopic dynamics, to get answers. It has been a very successful method. the CDT authors found out how to apply it to spacetimes.
A spacetime is like a path, from space being this way to space having evolved to be that way, or more grandly from the beginning of a universe to its end. In QUANTUM gravity, that is in quantum spacetime dynamics, one is not certain exactly which path it took. One only has amplitudes of various ways of evolving from this shape to that shape. It is very much analogous to the particle path. You can even think of the universe wandering around in the space of all geometries and its evolution an actual path, but I can see no compelling reason to think so abstractly as that about it.
to put it simply, the CDT authors found a way to approximate (by piecewise flat geometries, made of flat Minkowski building blocks) all the possible spacetimes that get you from here to there, or from the beginning to the end. And they found a way to compute experimental answers from the STATE SUM of all these geometries.
After that it almost seems obvious and really straightforward. They can generate random spacetimes, random histories of the universe, as 4D worlds living in the computer memory, and they can HAVE LITTLE IMAGINARY MEN RUN AROUND IN THEM TO EXPLORE THEM, by taking random walks----a so called diffusion process---which is a way of finding out about the geometry, like what dimension it really is in there.
then after studying each random example they can add everything up with the usual weights (there are actually two sets of weights connected by the Wick trick, one set is simply real numbers like ordinary probabilities and the other set of weights is complex amplitude-type numbers but this doesnt matter to the overall picture) So they add everything up in a weighted average and get the state sum report (from the little imaginary men) on how it is in there.
Now having done this, Loll and co-workers are catching results like the fish are running. They are just pulling them in hand over hand. throw in the line and hook one every time.
This is a big change from the Nineties when many people worked the state sum triangulations approach but didnt catch anything edible. everything they got was the wrong dimension.
so this is part of an overview.
what I have to EXPLAIN is how they set up one of these layered triangulated geometries----and how they then shuffle the cards so as to get a series of random geometries. this is the nutsandbolts part.
a 4-simplex is the 4D analog of a triangle and they build these appoximate piecewise flat geometries out of two TYPES of 4-simples, the
"level"-kind and the "tilt"-kind
they call them the (4,1) kind and the (3,2) kind. it is how the vertices are destributed between two causal layers
I have to balance giving an overview with giving some introductory nutsandbolts.
Here is some more overview. It elucidates the "state sum" idea of adding up all possible geometries. and the essential business of reducing the calculation to COUNTING.
In this case what we have is something from an American Physical Society publiscation
http://focus.aps.org/story/v14/st13
The American Physical Society sponsors the major peer-review journals series Phys. Rev. and Physical Review Letters. And they pick out articles for highlighting journalistically in the accompanying publication Physical Review Focus.
This is from Adrian Cho's Focus article on a paper by Loll and co-workers.
<<The researchers added up all the possible spacetimes to see if something like a large-scale four-dimensional spacetime would emerge from the sum. That was not guaranteed, even though the tiny bits of spacetime were four-dimensional. On larger scales the spacetime could curve in ways that would effectively change its dimension, just as a two-dimensional sheet of paper can be wadded into a three-dimensional ball or rolled into a nearly one-dimensional tube. This time the researchers found that they could achieve something that appeared to have one time dimension and three space dimensions--like the universe we know and love.
"It's exceedingly important" work, says Lee Smolin of the Perimeter Institute for Theoretical Physics in Waterloo, Canada. "Now at least we know one way to do this." Des Johnston of Heriot-Watt University in Edinburgh, Scotland, agrees the work is "very exciting" and says it underlines the importance of causality. "The other neat thing about this work is that you're essentially reducing general relativity to a counting problem," Johnston says. "It's a very minimalist approach to looking at gravity.">>
...
...this is part of an overview.
what I have to explain is how they set up one of these layered triangulated geometries----and how they then shuffle the cards so as to get a series of random geometries. this is the nutsandbolts part.
a 4-simplex is the 4D analog of a triangle and they build these appoximate piecewise flat geometries out of two TYPES of 4-simples, the
"level"-kind and the "tilt"-kind
they call them the (4,1) kind and the (3,2) kind. it is how the vertices are destributed between two causal layers
I have to balance giving an overview with giving some introductory nutsandbolts.
the best source on the basics is http://arxiv.org/hep-th/0105267
we have to COUNT THE CAUSAL GEOMETRIES of spacetime, it sounds terribly hard but it isnt and they managed to program it, and it's the basic job we cant get around
causal means LAYERED, each model of spacetime gets laid down in sheets or slices, like a book with pages or a tree-trunk with rings, an event in one layer can only be caused by something from a deeper layer----or think of it like a many-storied building.
so we have to BUILD ALL POSSIBLE LAYERED SPACETIME GEOMETRIES in such a way that we can COUNT THEM or anyway explore to find what are the most numerous kind or the most likely kind, or somehow average them.
Maybe in the end we wont be able to count them exactly but we will have statistics and averages and random samples about them just as if we could actually count them. We will take the census of these layered spacetime geometries.
The technique will be to learn how to build layered geometries using "triangular" building blocks cut out of the txyz space of special relativity
these blocks will all be the same size----their spatial edges will be a fixed length 'a' that we will successively make smaller and smaller---and they will be of two kinds. the LEVEL kind and the TILT kind. The level kind is like a pyramid which has a 3D spatial tetrahedron as its base, on one floor of the building, and its 5-th vertex on the floor above or, the upsidedown version, the floor below.
the authors write the level kind as either (4,1) or (1,4), because it has 4 vertexes (the 4 vertices of the tetrahedron) on this floor and 1 vertex on the floor above, or viceversa one vertex on this floor and 4 on the floor above
intuitively one layer is all of 3D space, and the spacetime history of the universe is being built 3D layer by 3D layer, so it is like a book except the pages are 3D.
a LEVEL kind of building block has 4 timelike edges going from each of the four corners of its spatial tetrahedron base up to the vertex on the floor above, or else going down to the solitary vertex on the floor below. the other kind of buildingblock is like the LEVEL kind but tilted over so that now one of those timelike edges becomes a ridge and is entirely in the floor above, and instead of sitting on a full tetrahedron base it is now only sitting on a triangle side of it.
the authors write the TILT kind of buildingblock as either (3,2) or (2,3)
because it has 3 vertices on one floor, that make its spatial triangle base, and it has 2 vertices on the floor above or below, that make this ridge I mentioned. Like the ridge of a roof or the keel of a boat, depending it is up or down.
the TILT kind has 4 spacelike edges (three for the triangle and one for the base) and it has 6 timelike edges, whereas the LEVEL kind had 6 spacelike (that you need to make a tetrahedron) and 4 timelike.
the quickest way to understand this business is to follow through the analogous 3D case which is spelled out in
http://arxiv.org/hep-th/0105267
there, the building blocks are tetrahedrons---spatial layers are intuitively 2D, like the pages of a book---everything is easy to imagine, and they have a lot of drawings
but I am trying to discuss modeling 4D spacetime geometry without first going thru the 3D case.
after that it is not too hard to say, in general terms, how the method works
you want to get the EFFECT of building a layered geometry with, say, a halfmillion identical LEVEL kind buildingblocks
and howevermany you need (which will also be about halfmillion) TILT kind blocks to fill in.
because when you try to build layers with the LEVEL kind it always turns out that you get gaps which are just right to fit the other kind into, so it turns out that to build up layer by layer you need approximately the same number of the other kind.
NOW YOU DONT ACTUALLY BUILD EVERY POSSIBLE LAYERED SPACETIME GEOMETRY with these million virtually identical blocks
it is like taking an opinion poll where you dont talk to everybody, you take a random sample.
you want the EFFECT of having built all of them, and studied each one, and counted and made statistics about how they all are. you dont want to actually do it. you want the effect as if you did it.
this is where "shuffling the deck of cards" comes in. the CDT authors call it "thermalizing" the geometry. you set up a very simple plain geometry to start with, in computer memory, and then you do RANDOMIZING PASSES thru it, until it gradually becomes totally unrecognizable.
like, have a look at Figures 4,5 and 6 in "Reconstructing the Universe"
http://arxiv.org/hep-th/0505154
they are all three quite different-looking but they all come from starting with a simple initial geometry and doing randomizing passes.
the authors call each pass "making a sweep", and each sweep involves doing a million or so "Monte Carlo moves" which are individual shuffles that change some of the building blocks around.
they use a lot of computer time. thermalizing (thoroughly randomizing) a geometry can take a week on a workstation. then you study it and measure things
when you have a random geometry you can run random walks in it, or diffusion process, and you can measure distances and volumes and see how they relate...
here is an example.
say you have built a layered spacetime geometry in your computer and you pick just one spatial layer and you want to explore that by a random walk.
well a spacelike slice is just made of the tetrahedrons which were the bases of the LEVEL buildingblocks!
So you have a set of things in your computer which are little 4-face pyramids (equilateral triangle bottom, so 3 side faces and a bottom face, except no way to distinguish the bottom from the other faces). And this bunch of tetrahedrons are fitted together some way so that every face of one is up against the face of some other.
So you can pick a random block to start in, and then TOSS A FOURSIDED COIN to select which face to go out of
and when you go out one face you are now in a new tetrahedron and you can toss the foursided coin to choose which face to pass thru, and again and again.
it will be a clue to the actual dimensionality of the spatial slice to see if you get completely lost by doing this random walk, or if you now and then get back home to where you started. the authors determine the probabilities EMPIRICALLY by actually running the random walks in the computer, and this tells them about the dimensionality of the spatial slices
the nice thing is the answers gotten this way are weird and quite Alice-in-Wonderland. at microscopic level the continuum (as pictured by CDT) is a non-classical, unexpected world which Lewis Carroll would have loved.
in the path integral or state sum approach you make a WEIGHTED sum using a badness or handicap function S(path) which is large for really kooky unphysical paths
this is how you introduce the classical dynamics into the quantum picture.
Feynmann has an essay about the "least action principle" in his Lectures, it is one of the core things in the Feynmann physics textbook. It is terribly important and he suddenly takes a serious tone of voice when he gets to it.
the way you do classical physics is you consider all the possible paths and you DIFFERENTIATE S(path) and set to zero so as pick the one and only one path that MINIMIZES S(path)-------you pick the unique path that minimizes the "action", which is a word for badness or silliness of paths.
we have inherited our "action" functions from great old classical guys like Lagrange and Einstein and Hamilton, directly or indirectly, whom we revere, and they have the feature that minimizing them gets you the expected classical equations of motion
the way you do quantum physics is when you consider all possible paths you dont try to pick the unique winner, you ADD THEM ALL TOGETHER, but you dont do this in a completely indiscriminate way! You handicap each one by putting a little real or complex number "weight" on it. this is incidentally how they used to handicap racehorses, with a little weight, but you can do it at a different level with the betting odds too.
one weight you might consider putting on is exp( - S(path))
that is:
"eee to the minus badness"
e-badness
so if the badness is large it make the weight exponentially very small and then the path tagged with that weight will not count for very much in the sum or weighted average of all paths
YOU DO NOT JUST PICK ONE HORSE THAT IS YOUR FAVORITE, you add together all the horses, but you weight each one so your favorites count for more and the bad ones count for less-------you get a "composite" horse.
another kind of weight you might consider putting on is exp(iS(path))
"eee to the eye badness"
ei badness
As you may know from elementary complex numbers "eee to the eye theta" is complex numbers going around and around the unit radius circle.
and this is very clever because if you go around the circle, around zero, very fast it will average out to ZERO ITSELF by simple vector addition.
taking a step N and S and E and W adds up to going nowhere
so if you are averaging things with rapidly increasing badness and tagging them with "eee to the eye badness" numbers then these things with lots of badness will CANCEL EACH OTHER OUT in the sum and not have much influence on the sum
this is the two kinds of handicaps, the real number weights and the complex number weights from around the unit radius circle.
YOU CAN GET FROM ONE SET OF WEIGHTS TO THE OTHER SET OF WEIGHTS by the simple expedient of changing the eye into a minus sign, or the minus into an eye. this is called the WICK ROTATION, in honor of Joe Wick born in Torino around 1906.
the Einstein action measures roughly speaking how much some spacetime is off from being a well behaved classical solution of the classical Einstein equation of General Relativity. So if you minimize the einstein action it you get the classical equation back.
so it measures how much the "path" is screwing up and getting distracted from its studies and cutting classes and taking dope and all what it isnt supposed to be doing---how "busy" it is with messing up---that "busy-ness" is the action. believe me you want to cut down on it.
a spacetime is just a path from the beginning of the world to the end, a path in "geometry space" if you can picture the space of all geometries.
the quantum idea is the universe doesnt just follow one path, it is a fuzzy mixture, well that is a rather distracting idea so lets not get into that.
the extremely beautiful thing is that with simplex geometries, with geometries built of triangles, YOU CAN IMPLEMENT THE ACTION FUNCTION JUST BY COUNTING DIFFERENT KINDS OF TRIANGLES
so even a computer, merely able to count up things in its memory, can do it
so we get back to our story where Loll and friends are running a computer model of spacetime, and the model is doing "sweeps" consisting of a million or so "Monte Carlo moves" which are localized elementary rearrangements of the simplex building blocks
each time they roll the dice and pick a monty move at random, they calculated some "badness" or "action" numbers to see whether to ACCEPT OR REJECT the proposed move!
this is how the localized microscopic "DYNAMICAL PRINCIPLE" that Loll talks about enters into the picture
it is this action principle operating at a microscopic Planckian or even maybe sub-Planckian level that the overall spacetime grows from. However it looks, whether it has 4 dimensions or 3 dimensions or some fraction etc, whatever its geometry, it grows out of many many local applications of the action principle at micro-scale.
I will try to find a quote.
Yeah, this is going to seem very dry and overdetailed but it shows how the quantum spacetime dynamics, the path integral action principle, was implemented:
<<3. Numerical implementation
We have investigated the infinite-volume limit of the ensemble of causal triangulated four-dimensional geometries with the help of Monte Carlo simulations at finite four-volumes N4 = N(4,1) + N(3,2) of up to 362,000 four-simplices. A simplicial geometry is stored in the computer as a set of lists, where the lists consist of dynamic sequences of labels for simplices of dimension n from zero to four, together with their position and orientation with respect to the time direction. Additional list data include information about nearest neighbours, i.e. how the triangulation “hangs together”, and other discrete data (for example, how many four-simplices meet at a given edge) which help improve the acceptance rate of Monte Carlo moves. The simulation is set up to generate a random walk in the ensemble of causal geometries of a fixed time extension t. The local updating algorithm consists of a set of moves that change the geometry of the simplicial manifold locally, without altering its topological properties. These can be understood as a Lorentzian variant of (a simplified version of) the so-called Alexander moves [21, 22, 23], in the sense that they are compatible with the discrete time slicing of our causal geometries. For example, the subdivision of a four-simplex into five four-simplices by placing a new vertex at its centre is not allowed, because vertices can only be located at integer times tau . Details of the local moves can be found in [8]. As usual, each suggested local change of triangulation is accepted or rejected according to certain probabilities depending on the change in the action and the local geometry. (Note that a move will always be rejected if the resulting triangulation violates the simplicial manifold property.) The moves are called in random order, with probabilities chosen in such a way as to ensure that the numbers of actually performed moves of each type are approximately equal. We attained a rather high average acceptance rate of about 12.5%, which was made possible by keeping ...>>
By the way Alexander wrote his book in 1930. that is how far these "Monty Carlo moves" go back. they are just modified Alexander moves. Pachner is also cited. So this his how they "shuffle the deck".
Now I can say what part the Wick rotation plays. The Wick rotation changes the complex weights into real weights which can be dealt with as PROBABILITIES in this process of choosing the next random move, in "shuffling the deck" or randomizing spacetime geometry by Monte Carlo moves.
the probabilities enter each time you do a local rearrangement of some building blocks, you check whether that local microscopic rearrangement would be favored or disfavored by the Einstein equation. you do that by comparing badness. and it is still random----there is still always a chance that you can do a move that increases the badness, that happens lots in fact---but the probabilities are weighted against it (the House of general relativity wins over the long run). well maybe that is too impressionistic an impression.
I promised in Quantum Graffiti thread to say something about Wick rotation and Einstein Hilbert action
Cinquero
Jun20-05, 04:35 AM
YOU CAN GET FROM ONE SET OF WEIGHTS TO THE OTHER SET OF WEIGHTS by the simple expedient of changing the eye into a minus sign, or the minus into an eye. this is called the WICK ROTATION, in honor of Joe Wick born in Torino around 1906.
Is there a general theorem available for that purpose? I believe to remember that the mathematics behind that is usually quite non-obvious.
selfAdjoint
Jun20-05, 08:43 AM
It's a procedure in complex variables, called analytic continuation.
Cinquero
Jun20-05, 09:06 AM
It's a procedure in complex variables, called analytic continuation.
So Wick rotation = analytic continuation?
selfAdjoint
Jun20-05, 03:52 PM
So Wick rotation = analytic continuation?
You have the integrals defined on the real axis, corresponding to Minkowski space, but they don't converge there, because they have factors like e^{ut}, which is unbounded as t goes to infinity. They are howeve analytic in the half plane above the real axis, and by continuation therefore on the imaginary axis, which correspond to i\tau = t, or euclidean four space. Then the integrals convege because the factors now read e^{ui\tau} which is bounded for all tau. Then after you evaluate the integrals (they mostly reduce to a gaussian quadrature) you can rotate back.
You have the integrals defined on the real axis, corresponding to Minkowski space, but they don't converge there, because they have factors like e^{ut}, which is unbounded as t goes to infinity. They are howeve analytic in the half plane above the real axis, and by continuation therefore on the imaginary axis, which correspond to i\tau = t, or euclidean four space. Then the integrals convege because the factors now read e^{ui\tau} which is bounded for all tau. Then after you evaluate the integrals (they mostly reduce to a gaussian quadrature) you can rotate back.
You've got that exactly reversed. It's the imaginary exponentials that fail to converge and are converted by Wick rotation. Another way of saying the same thing is that a Wick rotation takes a QFT (which has a i\hbar in the exponential) to a statistical mechanics (which has a -k/T in the exponential). Your note is essentially saying that +k/T diverges and this is true, but the solution in a Wick rotation is to rotate in the opposite direction. That way you end up with exponentials that converge. This all reminds me of the method of "steepest descent"[sp] that is used in Schroedinger's equation.
But that's not why I was reading the thread.
Stephen Hawking's latest paper uses "Euclidean Quantum Gravity":
http://arxiv.org/PS_cache/hep-th/pdf/0507/0507171.pdf
Does EQG have anything to do with LQG? My field is elementary particles, not gravitation. Sorry for the laziness. Hawking references a book I don't have immediate access to.
Carl
...
Stephen Hawking's latest paper uses "Euclidean Quantum Gravity":
http://arxiv.org/PS_cache/hep-th/pdf/0507/0507171.pdf
Does EQG have anything to do with LQG? My field is elementary particles, not gravitation. Sorry for the laziness. Hawking references a book I don't have immediate access to.
Carl
"Euclidean QG" developed by hawking and friends in 1980s was a path integral AFAIK
and so it would be closer akin to Renate Loll Lorentzian path integral by CDT method ("causal dynamical triangulations") that we hear a lot about these days
Hawking never got Euclidean path integral to work, but he uses it to think with. It sounds a bit eccentric for him to call it the "only sane way to do nonperturbative QG"
the Lorentzian path integral people (Loll et al) have an equally nonperturbative approach that they are getting results with, including confirming a conjecture or two of hawking. No way is Loll's approach not sane. It is at least as sane as the Euclidean version.
I need to get you some online links. there is a 1998 survey of QG methods by rovelli which describes hawking Euclid. path integral. More recent online stuff do not discuss hawking's method very much because it is long obsolete except for him and one or two proteges. But I will get the link to the 1998 survey
Yes, here:
http://arxiv.org/abs/gr-qc/9803024
Strings, loops and others: a critical survey of the present approaches to quantum gravity
Carlo Rovelli
Plenary lecture on quantum gravity at the GR15 conference, Pune, India
"I review the present theoretical attempts to understand the quantum properties of spacetime. In particular, I illustrate the main achievements and the main difficulties in: string theory, loop quantum gravity, discrete quantum gravity (Regge calculus, dynamical triangulations and simplicial models), Euclidean quantum gravity, perturbative quantum gravity, quantum field theory on curved spacetime, noncommutative geometry, null surfaces, topological quantum field theories and spin foam models. I also briefly review several recent advances in understanding black hole entropy and attempt a critical discussion of our present understanding of quantum spacetime."
http://arxiv.org/abs/gr-qc/9803024
Strings, loops and others: a critical survey of the present approaches to quantum gravity
Carlo Rovelli
Section B. "Old hopes (becoming) approximate theories"
---quote Rovelli---
B. Old hopes -> approximate theories
1. Euclidean quantum gravity
Euclidean quantum gravity is the approach based on a formal sum over Euclidean geometries [[my comment: HERE ROVELLI GIVES THE PATH INTEGRAL, BUT I CAN'T COPY IT EASILY, it is labelled equation (6)]] As far as I understand, Hawking and his close collaborators do not anymore view this approach as an attempt to directly define a fundamental theory. The integral is badly ill defined, and does not lead to any known viable perturbation expansion. However, the main ideas of this approach are still alive in several ways. First, Hawking’s picture of quantum gravity as a sum over spacetimes continues to provide a powerful intuitive reference point for most of the research related to quantum gravity. Indeed, many approaches can be sees as attempts to replace the ill defined and non-renormalizable formal integral (6) with a well defined expression. The dynamical triangulation approach (Section IVA) and the spin foam approach (Section VC2) are examples of attempts to realize Hawking’s intuition. Influence of Euclidean quantum gravity can also be found in the Atiyah axioms for TQFT (Section VC1). Second, this approach can be used as an approximate Second, this approach can be used as an approximate method for describing certain regimes of nonperturbative quantum spacetime physics, even if the fundamental dynamics is given by a more complete theory. In this spirit, Hawking and collaborators have continued the investigation of phenomena such as, for instance, pair creation of black holes in a background de Sitter spacetime. Hawking and Bousso, for example, have recently studied the evaporation and “anti-evaporation” of Schwarzschild-de Sitter black holes [61]...
---end quote---
Equation (6) here looks very much like Loll's dynamical triangulations path integral. but they start with exp(iS) where S is the Regge form of Einst action.
Loll et al do a Wick rotation to get a euclidean version which gets used in the computer calculations.
This equation (6) is still very much like what Loll CDT starts with, but instead of a metric [g] there is a TRIANGULATION T. so they are summing over all triangulations of a particular kind. Otherwise it looks formally the same.
However there is a practical difference in that Loll et al can actually calculate. they do the sum (using montecarlo method) and get results.
some of these results have born out hawking conjectures, so they cite him a lot.
but his particular type of (euclidean) path integral i dont think any significant effort is being made to use it.
to compare hawking EQG with current CDT path integral, have a look at the first 2 or 3 pages of these two papers
http://arxiv.org/hep-th/0105267
http://arxiv.org/hep-th/0505154
you will see how close the CDT path integral is to Hawking's euclidean one.
in the past couple of pages of this thread we have been responding to questions from CarlB and cinquero and it may be time to regroup. I decided earlier that unless there is some reason not to do so we ought to make this thread serve as an introduction NOT ONLY to narrowly defined canonical LQG but to the main approaches to NONPERTURBATIVE QUANTUM GRAVITY.
That includes canonical LQG but also spin foams, and other path integral approaches like CDT. selfAdjoint, at one point, proposed the term "Background Independent Quantum Gravity" for the general field. Renate Loll seems to favor "Nonperturbative QG". The organizers of the Loop 05 conference use the collective modifier
"background independent/nonperturbative"
And Lee Smolin has started to say "relational".
But I think "nonperturbative" is going to win out as the mainest of mainstream term. As sideline observers we can't reform language, just have to go with the prevailing talk.
I think one of the ambient ideas in the Loop 05 conference is that if you can forge a concept "NQG" and impress on people's minds the idea that there is research in "nonperturbative quantum gravity" then maybe a few more universities will establish professorships in NQG or faculty positions of some kind in NQG. It will be perceived as a lack not to have some research in nonperturbative QG being conducted in the physics department.
It also means recommending each other's graduate students. if it is a field then there is more solidarity than if it is just a bunch of splinter group research lines.
Hermann Nicolai definitely would like some professorships in German universities that are echo or counterpart to his lines of reseach at AEI, he has talked about that in Die Zeit interview. And AEI is hosting Loop 05.
so it is time to assemble into a research field with an identifying label which is not String, and to get it recognized that a physics department has an embarrassing GAP if it doesnt have some research under way in Nonper Quavity.
Let's recap the introduction to the triangulations approach---Loll CDT.
Here is a reading list from earlier in this thread
http://www.physicsforums.com/showthread.php?p=585294#post585294
Here's a short popularization by Loll, at her website, written for general audience
http://www.phys.uu.nl/~loll/Web/research/research.html
This PF thread has more stuff like that
http://www.physicsforums.com/showthread.php?t=77639&page=1&pp=15
========================
To give an idea of where the field is at the moment, I am simply going to quote, in its entirety, the first paragraph of each of Loll's three most recent papers. These papers are dated May, June, July 2005. The first paragraph of a research paper often gives a bit of an overview or some perspective on the field. This is a fastmoving field and this will be one way to keep up with where things are at the moment. We have no more recent survey available.
http://arxiv.org/hep-th/0505154
Reconstructing the Universe
http://arxiv.org/gr-qc/0506035
Counting a black hole
http://arxiv.org/hep-th/0507012
Taming the cosmological constant...topology change
Very encouraging progress has been made recently in constructing spacetime dynamically from a nonperturbative gravitational path integral, by studying the continuum limit of causal dynamical triangulations [1, 2, 3, 4]. The quantum geometries generated in this way exhibit semiclassical properties at sufficiently large scales: they are four-dimensional [5, 6] and the large-scale dynamics of their spatial volume is described by an effective cosmological minisuperspace action [7]. Their short-distance behaviour is highly nonclassical, including a smooth dynamical reduction of the spectral dimension from four to two [8] and evidence of fractality [6].
Despite recent progress [1, 2], little is known about the ultimate configuration space of quantum gravity on which its nonperturbative dynamics takes place. This makes it difficult to decide which (auxiliary) configuration space to choose as starting point for a quantization. In the context of a path integral quantization of gravity, the relevant question is which class of geometries one should be integrating over in the first place. Setting aside the formidable difficulties in “doing the integral”, there is a subtle balance between including too many geometries – such that the integral will simply fail to exist (nonperturbatively) in any meaningful way, even after renormalization – and including too few geometries, with the danger of not capturing a physically relevant part of the configuration space.
Nonperturbative quantum gravity can be defined as the quest for uncovering the true dynamical degrees of freedom of spacetime geometry at the very shortest scales. Because of the enormous quantum fluctuations predicted by the uncertainty relations, geometry near the Planck scale will be extremely rugged and nonclassical. Although different approaches to quantizing gravity do not agree on the precise nature of these fundamental excitations, or on how they can be determined, most of the popular formulations agree that they are neither the smooth metrics... (or equivalent classical field variables) of general relativity nor straightforward quantum analogues thereof. In such scenarios, one expects the metric to re-emerge as an appropriate description of spacetime geometry only at larger scales.
I'll try to interpret some---as time permits. but hopefully this is already fairly clear and doesn't need much explication
I had better keep a list of links to the prediction polls that folks at PF have so that when the time comes to look we can easily find the thread with the predictions
Background independence talks at Strings 06
http://www.physicsforums.com/showthread.php?t=85207
(when the programme of talks is posted, check to see who was right)
August-September hits on Smolin latest
http://www.physicsforums.com/showthread.php?t=83578
(in late September 2005, start checking
http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:hep-th/0507235
to see if they are counting and registering downloads of "The case for background independence")
String Forecast Poll
http://www.physicsforums.com/showthread.php?t=81739
(around March 2006 check SLAC/Stanford for the 2005 HEP Topcites. This year around March 2005 they brought out the 2004 Topcites as usual. But they have not yet done the full job with Michael Peskin's review, which is worrisome. the list to check is whatever is analogous to this
http://www.slac.stanford.edu/library/topcites/2004/annual.shtml )
Will Loll etc. achieve sum over topologies in 4D?
http://www.physicsforums.com/showthread.php?t=81626
(this prediction poll has no definite declared cut-off date, which was an oversight. we will have to use reasonableness and see whether, in a reasonable time, Loll et al manage to extend the results on topology change to higher dimensions)
A major chronological bibliography for LQG
Over a thousand papers (arranged by date) often with arxiv numbers making online access easy
Over forty books and PhD dissertations.
Plus miscellaneous other useful sources of information.
http://www.arxiv.org/abs/gr-qc/0509039
Bibliography of Publications related to Classical Self-dual variables and Loop Quantum Gravity
Alejandro Corichi, Alberto Hauser
45 pages
"This bibliography attempts to give a comprehensive overview of all the literature related to what is known as the Ashtekar-Sen connection and the Rovelli-Smolin loop variables, from which the program currently known as Loop Quantum Gravity emerged..."
Corichi gives some guidance as to his own judgement of what are good introductions, primers, surveys, mathematical treatments.
======================================
Dan Christensen's SpinFoam website at U Western Ontario
is another resource for people wanting to get acquainted with LQG and related QG
http://jdc.math.uwo.ca/spin-foams/
he has links to things sorted out by topic, and level and different users' needs and purposes, and he has some links to some Greg Egan JAVA applets. Seeing how he organizes things gives you a practical overview of QG from his perspective.
Dan says he has room for some more grad students and postdocs in his QG/computation program. It looks like anybody who might want to study QG (or massive parallel computation applied to QG) should probably check this out.
----------------------------
EDIT TO REPLY TO CINQUERO
Hi Cinquero, since i can still edit this I will reply this way and save making a new post. Please go to Dan Christensen site. He has many links in an organized convenient form. If there is anything that you need a further PDF link for, tell me what it is is and I will try to find it. I am not certain I understand your request for links to PDF----was it links to things found at Dan's UWO page or for something else?
Cinquero
Sep13-05, 04:20 AM
Thx!
But could someone please add hyperlinks to the PDF output? :-)))
Hi Cinquero, I responded to your post #82 by editing the previous post. Hope you saw the note.
At the moment just need a place to stash the links to the audio of a two-part Bojowald talk given last Friday and concluded today at Penn State. He is talking about the LQG model Black Hole.
the audio of the first part is here
http://www.phys.psu.edu/events/index.html?event_id=1255;event_type_ids=0;span=200 5-08-20.2005-12-25
Loop Quantum Cosmology of the Kantowski-Sachs Model
Gravity Theory Seminar by Martin Bojowald from Albert Einstein Institute (Germany)
Friday at 11:00 AM in 318 Osmond (9/16/2005)
and the second part (which was today) is here
http://www.phys.psu.edu/events/index.html?event_id=1256&event_type_ids=0&span=
Spherically Symmetric Quantum Geometry
Gravity Theory Seminar by Martin Bojowald from Albert Einstein Institute
Friday at 11:00 AM in 318 Osmond (9/23/2005)
at the same page there was also this audio
http://www.phys.psu.edu/events/index.html?event_id=1268;event_type_ids=0;span=
Generalizing Quantum Mechanics for Quantum Gravity
IGPG Seminar by James Hartle from University of California, Santa Barbara
Monday at 3:00 PM in 318 Osmond (9/19/2005)
and this audio as well
http://www.phys.psu.edu/events/index.html?event_id=1260;event_type_ids=0;span=200 5-08-20.2005-12-25
Quantum Nature of the Big-Bang: Numerical Issues
Gravity Theory Seminar by Thomas Pawlowski & Parampreet Singh
Friday at 11:00 AM in 318 Osmond (9/9/2005)
Ashtekar has announced that he has a paper, written with Thomas Pawlowski & Parampreet Singh, to appear about this topic: LQG picture of the big bang.
Several of these seminar talks relate to the Ashtekar Bojowald collaboration about LQG of big bang and black hole, see for example their recent paper
http://www.arxiv.org/gr-qc/0509075
Quantum geometry and the Schwarzschild singularity
Cinquero
Sep24-05, 03:24 AM
Actually, mys request for hyperlinks was in regard to:
"Bibliography of Publications related to Classical Self-dual variables and Loop Quantum Gravity"
:)
Actually, mys request for hyperlinks was in regard to:
"Bibliography of Publications related to Classical Self-dual variables and Loop Quantum Gravity"
:)
Ah!, I see what you mean. Corichi writes the URLs out for online sources, so one could paste them in and get to them, but in the PDF version these URLs do not automatically function as hyperlinks, as they might if he had provided an HTML version. I understand you may be joking, but it wouldn't be a bad idea for Corichi to make an up-to-date selective HTML bibliography of online quantum gravity sources.
If you want to encourage him to do this you could email him. Be sure to mention PF. He--or else a good friend of his--has often visited us, I believe, and supplied helpful information.
This is an update of post #56 which was about a book edited by Abhay Ashtekar scheduled to be published this year by World Scientific. here is the publisher's webpage
http://www.worldscibooks.com/physics/5876.html
A Hundred Years of Relativity.
Several chapters of this book are already online as preprints:
Martin Bojowald
http://arxiv.org/abs/gr-qc/0505057
Elements of Loop Quantum Cosmology
Larry Ford
http://arxiv.org/abs/gr-qc/0504096
Rodolfo Gambini and Jorge Pullin
http://arxiv.org/abs/gr-qc/0505023
Discrete space-time
Hermann Nicolai
http://www.arxiv.org/abs/gr-qc/0506031
Gravitational Billiards, Dualities and Hidden Symmetries
Thanu Padmanabhan
http://arxiv.org/abs/gr-qc/0503107
Understanding Our Universe: Current Status and Open Issues
Alan Rendall
http://arxiv.org/abs/gr-qc/0503112
Clifford Will
http://arxiv.org/abs/gr-qc/0504086
Was Einstein Right? Testing Relativity at the Centenary
========
other stuff:
Ashtekar there are several useful surveys, such as
http://arxiv.org/abs/gr-qc/0410054
Gravity and the Quantum
http://arxiv.org/abs/gr-qc/0404018
Background Independent Quantum Gravity: A Status Report
Agons, moments of truth.
for some reason I keep thinking back to the times Smolin spoke up at the Toronto string panel discussion, and each time immediately afterwards he was put down by you know who.
http://www.physicsforums.com/showthread.php?t=84585
http://www.fields.utoronto.ca/programs/scientific/04-05/string-theory/strings2005/panel.html
and I remember Atiyah at Santa Barbara interrupted and almost derailed as he tried to get across his "old man's crazy thoughts".
http://www.physicsforums.com/showthread.php?t=96806
http://online.kitp.ucsb.edu/online/strings05/atiyah/
and as if to compensate there is Gerard 't Hooft's response after listening to some strange and quite possibly wrong ideas from Atiyah---That sounds like physics!
There may be hints of slow shift in research interest from string to non-string approaches to quantum gravity. The latter include Causal Dynamical Triangulations (CDT), spinfoams, Loop Quantum Gravity (LQG) and others on the Loops '05 conference programme.
this shift in research activity, if it exists, is hard to verify and measure statistically. here is one indicator---by itself not conclusive but something to watch along with the rest.
Last month at selfAdjoint's suggestion I included "heterotic, superstring" in the list of keywords and did a search using the Harvard ADS abstract service engine.
http://www.physicsforums.com/showthread.php?p=789185#post789185
I'll be glad to try. The main thing is just to have a fixed set of keywords you can apply year by year, to get the trend in papers with those keywords.
In accordance with your suggestion, I checked how many papers were published each year (October thru September) with the words "brane" or "M-theory" or "AdS/CFT" or "superstring" or "heterotic" in the abstract.
2001 1202
2002 1097
2003 970
2004 959
For continuity I tried the same check today. This is now the papers November thru October, year by year, with any of the same keywords in the abstract.
2001 1220
2002 1083
2003 972
2004 938
Part of this could certainly have nothing to do with a concurrent increase in QG research output in the non-string lines of investigation. It is very iffy and difficult to link the two trends! But at a level of anecdotal evidence one does encounter cases of people who have switched over.
Since the effort in non-string QG is still small compared with string, this shift (if it is occurring) could be viewed simply as diversification. One could take it NOT AS A SIGN THAT ONE THING IS RIGHT AND ANOTHER WRONG but that for whatever reason people are branching out in more directions, and trying non-string ones.
I will try to get some figures on non-perturbative QG research output trends.
non-string QG research seems to have increased during the same period.
For a rough indication of this I use the keyword search engine at arxiv.org, to find the number of preprints submitted each year with certain terms in the abstract. It gets some papers it shouldn't (that just happen to have the right keywords) and it misses some. Here the results:
2001 98
2002 121
2003 140
2004 184
In case anyone is interested here are links to these arxiv.org searches, and to some others just to have them handy.
Year 2001:
http://arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2001/0/1
Year 2002:
http://arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2002/0/1
Year 2003:
http://arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2003/0/1
Year 2004:
http://arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2004/0/1
Last twelve months:
http://arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/past/0/1
Year to date, 2005:
http://arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2005/0/1
BTW here I have been looking only at the 2001-2004 period. Can we say anything about current trends? Well it may take a while for the 2005 numbers to stabilize and it may be too soon to say anything much. But I think nonperturbative QG research is experiencing LOLL-SHOCK and is in a temporary lull where people are considering re-directing their efforts more in line with Causal Dynamical Triangulations (because of recent seemingly important results).
John Baez has been very frank about this. Last month (October) he presented an overview of Spinfoam where he pointed out CDT results and asked could Spinfoam be modified (introducing an analogous causality structure?) to be more like CDT and could it get similar results, and then maybe it would surpass CDT because of inherent advantage in some other department.
this was the talk he gave at Loops '05 and posted at his website.
There is a lot of new stuff to digest right now, besides CDT there is Thiemann single constraint program, another approach which is not standard LQG and which look attractive to some LQG people, and there is Freidel's result that highlights DSR as a possibly necessary feature of QG.
For whatever reason there has been almost no QG appearing on arxiv.org since the 10-14 October conference. Loll-shock is my best guess but their could be other reasons.
Here is a great talk by Sundance Bilson-Thompson given 16 November 2005 at Perimeter Institute
http://streamer.perimeterinstitute.ca:81/Mediasite/Viewer/Viewer.aspx?layoutPrefix=LayoutTopLeft&layoutOffset=Skins/Clean&width=800&height=631&peid=2e5425f4-3f47-4e5a-a86a-804a6d499b17&pid=e949d11b-a1a5-4365-a152-7e2014cb3867&pvid=1&playerType=WM64Lite&mode=Default&shouldResize=true
it is split screen, slides and video, he occasionally goes to the blackboard to explain stuff and the camera gets that too.
he is talking about his preon model (simple basis for a sketchy approximation of the standard model) which he and Lee Smolin are currently trying to connect with the spin networks of LQG.
Please let me know if this link does not work for you. It worked for me when I tried it.
Loll aside, this is my guess as to the most influential quantum gravity paper of 2005:
http://arxiv.org/abs/hep-th/0512113
Effective 3d Quantum Gravity and Non-Commutative Quantum Field Theory
Laurent Freidel, Etera R. Livine
9 pages
"We show that the effective dynamics of matter fields coupled to 3d quantum gravity is described after integration over the gravitational degrees of freedom by a braided non-commutative quantum field theory symmetric under a kappa-deformation of the Poincaré group."
This paper (summarizing rapid development during the past year or so) pretty well takes care of the 3D case. In the conclusions Freidel discusses the extension to 4D, and cites a paper by Freidel and Baratin in preparation, called Hidden quantum gravity in Feymnan graphs.
but this was also the title of the talk which Aristide Baratin gave at October Loops '05. And we can download the slides. This has a link to the video as well, but i cannot get it to work:
http://loops05.aei.mpg.de/index_files/abstract_baratin.html
Here are Baratin slides for his talk "Hidden quantum gravity in Feymnan graphs".
http://loops05.aei.mpg.de/index_files/PDF_Files/baratin.ppt
Who is Aristide Baratin? Perimeter lists him as one of their grad students. I think Baratin finished Lycee in Paris around 1997 (won an essay prize) and went to Ecole Normal in Lyon (where Freidel works part-time). Perhaps he did his Bac at Lyon and after becoming a grad student moved from Lyon to Perimeter in 2005. I think probably he was born around 1980 and is now in mid Twenties. Anyway he is collaborating with Freidel on the paper where Freidel starts seriously to work on 4D.
There was already some preparation in that paper of Freidel with Artem Starodubtsev, which was also about 4D. I will get some quotes where Freidel gives an idea of what his strategy is.
this gives an idea of the success in 3D which Freidel intends to duplicate, if it is possible, in 4D.
--quote from Freidel paper hep-th/0512113--
CONCLUSIONS AND OUTLOOK
To sum up, we have shown that the 3d quantum gravity amplitudes, defined through the Ponzano-Regge spinfoam model, are actually the Feynman diagram evaluations of a (braided) non-commutative quantum field theory. This effective field theory describe the dynamics of the matter field after integration of the gravitational degrees of freedom. This applies as well in the Euclidean case as in the true Lorentzian theory. The noncommutative action is invariant under a kappa-deformation of the Poincaré algebra, which acts non-trivially on the many-particle states.
This is an explicit realization of a quantum field theory in the framework of deformed special relativity. Moreover, the theory naturally comes with a momentum cut-off which does not break the Poincaré symmetry but only deforms it.
This alternative to dimensional regularization was originally proposed by Snyder[15]. However, here we have explicitly shown that the gravitational field acts as such a regulator in the Euclidean sector. Moreover, we have checked that the quantum gravity amplitudes for the trivial topology reduces in the nogravity limit kappa -> 0 to the standard QFT amplitudes, as expected in the semi-classical limit of the theory.
We can see two natural extensions. The first one is that the spinfoam amplitudes provide a generalization of the Feynman rules for non-trivial topology. The second one is the generalization to the four-dimensional space-time. Indeed, we propose a new point of view. We have shown how to write the 3d Feynman evaluations as expectation values of certain observables of a topological (abelian) theory. This (abelian) theory was then identified as a particular limit of the quantum gravity theory. This result suggests that the Feynman evaluations of 4d QFT could be reformulated as expectation values of a 4d topological model. This is supported by the fact that 4d gravity becomes topological in the G ->0 limit [16]. This would be interpreted as the zeroth order of the spinfoam model for 4d quantum gravity [17]
---endquote---
REF [16] IS TO FREIDEL STARODUBTSEV
REF [17] IS TO FREIDEL BARATIN (Hidden quantum gravity in Feynman graphs).
Freidel talk at October conference was essentially this paper that he just posted, but with a differerent title
The paper is
http://arxiv.org/abs/hep-th/0512113
Effective 3d Quantum Gravity and Non-Commutative Quantum Field Theory
the talk was
http://loops05.aei.mpg.de/index_files/abstract_freidel.html
Effective Field theory from quantum gravity
"The Coupling of matter fields to spin foam models of quantum gravity will be discussed. We will show in the case of three dimensional gravity how the integration of quantum gravity degrees of freedom coupled to matter can be explicitely described in terms of an effective field theory. This theory is a new non commutative field theory obeying the principle of doubly special relativity. We will conclude on the extension of this approach to the four dimensional case."
the slides to the talk are not available, but there was a video. But I can't get it to download. too bad. I think AEI-Golm posted the video files only a limited time. I downloaded a number of them and have them on my hard-drive, but I find that I cannot download the same ones now. the link that USED to work, to get the freidel talk video was:
http://loops05.aei.mpg.de/index_files/Video_freidel.wmv
...
Last month at selfAdjoint's suggestion I included "heterotic, superstring" in the list of keywords and did a search using the Harvard ADS abstract service engine.
http://www.physicsforums.com/showthread.php?p=789185#post789185
For continuity I tried the same check today. This is now the papers November thru October, year by year, with any of the same keywords in the abstract.
2001 1220
2002 1083
2003 972
2004 938
... it NOT AS A SIGN THAT ONE THING IS RIGHT AND ANOTHER WRONG but that for whatever reason people are branching out in more directions, and trying non-string ones.
...
this time of year data becomes available and we can update. this is now for JANUARY THRU DECEMBER year by year----the same keywords
(heterotic, superstring, M-theory, brane, AdS/CFT)
2001 1204
2002 1188
2003 1081
2004 1012
2005 843
http://adsabs.harvard.edu/physics_service.html
these are figures on stuff that has gotten PUBLISHED in the indicated year. there is also the current rate of preprint postings---here is an arxiv link that may sometimes be useful
http://lanl.arxiv.org/find/nucl-ex,astro-ph,nucl-th,math-ph,hep-ex,physics,cond-mat,hep-lat,quant-ph,gr-qc,hep-ph,hep-th/1/OR+OR+abs:+OR+string+brane+abs:+OR+braneworld+D-brane+abs:+OR+M-theory+p-brane/0/1/0/2006/0/1
Early in 2005, Freidel and Livine posted
http://arxiv.org/abs/hep-th/0502106
Ponzano-Regge model revisited III: Feynman diagrams and Effective field theory
Laurent Freidel, Etera R. Livine
46 pages
"We study the no gravity limit G_{N}-> 0 of the Ponzano-Regge amplitudes with massive particles and show that we recover in this limit Feynman graph amplitudes (with Hadamard propagator) expressed as an abelian spin foam model. We show how the G_{N} expansion of the Ponzano-Regge amplitudes can be resummed. This leads to the conclusion that the dynamics of quantum particles coupled to quantum 3d gravity can be expressed in terms of an effective new non commutative field theory which respects the principles of doubly special relativity. We discuss the construction of Lorentzian spin foam models including Feynman propagators"
In October Freidel's Loops '05 talk was
http://loops05.aei.mpg.de/index_files/abstract_freidel.html
Effective Field theory from quantum gravity
"The Coupling of matter fields to spin foam models of quantum gravity will be discussed. We will show in the case of three dimensional gravity how the integration of quantum gravity degrees of freedom coupled to matter can be explicitely described in terms of an effective field theory. This theory is a new non commutative field theory obeying the principle of doubly special relativity. We will conclude on the extension of this approach to the four dimensional case."
In December 2005 a related paper appeared
http://arxiv.org/abs/hep-th/0512113
Effective 3d Quantum Gravity and Non-Commutative Quantum Field Theory
"We show that the effective dynamics of matter fields coupled to 3d quantum gravity is described after integration over the gravitational degrees of freedom by a braided non-commutative quantum field theory symmetric under a kappa-deformation of the Poincaré group."
Laurent Freidel's most recent paper was with Shahn Majid:
http://arxiv.org/abs/hep-th/0601004
Noncommutative Harmonic Analysis, Sampling Theory and the Duflo Map in 2+1 Quantum Gravity
54 pages, 2 figs
We show that the *-product for U(su_2) arising in [1] in an effective theory for the Ponzano-Regge quantum gravity model is compatible with the noncommutative bicovariant differential calculus previously proposed for 2+1 Euclidean quantum gravity using quantum group methods in [2]. We show that the effective action for this model essentially agrees with the noncommutative scalar field theory coming out of the noncommutative differential geometry. We show that the required Fourier transform essentially agrees with the previous quantum group Fourier transform. In combining these methods we develop practical tools for noncommutative harmonic analysis for the model including radial quantum delta-functions and Gaussians, the Duflo map and elements of `noncommutative sampling theory' applicable to the bounded SU_2,SO_3 momentum groups. This allows us to understand the bandwidth limitation in 2+1 quantum gravity arising from the bounded momentum. We also argue that the the anomalous extra `time' dimension seen in the noncommutative differential geometry should be viewed as the renormalisation group flow visible in the coarse graining in going from SU_2 to SO_3. Our methods also provide a generalised twist operator for the *-product."
[1] refers to the two 2005 Freidel and Livine papers
[2] is a 2003 paper of Majid and Batista
for quotes and more discussion of this series of papers please scroll back three or four posts to post #91 and #92
at the moment I am trying to connect the dots and understand a little better what is happening here. please help if you think you can explain. It looks like Freidel has found a connection at the 3D level between Regge gravity, Feynmann diagrams for particles, and DSR (deformed Poincaré). the same laws that govern gravity also govern particles and produce Feynman vertex amplitudes in the flat limit. It looks like Freidel together with Shahn Majid and others are preparing to try to raise this setup to the 4D level. A fifth dimension has appeared and is being interpreted as a renormalization group parameter (instead of a second dimension of time). If you ask me it is real hard to comprehend, but maybe others will have an easier time with it.
If I am right in my guess about where QG is going, then this paper should serve as a kind of FILTER---
Early in 2005, Freidel and Livine posted
http://arxiv.org/abs/hep-th/0502106
Ponzano-Regge model revisited III: Feynman diagrams and Effective field theory
Laurent Freidel, Etera R. Livine
46 pages
"We study the no gravity limit G_{N}-> 0 of the Ponzano-Regge amplitudes with massive particles and show that we recover in this limit Feynman graph amplitudes (with Hadamard propagator) expressed as an abelian spin foam model. We show how the G_{N} expansion of the Ponzano-Regge amplitudes can be resummed. This leads to the conclusion that the dynamics of quantum particles coupled to quantum 3d gravity can be expressed in terms of an effective new non commutative field theory which respects the principles of doubly special relativity. We discuss the construction of Lorentzian spin foam models including Feynman propagators"
...
what I mean is that for the immediate future a good way to find interesting QG papers is to LOOK FOR THOSE WHICH HAVE CITED THIS ONE AS A REFERENCE.
if this is an important germinal paper then it makes our job easier, we can just look here
http://www.citebase.org/cgi-bin/citations?id=oai:arXiv.org:hep-th/0502106
and it says that this February 2005 paper has 11 citations (including some ones that are new to me---that I hadn't noticed when I was scanning arxiv) and these citations are
http://arxiv.org/cits/hep-th/0502106
(but this only gives the titles/authors and not the abstracts)
to see the same list with brief summaries:
http://www.citebase.org/cgi-bin/search?type=identifier&rank=Citations+(Paper)&submit=Cited+By&identifier=oai:arXiv.org:hep-th/0502106
Great! I have been trying to observe QG, and using these search tools, for several years and I am only just learning some laborsaving ways to use the tools.
the thing is: this February 2005 Freidel-Livine paper treats QG DYNAMICS AND MATTER ON THE SAME PLATFORM and unites Feynman diagrams (for the matter) with quantum Gen Rel dynamics for the spacetime
and this paper does it for 3D, so probably the future of QG will be doing similar stuff in 4D-----so this paper filters out future interesting QG papers
if a future paper cites this one, then it has a chance of being interesting.
so we have a new window----namely this citebase.org link.
BTW another link similar to the one a couple of posts back
http://lanl.arxiv.org/find/grp_physics/1/OR+OR+abs:+OR+OR+heterotic+M-theory+brane+abs:+OR+superstring+AdSCFT+abs:+OR+st ring+braneworld/0/1/0/2006/0/1
Sorry by the slight off-topic.
I am currently reading the complete thread "intuitive content of loop..." that i had followed discontinously untill now.
These one seems to be much of the same stuff ¿Why two duplicate threads?
¿Are topics covered here and uncovered in the other?
Sorry by the slight off-topic.
I am currently reading the complete thread "intuitive content of loop..." that i had followed discontinously untill now.
These one seems to be much of the same stuff ¿Why two duplicate threads?
¿Are topics covered here and uncovered in the other?
One difference is I try to make the older, larger thread more INCLUSIVE.
I suppose the other thread gets about 10 times more links per month, although I do not know the exact numbers.
I guess that in a month where I add 2 links to this more selective thread, I might add perhaps 20 links to the more inclusive one.
In the other thread, I try to put in any new QG paper that I think someone of us might be interested in. Even if I am not sure about it, I may put it in just so that it is less likely to be lost---and just in case someone else might be interested. So my own personal bias and interest does not influence it so much.
In this thread the links I put in reflect my own personal judgment of what is most essential and what are the most interesting directions in QG research. I am not always consistent. Last year I focused a lot of my attention on Loll Triangulations gravity (CDT). This year, so far, I am focusing mainly on the Freidel Spinfoam gravity (with its connection to matter and to DSR).
I would like to put in this thread only things that I think are of the utmost importance---and if a month or two pass by with nothing new that is OK, it just means that for me nothing especially important came out for a couple of months. But not being omniscient and clairvoyant, how can I tell what is really important? So in the other thread, to be on the safe side, I include stuff that I think has a chance to be of interest.
If you would like to contribute to our bibliography, Sauron, perhaps you would follow the same plan and preserve the "short list/long list" idea.
(non-string) Quantum Gravity is emerging as a field and becoming more articulate. One of the major milestones marking this is Lee Smolin's course of lectures Introduction to Quantum Gravity
Notice that the title is not LOOP quantum gravity, but more general. Lecture #7 that I watched yesterday was BF theory----Lecture #8 touched on Chern-Simons. In response to a question Smolin also spent some of that day's session introducing the inclusion of matter in QG (by Laurent Freidel and others).
Besides this video course in QG, another signpost is Christine Dantas blog
http://christinedantas.blogspot.com
and her QG reading list.
http://christinedantas.blogspot.com/2006/02/basic-curriculum-for-quantum-gravity.html
As a kind of footnote, I will keep an eye out for other QG BLOGS, which in some sense indicate the growing self-awareness of the field.
One of the members of the Nottingham QG group has
http://realityconditions.blogspot.com
http://realityconditions.blogspot.com/2006/02/monday-quantum-gravity-group-meeting.html
Nottingham University has a major QG research group headed by John Barrett ("Barrett-Crane spinfoam model") and Kiril Krasnov (spinfoam and GFT parallels Freidel's)
http://www.maths.nottingham.ac.uk/QG/QG.html
and the blogger belongs to that group.
the "Reality Conditions" blogger Alejandro Katz just flagged Christine's QG reading list
http://realityconditions.blogspot.com/2006/02/study-guide-for-lqg.html
likewise Nigel's LQG blog
http://lqg.blogspot.com/2006/02/dr-dantas-has-lqg-reading-list.html
and also Victor Rivelles blog "SUM OVER HISTORIES", a mostly in Portuguese QG blog that I did not know of until today.
http://rivelles.blogspot.com/2006/02/road-to-loop-quantum-gravity.html
To get to the video of the Smolin Lectures go to
http://streamer.perimeterinstitute.ca:81/mediasite/viewer/FrontEnd/Front.aspx?&shouldResize=False
and scroll down to Introduction to Quantum Gravity around item #22 on the sidebar menu. It is currently one of the most recent additions to Perimeter online resources and so is near the bottom
as of now, the best short overview of LQG so far, in my opinion,
is Rovelli's Slides for a talk he gave in January 2006 at Lyon
it would be great if we had the audio that went with the slides
but the slides are fairly self-explanatory especially you have heard other Rovelli talks
http://www.cpt.univ-mrs.fr/~rovelli/Lyon2006II.pdf
these 59 slides make an excellent summary of the essential ideas, with lots of sketches and diagrams (pointers to the history of how QG developed are given parenthetically by listing names and dates so you could look it up, but the emphasis is on giving intuitive grasp of the subject at present)
there are other resources at Rovelli homepage
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html
including a link to a downloadable draft of his book "Quantum Gravity" published by Cambridge University Press in 2004.
the SMOLIN LECTURES available as streaming video here
http://streamer.perimeterinstitute.ca:81/mediasite/viewer/FrontEnd/Front.aspx?&shouldResize=False
(scroll down to Introduction to Quantum Gravity on the sidebar menu)
now comprise 12 lectures-----the table of contents is on two pages so you have to flip the page to find lectures 11 and 12.
the Smolin Lectures are more technical and in-depth, so they complement Rovelli's easy conceptual overview. it helps to look at it from both perspectives
so as not to lose track of the link, we have a forecast poll on the most influential first-quarter 2006 paper
http://www.physicsforums.com/showthread.php?t=116791
=================
this is the thread that has updates of the TOC of the book by Daniele Oriti "Towards QG----a new understanding of space and time" or words to that effect.
last time i checked arXiv had preprints for 7 of the chapters, may be more now
http://www.physicsforums.com/showthread.php?t=113282
in particular see post #3 and 4
http://www.physicsforums.com/showthread.php?p=931982#post931982
as a convenience, here is a list of selected threads
(lot of threads these days, hard to keep track of all)
distler's paper
http://www.physicsforums.com/showthread.php?t=119368
Loop-and-allied QG link thread
http://www.physicsforums.com/showthread.php?t=7245
Bojo gig at KITP, and Brazil Cosmology School
http://www.physicsforums.com/showthread.php?t=119283
Spinfoam hazards a prediction
http://www.physicsforums.com/showthread.php?t=119156
Notices (congratulatory)
http://www.physicsforums.com/showthread.php?t=119305
Randall-Sundrun
http://www.physicsforums.com/showthread.php?t=119294
F-H thread on Livine Terno
http://www.physicsforums.com/showthread.php?t=117710
Graber thread on APS meeting
http://www.physicsforums.com/showthread.php?t=119292
guesses about next 6 months QG trends
http://www.physicsforums.com/showthread.php?t=118790
Sabine's thread about Hedrich warning Physics could decline into Metaphysics
http://www.physicsforums.com/showthread.php?t=119004
Baez 4D beef article
http://www.physicsforums.com/showthread.php?t=115082
Majid
http://www.physicsforums.com/showthread.php?t=118079
Marseille Interpretation of Quantum Mechanics
http://www.physicsforums.com/showthread.php?t=117701
Elephant
http://www.physicsforums.com/showthread.php?t=117286
Smolin Lectures video
http://www.physicsforums.com/showthread.php?t=107445
SLAC/Stanford topcites
http://www.physicsforums.com/showthread.php?t=114925
there is always a danger of losing rare threads, after they are done, unless you keep a list
Mike2 started this one
Quantum foam producing both particles and spacetime
http://www.physicsforums.com/showthread.php?t=121527
it has John Baez telling Carlo Rovelli's Gedankenexperiment where a bolt of gravity wave comes and knocks down the Eiffel Tower
and also it has selfAdjoint's reply to a Zen koan posed by Carl Brannan.
Carl said "What is Energy made of?"
and sA said "Cobordisms"
In this case the answer is as bad as the question.
I forget why this one is good. It has some John Baez remarks but I forget what exactly
Non-string QG positions in US (some data)
http://www.physicsforums.com/showthread.php?t=121501
Oh yeah, I remember several interesting things---about FQX and Huck Finn and various such.
(apparently Baez was holed up with a bad cold in an apartment in Waterloo Ontario and had some time so he posted on this thread)
Baez and Perez beef strings and branes
http://www.physicsforums.com/showthread.php?t=120985
in the first week this got 34 replies and 774 views
must have generated some controversy. Kea was active IIRC and a bunch of others.
Kea has apparently been writing a PhD thesis and hasnt been posting much.
I guess everybody realizes without my needing to say it that the topic of
this thread is potentially kind of important. matter arising in a 4D model
Please help me build a list of references
http://www.physicsforums.com/showthread.php?t=120779
I confess to gross negligence here. We should have done a better job of responding to Kakarukeys.
Kakarukeys (Jiang-Fung Wong) is starting a QG group at Singapore U. He started this thread to get
links for his reading list. Francesca helped. What a serious person she is, never goofing off, just being helpful. Maybe she will become a professor of Quantum Gravity at an Italian university some day.
Nominations 2nd quarter M.I.P. prediction poll
http://www.physicsforums.com/showthread.php?t=117269
there are a lot more but you cant be complete or the list would be useless
In case anyone is interested, here are links to these arxiv.org searches.
Year 2001:
http://lanl.arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2001/0/1
Year 2002:
http://lanl.arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2002/0/1
Year 2003:
http://lanl.arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2003/0/1
Year 2004:
http://lanl.arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2004/0/1
Year 2005:
http://arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2005/0/1
Year 2006:
http://lanl.arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/2006/0/1
Past 12 months:
http://lanl.arXiv.org/find/grp_physics/1/OR+OR+abs:+AND+AND+loop+quantum+OR+cosmology+gravi ty+abs:+AND+AND+quantum+gravity+OR+OR+discrete+phe nomenology+OR+canonical+nonperturbative+abs:+OR+OR +spinfoam+AND+spin+foam+AND+OR+triply+doubly+speci al/0/1/0/past/0/1
arxiv stats link (thanks to arivero):
http://arxiv.org/Stats/hcamonthly.html
Harvard adsabs link (published articles only)
[e.g. kywd heterotic, superstring, M-theory, brane, AdS/CFT, jan-jun 2001]
http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2001&end_mon=06&end_year=2001&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1)
[e.g. kywd heterotic, superstring, M-theory, brane, AdS/CFT, jan-jun 2006]
http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=06&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1)
Wikipedia articles:
http://en.wikipedia.org/wiki/Background_independence
http://en.wikipedia.org/wiki/Quantum_gravity
http://en.wikipedia.org/wiki/Loop_quantum_gravity
A recent contributor to Wikipedia active since early 2006 is
147.188.42.5
who, among others, seems to have worked hard and made a significant improvement----I see less evidence of hostile obfuscation than in prior versions.
I think he did a good job. AFAICS.
Lubos Motl immediately attacked him with resounding snorts of contempt. hee hee.
Hans Kastrup, a mentor to both Thiemann and Bojowald, had been urging Thomas to write a reply and rebuttal to Herman Nicolai's "Outsider View" paper. So Thiemann called this an "inside" view.
http://arxiv.org/abs/hep-th/0608210
Loop Quantum Gravity: An Inside View
Thomas Thiemann
58 pages
Report-no: AEI-2006-066
"This is a (relatively) non -- technical summary of the status of the quantum dynamics in Loop Quantum Gravity (LQG). We explain in detail the historical evolution of the subject and why the results obtained so far are non -- trivial. The present text can be viewed in part as a response to an article by Nicolai, Peeters and Zamaklar [hep-th/0501114]. We also explain why certain no go conclusions drawn from a mathematically correct calculation in a recent paper by Helling et al [hep-th/0409182] are physically incorrect."
this might turn out to be a useful resource for people interested in learning about LQG
http://relativity.phys.lsu.edu/ilqgs/
International Loop Quantum Gravity Seminar
"This is a seminar on research ... Tuesday at 9am (US Central Time). Audio is distributed via telephone. Slides of the talks are posted in advance here. Talks are recorded and the audio posted here. Among the groups that participate live are PennState, Perimeter Institute, Marseille, AEI-Potsdam, Utrecht, UNAM-Mexico, FUW-Poland, LSU. Others may join soon. Unfortunately, the phone bridge we have has a limited number of lines so we cannot open live participation to everyone. If your group wishes to participate, please write to pullin@lsu.edu You are welcome to join the mailing list."
Seminar Schedule Fall 2006
http://relativity.phys.lsu.edu/ilqgs/schedule.html
Tuesday Sept. 19
LQG FAQ Abhay Ashtekar PennState
Tuesday Sept. 26
Spinfoam graviton propagator: introduction Carlo Rovelli CPT Marseille
Tuesday Oct. 3
Spinfoam graviton propagator Simone Speziale PI
=================
this is a new thing, as of now they have an archive of audio and PDF slides from 3 or 4 past talks and just a few future talks scheduled
some links to the Harvard abstract search tool:
these are for the Jan-August period in six successive years
keywords = superstring, M-theory, brane, heterotic, AdS/CFT
2001: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2001&end_mon=08&end_year=2001&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2002: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2002&end_mon=08&end_year=2002&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2003: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2003&end_mon=08&end_year=2003&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2004: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2004&end_mon=08&end_year=2004&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2005: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2005&end_mon=08&end_year=2005&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=08&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
868, 843, 816, 667, 682 621
===========
2003-2005. keywords AND: loop quantum cosmology
http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=AST&sim_query=YES&ned_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=2003&end_mon=&end_year=2003&ttl_logic=OR&title=&txt_logic=AND&text=loop+quantum+cosmology&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=AST&sim_query=YES&ned_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=2004&end_mon=&end_year=2004&ttl_logic=OR&title=&txt_logic=AND&text=loop+quantum+cosmology&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=AST&sim_query=YES&ned_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=2005&end_mon=&end_year=2005&ttl_logic=OR&title=&txt_logic=AND&text=loop+quantum+cosmology&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
11, 31, 43
someone watching non-string QG might want to have this link to Utrecht ITP
http://www1.phys.uu.nl/wwwitf/
and in particular to consult this page
http://www1.phys.uu.nl/wwwitf/People/Postdocs.htm
(some postdocs: Artem Starodubtsev, Frank Saueressig, Joe Henson, Hanno Sahlmann, possibly Daniele Oriti)
==========
this gives a window on the QG group's seminars at Nottingham
http://www.maths.nottingham.ac.uk/QG/seminars.html
Fall term begins 15 September
PF poster "fh" may be starting there this Fall.
(main people: John Barrett, Kirill Krasnov)
some links to the Harvard abstract search tool:
these are for the Jan-Sept period in six successive years
keywords = superstring, M-theory, brane, heterotic, AdS/CFT
2001: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2001&end_mon=09&end_year=2001&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2002: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2002&end_mon=09&end_year=2002&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2003: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2003&end_mon=09&end_year=2003&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2004: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2004&end_mon=09&end_year=2004&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2005: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2005&end_mon=09&end_year=2005&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=09&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
the last of these is still collecting abstracts since it is not yet the end of the month.
===========
2003-2006. keywords AND: loop quantum cosmology
2003: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=AST&sim_query=YES&ned_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=2003&end_mon=&end_year=2003&ttl_logic=OR&title=&txt_logic=AND&text=loop+quantum+cosmology&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2004: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=AST&sim_query=YES&ned_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=2004&end_mon=&end_year=2004&ttl_logic=OR&title=&txt_logic=AND&text=loop+quantum+cosmology&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2005: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=AST&sim_query=YES&ned_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=2005&end_mon=&end_year=2005&ttl_logic=OR&title=&txt_logic=AND&text=loop+quantum+cosmology&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=AST&sim_query=YES&ned_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=2006&end_mon=&end_year=2006&ttl_logic=OR&title=&txt_logic=AND&text=loop+quantum+cosmology&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
the last of these (2006) is still accumulating abstracts.
The University of Nottingham Maths department has a new website
http://www.maths.nottingham.ac.uk/wp/2006/09/
the link I gave in post #109 no longer works.
a new link to the programme in Quantum Geometry and Gravity is
http://www.maths.nottingham.ac.uk/qg/
Note that PF poster "fh" who just did his Masters with Rovelli at Marseille has gone to Nottingham for PhD.
Nottingham has John Barrett (Barrett-Crane spinfoam model) and Kirill Krasnov (group field theory, with L. Freidel).
Barrett got an important result in Non-Commutative Geometry the same time Alain Connes did, this summer.
the links may continue to change, please let me know if these cease working. I want to be able to keep track of what seminar talks they have in the
Nottingham "Quantum Geometry and Quantum Gravity" program.
(there appears to be some connection with the European Science Foundation---does the ESF officially have a QGQG programme?)
the Nottingham QGQG page says:
"Loop Quantum Cosmology
Loop Quantum Cosmology gives a description of the big bang at the beginning of the universe.
Quantum Groups
Quantum groups enable the calculation of this Feynman diagram coupled to 3d quantum gravity. It shows the diagram is knotted.
Quantum Gravity
The black hole in galaxy NGC 4261 pulls in surrounding dust. The challenge is to describe a black hole according to the laws of quantum mechanics."
I see, John Barrett is the chairman of the governing committee of the european-wide QGQG program, the committee is listed here:
http://www.maths.nottingham.ac.uk/qg/AboutQG.html
Here is the list of QG seminars but so far it is from LAST term (spring 2006):
http://wwwold.maths.nottingham.ac.uk/QG/seminars.html
the Utrecht QG team has been expanded
http://www1.phys.uu.nl/wwwitf/People/Postdocs.htm
Daniele Oriti has joined the research group there
Here are some of the postdocs now at Utrecht
Dr. Joe Henson
Dr. Daniele Oriti
Dr. Irina Pushkina
Dr. Hanno Sahlmann
Dr. Frank Saueressig
Dr. Artem Starodubtsev
some links to the Harvard abstract search tool:
these are for the Jan-August period in six successive years
keywords = superstring, M-theory, brane, heterotic, AdS/CFT
2001: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2001&end_mon=08&end_year=2001&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2002: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2002&end_mon=08&end_year=2002&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2003: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2003&end_mon=08&end_year=2003&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2004: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2004&end_mon=08&end_year=2004&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2005: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2005&end_mon=08&end_year=2005&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=08&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
...
update on the numbers given earlier
2001---868
2002---843
2003---817
2004---668
2005---704
2006---649
===============
update on the QG group at Utrecht
http://www.phys.uu.nl/~loll/Web/group/group.html
Renate Loll lists 8 students (Masters and PhD) plus these postdocs in her group:
Daniele Oriti
Irina Pushkina
Hanno Sahlmann
Artem Starodubtsev
Joe Henson
the main directory for the Utrecht ITF has more information
http://www1.phys.uu.nl/wwwitf/People/Postdocs.htm
some links to the Harvard abstract search tool:
these are for the Jan-Sept period in six successive years
keywords = superstring, M-theory, brane, heterotic, AdS/CFT
2001: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2001&end_mon=09&end_year=2001&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2002: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2002&end_mon=09&end_year=2002&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2003: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2003&end_mon=09&end_year=2003&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2004: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2004&end_mon=09&end_year=2004&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2005: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2005&end_mon=09&end_year=2005&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=09&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
the last of these is still collecting abstracts since it is not yet the end of the month.
...
tentatively,
947, 948, 875, 740, 787, 735
======================
similar links but for January-October
2001: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2001&end_mon=10&end_year=2001&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2002: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2002&end_mon=10&end_year=2002&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2003: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2003&end_mon=10&end_year=2003&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2004: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2004&end_mon=10&end_year=2004&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2005: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2005&end_mon=10&end_year=2005&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=10&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
notknowing
Nov4-06, 02:42 AM
The challenge for string theorists and LQG theorists is to explain why the vacuum energy exists at 10^120 J/m^3 ( there is no reason to think there is anything wrong with the QM calculation) but does not curve space-time.How can
quantum gravity be proved if gravity is not understood on its own yet?
It is very simple why it doesn't curve space-time. The cosmological constant term should simply not be present in the Einstein Field equations. It is a big mistake.
this might turn out to be a useful resource for people interested in learning about LQG
http://relativity.phys.lsu.edu/ilqgs/
International Loop Quantum Gravity Seminar
"This is a seminar on research ... Tuesday at 9am (US Central Time). Audio is distributed via telephone. Slides of the talks are posted in advance here. Talks are recorded and the audio posted here. Among the groups that participate live are PennState, Perimeter Institute, Marseille, AEI-Potsdam, Utrecht, UNAM-Mexico, FUW-Poland, LSU. ...
Seminar Schedule Fall 2006
http://relativity.phys.lsu.edu/ilqgs/schedule.html
Tuesday Sept. 19
LQG FAQ Abhay Ashtekar PennState
Tuesday Sept. 26
Spinfoam graviton propagator: introduction Carlo Rovelli CPT Marseille
Tuesday Oct. 3
Spinfoam graviton propagator Simone Speziale PI
Winston Fairbairn Fermions in 3D spinfoam QG 7 november
Bianca Dittrich Approximate Observables 28 november
more:
http://relativity.phys.lsu.edu/ilqgs/schedulefa06.html
==================
Spring 2007 schedule starts 8 February, nothing lined up yet
Christine blogged for exactly one year and did very nicely at it. One of the last blogs was an invited contribution from Daniele Oriti. He gives a draft table of contents for his book, supposed to come out early 2007.
[/b]Approaches to Quantum Gravity: Towards a New Understanding of Space Time and Matter[/b]
In the book he puts together writings by some 20 or so authors and has Q&A discussion with them at the end of each section. The table of contents can be thought of as giving an overview or schematic picture of current state of QG. I will copy Oriti's guest contribution here, for ready access, in case any of us want to refer to it.
===Daniele Oriti November 2006 at Christine's Background Independence===
Invited contribution: Daniele Oriti
Hi Christine,
Thanks once more for the invitation to contribute to your blog. And, once more, let me congratulate for its well-deserved success, so: happy blog-birthday and keep up the good work!
So, you suggested I could write about the book I am editing (Approaches to quantum grvity: towards a new understanding of space, time and matter) and that is going to be published by C.U.P.
Ok.
The idea is to present an overview of most of the current approaches to quantum gravity, through a collection of introductory papers and reviews each devoted either to one of them or to one particular aspect of one of them. If you are interested, the exact (but provisional, as for the sectioning) table of content is as follows:
- Foreword; Daniele Oriti
-- Ideas and general formalisms
* Unfinished revolution; Carlo Rovelli
* The fundamental nature of space and time; Gerardus 't Hooft
* Choice of variables and initial value problems in classical General
* Relativity: prolegomena to any future Quantum Gravity; John Stachel
* Non-locality in Quantum Gravity; Rafael Sorkin
* Spacetime symmetries in histories canonical gravity; Ntina Savvidou
* Categorical geometry and the mathematical foundations of quantum gravity; Louis Crane
* Holography: a keystone of any quantum gravity theory? Rafael Bousso
* Questions and Answers
-- String/M-Theory
* Gauge/Gravity duality; Gary Horowitz and Joe Polchinski
* String theory, holography and quantum gravity; Tom Banks
* String field theory; Washington Taylor
* Mirror symmetry and quantum gravity; Brian Greene
* Questions and Answers
-- Loop Quantum Gravity
* Loop Quantum Gravity; Thomas Thiemann
* Towards a covariant loop quantum gravity; Etera Livine
* Questions and Answers
-- Spin Foam Models
* The spin foam representation of loop quantum gravity; Alejandro Perez
* 3-dimensional spin foam quantum gravity; Laurent Freidel
* The group field theory approach to Quantum Gravity; Daniele Oriti
* Questions and Answers
-- Discrete Quantum Gravity
* Quantum Gravity, or The Art of Building Spacetime; Renate Loll, J. Jurkiewicz and Jan Ambjorn
* Quantum Regge calculus; Ruth Williams
* Consistent discretizations as a road to quantum gravity; Rodolfo Gambini and Jorge Pullin
* Questions and Answers
-- Causal Sets
* The causal set approach to Quantum Gravity; Joe Henson
* Towards gravity from the quantum; Fotini Markopoulou
* Questions and Answers
-- Other approaches
* Quantum gravity and precision tests; Cliff Burgess
* Asymptotic safety; Roberto Percacci
* Emergent General Relativity; Olaf Dreyer
* Questions and Answers
-- Effective models and Quantum Gravity phenomenology
* Quantum Gravity phenomenology; Giovanni Amelino-Camelia
* Algebraic approach to quantum gravity II: noncommutative spacetime; Shahn Majid
* Effective non-commutative models of quantum flat spacetime; Florian Girelli
* Doubly special relativity; Jurek Kowalski-Glikman
* Lorentz invariance violation and its role in quantum gravity phenomenology; Daniel Sudarsky, John Collins and Alejandro Perez
* Generic predictions of quantum theories of gravity; Lee Smolin
* Questions and Answers
Most of the contributed papers are ready, four of them are still missing (I am not going to tell which ones!), but should be ready soon (hopefully). Some of the papers (around 15 o so out of 30) are available online on the archives. I would say we are almost there....I expect the whole thing to be ready in the beginning of 2007, included all the editing work etc, and to be published soon after. But that depends also on the CUP and I am not sure of their timetable.
Oveall I am quite happy with it. I think it is going to fulfill its scope and motivations, which were (at least for me): a) to show how active and diverse is quantum gravity research at present, and that there is a variety of approaches being pursued, and lots of new work, new ideas (radical, speculative and solidly grounded in physics and mathematics at the same time), new directions and results (some partial but suggestive, some well-established, some surprising); b) to provide a comparative perspective on what's going on in the field; to foster not only this comparative perspective, but also, possibly, future collaboration ad 'cross-fertilisation' among different approaches; c) to allow newcomers and students as well as whoever is interested in the subject to be introduced nicely to it. Ultimately, and most importantly, d) to show that this stuff is fun and exciting to work on and to read about!
You may have noticed the Q&A sections at the end of each part. The idea is that authors can ask questions to each other, put forward comments and criticisms, and get/give answers. The aim is twofold: first, to improve the comparative aspect of the book, in that possible difficulties of the various approaches could be pointed out if not already discussed in the papers, and to present additional ideas and points of view that can be relevant for a given approach, but maybe originated or suggested by another; second, to give an example of how research progresses: out of discussions, criticisms, debate, indeed, questions and answers...This part is being prepared, and I really hope it is going to be rich in content and useful.
I enjoyed reading all the papers, and the Q&A, received so far, so I hope other readers will enjoy them to, and find the whole thing useful. Ultimetely, we don't know yet what quantum gravity is, how long it is going to take still to find out (not much, I hope!), and which, if any, of all these approaches will be found to be the closest to the final theory. It is well possible that none of them, as they are currently understood, matches reality as it will look once we have understood more of it; I wouldn't be too surprised. However, I also believe that we can learn a lot from all of them, and that the final theory will involve aspects (formalisms and techniques, ideas, motivations, results, we don't know yet) of many, if not all, of them. If this is the case, this book may be of help.
====end quote===
some links to the Harvard abstract search tool:
these are for the whole year, in six successive years
keywords = superstring, M-theory, brane, heterotic, AdS/CFT
2001: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2001&end_mon=&end_year=2001&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2002: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2002&end_mon=&end_year=2002&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2003: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2003&end_mon=&end_year=2003&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2004: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2004&end_mon=&end_year=2004&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2005: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2005&end_mon=&end_year=2005&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
the last is still accumulating publications
(additional entries may also show up in earlier years if they come to the librarian's attention belatedly)
the present gross annual publication counts are
1207, 1192, 1107, 1048, 1062, 839 (this last only goes halfway thru November so is bound to increase substantially)
some more links to the Harvard abstract search tool:
these are for the whole year, in four successive years
keywords = superstring, worldsheet, M-theory, brane, heterotic, AdS/CFT
2003: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2003&end_mon=&end_year=2003&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+worldsheet+superstring+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2004: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2004&end_mon=&end_year=2004&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+worldsheet+superstring+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2005: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2005&end_mon=&end_year=2005&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+worldsheet+superstring+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+worldsheet+superstring+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
the last is still accumulating publications since the year is not over---this is as of 20 December
3246, 3153, 3132, 2958
(additional entries may also show up in earlier years if they come to the librarian's attention belatedly)
Francesca alerted us to the QGQG school taking place in March and April at a mountain resort in Poland.
=============
QGQG stands for Quantum Geometry and Quantum Gravity
Formulations of Quantum Gravity based on quantum geometry can be understood to be background independent because the geometry of space is indeterminate and is therefore not fixed in advance, as it would be in a background dependent approach. The school will help to define the field of background independent QG. It is the first project undertaken by the European Science Foundation's newly-formed QGQG Research Network, coordinated by John Barrett (Barrett-Crane spin networks, standard particle model derived from NCG) and by Hermann Nicolai of Albert Einstein Institute (AEI-Golm).
for more information:
http://www.fuw.edu.pl/~kostecki/school.html
The list of those invited to lecture at the school:
Jan Ambjorn (Utrecht)
Abhay Ashtekar (Penn State)
Alain Connes* (Paris)
Laurent Freidel (Perimeter)
Etera Livine (Lyon)
Shahn Majid (London)
Martin Reuter (Mainz)
Jean-Marc Schlenker (Toulouse)
Thomas Thiemann (AEI-Golm)
Ruth Williams* (Cambridge)
* - to be confirmed
===============
here are some guesses as to what these people might talk about
Jan Ambjorn---causal dynamical triangulation (CDT: one of several simplicial QG approaches)
Abhay Ashtekar----(loop) quantum cosmology---the deterministic evolution that replaces the bang singularity
Alain Connes*----obtaining the standard model from non-commutative geometry (NCG)
Laurent Freidel----obtaining Feynman diagrams of usual QFT from spinfoam, the emergence of matter from QG.
Etera Livine----covariant loop quantum gravity (CLQG)
Shahn Majid----NCG---possible connection to DSR and GLAST testability.
Martin Reuter----quantum Einstein gravity (QEG)---showing quantized general relativity to be asymptotically safe
Jean-Marc Schlenker---differential geometry and topology (application?)
Thomas Thiemann----algebraic quantum gravity (AQG) and/or the master constraint program
Ruth Williams*----simplicial QG
first quarter 2006
http://www.physicsforums.com/showthread.php?t=116791
second quarter 2006
http://www.physicsforums.com/showthread.php?t=124951
third quarter 2006
http://physicsforums.com/showthread.php?t=134513
It is still early to be counting citations for most of these---and cite numbers don't tell the whole story.
but in the first quarter poll, five people picked Padmanabhan's paper and it has already 36 cites (Ashtekar's was next with 17)
the five people were arivero, selfAdjoint, Kea, Turbo, and Feynmania.
cites are not conclusive but i think they did indeed pick the paper which is proving the most influential.
in second quarter, arivero and Viking picked the two Ashtekar papers, which so far have been the most-cited choice in that poll, with combined 34 citations
in the third quarter Etera Livine and Energex chose the Freidel paper which has 4 cites as of today------there has not been much time yet for follow-up research papers to be written
arivero picked the pair of papers by Barrett and by Connes (deriving the standard model from Noncommutative Geometry) and they have a total of 6 to date
To continue where the preceding post left off, here is a link to the fourth quarter MIP prediction poll
http://physicsforums.com/showthread.php?t=149466
Also updating (7 January) links to the Harvard abstract search tool:
They are for the whole year, in four successive years,
keywords = superstring, worldsheet, M-theory, brane, heterotic, AdS/CFT.
2003: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2003&end_mon=&end_year=2003&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+worldsheet+superstring+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2004: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2004&end_mon=&end_year=2004&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+worldsheet+superstring+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2005: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2005&end_mon=&end_year=2005&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+worldsheet+superstring+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+worldsheet+superstring+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
As of today, these give the following raw publication numbers:
3248, 3154, 3139, 3049
(additional publications may come to the librarian's attention belatedly and be included later.)
A link for the new year,
2007: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2007&end_mon=&end_year=2007&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+worldsheet+superstring+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
some further links to the Harvard abstract search tool:
these are for the whole year, in seven successive years
keywords = superstring, M-theory, brane, heterotic, AdS/CFT
2001: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2001&end_mon=&end_year=2001&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2002: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2002&end_mon=&end_year=2002&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2003: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2003&end_mon=&end_year=2003&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2004: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2004&end_mon=&end_year=2004&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2005: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2005&end_mon=&end_year=2005&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2007: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2007&end_mon=&end_year=2007&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
the present gross annual publication counts for 2001, 2002, 2003, 2004, 2005, 2006 are
1224, 1193, 1109, 1049, 1062, 1010
including the keyword "worldsheet" in the search has the disadvantage that it picks up a lot of non-string papers from other fields whose abstracts happen to mention the word "sheet", so in these not-too-skillful searches one either gets too few papers or too many. At least one can gauge the trend in annual output, if not the absolute size.
francesca
Jan13-07, 03:17 PM
LOOPS '07
25 - 30 June 2007 Morelia, Mexico
As in previous years, the conference is meant to provide the main international event on quantum gravity with emphasis on non-perturbative and background independent approaches.
Topics include:
* Foundational questions of quantum gravity
* Loop quantum gravity
* Spin foam models
* Dynamical triangulations
* Causal sets
* String theory
* Cosmology related to quantum gravity
* Phenomenology of quantum gravity
The conference is organized through the Instituto de Matemáticas, UNAM, Morelia:
http://www.matmor.unam.mx
Organizing committee:
Alejandro Corichi
Robert Oeckl
José Antonio Zapata
Daniele Colosi
thanks for noticing this Francesca.
I hope we get more information before long. This, I think, was the November 2006 announcement
http://mail.sissa.it/pipermail/ap-sem/2006-November/000196.html
and I have not seen anything more.
to amplify what Francesca said, the city of
Morelia, where LOOPS '07 meeting will be held, is about 200 miles west of mexico city. The National University of Mexico (UNAM) has a campus at Morelia with several research institutes.
Ashtekar, one of the initiators of the LQG approach, has an article whose title contains the words "Introduction to Loop Quantum Gravity...", and which might be a good place to touch base, for anyone who wants an introduction.
http://arxiv.org/abs/gr-qc/0702030
An Introduction to Loop Quantum Gravity Through Cosmology
Abhay Ashtekar
20 pages, 4 figures, Introductory Review
"This introductory review is addressed to beginning researchers. Some of the distinguishing features of loop quantum gravity are illustrated through loop quantum cosmology of FRW models. In particular, these examples illustrate: i) how 'emergent time' can arise; ii) how the technical issue of solving the Hamiltonian constraint and constructing the physical sector of the theory can be handled; iii) how questions central to the Planck scale physics can be answered using such a framework; and, iv) how quantum geometry effects can dramatically change physics near singularities and yet naturally turn themselves off and reproduce classical general relativity when space-time curvature is significantly weaker than the Planck scale."
this paper of Ashtekar's grew out of a talk he gave in Summer 2006 at the First Stueckelberg Workshop at Pescara, italy.
http://www.icra.it/ICRA_Networkshops/INw20_Stueckelberg/Welcome.htm
=======================
here is the Spring 2007 of Jorge Pullin's ONLINE
INTERNATIONAL LQG SEMINAR
http://relativity.phys.lsu.edu/ilqgs/schedulesp07.html
You can listen to the seminar talks online at
http://relativity.phys.lsu.edu/ilqgs/
Just scroll to the bottom of the page and click on PDF to get the slides and click on one of the audio options to hear it.
NOTE: All seminars will be held at 9:00 AM Central Time
Feb 13 UV properties of N=8 supergravity: is it finite? Radu Roiban PennState
Feb 20 KITP program on singularities summary Martin Bojowald PennState
Feb 27 Diffeomorphism invariance in loop quantum gravity Abhay Ashtekar PennState
Mar 13 Kappa Poincare space-time symmetries Michele Arzano Perimeter Institute
Mar 20 TBA Kirill Krasnov Perimeter Institute
Mar 27 Loop quantization of spherically symmetric spacetimes Jorge Pullin Louisiana State University
Apr 3 TBA (about Trinions) Lee Smolin Perimeter Institute
The speaker-list for the QGQG school has been finalized. The lecturers at the school are to be:
Jan Ambjorn
Abhay Ashtekar
Laurent Freidel
Etera Livine
Paweł Kasprzak
Martin Reuter
Jean-Marc Schlenker
Thomas Thiemann
Ruth Williams
Alain Connes and Shahn Majid were possibilities. As of now they will not be lecturing.
Francesca alerted us to the QGQG school taking place in March and April at a mountain resort in Poland.
=============
QGQG stands for Quantum Geometry and Quantum Gravity
Formulations of Quantum Gravity based on quantum geometry can be understood to be background independent because the geometry of space is indeterminate and is therefore not fixed in advance, as it would be in a background dependent approach. The school will help to define the field of background independent QG. It is the first project undertaken by the European Science Foundation's newly-formed QGQG Research Network, coordinated by John Barrett (Barrett-Crane spin networks, standard particle model derived from NCG) and by Hermann Nicolai of Albert Einstein Institute (AEI-Golm).
for more information:
http://www.fuw.edu.pl/~kostecki/school.html
The list of those invited to lecture at the school:
Jan Ambjorn (Utrecht)
Abhay Ashtekar (Penn State)
Alain Connes* (Paris)
Laurent Freidel (Perimeter)
Etera Livine (Lyon)
Shahn Majid (London)
Martin Reuter (Mainz)
Jean-Marc Schlenker (Toulouse)
Thomas Thiemann (AEI-Golm)
Ruth Williams* (Cambridge)
* - to be confirmed
===============
here are some guesses as to what these people might talk about
Jan Ambjorn---causal dynamical triangulation (CDT: one of several simplicial QG approaches)
Abhay Ashtekar----(loop) quantum cosmology---the deterministic evolution that replaces the bang singularity
Alain Connes*----obtaining the standard model from non-commutative geometry (NCG)
Laurent Freidel----obtaining Feynman diagrams of usual QFT from spinfoam, the emergence of matter from QG.
Etera Livine----covariant loop quantum gravity (CLQG)
Shahn Majid----NCG---possible connection to DSR and GLAST testability.
Martin Reuter----quantum Einstein gravity (QEG)---showing quantized general relativity to be asymptotically safe
Jean-Marc Schlenker---differential geometry and topology (application?)
Thomas Thiemann----algebraic quantum gravity (AQG) and/or the master constraint program
Ruth Williams*----simplicial QG
Francesca pointed out today that the program of talks has now been posted for the QGQG school
http://www.fuw.edu.pl/~kostecki/school.html
this is specifically aimed at getting grad students started in one of the several branches of QG2 research, so you don't necessarily have to be following all the talks to benefit from the school
it is like a Smorgasbord where you only take what you want and can handle.
Jan Ambjorn - Matrix models in non-critical string theory and quantum gravity
Abhay Ashtekar - Loop Quantum Cosmology
Laurent Freidel - Spin-Foam Models
Etera Livine -
Paweł Kasprzak - Locally compact quantum Lorentz groups
Martin Reuter - Asymptotic Safety in Quantum Einstein Gravity
Jean-Marc Schlenker - Hyperbolic geometry for 3d gravity
Thomas Thiemann - Loop Quantum Gravity
Ruth Williams - Introduction to Regge Calculus
If I were there I probably would just go to these series
Abhay Ashtekar - Loop Quantum Cosmology
Laurent Freidel - Spin-Foam Models
Etera Livine -
Thomas Thiemann - Loop Quantum Gravity
So I would just list the series of talks to be given by AA, LF, EL, TT.
Of these, only LF has already given titles of individual talks
Laurent Freidel: Spin-Foam Models
1. General introduction to spin foams
2. 3D Gravity and introduction to some group theory
3. The Ponzano-Regge model derivation and its properties
4. The Ponzano-Regge model + matter
5. Effective field theory
for the other three we only know how many talks each is giving and the timeslots. What follows are exerpts from the program:
Lectures will start everyday at 14.00. Every lecture will take 45 minutes, and there will be 15 minutes of break between lectures. Note that first lecture starts Mar, 23 at 14.00, while the last lecture ends Apr, 3 at 19.00.
Friday, Mar 23
Abhay Ashtekar: Loop Quantum Cosmology (1)
Saturday, Mar 24
Abhay Ashtekar: Loop Quantum Cosmology (2)
Abhay Ashtekar: Loop Quantum Cosmology (3)
Sunday, Mar 25
Abhay Ashtekar: Loop Quantum Cosmology (4)
Abhay Ashtekar: Loop Quantum Cosmology (5)
Monday, Mar 26
Abhay Ashtekar: Loop Quantum Cosmology (6)
Abhay Ashtekar: Loop Quantum Cosmology (7)
Laurent Freidel: Spin-Foam Models (1)
Tuesday, Mar 27
Informal discussion, excursion, attractions
Wednesday, Mar 28
Thomas Thiemann: Loop Quantum Gravity (1)
Laurent Freidel: Spin-Foam Models (2)
Thursday, Mar 29
Laurent Freidel: Spin-Foam Models (3)
Thomas Thiemann: Loop Quantum Gravity (2)
Friday, Mar 30
Laurent Freidel: Spin-Foam Models (4)
Laurent Freidel: Spin-Foam Models (5)
Thomas Thiemann: Loop Quantum Gravity (3)
Saturday, Mar 31
Informal discussion, excursion, attractions
Sunday, Apr 1
Thomas Thiemann: Loop Quantum Gravity (4)
Thomas Thiemann: Loop Quantum Gravity (5)
Etera Livine (1)
Monday, Apr 2
Thomas Thiemann: Loop Quantum Gravity (6)
Thomas Thiemann: Loop Quantum Gravity (7)
Etera Livine (2)
Tuesday, Apr 3
Etera Livine (3)
Thomas Thiemann's student (1)
I think the last talk is being given by Kristina Giesel, a postdoc at Perimeter.
It looks like AA is giving 7 talks, LF is giving 5 talks, TT is giving 7 with an additional talk by Kristina.
LOOPS '07
25 - 30 June 2007 Morelia, Mexico
...
...
http://www.matmor.unam.mx
...
Some more detail has been posted at the UNAM Morelia website
http://www.matmor.unam.mx/eventos/loops07/index.html
====some exerpts from the announcement====
Scientific Advisory Committee
* Jan Ambjørn
* Abhay Ashtekar
* John W. Barrett
* Fay Dowker
* Jerzy Lewandowski
* Hugo Morales Tecotl
* Jorge Pullin
* Carlo Rovelli
* Lee Smolin
* Thomas Thiemann
At this time the program is in an early planning stage. Below is the list of plenary speakers with titles of talks. Abstracts can be displayed by clicking on the title of the respective talk or by going to the abstracts page. When more detailed information on the program is available it will be posted on this site.
Plenary Speaker--------- Title
Jan Ambjørn
Abhay Ashtekar "LQG: Lessons from models"
Martin Bojowald "Loop quantum cosmology and effective theory"
John F. Donoghue
Klaus Fredenhagen
Lucien Hardy "The causaloid formalism: a tentative framework for quantum gravity"
James B. Hartle "Generalizing Quantum Mechanics for Quantum Gravity"
Sabine Hossenfelder "Phenomenological Quantum Gravity"
Bei-Lok B. Hu
Fotini Markopoulou
Daniele Oriti
Alejandro Perez
Hendryk Pfeiffer "Quantum gravity, TQFTs and categorification"
Jorge Pullin "Uniform discretizations and spherically symmetric loop quantum gravity"
Michael Reisenberger
Martin Reuter "Asymptotically safe quantum gravity and cosmology"
David Rideout
Carlo Rovelli
Moshe Rozali*
Lee Smolin
Rafael Sorkin*
Artem Starodubtsev
Jörg Teschner*
Thomas Thiemann
(* to be confirmed) Last updated 2 March 2007.
Abstracts are already available for some of the invited plenary talks to be given at this years Loops '07
===quote from Loops '07 site===
Abstracts of plenary talks:
Martin Bojowald: Loop quantum cosmology and effective theory
Several models have been defined to study the broad framework of loop quantum gravity. We present a common perspective for cosmology where configurations are close to being isotropic. Effective techniques are then used to illustrate important features of the semiclassical limit and to show examples of correction terms to Einstein's equation. Applications include corrections to the Newton potential and to cosmological perturbation equations relevant for the CMB power spectrum.
John F. Donoghue: Effective field theory and quantum general relativity
I will review the foundations and recent progress in the use of effective field theory to elucidate the quantum predictions of general relativity.
Lucien Hardy: The causaloid formalism: a tentative framework for quantum gravity
General Relativity is a deterministic theory with non-fixed causal structure. Quantum Theory is an inherently probabilistic theory with fixed causal structure. A theory of Quantum Gravity must reduce, in appropriate limits, to General Relativity and Quantum Theory. It seems likely, therefore, that Quantum Gravity will inherit the radical aspects of these two less fundamental theories – namely that it will be a probabilistic theory with non-fixed causal structure. In this talk I will present the causaloid formalism which is a general framework for such theories. I will show how Quantum Theory can be formulated in the causaloid framework and provide tentative results for how it may be possible to formulate General Relativity in the framework. Finally, I will discuss the issue of formulating a theory of Quantum Gravity using the causaloid formalism.
James Hartle: Generalizing Quantum Mechanics for Quantum Spacetime
Familiar textbook quantum mechanics assumes a fixed background spacetime to define states on spacelike surfaces and their unitary evolution between them. Quantum theory has been generalized as our conceptions of space and time have evolved. But quantum mechanics needs to be generalized further for quantum gravity where spacetime geometry is fluctuating and without definite value. This talk will review a fully four-dimensional, sum-over-histories, generalized quantum mechanics of cosmological spacetime geometry. In this generalization, states of fields on spacelike surfaces and their unitary evolution are emergent properties appropriate when spacetime geometry behaves approximately classically. The principles of generalized quantum theory would allow for further generalization that would be necessary were spacetime not fundamental. Emergent spacetime phenomena are discussed in general and illustrated with the examples of the classical spacetime geometries with large spacelike surfaces that emerge from the `no-boundary' wave function of the universe. These must be Lorentzian with one, and only one, time direction. The question will be raised as to whether quantum mechanics itself is emergent.
Jorge Pullin: Uniform discretizations and spherically symmetric loop quantum gravity
We discuss the application of the uniform discretization procedure to handle the dynamics of loop quantum gravity with spherical symmetry.
Martin Reuter: Asymptotically safe quantum gravity and cosmology
The basic ideas and main results of the asymptotic safety scenario in Quantum Einstein Gravity (QEG) are reviewed and possible implications for the cosmology of the early universe are discussed.
Moshe Rozali: Background Independence in String Theory
I review several notion of background independence in quantum gravity: full or partial, manifest or not etc., and discuss the evidence for and against taking the notion seriously as a guide for research. I review the current status in string theory with regard to this question and discuss the extent to which existing non-perturbative formulations of string theory are background independent.
Artem Starodubtsev: Some physical results from spinfoam models
Given the known mathematical fact that a spinfoam is a Feynmann diagram the data relevant for particle scattering amplitudes could be identified in it.
==endquote==
http://www.matmor.unam.mx/eventos/loops07/index.html
Updating some useful benchmarks from the Harvard abstract search tool:
these are for the whole year
keywords = superstring, M-theory, brane, heterotic, AdS/CFT
2002: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2002&end_mon=&end_year=2002&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2006&end_mon=&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2007: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=&start_year=2007&end_mon=&end_year=2007&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
the following are for the first three months of the year, same years and keywords
2002: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=00&start_year=2002&end_mon=03&end_year=2002&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2006: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=00&start_year=2006&end_mon=03&end_year=2006&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
2007: http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&qform=PHY&aut_logic=OR&author=&ned_query=YES&sim_query=YES&start_mon=00&start_year=2007&end_mon=03&end_year=2007&ttl_logic=OR&title=&txt_logic=OR&text=heterotic+M-theory+brane+superstrings+AdS%2FCFT&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1
Using these one can at least gauge the trend in annual output, if not the absolute size.
as of now, first triple: 1130, 947, ?
second triple (provis.) 401, 323, 199
Followup on QGQG-1 school in Zakopane Poland (program listed above):
QGQG-2 school will be in June 2008, in Denmark.
The most complete blog report on the first QGQG school is here:
Part 1 of report---Thomas Thiemann's lectures including the Master Constraint, discussion with T.T. of (semi) classical limit; Eugenio Bianchi's explanation of the LQG graviton paper of Rovelli et al; Laurent Freidel and Etera Livine spinfoam talks development of Feynman diagram for matter from QG
http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_08.html
Part 2 of report---Martin Reuter's QEG assymptotic safety
http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_10.html
General comment and pictures:
http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school.html
QGQG conference will be held in Nottingham UK in July 2008
windscar
Apr16-07, 07:31 AM
I think if you really wanted to explain what the loops are in loop quantum gravity, you would have to at least add one extra dimension. General Relativity added a higher space dimension and if quantum loop gravity wishes to combine this theory with quantum theory, I think it would only be fair. One thing about General Relativity is that it explained eliptical orbits by explaining that space was curved. I once wondered how matter could actually curve space, and I thought what if matter is actual indentions in space time itself or intersection with a higher dimension that we can not move in. If you were too look at a particle as an indention of space time itself, then as other particles passed by it, they would "loop".
AUDIO for the Zakopane QG school lectures are available online
Here is Carlo Rovelli's first talk
http://www.maths.nottingham.ac.uk/qg/Meetings/Zakopane/recordings/cr1.mp3
this is an insightful and foresightful non-technical talk. it comes across well on audio because he does not have to use the whiteboard very much.
people liked this talk because it stimulated them very much to think.
the other lectures were depending on handout pieces of paper and writing on the board, so not all of it comes through in audio.
however Etera Livine seemed to give a very good lecture and also I was interested in some of what Jan Ambjorn said by way of introduction. I have only sampled a few so far.
Richard Kostecki "Path-Integral" the local organizer of the Zakopane school has put links to all the audio here
http://www.fuw.edu.pl/~kostecki/school.html
==============
The homebase for the European Union Quantum Gravity network is here
http://www.maths.nottingham.ac.uk/qg/
the name of the network is "Quantum Geometry and Quantum Gravity" or "QGQG"
the main director is John Barrett
I think in the name it is important to say Geometry first, not as an afterthought. IOW it means "Quantum Geometrical Gravity".
Approaches in which gravity is not merely one of many forces but is the geometry of space and time.
We are dealing with quantum theories, therefore, in which spacetime is NOT A MANIFOLD but a web of relations between geometrical operators---relations between geometric observables---background independent quantum theories
===============
Some detail is available about the "QG-squared 2008 conference to be at Nottingham UK in July 2008.
http://www.maths.nottingham.ac.uk/conferences/qgsquared-2008/
"Monday June 30th - Friday July 4th 2008
University of Nottingham, UK
Topics:
* Quantum gravity, including loop quantum gravity, spin foam models, 1+1 and 2+1 quantum gravity, perturbative approaches and other discrete approaches.
* Quantum geometry, including physical aspects of non-commutative geometry, quantum groups and quantum topology. Non-commutative field theory and deformed special relativity.
The meeting is sponsored by the QG network of the European Science Foundation."
=========
the orange paperback edition of Smolin's book is scheduled to go on sale 4 September 2007, that is in a little over 2 months from now. advance ordering has begun on UK-amazon, US-amazon, and in Canada.
=========
Garrett Lisi's surprising paper to be delivered at Loops '07 in Mexico 4 days from now (Tuesday 26 June) is available in slides+audio form at his website
http://deferentialgeometry.org/
advice: use two screens, download the PDF of the slides and view on one screen scrolling down
while keeping the menu of the audio segments on the other screen and click on them in sequence
so you hear the whole 20 minute talk without interruption
==========
just realized that Richard Kostecki website might be useful to keep a link to
http://www.fuw.edu.pl/~kostecki/
besides organizing the Zakopane school he does other things and has a useful set of links
==========
Martin Bojowald gave a report on the KITP Singularities workshop (which he co-organized with Gary Horowitz and others).
He gave it in April 2007. three months after the workshop, on the International LQG Seminar (ilqgs)
http://relativity.phys.lsu.edu/ilqgs/
One thing to realize is that the LQG community is very young.
IT ONLY JUST STARTED having a international conference on a nearly annual basis. The annual conference is a conventional way that research communities define themselves.
I would say that the three most visible defining events were the two conferences (Loops 05 and Loops 07) and the 2007 Zakopane QG school. Another important landmark was the 2006 founding by the ESF of the European Science Foundation QG network---supported by 8 countries. The QG Network organizes and sponsors workshops, conferences, and gives individual research grants. It's first conference will be summer 2008. Its first school for graduate students and postdocs was the one at Zakopane. Invitation to lecture at the school is to some extent defining: like being invited to give a plenary talk.
One can see what research lines are pursued in the LQG community (more correctly the non-string QG community, but people seem to prefer to say LQG) by looking at the programs of the Loops conferences and the Zakopane school.
Lines of research in the community are Spinfoam, Group Field Theory, CDT, Causal Sets, applications to Cosmology (LQC), Assymptotically safe QG (Reuter et al), AQG and Master Constraint (Thiemann et al.), Braided LQG and matter. These are the main approaches that I know of. Except for Causal Sets and Reuter's, all of these approaches date from 1998 or later. Thiemann's AQG and Master Constraint program is an outgrowth of vintage 1990s canonical LQG. So we have a community doing lines of research that are mostly less than 10 years old, which just started having an annual conference---just barely annual if it has one next year.
Research communities define themselves in part by having leaders, and you can often tell who the leaders are by who gives the INVITED TALKS at the main annual conference. This is hardly a surefire method! The LQG community has a practice of inviting OUTSIDERS at least on a one-time basis---as a way of encouraging interchange and of keeping open to the outside. Loops 05 had an invited talk by Robbert Dijkgraaf, a prominent string thinker. But for what it's worth we can check to see who were the REPEAT invited speakers at Loops 05, Loops 07, and the Zakopane school.
This has the merit of being a little objective, instead of my just telling you my opinion. I'll just score individuals and list those who score 2 or more. Two individuals, Rovelli and Reuter, gave invited presentations at all three events.
Carlo Rovelli 3
Martin Reuter 3
Jan Ambjorn 2
Abhay Ashtekar 2
Martin Bojowald 2
Laurent Freidel 2
Etera Livine 2
Daniele Oriti 2
Alejandro Perez 2
Lee Smolin 2
Raphael Sorkin 2
Thomas Thiemann 2
Here are links if you would like to see if I have missed anyone.
2005 plenaries
http://loops05.aei.mpg.de/index_files/Programme.html
2007 plenaries
http://www.matmor.unam.mx/eventos/loops07/plen_abs.html
first QG Network school
http://www.fuw.edu.pl/~kostecki/school.html
One obvious omission is John Barrett, whose research is in Non-commutative Geometry (NCG) and Spinfoam models, e.g. the familiar Barrett-Crane model. John Barrett is the director of the QG Network. And there's Renate Loll, who directs another ESF funding network--in random geometry--which supports a considerable amount of LQG community research. But there are a lot of omissions, in my subjective view, so I won't labor the point.
I'm using some simple objective measures to say what the main lines of research, who the leaders---instead of just giving a summary of my impressions from watching over the past 3 or 4 years. The previous post lists the main lines of research represented at Loops '07 and the people usually invited to speak at the community's defining events. Quantitative measures like this aren't perfect but they might catch detail that subjective impressions miss.
Something to point out is that 3 of the leading people in the LQG (more correctly the non-string QG) community are among the recently most cited people in quantum cosmology (QC).
QC has a strategic place in QG as a whole. It is where TESTABILITY is apt soonest to show up. Also because of the simplifying assumptions made in cosmology the QC people can symmetry-reduce and get tractible models and calculate numbers readily. Calculation can also be done, and is being done, in the full theory (in several non-string QG approaches) but it is less tractible and takes more computing power.
The three I refer to are Ashtekar, Bojowald, and Reuter. They have done noteworthy, in some cases famous, research outside quantum cosmology, but all three have at least a few RECENT papers focusing on QC, and their cosmology work has been widely cited. I will include quantum black holes papers since both the topics themselves and methods used are closely related. For simplicity I will only count papers from after 1999, and only those with 35+ cites to date. Some of the 2000-2003 papers, which have had time to accumulate cites, are in the 100+ category. The numbers for Bojowald are different partly because his work has always focused on quantum cosmology and closely allied topics.
As of 31 July. The number of 35+ papers is in parens and the total cites to just those papers is given.
Bojowald (23) 1550
Ashtekar (6) 488
Reuter (5) 267
The three have numerous collaborators. Some of their co-workers are themselves also highly cited recent QC authors. I'm not trying to make a complete list, but simply to see who among the dozen or so leaders in the LQG community that I listed in the previous post are especially active in quantum cosmology. I think it's just these three.
Quantum cosmology is a small field---other people you may think of as important figures in the field were, in several cases, active during the 1980s and 1990s, but have very little output after 1999 (particularly if one restricts to papers with 35+ cites.)
One thing to realize is that the LQG community is very young.
IT ONLY JUST STARTED having a international conference on a nearly annual basis. The annual conference is a conventional way that research communities define themselves.
I would say that the three most visible defining events were the two conferences (Loops 05 and Loops 07) and the 2007 Zakopane QG school. Another important landmark was the 2006 founding by the ESF of the European Science Foundation QG network...
To followup on this. The QG Network of the ESF is hosting a weeklong conference in the UK starting 30 June 2008 and calling it
QG2 2008
Part of the point is that it will include physical aspects of Noncommutative Geometry under the heading "Quantum Geometry".
The QG Network official title is ESF Network for "Quantum Geometry and Quantum Gravity", with geometry coming first, and this makes a point.
On the whole I think the terminology is more descriptive of the actual range of research in the non-string QG community----more accurately descriptive than the lump term "LQG community" that people, especially outsiders, tend to use.
ONE OF THE POSTERS HERE AT PF IS ON THE LOCAL ORGANIZING COMMITTEE for QG2 2008
http://www.maths.nottingham.ac.uk/conferences/qgsquared-2008/organizers/
The director of the QG Network, John Barrett, has done research BOTH in Noncommutative Geometry and in Spinfoam quantum gravity. He and Alain Connes came out with the same result about realizing the particletheory Standard Model, the same week last year (fall 2006). John Barrett is also on the local organizing committee.
this has to be the moral equivalent of "Loops 08" but by a different name (and maybe a better name!).
Also even stronger conference than Loops 05 and Loops 07 were because including NCG. It is not impossible that Alain Connes would show up and give a talk.
Here is the QG2 2008 Scientific Committee
Victor Aldaya (Granada)
Abhay Ashtekar (Penn State)
John Baez (UC Riverside)
Jürg Fröhlich (ETH, Zürich)
Harald Grosse (Vienna)
Shahn Majid (QMUL)
Carlo Rovelli (Marseille)
Thomas Schücker (Provence)
Lee Smolin (Perimeter)
Here's the website for the conference
http://www.maths.nottingham.ac.uk/conferences/qgsquared-2008/
Lately I've been finding it useful to cite the video and slides of Carlo Rovelli's talk at Strings 2008.
It is a very good introductory overview for people who don't know much about LQG,
Here are the links:
Video:
http://cdsweb.cern.ch/record/1121957?ln=en
Slides:
http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917[/QUOTE]
To find this post again, click on the sticky Possibly Useful Threads, and then click on Introduction to LQG,
and then topright where it says "page 1 of 9" click on "last" (or whatever it takes to get to page 9)
Perhaps the simplest way to take a group snapshot of recent LQG research is to record the ten most cited papers that have appeared in the last three years. That is "date > 2005" in Spires language.
This snapshot will change from year to year. If I remember to record it one year from today, on 1 Jan 2010, then it will be "date > 2006" (namely the most cited papers from 2007, 2008, and 2009.)
The titles and abstracts of most-cited papers can help to indicate any shifts in focus and delineate current frontiers. This possibly-useful-thread component seems like a good place to keep this kind of record because it stays within reach.
So here is what the Spires link says as of today:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+GRAVITY+AND+DK+LOOP+SPA CE+AND+DATE+%3E+2005&FORMAT=www&SEQUENCE=citecount%28d%29
1) Loop quantum cosmology.
Martin Bojowald
http://arxiv.org/abs/gr-qc/0601085
Cited 155 times
2) Graviton propagator in loop quantum gravity.
Eugenio Bianchi, Leonardo Modesto, Carlo Rovelli, Simone Speziale
http://arxiv.org/abs/gr-qc/0604044
Cited 61 times
3) The Loop-quantum-gravity vertex-amplitude.
Jonathan Engle, Roberto Pereira, Carlo Rovelli
http://arxiv.org/abs/0705.2388
Cited 45 times
4) An Introduction to Loop Quantum Gravity Through Cosmology.
Abhay Ashtekar
http://arxiv.org/abs/gr-qc/0702030
Cited 41 times
5) A New Spin Foam Model for 4d Gravity.
Laurent Freidel, Kirill Krasnov
http://arxiv.org/abs/0708.1595
Cited 41 times
6) Flipped spinfoam vertex and loop gravity.
Jonathan Engle, Roberto Pereira, Carlo Rovelli
http://arxiv.org/abs/0708.1236
Cited 35 times
7) The Complete LQG propagator. I. Difficulties with the Barrett-Crane vertex.
Emanuele Alesci, Carlo Rovelli
http://arxiv.org/abs/0708.0883
Cited 34 times
8) Loop Quantum Gravity: An Inside View.
Thomas Thiemann
http://arxiv.org/abs/hep-th/0608210
Cited 31 times
9) LQG vertex with finite Immirzi parameter.
Jonathan Engle, Etera Livine, Roberto Pereira, Carlo Rovelli
http://arxiv.org/abs/0711.0146
Cited 30 times
10) Hamiltonian cosmological perturbation theory with loop quantum gravity corrections.
Martin Bojowald, Hector H. Hernandez, Mikhail Kagan, Parampreet Singh, Aureliano Skirzewski
http://arxiv.org/abs/gr-qc/0609057
Cited 28 times
Some helpful links, for staying informed
http://www.gr19.com/index.php
http://grg.maths.qmul.ac.uk/hyperspace/conference/08Dec.8.html
http://www.icra.it/MG/mg12/en/parallel_session.htm#
http://www.icra.it/MG/mg12/en/
http://grg.maths.qmul.ac.uk/hyperspace/conference/
http://strings2009.roma2.infn.it/home.html
Rovelli's 2008 LQG overview:
http://relativity.livingreviews.org/Articles/lrr-2008-5/
His 2008 LQG survey talk to the Strings '08 conference, video
http://cdsweb.cern.ch/record/1121957?ln=en
Page for Yongge Ma, a principal organizer of the August 2009 Loops 09 conference.
http://physics.bnu.edu.cn/application/research/gravity/LQG/eng/research.html
Most cited quantum cosmology papers, 2006 and later:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+cosmology+AND+DATE+%3E+ 2005&FORMAT=www&SEQUENCE=citecount%28d%29
Preliminary list of speakers for the XXV Max Born
(Warsaw 29 June-3 July)
J. Ambjorn (NBI, Copenhagen)
G. Amelino-Camelia (La Sapienza, Rome)
M. Arzano (PI, Waterloo)
A.P. Balachandran (Syracuse Univ.)
J. Barrett (Univ. Nottingham)
E. Bergshoeff (Univ. Groeningen)
M. Bojowald (Penn State)
S. Carlip (UC Davis)
M. Chaichian (Univ. Helsinki)
A. Chamseddine (Univ. Beirut)
L. Dabrowski (SISSA)
S. Doplicher (La Sapienza, Rome)
O. Dreyer (MIT)
M. Duff (Imperial Coll. London)
J. Figueroa-O'Farrill (Univ. Edinburgh)
L. Freidel (PI, Waterloo)
G. Gibbons (DAMTP Cambridge)
S. Giddings (UC Santa Barbara)
T.R. Govindarayan (Chennai)
A. Grillo (Gran Sasso)
J. Jurkiewicz (Jagiellonian Univ.)
F. Lizzi (Univ. Naples)
R. Loll (Univ. Utrecht)
J. Lukierski (Univ. Wroclaw)
J. Magueijo (Imperial Coll. London)
F. Markopoulou (PI, Waterloo)
D. Marolf (UC Santa Barbara)
N. Mavromatos (King's Coll. London)
C. Meusburger (Univ. Nottingham)
L. Modesto (PI, Waterloo)
H. Nicolai (AEI, Golm)
D. Oriti (PI, Waterloo)
K. Peeters (Univ. Utrecht)
G. Piacitelli (SISSA)
M. Pospelov (Victoria Univ & PI)
C. Rovelli (Marseille, CPT)
B. Schroers (Heriot-Watt Univ. Edinburgh)
B. Sidharth (Udine Univ.)
K. Skenderis (Univ. Amsterdam)
L. Smolin (PI, Waterloo)
R. Szabo (Univ. Edinburgh)
T. Thiemann (AEI, Golm)
A. Tureanu (Univ. Helsinki)
S. Vaidya (Indian Inst. Sci. Bangalore)
Ch. Young (Univ. Durham)
The five major themes of the Symposium will be:
Loops and spin foams
Strings, AdS/CFT, and quantum gravity
Field theoretical perspective on Planck scale
Noncommutative spacetimes
Quantum gravity phenomenology
Organizers:
Jerzy Kowalski-Glikman (University of Wroclaw)
Krzysztof Meissner (University of Warsaw)
The Warsaw symposium is interesting in part because of the preliminary mix of speakers. Here's a partial list of some you might recognize from their association with nonperturbative background independent QG (Loop and related, Causal Dynamical Triangulations, Noncommutative Geometry, QG Phenom)
J. Ambjorn (NBI, Copenhagen)
G. Amelino-Camelia (La Sapienza, Rome)
J. Barrett (Univ. Nottingham)
M. Bojowald (Penn State)
S. Carlip (UC Davis)
A. Chamseddine (Univ. Beirut)
O. Dreyer (MIT)
L. Freidel (PI, Waterloo)
J. Jurkiewicz (Jagiellonian Univ.)
R. Loll (Univ. Utrecht)
J. Lukierski (Univ. Wroclaw)
J. Magueijo (Imperial Coll. London)
F. Markopoulou (PI, Waterloo)
L. Modesto (PI, Waterloo)
D. Oriti (PI, Waterloo)
C. Rovelli (Marseille, CPT)
L. Smolin (PI, Waterloo)
T. Thiemann (AEI, Golm)
Updated helpful links, for staying informed
General
http://www.maths.nottingham.ac.uk/qg/
http://grg.maths.qmul.ac.uk/hyperspace/conference/
Rome 22-26 June
http://strings2009.roma2.infn.it/home.html
Warsaw (XXV Max Born) 29 June-3 July
http://www.ift.uni.wroc.pl/~planckscale/
http://www.ift.uni.wroc.pl/~planckscale/index.html?page=speakers
http://www.fuw.edu.pl/~meissner/home.html
Paris (MG12) 12-18 July
http://www.icra.it/MG/mg12/en/
http://www.icra.it/MG/mg12/en/parallel_session.htm#
Beijing (Loops09) 2-8 August
http://grg.maths.qmul.ac.uk/hyperspace/conference/08Dec.8.html
Mexico City (GR19)
http://www.gr19.com/index.php
Rovelli's 2008 LQG overview:
http://relativity.livingreviews.org/Articles/lrr-2008-5/
2008 LQG survey talk to the Strings '08 conference, video and slides
http://cdsweb.cern.ch/record/1121957?ln=en
http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917
2008 LQG survey talk to Loops '08, general, slides, audio
http://www.maths.nottingham.ac.uk/qg/wiki/index.php/QGsquared-slides
http://www.maths.nottingham.ac.uk/qg/wiki/images/3/3f/RovelliCarlo1214510081.pdf
Most cited Loop QG papers, 2006 and later:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+GRAVITY+AND+DK+LOOP+SPA CE+AND+DATE+%3E+2005&FORMAT=www&SEQUENCE=citecount%28d%29
Most cited (all types of) quantum cosmology papers, 2006 and later:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+cosmology+AND+DATE+%3E+ 2005&FORMAT=www&SEQUENCE=citecount%28d%29
A list of plenary speakers for MG12 (Paris 12-16 July) has been posted:
http://www.icra.it/MG/mg12/en/invited_speakers.htm
Speakers include Alain Connes, Laurent Freidel, Herbert Hamber
Hamber is known for discrete nonperturbative QG work, Regge-related and lattice QG methods. Here is a recent review paper of his:
http://arxiv.org/abs/0901.0964
Speakers list has been posted for
Black Holes and Loop Quantum Gravity
Valencia, Spain 26-28 March, 2009.
Abhay Ashtekar
Martin Bojowald *
Alejandro Corichi
Bianca Dittrich
Jonathan Engle
Amit Ghosh
Viqar Husain
Jerzy Lewandowski *
Jorge Pullin
Hanno Sahlmann
Madhavan Varadarajan
* To be confirmed
http://www.uv.es/bhlqg/speakers.htm
http://www.uv.es/bhlqg/
Topics for the BH and LQG workshop:
- Black hole entropy in LQG
- Spin foam approach to black holes
- Singularity resolution and information loss
- Prospects for a detailed description of the Hawking radiation
- Comparison between results from LQG and other approaches
Another useful link for keeping informed:
http://www.maths.nottingham.ac.uk/qg/Meetings.html
The names of the main speakers have been posted for the Second Quantum Geometry and Quantum Gravity School.
In addition there will be invited seminars by a number of others (not yet listed.)
Two PF members were at the first QGQG school, and reported on it. It was at Zakopane (ski resort in Poland.)
This time the school will be at Corfu,13-20 September.
http://www.maths.nottingham.ac.uk/qg/CorfuSS.html
Each of the main speakers will give a series of lectures during the course of the week (a minicourse):
Abhay Ashtekar Loop Quantum Gravity
John Baez Categorification in Fundamental Physics
John Barrett Spin networks and quantum gravity
Vincent Rivasseau Renormalization in Fundamental Physics
Carlo Rovelli (*) Covariant loop quantum gravity and its low-energy limit
Projected course descriptions are at the website. I quote here just one--Rovelli's:
"I present a new look on Loop Quantum Gravity, aimed at giving a better grasp on its dynamics and its low-energy limit. Following the highly succesful model of QCD, general relativity is quantized by discretizing it on a finite lattice, quantizing, and then studying the continuous limit of expectation values. The quantization can be completed, and two remarkable theorems follow.
The first gives the equivalence with the kinematics of canonical Loop Quantum Gravity.
This amounts to an independent re-derivation of all well known Loop Quantum gravity kinematical results.
The second [gives] the equivalence of the theory with the Feynman expansion of an auxiliary field theory. Observable quantities in the discretized theory can be identified with general relativity n-point functions in appropriate regimes. The continuous limit turns out to be subtly different from that of QCD, for reasons that can be traced to the general covariance of the theory.
I discuss this limit, the scaling properties of the theory, and I pose the problem of a renormalization group analysis of its large distance behavior."
(my highlighting etc.)
Here's an updated "top 20" snapshot of the field, the 20 most-cited papers from the past 2 years (date > 2006).
The list makes clear which have been the predominant themes of research recently: the new vertex, establishing a new covariant version of LQG consistent with the older canonical version, checking that the low energy limit comes out right (graviton propagator), and as always cosmology (LQC).
There is one new theme that did not show up until paper number 23 in the list. The bridge between LQG and LQC--which may lead to cosmological tests of LQG. Although it didn't make the top 20 this time, I will append that paper.
1) The Loop-quantum-gravity vertex-amplitude.
Jonathan Engle, Roberto Pereira, Carlo Rovelli (Marseille, CPT) . May 2007. 6pp.
Published in Phys.Rev.Lett.99:161301,2007.
e-Print: arXiv:0705.2388 [gr-qc]
Cited 49 times
2) An Introduction to Loop Quantum Gravity Through Cosmology.
Abhay Ashtekar (Penn State U. & Santa Barbara, KITP) . 20pp.
Published in Nuovo Cim.122B:135-155,2007.
e-Print: gr-qc/0702030
Cited 46 times
3) A New Spin Foam Model for 4d Gravity.
Laurent Freidel (Perimeter Inst. Theor. Phys.) , Kirill Krasnov (Perimeter Inst. Theor. Phys. & Nottingham U.) . 40pp.
Published in Class.Quant.Grav.25:125018,2008.
e-Print: arXiv:0708.1595 [gr-qc]
Cited 46 times
4) Flipped spinfoam vertex and loop gravity.
Jonathan Engle, Roberto Pereira, Carlo Rovelli (Marseille, CPT) . 37pp.
Published in Nucl.Phys.B798:251-290,2008.
e-Print: arXiv:0708.1236 [gr-qc]
Cited 38 times
5) The Complete LQG propagator. I. Difficulties with the Barrett-Crane vertex.
Emanuele Alesci (Rome U. & Marseille, CPT) , Carlo Rovelli (Marseille, CPT) . 31pp.
Published in Phys.Rev.D76:104012,2007.
e-Print: arXiv:0708.0883 [gr-qc]
Cited 36 times
6) LQG vertex with finite Immirzi parameter.
Jonathan Engle (Marseille, CPT) , Etera Livine (Lyon, Ecole Normale Superieure) , Roberto Pereira, Carlo Rovelli (Marseille, CPT) . 8pp.
Published in Nucl.Phys.B799:136-149,2008.
e-Print: arXiv:0711.0146 [gr-qc]
Cited 33 times
7) Singularities and Quantum Gravity.
Martin Bojowald (Penn State U. & Santa Barbara, KITP) . 41pp.
Lectures given at 12th Brazilian School of Cosmology and Gravitation (XII BSCG), Rio de Janeiro, Brazil, 10-23 Sep 2006.
Published in AIP Conf.Proc.910:294-333,2007. Also in *Rio de Janeiro 2006, Cosmology and gravitation* 294-333
e-Print: gr-qc/0702144
Cited 20 times
8) The Perturbative Regge-calculus regime of loop quantum gravity.
Eugenio Bianchi (Pisa, Scuola Normale Superiore & INFN, Pisa) , Leonardo Modesto (Bologna U. & INFN, Bologna & Marseille, CPT) . 43pp.
Published in Nucl.Phys.B796:581-621,2008.
e-Print: arXiv:0709.2051 [gr-qc]
Cited 20 times
9) Loop quantum gravity corrections to gravitational wave dispersion.
Martin Bojowald, Golam Mortuza Hossain (Penn State U.) . 27pp.
Published in Phys.Rev.D77:023508,2008.
e-Print: arXiv:0709.2365 [gr-qc]
Cited 20 times
10) Lorentzian LQG vertex amplitude.
Roberto Pereira (Marseille, CPT) . 9pp.
Published in Class.Quant.Grav.25:085013,2008.
e-Print: arXiv:0710.5043 [gr-qc]
Cited 20 times
11) Spin foam model from canonical quantization.
Sergei Alexandrov (Montpellier U., Astropart. Group) . 25pp.
Published in Phys.Rev.D77:024009,2008.
e-Print: arXiv:0705.3892 [gr-qc]
Cited 17 times
12) The Complete LQG propagator. II. Asymptotic behavior of the vertex.
Emanuele Alesci (Rome III U. & Marseille, CPT) , Carlo Rovelli (Marseille, CPT) . 16pp.
Published in Phys.Rev.D77:044024,2008.
e-Print: arXiv:0711.1284 [gr-qc]
Cited 17 times
13) The Dark Side of a Patchwork Universe.
Martin Bojowald (Penn State U.) . 24pp.
Published in Gen.Rel.Grav.40:639-660,2008.
e-Print: arXiv:0705.4398 [gr-qc]
Cited 15 times
14) Inflationary universe in loop quantum cosmology.
Xin Zhang (Beijing, KITPC) , Yi Ling (Nanchang U.) . 25pp.
Published in JCAP 0708:012,2007.
e-Print: arXiv:0705.2656 [gr-qc]
Cited 14 times
15) Quantum Gravity Phenomenology.
Giovanni Amelino-Camelia . 82pp.
e-Print: arXiv:0806.0339 [gr-qc]
Cited 14 times
16) Path integral representation of spin foam models of 4d gravity.
Florian Conrady, Laurent Freidel (Perimeter Inst. Theor. Phys.) . 29pp.
Published in Class.Quant.Grav.25:245010,2008.
e-Print: arXiv:0806.4640 [gr-qc]
Cited 14 times
17) Loop quantum cosmology.
Martin Bojowald (Penn State U. & Potsdam, Max Planck Inst.) . 131pp.
Published in Living Rev.Rel.11:4,2008.
Cited 14 times
18) Loop quantization of spherically symmetric midi-superspaces.
Miguel Campiglia, Rodolfo Gambini (Republica U., Montevideo) , Jorge Pullin (Louisiana State U.) . 18pp.
Published in Class.Quant.Grav.24:3649-3672,2007.
e-Print: gr-qc/0703135
Cited 13 times
19) Loop Quantum Gravity: Four Recent Advances and a Dozen Frequently Asked Questions.
Abhay Ashtekar (Penn State U.) . 21pp.
To appear in the proceedings of 11th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation, and Relativistic Field Theories, Berlin, Germany, 23-29 Jul 2006.
e-Print: arXiv:0705.2222 [gr-qc]
Cited 13 times
20) Linearized dynamics from the 4-simplex Regge action.
Bianca Dittrich, Laurent Freidel, Simone Speziale (Perimeter Inst. Theor. Phys.) . 25pp.
Published in Phys.Rev.D76:104020,2007.
e-Print: arXiv:0707.4513 [gr-qc]
Cited 13 times
=========================================
The following represents an important new direction in research which I expect to become increasingly important in the next couple of years. I'll tack it on here even though it did not make the top 20:
23) Relating loop quantum cosmology to loop quantum gravity: Symmetric sectors and embeddings.
Jonathan Engle (Marseille, CPT & Provence U. & Marseille U., Luminy) . 20pp.
Published in Class.Quant.Grav.24:5777-5802,2007.
e-Print: gr-qc/0701132
Cited 12 times
A certain amount can be told about how things are going in a field by noting who the invited plenary speakers are to be at upcoming meetings. They tend to be people who have things to report that everybody wants to hear about. At the time it struck me as remarkable that the last GR meeting, GR17 Sydney 400-500 participants, had Renate Loll and Laurent Freidel as plenary speakers. Now the upcoming MG12 Paris, another biggie, will have Alain Connes and Laurent Freidel. There may be a general waking up to nonstring quantum gravity on the part of cosmologists, astrophysicists, GR-theorists, GR and gravity experimentalists, etc. I'll list some upcoming meetings and workshops in chrono order, along with a few of those giving talks.
Black Holes and Loop Quantum Gravity (Valencia 26-28 March)
http://www.uv.es/bhlqg/
Ashtekar, Bojowald, Corichi, Dittrich, Engle,..., Sahlmann...
Topic list is interesting, two of those included are:
- Spin foam approach to black holes
- Singularity resolution and information loss
Strings 2009 (Rome 22-26 June)
http://strings2009.roma2.infn.it/home.html
Last year they had Rovelli give a plenary talk on LQG. Let's see if they get anyone from the outside this year.
XXV Max Born (Wroclaw 29 June-3 July)
http://www.ift.uni.wroc.pl/~planckscale/
John Barrett, Laurent Freidel, Renate Loll,....many other outstanding speakers...
MG12 (Paris 12-16 July)
http://www.icra.it/MG/mg12/en/invited_speakers.htm
Alain Connes, Laurent Freidel
Loops 2009 (Beijing 2-8 August)
http://grg.maths.qmul.ac.uk/hyperspace/conference/08Dec.8.html
no speakers list posted so far
QG School 2 (Corfu 13-20 September)
http://www.maths.nottingham.ac.uk/qg/CorfuSS.html
Ashtekar, Baez, Barrett, Rivasseau, Rovelli
GR 19 (Mexico City 5-9 July 2010)
http://www.gr19.com/index.php
Rovelli
Helpful links, for staying informed
http://www.maths.nottingham.ac.uk/qg/
http://grg.maths.qmul.ac.uk/hyperspace/conference/
http://grg.maths.qmul.ac.uk/hyperspace/conference/latest.html
Loops 2009 has posted speakers now
http://www.loops09.org/asp/xtgl/zzview.asp?id=10
==quote==
The incomplete list of plenary speakers：
A. Ashtekar (Penn state)
J. Barrett (Nottingham)
M. Bojowald (Penn state)
A. Corichi (Morelia)
B. Dittrich (Utrecht)
L. Freidel (Perimeter)
H.Y. Guo (ITP, CAS)
J. Lewandowski (Warsaw)
R. Maartens (Portsmounth)
J. Pullin (Louisiana)
V. Rivasseau (Paris-Sud XI)
C. Rovelli (Marseille)
H. Sahlmann (Karlsruhe)
P. Singh (Perimeter)
L. Smolin (to be confirmed, Perimeter)
S. Speziale (Marseille)
T. Thiemann (AEI)
M. Varadarajan (Raman Inst)
==endquote==
There is a now a Loops 2009 website. Here's how they list the topics
==quote==
* Loop quantum gravity
* Loop quantum cosmology and other symmetric models
* Spin foams and their low energy ramifications
* Fundamental questions of quantum gravity
* Black holes and Cosmology related to quantum gravity
* Phenomenology of quantum gravity.
==endquote==
I believe this will be the first time that Bianca Dittrich will be a featured plenary speaker at a major international conference.
Maybe also a first for Simone Speziale, I don't recall for sure.
Hey Marcus,
sorry for the self-advertisement... but each time people talk about the nex spinfoam models by Rovelli and al or Freidel and al, they keep forgetting these two papers where we introduced the coherent state techniques used for the semi-classical analysis of these models... and which could make it hopefully in the top 20 of the last couple of years...
A New spinfoam vertex for quantum gravity.
Etera R. Livine (Lyon, Ecole Normale Superieure) , Simone Speziale (Perimeter Inst. Theor. Phys.) . PI-QG-45, May 2007. 25pp.
Published in Phys.Rev.D76:084028,2007.
e-Print: arXiv:0705.0674 [gr-qc]
Cited 43 times
Consistently Solving the Simplicity Constraints for Spinfoam Quantum Gravity.
Etera R. Livine (Lyon, Ecole Normale Superieure) , Simone Speziale (Perimeter Inst. Theor. Phys.) . Aug 2007. 6pp.
Published in Europhys.Lett.81:50004,2008.
e-Print: arXiv:0708.1915 [gr-qc]
Cited 37 times
and there's even another one:
Numerical evidence of regularized correlations in spin foam gravity.
J.Daniel Christensen (Western Ontario U.) , Etera R. Livine (Lyon, Ecole Normale Superieure) , Simone Speziale (Perimeter Inst. Theor. Phys.) . PI-QG-57, Oct 2007. 5pp.
Published in Phys.Lett.B670:403-406,2009.
e-Print: arXiv:0710.0617 [gr-qc]
Cited 15 times
~etera
[QUOTE=marcus;2096329]Here's an updated "top 20" snapshot of the field, the 20 most-cited papers from the past 2 years (date > 2006).
The list makes clear which have been the predominant themes of research recently: the new vertex, establishing a new covariant version of LQG consistent with the older canonical version, checking that the low energy limit comes out right (graviton propagator), and as always cosmology (LQC).
There is one new theme that did not show up until paper number 23 in the list. The bridge between LQG and LQC--which may lead to cosmological tests of LQG. Although it didn't make the top 20 this time, I will append that paper.
1) The Loop-quantum-gravity vertex-amplitude.
Jonathan Engle, Roberto Pereira, Carlo Rovelli (Marseille, CPT) . May 2007. 6pp.
Published in Phys.Rev.Lett.99:161301,2007.
e-Print: arXiv:0705.2388 [gr-qc]
Cited 49 times
2) An Introduction to Loop Quantum Gravity Through Cosmology.
Abhay Ashtekar (Penn State U. & Santa Barbara, KITP) . 20pp.
Published in Nuovo Cim.122B:135-155,2007.
e-Print: gr-qc/0702030
Cited 46 times
3) A New Spin Foam Model for 4d Gravity.
Laurent Freidel (Perimeter Inst. Theor. Phys.) , Kirill Krasnov (Perimeter Inst. Theor. Phys. & Nottingham U.) . 40pp.
Published in Class.Quant.Grav.25:125018,2008.
e-Print: arXiv:0708.1595 [gr-qc]
Cited 46 times
4) Flipped spinfoam vertex and loop gravity.
Jonathan Engle, Roberto Pereira, Carlo Rovelli (Marseille, CPT) . 37pp.
Published in Nucl.Phys.B798:251-290,2008.
e-Print: arXiv:0708.1236 [gr-qc]
Cited 38 times
5) The Complete LQG propagator. I. Difficulties with the Barrett-Crane vertex.
Emanuele Alesci (Rome U. & Marseille, CPT) , Carlo Rovelli (Marseille, CPT) . 31pp.
Published in Phys.Rev.D76:104012,2007.
e-Print: arXiv:0708.0883 [gr-qc]
Cited 36 times
6) LQG vertex with finite Immirzi parameter.
Jonathan Engle (Marseille, CPT) , Etera Livine (Lyon, Ecole Normale Superieure) , Roberto Pereira, Carlo Rovelli (Marseille, CPT) . 8pp.
Published in Nucl.Phys.B799:136-149,2008.
e-Print: arXiv:0711.0146 [gr-qc]
Cited 33 times
Etera, thanks for pointing that out. The omissions were certainly not intentional!
If you have some tips about using Spires, please let me know. I gather they have no Boolean OR. So if I want keyword "loop space" or keyword "spin, foam" I need to do two searches and merge the lists manually.
I just realized that when I search with keywords "quantum gravity AND loop space" it does not come up with some papers tagged "spin, foam" like the ones you mentioned.
So now we need a new routine for getting the LQG top 20.
First we do this "spin, foam" search:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND++DK+SPIN%2C+FOAM+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29
Then we do a "quantum gravity" and "loop space" search:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=dk+quantum+gravity+and+dk+loop+space+an d+date+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29
Then we merge the lists by hand:
1) The Loop-quantum-gravity vertex-amplitude.
Jonathan Engle, Roberto Pereira, Carlo Rovelli (Marseille, CPT) . May 2007. 6pp.
Published in Phys.Rev.Lett.99:161301,2007.
e-Print: arXiv:0705.2388 [gr-qc]
Cited 49 times
2) An Introduction to Loop Quantum Gravity Through Cosmology.
Abhay Ashtekar (Penn State U. & Santa Barbara, KITP) . IGPG-07-01-02, NSF-KITP-07-05, Feb 2007. 20pp.
Published in Nuovo Cim.122B:135-155,2007.
e-Print: gr-qc/0702030
Cited 47 times
3) A New Spin Foam Model for 4d Gravity.
Laurent Freidel (Perimeter Inst. Theor. Phys.) , Kirill Krasnov (Perimeter Inst. Theor. Phys. & Nottingham U.) . Aug 2007. 40pp.
Published in Class.Quant.Grav.25:125018,2008.
e-Print: arXiv:0708.1595 [gr-qc]
Cited 47 times
4) A New spinfoam vertex for quantum gravity.
Etera R. Livine (Lyon, Ecole Normale Superieure) , Simone Speziale (Perimeter Inst. Theor. Phys.) . PI-QG-45, May 2007. 25pp.
Published in Phys.Rev.D76:084028,2007.
e-Print: arXiv:0705.0674 [gr-qc]
Cited 43 times
5) Flipped spinfoam vertex and loop gravity.
Jonathan Engle, Roberto Pereira, Carlo Rovelli (Marseille, CPT) . Aug 2007. 37pp.
Published in Nucl.Phys.B798:251-290,2008.
e-Print: arXiv:0708.1236 [gr-qc]
Cited 39 times
6) Consistently Solving the Simplicity Constraints for Spinfoam Quantum Gravity.
Etera R. Livine (Lyon, Ecole Normale Superieure) , Simone Speziale (Perimeter Inst. Theor. Phys.) . Aug 2007. 6pp.
Published in Europhys.Lett.81:50004,2008.
e-Print: arXiv:0708.1915 [gr-qc]
Cited 37 times
7) The Complete LQG propagator. I. Difficulties with the Barrett-Crane vertex.
Emanuele Alesci (Rome U. & Marseille, CPT) , Carlo Rovelli (Marseille, CPT) . Aug 2007. 31pp.
Published in Phys.Rev.D76:104012,2007.
e-Print: arXiv:0708.0883 [gr-qc]
Cited 36 times
8) LQG vertex with finite Immirzi parameter.
Jonathan Engle (Marseille, CPT) , Etera Livine (Lyon, Ecole Normale Superieure) , Roberto Pereira, Carlo Rovelli (Marseille, CPT) . Nov 2007. 8pp.
Published in Nucl.Phys.B799:136-149,2008.
e-Print: arXiv:0711.0146 [gr-qc]
Cited 34 times
9) The Perturbative Regge-calculus regime of loop quantum gravity.
Eugenio Bianchi (Pisa, Scuola Normale Superiore & INFN, Pisa) , Leonardo Modesto (Bologna U. & INFN, Bologna & Marseille, CPT) . Sep 2007. 43pp.
Published in Nucl.Phys.B796:581-621,2008.
e-Print: arXiv:0709.2051 [gr-qc]
Cited 20 times
10) Singularities and Quantum Gravity.
Martin Bojowald (Penn State U. & Santa Barbara, KITP) . IGPG-07-2-4, Feb 2007. 41pp.
Lectures given at 12th Brazilian School of Cosmology and Gravitation (XII BSCG), Rio de Janeiro, Brazil, 10-23 Sep 2006.
Published in AIP Conf.Proc.910:294-333,2007. Also in *Rio de Janeiro 2006, Cosmology and gravitation* 294-333
e-Print: gr-qc/0702144
Cited 20 times
11) The Perturbative Regge-calculus regime of loop quantum gravity.
Eugenio Bianchi (Pisa, Scuola Normale Superiore & INFN, Pisa) , Leonardo Modesto (Bologna U. & INFN, Bologna & Marseille, CPT) . Sep 2007. 43pp.
Published in Nucl.Phys.B796:581-621,2008.
e-Print: arXiv:0709.2051 [gr-qc]
Cited 20 times
12) Loop quantum gravity corrections to gravitational wave dispersion.
Martin Bojowald, Golam Mortuza Hossain (Penn State U.) . IGC-07-9-1, Sep 2007. 27pp.
Published in Phys.Rev.D77:023508,2008.
e-Print: arXiv:0709.2365 [gr-qc]
Cited 20 times
13) Lorentzian LQG vertex amplitude.
Roberto Pereira (Marseille, CPT) . Oct 2007. 9pp.
Published in Class.Quant.Grav.25:085013,2008.
e-Print: arXiv:0710.5043 [gr-qc]
Cited 20 times
14) Spin foam model from canonical quantization.
Sergei Alexandrov (Montpellier U., Astropart. Group) . PTA-07-24, May 2007. 25pp.
Published in Phys.Rev.D77:024009,2008.
e-Print: arXiv:0705.3892 [gr-qc]
Cited 17 times
15) The Complete LQG propagator. II. Asymptotic behavior of the vertex.
Emanuele Alesci (Rome III U. & Marseille, CPT) , Carlo Rovelli (Marseille, CPT) . Nov 2007. 16pp.
Published in Phys.Rev.D77:044024,2008.
e-Print: arXiv:0711.1284 [gr-qc]
Cited 17 times
16) The Dark Side of a Patchwork Universe.
Martin Bojowald (Penn State U.) . IGPG-07-5-5, May 2007. 24pp.
Published in Gen.Rel.Grav.40:639-660,2008.
e-Print: arXiv:0705.4398 [gr-qc]
Cited 15 times
17) Path integral representation of spin foam models of 4d gravity.
Florian Conrady, Laurent Freidel (Perimeter Inst. Theor. Phys.) . PI-QG-84, Jun 2008. 29pp.
Published in Class.Quant.Grav.25:245010,2008.
e-Print: arXiv:0806.4640 [gr-qc]
Cited 15 times
18) Inflationary universe in loop quantum cosmology.
Xin Zhang (Beijing, KITPC) , Yi Ling (Nanchang U.) . May 2007. 25pp.
Published in JCAP 0708:012,2007.
e-Print: arXiv:0705.2656 [gr-qc]
Cited 14 times
19) Quantum Gravity Phenomenology.
Giovanni Amelino-Camelia . Jun 2008. 82pp. Temporary entry
e-Print: arXiv:0806.0339 [gr-qc]
Cited 14 times
20) Loop quantum cosmology.
Martin Bojowald (Penn State U. & Potsdam, Max Planck Inst.) . 2008. 131pp.
Published in Living Rev.Rel.11:4,2008.
Cited 14 times
21) Loop quantization of spherically symmetric midi-superspaces.
Miguel Campiglia, Rodolfo Gambini (Republica U., Montevideo) , Jorge Pullin (Louisiana State U.) . LSU-REL-032707, NSF-KITP-07-28, Mar 2007. 18pp.
Published in Class.Quant.Grav.24:3649-3672,2007.
e-Print: gr-qc/0703135
Cited 13 times
22) Loop Quantum Gravity: Four Recent Advances and a Dozen Frequently Asked Questions.
Abhay Ashtekar (Penn State U.) . IGPG-07-5-3, May 2007. 21pp.
To appear in the proceedings of 11th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation, and Relativistic Field Theories, Berlin, Germany, 23-29 Jul 2006.
e-Print: arXiv:0705.2222 [gr-qc]
Cited 13 times
23) Harmonic cosmology: How much can we know about a universe before the big bang?
Martin Bojowald (Penn State U., Astron. Astrophys.) . Oct 2007. 16pp.
Published in Proc.Roy.Soc.Lond.A464:2135-2150,2008.
e-Print: arXiv:0710.4919 [gr-qc]
Cited 13 times
24) Linearized dynamics from the 4-simplex Regge action.
Bianca Dittrich, Laurent Freidel, Simone Speziale (Perimeter Inst. Theor. Phys.) . PI-QG-48, Aug 2007. 25pp.
Published in Phys.Rev.D76:104020,2007.
e-Print: arXiv:0707.4513 [gr-qc]
Cited 13 times
Periodically checking to see how the major conference/workshop programs take shape, which are the invited talks, the topics of the parallel sessions and who is chairing them, helps to get an idea of what directions of research are currently attracting interest. Here is an updated list of links
Black Holes and Loop Quantum Gravity (Valencia 26-28 March)
http://www.uv.es/bhlqg/
Speakers include Ashtekar, Bojowald, Corichi, Dittrich, Engle,..., Sahlmann...
XXV Max Born (Symposium on the Planck Scale; Wroclaw 29 June-3 July)
http://www.ift.uni.wroc.pl/~planckscale/
Many speakers including John Barrett, Laurent Freidel, Renate Loll,...
MG12 (Paris 12-16 July)
http://www.icra.it/MG/mg12/en/invited_speakers.htm
Alain Connes, Laurent Freidel among others
Loops 2009 Preparatory (Beijing 26 July-1 August)
http://www.loops09.org/School/School-en.htm
introductory week of lectures prior to conference
Loops 2009 (Beijing 2-8 August)
Now has a website and a list of speakers.
http://www.loops09.org/asp/xtgl/zzview.asp?id=10
QG School 2 (Corfu 13-20 September)
http://www.maths.nottingham.ac.uk/qg/CorfuSS.html
Ashtekar, Baez, Barrett, Rivasseau, Rovelli
GR 19 (Mexico City 5-9 July 2010)
http://www.gr19.com/index.php
Rovelli among others
The topics list for the March BH+LQG workshop is
- Black hole entropy in LQG
- Spin foam approach to black holes
- Singularity resolution and information loss
- Prospects for a detailed description of the Hawking radiation
- Comparison between results from LQG and other approaches
Themes listed for the June Max Born symposium are
Loops and spin foams
Strings, AdS/CFT, and quantum gravity
Field theoretical perspective on Planck scale
Noncommutative spacetimes
Quantum gravity phenomenology
The listed topics for the August Loops '09 conference are
* Loop quantum gravity
* Loop quantum cosmology and other symmetric models
* Spin foams and their low energy ramifications
* Fundamental questions of quantum gravity
* Black holes and Cosmology related to quantum gravity
* Phenomenology of quantum gravity.
Other links to check.
http://www.maths.nottingham.ac.uk/qg/
http://grg.maths.qmul.ac.uk/hyperspace/conference/
http://grg.maths.qmul.ac.uk/hyperspace/conference/latest.html
It will be interesting to see how Yong-ge Ma and Thomas Thiemann structure the week-long school for students and postdocs interested in getting into LQG research, that will precede the August Loops 09 conference. Let's see who they got to give lectures.
It's an intensive cram course to get young researchers up to speed so they can benefit as much as possible from the main Loops 09 conference that takes place the following week.
http://www.loops09.org/School/School-en.htm
Topics and lecturers will be:
Loop quantum cosmology, Martin Bojowald (Penn State, USA)
Group field theory, Daniele Oriti (AEI, Germany)
Spin foams, Carlo Rovelli (Univ of Mediterranee, France)
Loop quantum gravity, Thomas Thiemann (AEI, Germany)
Regge calculus, Ruth Williams (Cambridge Univ, UK)
BNU (Beijing Normal U) is emerging as a center for LQG research in China. Hosting the conference at BNU will help to establish it in this position. I see Dah-wei Chiou is there now. He was a postdoc 2006-2008 in Ashtekar's group at Penn State. Most of his papers were then about the LQG black hole, confirming a bounce at the singularity in various cases. Chiou is helping to organize the pre-conference school.
ccdantas
Mar18-09, 06:05 AM
From the Loops'09 site main title: "Quanturn Granvity" [sic] -- typos or something I don't get? (like the "turn" of a "grand" theory??? :biggrin:)
From the Loops'09 site main title: "Quanturn Granvity" [sic] -- typos or something I don't get? (like the "turn" of a "grand" theory??? :biggrin:)
Typos obviously, Christine. :biggrin: Actually it looks to me as if Beijing Normal University has acquired the services of a professional website designer (one with a highly unreliable grasp of the roman alphabet).
Either that or one of Yongge Ma's departmental secretaries is not comfortable with English text. For there are many typos. Many. Or were the last time I looked.
However I thought the website graphic design was very pretty along traditional Chinese lines.
That complex knot in the tasseled red silken cord works graphically as a kind of ideogram for Loop gravity, I think.
There is a press release for Dario Benedetti and some comments of him about a new article published on PRL.
“Fractal Properties of Quantum Spacetime.” Physical Review Letters 102, 111303 (2009).
http://www.physorg.com/news157203574.html
The abstracts for most of the plenary talks planned for MG12 in Paris are available.
http://www.icra.it/MG/mg12/en/invited_speakers_details.htm#freidel
Laurent Freidel
Talk: Spin Foam models: models of quantum dynamical space time
Abstract: In this talk I will give an overview of spin foam models which describe the dynamics of quantum gravity in a background independent context. I will focus especially and the recent developments which concerns the construction of these models in 4 dimensional gravity and present some of the key results obtained in this context like the construction of the model, the proof of the semi-classical limit and the relationship with loop quantum gravity and SU(2) spin network states.
Alain Connes is also one of the invited speakers, but the abstract of his talk is not posted.
Another invited QG talk is:
Herbert W. Hamber
Talk: Ultraviolet Divergences and Scale-Dependent Coupling in Quantum Gravity
Abstract: I will discuss how non-perturbative approaches to the problem of ultraviolet divergences in quantum gravity, similar in spirit and methods to what is done in the modern renormalization group treatment of non-abelian gauge theories, point to a possible weak scale dependence of Newton's constant at very large distances. I will then discuss ways by which such a scale dependence could in principle be verified observationally.
ensabah6
Apr3-09, 12:27 PM
The abstracts for most of the plenary talks planned for MG12 in Paris are available.
http://www.icra.it/MG/mg12/en/invited_speakers_details.htm#freidel
Laurent Freidel
Talk: Spin Foam models: models of quantum dynamical space time
Abstract: In this talk I will give an overview of spin foam models which describe the dynamics of quantum gravity in a background independent context. I will focus especially and the recent developments which concerns the construction of these models in 4 dimensional gravity and present some of the key results obtained in this context like the construction of the model, the proof of the semi-classical limit and the relationship with loop quantum gravity and SU(2) spin network states.
How would SF prove it has the right semiclassical limit -- via graviton and perturbation theory or some other mechanism
Anyone interested in forefront of QG research, LQG in particular, will probably have noticed that a bunch of spin foam graviton papers appeared since 2007, actually goes back to 2006 if I remember right.
Folks may not have seen Perini's recent seminar talk on that, though. Just this past February. The title of the talk is
Graviton propagator from EPRL spinfoam model
More information is here, for instance:
http://physicsforums.com/showpost.php?p=2145438&postcount=10
Some of the talks planned for the XXV Max Born (Symposium on the Planck Scale)
have been listed. Notice the wide range of approaches:
asymptotic safety/renormalization group
supergravity
loop/spinfoam
group field theories
string theories
non-commutative geometry
etc.
A.P. Balachandran Moyal versus Voros
A. Ballesteros On noncommutative velocity spaces
D. Benedetti Asymptotic safety and higher-derivative gravity
E. Bergshoeff (Super-)gravity in Three Dimensions
M. Bojowald Quantum geometry and quantum dynamics at the Planck scale
B. Dittrich Diffeomorphism invariance in quantum gravity models
S. Doplicher Quantum Spacetime and Noncommutative Geometry
M. Duff Black holes, qubits and octonions
J. Figueroa-O'Farrill 3-algebras and M2-branes
F. Girelli Group field theories: from spinfoam to non-commutative geometries
H. Gomes Asymptotic analysis of the EPRL four-simplex amplitude
R. Helling Allowing Spontaneous Breaking of Diffeomorphism Invariance
B. Koch Quantum gravity or quantum due to gravity?
D. Litim Quantum Gravity and the Renormalisation Group
F. Lizzi Twisting and star products
J. Magueijo Quantum gravity and cosmological fluctuations
N. Mavromatos High Energy Gamma Ray Astrophysics and Quantum-Gravity/String Theory
M. Montesinos n-dimensional non-Abelian BF theory as interacting (n-2)-forms
G. Piacitelli Models of Quantum Spacetime, and Approaches to Covariance
W. Piechocki Energy Scale of the Big Bounce
J. Pullin Spherically symmetric quantum scalar field in a quantum space time in loop quantum gravity the vacuum and the cosmological constant
Y. Sasai The Cutkosky rule of three dimensional noncommutative field theory in Lie algebraic noncommutative spacetime
D. Terno Dynamics and entanglement in spherically symmetric quantum gravity
S. Vaidya Unruh Effect in Noncommutative Spacetime
S. Weinfurtner The effective Planck-scale in emergent gravity
The Symposium will be held at the Polish city of Breslau (now Wroclaw) and will go on for one week at the beginning of July. (June 29 - July 3)
Breslau (or Wroclaw) looks to be only about 150 miles from Prague, and about the same distance to Dresden. Not much farther than that from Berlin and from Vienna as well.
The main QG session at the annual meeting of the American Physical Society (APS) was
http://meetings.aps.org/Meeting/APR09/sessionindex2/?SessionEventID=103077.
Session G5: Developments in Quantum Gravity
Chair: Jorge Pullin, Louisana State University
Sunday, May 3, 2009
8:30AM - 9:06AM
G5.00001: Einstein Prize Talk: The Quantum Origin of Our Classical Universe
Invited Speaker: James Hartle
Sunday, May 3, 2009
9:06AM - 9:42AM
G5.00002: Spin Foam models: models of quantum space time
Invited Speaker: Laurent Freidel
Sunday, May 3, 2009
9:42AM - 10:18AM
G5.00003: The Formulation of Quantum Field Theory in Curved Spacetime
Invited Speaker: Robert Wald
These were 36 minute invited talks. James Hartle and Robert Wald are prominent senior figures. Laurent Freidel made faculty in 2006 if I remember. He is also giving an invited talk at the Marcel Grossmann (MG12) meeting in Paris this summer.
Here is Freidel's abstract:
Spin Foam models: models of quantum space time
Laurent Freidel (Perimeter Institute)
"I will give an overview of spin foam models which describe the dynamics of quantum gravity in a background independent context. I will focus especially and the recent developments which concerns the construction of these models in 4 dimensional gravity and present some of the key results obtained in this context like the proof of the semi-classical limit and the relationship with loop quantum gravity and SU(2) spin network states."
http://meetings.aps.org/Meeting/APR09/Event/103078
There were also some 12 minute talks in various other sessions, mixed in with other topics. For instance, in session D11 there was a talk by Raj Konnu on Causal Dynamical Triangulations (CDT). In session T14 there was a 12 minute talk that had something to do with string theory--Kezerashvili et al.
=======================
't Hooft's chapter in Oriti's book is here:
http://www.phys.uu.nl/~thooft/gthpub/QuantumGrav_06.pdf.
Rovelli's chapter in Oriti's book is here:
http://arxiv.org/abs/gr-qc/0604045
The amazon page:
http://www.amazon.co.uk/Approaches-Quantum-Gravity-Toward-Understanding/dp/0521860458/
The Cambridge U. Press page:
http://cambridge.org/uk/catalogue/catalogue.asp?isbn=9780521860451
The CUP page is set up for extensive browsing in the book.
=======================
I notice that Laurent Freidel, as invited speaker at both the Denver APS and the Paris Marcel Grossmann meeting, if you judge by the abstract, is giving essentially the same talk. (Spin foam, semiclassical limit, compatibility with earlier LQG) This must be a quantum gravity talk that a lot of physicists want to hear. At the APS meeting they have him bracketed by Robert Wald and James Hartle (the only other invited speakers in the QG session). I think it is another sign that we are passing a kind of landmark this year.
I'm seeing more conferences where there is a mix of different research lines. For example:
http://www.mth.uct.ac.za/~jeff/Quantum_Gravity/About.html
The statement of purpose for this week-long conference in August 2009 South Africa (winter, cool) is very clear about that. Time to get the different parties together.
Same theme surfaced with several other 2009 workshops, schools etc.
Like the June school for Nonperturbative Gravity and QCD at Zakopane.
http://th-www.if.uj.edu.pl/school/2009/
And the Conference on Planck Scale
http://www.ift.uni.wroc.pl/~planckscale/
Ten new speakers have been added since the last time I listed the talks---some 35 titles so far.
Program of talks for Abhay Ashtekar's 60th birthday party, the "Abhayfest"
http://igc.psu.edu/events/abhayfest/program.shtml
One of our PF members has compiled some lists of selected LQG resources, with links.
http://mushfiq.net/loop-quantum-gravity/
I think this could be helpful to a newcomer to the subject. And also for someone who has been reading the research literature already for some time---maybe you will see something you missed.
The site also lists select resource links for other topics besides quantum gravity.
SuperStringboy
May18-09, 05:20 AM
One of our PF members has compiled some lists of selected LQG resources, with links.
http://mushfiq.net/loop-quantum-gravity/
I think this could be helpful to a newcomer to the subject. And also for someone who has been reading the research literature already for some time---maybe you will see something you missed.
The site also lists select resource links for other topics besides quantum gravity.
Here is a correction. This page is shifted to http://cosmicposts.wordpress.com/loop-quantum-gravity/
The Abhayfest* takes place in just a few days from now, June 4-6, at Penn State.
celebrating Abhay Ashtekar's 60th birthday.
http://igc.psu.edu/events/abhayfest/program.shtml
Here is a sampling of some of the speakers and talks:
Jim Hartle TBA
Gary Horowitz TBA
Steve Fairhurst "Searching for Gravitational Waves from Coalescing Binary Systems"
Alex Corichi "Black Hole Entropy"
Rodolfo Gambini The Issue of Time in Generally Covariant Theories and Quantum Gravity
Carlo Rovelli "What is a Particle"
Robert Wald "The Formulation of Quantum Field Theory in Curved Spacetime"
Lee Smolin "Unimodular Gravity and the Cosmological Constant Problem"
Thomas Thiemann TBA
Laurent Freidel "Quantum Geometry from Spin Foam"
Jerzy Lewandowski TBA
John Stachel TBA
Roger Penrose "Conformal Cyclic Cosmology: Its Present Status"
Here is a partial list of upcoming conferences, workshops, schools, in case anyone wants to check who and what are on the programs. This helps get an idea of current directions in research and areas of interest.
XXV Max Born (Symposium on the Planck Scale; Wroclaw 29 June-3 July)
http://www.ift.uni.wroc.pl/~planckscale/
MG12 (Paris 12-16 July)
http://www.icra.it/MG/mg12/en/invited_speakers.htm
Loops 2009 Prep (Beijing 26 July-1 August)
http://www.loops09.org/School/School-en.htm
Loops 2009 (Beijing 2-8 August)
http://www.loops09.org/asp/xtgl/zzview.asp?id=10
QG School 2 (Corfu 13-20 September)
http://www.maths.nottingham.ac.uk/qg/CorfuSS.html
GR 19 (Mexico City 5-9 July 2010)
http://www.gr19.com/index.php
Links to check for new announcements.
http://www.maths.nottingham.ac.uk/qg/
http://grg.maths.qmul.ac.uk/hyperspace/conference/
http://grg.maths.qmul.ac.uk/hyperspace/conference/latest.html
*BTW at the Abhayfest, coming up in a few days, Roger Penrose will also be giving a public lecture Fashion Faith and Fantasy: How big is infinity?
This will presumably have some of the same themes as the talk he gave in Berkeley in 2006, video available free from the Math Science Research Institute.
http://www.msri.org/communications/vmath/special_productions/
This was an integrated sociology&physics critique called
Fashion, Faith, and Fantasy in Modern Physical Theory
(raises foundational issues re string thinking, inflation cosmology and other possible physics fads, unscientific beliefs, and comments on sociology of intellectual fads in physics)
http://www.msri.org/communications/vmath/VMathVideosSpecial/VideoSpecialInfo/3005/show_video
The video and slides of Carlo Rovelli's talk at Strings 2008 provides a good introductory overview of LQG.
Here are the links:
Video:
http://cdsweb.cern.ch/record/1121957?ln=en
Slides:
http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917
An early draft of Rovelli's book online free for anyone who doesn't have the published version:
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
Another good overview of the whole field of quantum geometry/gravity, Rovelli's chapter in Oriti's book:
http://arxiv.org/abs/gr-qc/0604045
Today (May 31) starts another school at Zakopane. Here are some sample lectures and seminar titles. The first four are Causal Dynamical Triangulations (CDT) talks. The other two speakers we know in connection with their work in Asymptotic Safe quantum gravity.
Jan Ambjorn (NBI) - ambjorn at nbi.dk
Quantum Gravity: The Self-Organizing Universe
Renate Loll (Utrecht) - R.Loll at uu.nl
CDT and the Quest for Observables
Andrzej Goerlich (Kraków/UJ) atg at th.if.uj.edu.pl
Geometry of the Universe in Causal Dynamical Triangulations
Willem Westra (Iceland Uni.) willemwestra at hotmail.com
Towards Solvable Matter Models in Causal Quantum Gravity
Roberto Percacci (Trieste) - percacci at sissa.it
A Particle Physicist's Approach to Gravity
Daniel Litim (Sussex) - litim at mail.cern.ch
Non-perturbative Gravitation and the Renormalisation Group
Together Ambjorn and Loll are scheduled to give three 1-hour talks.
Percacci and Litim each give a series of three 1-hour talks.
http://th-www.if.uj.edu.pl/school/2009/lectures.html
The title of the school is "Non-perturbative gravity and QCD". Besides the quantum gravity lectures there are many other speakers.
A central idea in quantum gravity is illustrated by Rovelli's parable of the whale.
In the published version of Quantum Gravity, this is on page 9.
In the free online draft it is in section 1.1.3 on page 7 of this PDF:
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
===========
This wide audience article by Smolin in PhysicsWorld (June 2, 2009) could turn out to be influential. It is part of the development of Unimodular Relativity (UR) in conjuctions with evolutionary cosmology (the conjectured evolutionary basis for the laws of physics).
It's a very readable article, called The Unique Universe.
http://physicsworld.com/cws/article/print/39306
It's a pity there is a time conflict between the Zakopane school (May 31-June 6) and the Abhayfest (June 4-6).
http://th-www.if.uj.edu.pl/school/2009/lectures.html
http://igc.psu.edu/events/abhayfest/program.shtml
Friday June 5 is the big day of the Abhayfest, with talks followed by a banquet in the evening. Friday's talks include:
9:30 AM - 10:15 AM Carlo Rovelli What is a Particle?
10:15 AM - 11:00 AM Robert Wald The Formulation of Quantum Field Theory in Curved Spacetime
2:00 PM - 2:30 PM Laurent Freidel Quantum Geometry from Spin Foam
2:30 PM - 3:00 PM Jerzy Lewandowski Spin Foams from Quantum Geometry
3:00 PM - 3:30 PM Lee Smolin Unimodular Gravity and the Cosmological Constant Problem
5:00 PM - 5:30 PM Rodolfo Gambini The Issue of Time in Generally Covariant Theories and Quantum Gravity
Quantum Geometry is the name used for LQG within the research community. It is how Ashtekar refers to it. That makes sense because General Relativity is a theory of dynamic geometry (not forces or gravitons) so a quantized version of GR is a theory of quantum geometry---and LQG is the leading approach. Anyway, for whatever reason that is how Ashtekar and his friends have been calling LQG (which after all is a misnomer since the theory is not about loops). I see that Freidel and Lewandowski have acknowledged that in the titles of their talks, which are about the relation of LQG to Spin Foam. Looks to me like a very nice 60th birthday party indeed!
Rovelli recently gave a thumbnail sketch of LQG. Around 10 slides illustrated by drawings. You can look at the original slides and listen to the audio here:
http://relativity.phys.lsu.edu/ilqgs/panel050509.pdf
http://relativity.phys.lsu.edu/ilqgs/panel050509.mp3
It is a 3-way discussion and Rovelli is the second in line, so when you open the slides PDF you must scroll down about 10 slides first to come to Rovelli's section, likewise with the Audio mp3 you have to fast forward to about one third of the way, and just get the middle third of the recording. He will tell you in the audio which slide, when to switch slides and so forth. The other presentations, by Ashtekar and Freidel, are also good. But here I am focusing just on this very short 20 minute sequence by Rovelli.
==quote Rovelli's slides, text only==
Some questions
1. Is quantum space made out of loops and spin-networks or tetrahedra and 4-simplices?
2. Is flat space formed by many small tetrahedra with low-spin, or by few large tetrahedra with with high-spin?
3. Is low-energy physics given by quantum gravity on a single 4-simplex? Or by an infinite triangulation limit?
4. How do we study the the continuum limit from Planck scale discretness to the macroscopic continuum?
5. A spinfoam model is like a new version of quantum Regge calculus. So, why it should work better than quantum Regge calculus?
Claim: these questions are ill posed.
***
1. Is quantum space made out of loops and spin-networks or tetrahedra and 4-simplices?
The meaningful question in quantum theory is not how something is, but how it responds to a measurement.
There is no space “between” quanta of space, and it makes no sense to ask what is the geometry between one quantum and another, or inside a quantum, or what is the “geometry of quantum”. It is like asking for the “shape of a photon”. Or “What do I measure if I measure the energy in the space occupied by half a photon?”
***
2. Is flat space formed by few tetrahedra with high spin, or by many tetrahedra (or loops) with low spin?
How many particles are there in the Fock vacuum?
How many particles are invoved in a two-particle interaction?
Quantum theory gives the probability for measurement outcomes: it does not describe “what is between measurements”.
“In between pictures” are just descriptions of the ways I decide to do calculations. They are different for different measurements, and at different orders in perturbation theory.
[my comment. Rov sometimes like Feyn has flashes of unusual common sense. they illuminate.]
***
The good question, I think, is:
What can we compute that makes sense?
and
How can we compute it?
***
The problem of quantum gravity is–in a sense–two problems:
1. What is the right (background independent) theory?
2. How do extract physics from a background independent QFT?
Difficulties:
1. In standard QFT distances and time intervals gives locations in spacetime where the field is measured. In quantum gravity distances and time interval are quantum measurements of the gravitational field.
2. I think it is interesting to compute scattering amplitudes. These depend on a background: they describe interactions of excitations in a flat space context. How do we tell a background independent theory that there is a background?
***
The only solution I know:
1. Boundary formalism
2. Vertex expansion
3. Large spin expansion
***
1. Boundary formalism
– Scattering amplitudes depend on the measured geometry around the scattering region.
– It is the boundary state that tells the theory about the background.
– Not different than in standard QFT:
W (x, x′) = ⟨0|φ(x)φ(x′)|0⟩ (1)
= ⟨0| eiHt φ(⃗x)e−iHt eiHt′ φ(⃗x′ )e−iHt′ |0⟩ (2)
= ⟨φ(⃗x)0t | e−iH(t′−t) |φ(⃗x′)0t′ ⟩. (3)
W (x, x′) = ⟨e−iH(t′−t) | φ(⃗x) φ(⃗x′) |0t ⊗ 0t′ ⟩Hin ⊗Hout (4)
In quantum gravity →
W (x, y, Ψboundary ) = ⟨W | φ(⃗x′) φ(⃗x′) |Ψboundary ⟩Hboundary
This quantity is a 4d diffeomorpism invariant and well-defined. It reduces to standard 2-point function in the flat space theory. Locations of x and x′ are well defined with respect to the boundary state.
***
2. Vertex expansion
1. There is no way in physics you can compute without a suitable approximation scheme.
2. QFT expansion = truncation to a finite number of degrees of freedom.
QED: a finite order in perturbation theory has a finite number of particles.
Lattice QCD: finite lattice with # of cells determined by (size of the phenomenon L )/(minimal relevant wavelength λ).
3. Is there a truncation to a finite number of d.of f. in gravity, which is physically good in some regimes?
4. Yes! Truncate GR to a finite triangulation of spacetime (vertex expansion). # of simplices determined by (size of the phenomenon L)/(minimal relevant wavelength λ).
5. It is background independent, in the same sense in which Regge calculus is.
6. Where is it good? Many instances: Cosmology! Long wavelength at fixed distance. Large distance expansion of the propagator...
7. Precise characterization of the regime of validity (on the boundary state)
require us to compute higher orders and compare.
***
2. Large spin limit
• In quantum gravity there is a built in scale, lPlanck . Unlikely quantum Regge calculus.
• The vertex expansion is not a large distance L ≪ lPlanck approximation.
• At fixed order in the vertex expansion, large distance with respect to the Planck scale means high spins; because Area ∼ j .
• High spins = high quantum numbers = semiclassical limit. Therefore the theory must go to GR (truncated on a fixed lattice) for high spins, at fixed triangulation.
***
Summary
1. “Loopy, polymer, triangulated” spaces are helps for intuition, not descriptions of reality. No incompatibility between them.
2. In quantum gravity, flat space is neither many small planck scale things not few big large-spin 4 simplices. It is a process with a transition amplitudes. We can represent it with different pictures, according to the measurements we are considering, the calculation scheme, and the approximation scheme.
3. We must compute diff-invariant amplitudes, including when dealing with excitations over a flat space. The only way of doing so that I know is to code the background into the boundary space. (Boundary formalism.)
4. We need an approximation scheme. For scattering amplitudes, we can truncate degrees of freedom to a finite number, very much like is done in computing in QED and QCD. (Vertex expansion.)
5. Regime of validity of the vertex expansion: processes whose size L is not much larger than the minimal relevant wavelength λ. Includes the large distance behavior of the scattering amplitudes in coordinate space.
6. At given ratio λ/L, the Large-spin Limit captures processes at scales larger than the Planck length. It gives the semiclassical limit.
→ This does not mean that flat space is “made out of large 4-simplices”!
→ It means that we describe measurements performed at scales larger that the
Planck scale, at low order.
Marcus, the links did not appear.
Thanks for catching that! I fixed the trouble.
Earlier in this thread I gave a link to the Strings 2009 website. The main annual string conference. Need to check out string theorizing from time to time for perspective and contrast.
http://strings2009.roma2.infn.it/cgi-bin/roma_program.pl.cgi
Recall that Strings 2008 was noteworthy for several reasons: Witten was not there (he has not been doing much string since around 2006), Susskind didn't give a talk (the organizers excluded all talk about Landscape and Multiverse and Anthropic principle) and Carlo Rovelli was invited to give a talk about Loop Quantum Gravity which got a lively response from the audience. Questions spilled over into the coffee break period after the talk. Excellent survey. Video is online.
Strings 2009 had Witten give a public lecture and he chose not to talk about string, he talked about the particle physics frontier, future prospects, instead. Again Landscape Multiverse talks were excluded from the conference itself. That stuff is in bad odor. No Susskind. None of the KKLT folks that gave us the 10500string vacua. Petr Horava talked, about his nonstring QG and he cited results by Ambjorn, Loll, Jurkiewicz from another type of non-string QG called causal dynamical triangulations. His slides #22 and #23 headline Loll's CDT results.
http://strings2009.roma2.infn.it/talks/Horava_Strings09.pdf
He cites them, on #22 and on the next slide he gives several of their numbers, verbatim. Great. A sign of opening to the outside. Velvet revo.
The most interesting set of slides, for me, were those of the Opening Lecture, by David Gross.
http://strings2009.roma2.infn.it/talks/Gross_Strings09.pdf
He seems to be the official string overview-giver, at each major conference.
He gave the concluding Summary Talk at both Strings 2007 (madrid) and Strings 2008 (geneva). So we listen up.
Here are some excerpts from Gross' slides.
"4. What is the nature of string perturbation theory?
Our present understanding of string theory has
been restricted to perturbative treatments. Does
this perturbation theory converge? Most likely it
does not. In that case when does it give a reliable
asympototic expansion of physical quantities? How
can one go beyond perturbation theory and what is
the nature of nonperturbative string dynamics?
This question is particularly difficult since we
currently lack a useful nonperturbative formulation
of the theory. "
"5. String Phenomenology?
Here there are many questions that can all be
summarized by asking whether one can construct a
totally realistic four-dimensional model which is
consistent with string theory and agrees with
observation?
Great progress, but still not constructed."
"8. Is There a Measurable, Qualitatively Distinctive
Prediction of String Theory?
... It would be nice to predict
a phenomenon, which would be accessible at
observable energies and is uniquely
characteristic of string theory."
"How many more string revolutions
are required?
What is the fundamental
formulation of string theory?
Quantum Space of all 2-d field theories
Second Quantized Functionals of loops (SFT)
M-theory . . .
Is string theory a framework, not a theory?
What is missing?"
The video and slides of Carlo Rovelli's talk at Strings 2008 provides a good introductory overview of LQG, so I keep the links handy.
Here are the links:
Video:
http://cdsweb.cern.ch/record/1121957?ln=en
Slides:
http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917
An early draft of Rovelli's book online free for anyone who doesn't have the published version:
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
Another good overview of the whole field of quantum geometry/gravity, Rovelli's chapter in Oriti's book:
http://arxiv.org/abs/gr-qc/0604045
Another prime source link we should have handy is Steven Weinberg's talk at Cern, 7 July 2009. It helps define a new mainstream direction (he cites papers by many people whose work we have discussed here at PF: Ambjorn, Loll, Smolin, Litim, Percacci (with Codello Rahmede and others) Reuter, Bonanno, Saueressig (with Dario Benedetti and others). The talk will bear study so here is the main Cern link for the talk:
http://indico.cern.ch/conferenceDisplay.py?confId=57283
Here is the video:
http://cdsweb.cern.ch/record/1188567/
The part of the talk where he references a lot of papers, including new work in AsymSafe QG and in CausDynTr QG is in the last 10 or 15 minutes, fast forward to 58 minutes.
He also mentioned a conference on AsymSafe QG at Perimeter to be held December 2009, which should be quite interesting.
Another 2009 event which can help define the New Mainstream for us is the Ellis-fest at Cape Town in August.
http://www.mth.uct.ac.za/~jeff/Quantum_Gravity/About.html
In the list of invited speakers I think it is the string, or former-string, people we should focus on and try to understand their being chosen. How do they fit in? Why were they invited instead of some other string researchers? I have highlighted some names of interest, people who (whether they are string theorists or something else) don't fit in to the expected Loop-and-allied pattern:
Jan Ambjorn (Niels Bohr Insititute)
Cliff Burgess (Perimeter)
Steve Carlip (UC Davis)
Brian Greene (Columbia)
Joe Henson (Perimeter)
Renate Loll (Neils Bohr Institute)
Hermann Nicolai (Albert Einstein Institute)
Daniele Oriti (Albert Einstein Institute)
Thanu Padmanabhan (IUCAA)
Roger Penrose (Oxford)
Malcolm Perry (DAMTP)
Carlo Rovelli (Marseille)
Lee Smolin (Perimeter)
Kelly Stelle (Imperial)
Rafael Sorkin (Perimeter)
Thomas Thiemann (Albert Einstein Institute)
The upcoming AsymSafe QG conference that Weinberg mentioned in his 7 July Cern talk is actually in early November (not December):
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
One way we tell the current status of Loop and allied QG research is by watching the programs at the major international conferences. The 12th Marcel Grossmann MG12 has just begun in Paris (12-18 July) and the two Loop-type QG sessions are Thursday and Friday.
Invited speakers Laurent Freidel and Alain Connes will speak on Tuesday at a session chaired by Abhay Ashtekar. Laurent's abstract is:
Spin Foam models: models of quantum dynamical space time
"In this talk I will give an overview of spin foam models which describe the dynamics of quantum gravity in a background independent context. I will focus especially and the recent developments which concerns the construction of these models in 4 dimensional gravity and present some of the key results obtained in this context like the construction of the model, the proof of the semi-classical limit and the relationship with loop quantum gravity and SU(2) spin network states."
Thursday session:
Ashtekar, Abhay Recent Developments in Loop Quantum Cosmology
Bojowald, Martin Perturbations in Loop Quantum Cosmology
Wilson-Ewing, Edward Loop quantum cosmology of Bianchi I space-times
Pawlowski, Tomasz Concept of evolution in Loop Quantum Cosmology on the example of a vacuum Bianchi I model
Mena Marugan, Guillermo Big Bounce in inhomogeneous cosmologies
Pullin, Jorge Spherically symmetric quantum scalar field in a quantum space time in loop quantum gravity: the vacuum and the cosmological constant
Puchta, Jacek Quantum corrections in quantum spacetime
Marciano, Antonino Stepping out of Homogeneity in Loop Quantum Cosmology, II Part: introducing inhomgeneities into a Bianchi IX model in LQG
Battisti, Marco Valerio Big-bounce in a Snyder-deformed quantum cosmology
Tsobanjan, Artur Effective Constraints for Quantum Systems
Barbero G., J. Fernando Generating functions for black holes in loop quantum gravity
Villaseñor, Eduardo J S Flux-area operator and black hole entropy in loop quantum gravity
Perez, Alejandro The Theta parameter in loop quantum gravity: Effects on quantum geometry and black hole entropy
F. Borja, Enrique Computing black hole entropy in LQG from a conformal field theory perspective
Yu, Hoi-Lai Black hole as elementary particle in superspace
The Bianchi cosmo models are not necessarily isotropic. Some of these papers are generalizing Loop cosmo to more complex realistic cases ( without the usual strong assumptions of uniformity, so more like the full theory.)
The Friday QG session:
Dowdall, Richard Asymptotic analysis of recent 4d spinfoam models
Alesci, Emanuele LQG propagator
Mikovic, Aleksandar Spin foam perturbation theory for quantum gravity
Conrady, Florian Quantum geometry from phase space reduction
Bianchi, Eugenio Spin networks and simplicial geometries
Bahr, Benjamin Perfect actions in Regge calculus
Lewandowski, Jerzy Extention of the recent SF modles to all the states of LQG
Görlich, Andrzej Quantum de Sitter Universe in 4D Causal Dynamical Triangulations
Velhinho, José Groups of flux-like transformations in Loop Quantum Gravity
Sahlmann, Hanno Chern-Simons theory, Stokes' Theorem, and generalized connections
Kazmierczak, Marcin The Poincaré Gauge Theory of Gravity and the Immirzi Parameter
Cianfrani, Francesco On the Removal of Time-Gauge in Loop Quantum Gravity, with and without Matter
Montesinos, Merced Topological field theories in n-dimensional spacetimes and Cartan's equations
Morrison, Ian Group Averaging for quantum fields in de Sitter
Velazquez , Mercedes Husain-Kuchar model as a constrained BF theory
Christodoulakis, Theodosios Towards Canonical Quantum Gravity for Geometries Admitting Maximally Symmetric Two-dimensional Surfaces
2009 is a pivotal year for Loop and allied QG. You can see here that considerable progress has been made on establishing the largescale limit. (See talks by Laurent Freidel for spinfoam, and Andy Goerlich, for CDT, plus various others listed here like Alesci's LQG graviton propagator talk.)
You can also see a trend I mentioned some 5 or 6 months ago---in Loop Cosmology they are getting out of homogeneity. That means to gradually reduce the simplifying assumptions in cosmology and bridge the gap between Loop Cosmology and the full LQG theory (which has no assumptions of homogeneity and isotropy.) This means introducing new degrees of freedom and shifting to more complex models. Several talks are about this.
It is important because testing of QG effects has begun in cosmology. The situation is still in disorder but everyone realizes that QG models will be tested thru astro observations, so there is a big need to connect the full LQG theory with Loop cosmology so that empirical tests of cosmo models will become phenomenologically relevant to the full theory.
Right now we have a disconnect. LQG by itself does not predict any kind of Lorentz violation. But various versions of DSR do! So far no one has been able to get LQG to imply any type of DSR.
=======================
EDIT Atyy That is such a kind thought. Do I wish! For various reasons I do not travel much. I would so like to be in Paris right now, right around Bastille day (14 July) and hear the talks of Laurent Freidel and Alain Connes and the others, go on a riverboat, watch the fireworks.
Even just thinking about it is fun.
Laurent's abstract is:
Spin Foam models: models of quantum dynamical space time
"In this talk I will give an overview of spin foam models which describe the dynamics of quantum gravity in a background independent context. I will focus especially and the recent developments which concerns the construction of these models in 4 dimensional gravity and present some of the key results obtained in this context like the construction of the model, the proof of the semi-classical limit and the relationship with loop quantum gravity and SU(2) spin network states."
Are you attending?
Atyy, thanks for asking. I did not attend Marcel XII. I think of all the conferences and workshops there have been so far this year the one I would most have enjoyed attending was the Planck Scale conference in June, in Broclaw Poland. (But the Paris Marcel XII would have been great as well.) And the one coming up that I would find most interesting is the QG Corfu School taking place in September.
Video is supposed to be posted from the Broclaw Planck Scale conference before too long:
http://www.ift.uni.wroc.pl/~planckscale/
Here is the link to the Corfu QG School
http://www.maths.nottingham.ac.uk/qg/CorfuSS.html
Another very interesting one would be the Perimeter Asymptotic Safety workshop in November:
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
Interesting list of participants:
an Ambjorn, Utrecht University
Alfio Bonanno, INAF, Catania
Daniel Litim, University of Sussex
Max Niedermaier, University of Sussex
Martin Reuter, Mainz University
Frank Saueressig, CEA, Saclay
Lee Smolin, Perimeter Institute
B.F.L. Ward, Baylor University
Steven Weinberg, University of Texas, Austin
Jean Zinn-Justin, CEA, Saclay
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Invited_Speakers/
The Ellis-fest website has a new list of invited speakers. Some earlier invitees have apparently had to cancel due to other commitments:
Jan Ambjorn (Niels Bohr Insititute)
Martin Bojowald (Penn State)
Cliff Burgess (Perimeter)
Steve Carlip (UC Davis)
Joe Henson (Perimeter)
Renate Loll (Utrecht University)
Hermann Nicolai (Albert Einstein Institute)
Daniele Oriti (Albert Einstein Institute)
Thanu Padmanabhan (IUCAA)
Roger Penrose (Oxford)
Malcolm Perry (DAMTP)
Hanno Sahlmann (Utrecht University)
*Lenny Susskind (Stanford/Perimeter)
Kelly Stelle (Imperial)
Rafael Sorkin (Perimeter)
http://www.mth.uct.ac.za/~jeff/Quantum_Gravity/About.html
I learned how to use the Spires search more efficiently (parentheses, duh!) and so can keep track of the most-cited recent Loop and Spinfoam papers with a single search command:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+GRAVITY+AND+DK+LOOP+SPA CE+AND+DATE+%3E+2006+or+%28k+spin%2C+foam+and+date +%3E+2006%29&FORMAT=www&SEQUENCE=citecount%28d%29
This corresponds to typing "FIND DK QUANTUM GRAVITY AND DK LOOP SPACE AND DATE > 2006 OR (K SPIN, FOAM AND DATE > 2006)" into the Spires window, and selecting citecount order.
The last time I did this kind of survey was in March, post #150:
http://physicsforums.com/showthread.php?p=2104022#post2104022
and the cites for the top 20 papers ranged from 49 down to 14.
This time the top 20 papers' citecounts range from 62 down to 17.
Going from 49 to 62 is a 26% improvement, in four months.
Scanning the top 20 helps get an idea what the hot topics have been since 2006 and who the most cited authors are.
I get the same result by putting this into the window:
"( (DK QUANTUM GRAVITY AND DK LOOP SPACE) OR K SPIN, FOAM) AND DATE > 2006"
or with this in the window:
K SPIN, FOAM OR (DK QUANTUM GRAVITY AND DK LOOP SPACE) AND DATE > 2006
Leonard Susskind, Lee Smolin, Roger Penrose and Herman Nicolain in the same conference. What do you think Marcus?
Leonard Susskind, Lee Smolin, Roger Penrose and Herman Nicolai in the same conference. What do you think Marcus?
I don't know of any upcoming conference that includes all those people as invited speakers.
A couple of posts back I listed speakers for two separate events.
One was the November AsymSafe one that included Steven Weinberg and Lee Smolin ( will also include Martin Reuter, Renate Loll and several others).
The other conference was the Ellisfest in Capetown. I think Smolin declined that one, but the speakers will include Loll, Nicolai, Penrose, Susskind...
Here is more information:
http://physicsforums.com/showthread.php?p=2274724#post2274724
Loll's website says she will be participating in the AsymSafe conference at Perimeter. I think that one will be interesting and quiter possibly productive. I admire and respect George Ellis, but do not expect great things from the Ellisfest. We'll see.
I think Smolin declined that one, but the speakers will include Loll, Nicolai, Penrose, Susskind...
Yes, sorry, didnt pay attention. That's why susskind will be there, Smolin wont go.
MTd2, thanks for reminding us about the Loops 2009 conference that starts about one week from now in Beijing! In another thread you gave the current link to the main conference page:
http://www.mighty-security.com/loop/index.htm
(I imagine that the earlier website was hacked and so they were obliged to move the site to "mighty-security.com".)
Maybe we can learn something about the current state of Loop/Spinfoam research from looking at this conference.
I note right away that Loops 2009 is highly unusual in one respect: previous Loops conferences have had plenary speakers from outside the immediate Loops community:
Loops 2005 Potsdam had Robbert Dijkgraaf (string), Renate Loll (CDTriangulations), Martin Reuter (AsymSafe), and Roy Maartens (mainstream obs. cosmology). In each conference there are only a limited number of plenary talk slots so they are very precious, it is remarkable that the Potsdam organizers (Hermann Nicolai, Abhay Ashtekar and friends) gave four plenary slots away to outside Loop. I think that openness has paid off enormously to the community.
Loops 2007 Morelia had Ambjorn (CDTriangulations) and Reuter (AsymSafe). There was an unintended time-conflict with Strings 2007 Madrid so they could not get anybody good to give a string talk, but they tried. The did the best they could under the circumstances.
Loops 2008 (aka QG2 2008 Nottingham) carried on the openness tradition with several plenary speakers discussing CDTriangulations, AsymSafe, and one String speaker named Maloney (a former co-author with Witten now at U Toronto). If I remember right there were also CausalSets and or Graphity speakers. And most notably NonCommutativeGeometry was represented! Even Connes main collaborator Chamseddine was plenary speaker. So last year was very inclusive.
So the Loops conference has the tradition of being inclusive of all the major nonstring QG programs, and also some openness to String talks.
Now this year it is different. Loops 2009 Beijing is exclusively drawing from Loop/Spinfoam research. Maybe this is good to happen now and then, just for variety, but I hope it is not going to be a permanent change. I think that the Planck Scale conference in June that we have seen turned out to be an important landmark precisely because it brought people from a number of programs together to talk to each other and question each other.
=====================
The brief Preparatory School before the conference does include a series of lectures by Ruth Williams on Regge Calculus.
Here is the Prep School description:
==quote from the Prep School page==
Topics:
Loop quantum gravity, Loop quantum cosmology, Spin foams, Group field theory, Regge calculus
Lecturers:
Martin Bojowald (Penn State, USA)
Daniele Oriti (AEI, Germany)
Carlo Rovelli (Univ of Mediterranee, France)
Thomas Thiemann (AEI, Germany)
Ruth Williams (Cambridge Univ, UK)
==endquote==
Now for the main Loops 2009 conference, I estimate that the number of participants will be about 230. There are 6 pages and about 40 names on each page.
Let's look at the list of Plenary Speakers:
http://www.mighty-security.com/loop/plenary.htm
A.Ashtekar (Penn state)
J.Engle (CPT, Marseille)
M.Bojowald (Penn state)
A.Corichi (Morelia)
B. Dittich (Utrecht)
L.Freidel (Perimeter)
H.Y.Guo (ITP, CAS)
J.Lewandowski (Warsaw)
R.Maartens (Portsmounth)
J.Pullin (Louisiana)
V.Rivasseau (Paris-Sud XI)
C.Rovelli (Marseille)
H.Sahlmann (Karlsrahe)
P.Singh (Perimeter)
S.Speziale (Marseille)
T.Thiemann (AEI)
M.Varadarajan (Raman Inst)
K.Giesel(Nordita)
A.Perez(CPT, Marseille)
It does have some diversity: Roy Maartens is a top person in observational cosmology (how to test various QG theories by looking at the imprint of gravitational waves on the CMB and all kinds of early universe signals, he runs the Portsmouth center for obs. cosmo.)
And Vincent Rivasseau could be talking about Noncommutative field theory or about Renormalization stuff (loosely related to AsymSafe QG).
So it is not totally focussed on core Loop/Spinfoam research. Dittrich has a Loops background but she has recently been working on quantum Regge calculus. (That could indicate something.) Madhavan Varadarajan has worked outside but I think currently his main focus is in Loop/Spinfoam.
We now have a more complete list of the speakers at the Corfu school (13-20 September).
http://www.physics.ntua.gr/corfu2009/qg.html
Scroll down to the end.
Earlier I listed the five lecturers giving mini-course series. Rovelli, Ashtekar, Baez, Barrett, Rivasseau.
But besides these five QG minicourses there are also to be workshop talks by the following people:
* Paolo Aschieri
* Glenn Barnich
* Maja Buric
* Leonardo Castellani
* Chong-San Chu
* Brian Dolan
* Michel Dubois-Violette
* Steven Giddings
* Kristina Giesel
* Harald Grosse
* Jerzy Lewandowski
* Fedele Lizzi
* Jerzy Lukierski
* John Madore
* Shahn Majid
* Catherine Meusburger
* Denjoe O'Connor
* Martin Reuter
* Peter Schupp
* Harold Steinacker
* Richard Szabo
* Satoshi Watamura
I have highlighted a few that people here at Beyond forum may happen to recognize.
Brian Dolan I seem to recall has co-authored with John Baez, in which case he would be talking about n-category and higher gauge theory. Steve Giddings formerly did a lot of string but lately not so much. Seems to be finding other QG topics to investigate.
Martin Reuter we know would surely be talking Asymptotic Safety. He ought to be happy about the recent strong support from Steven Weinberg and AsymSafe's increased prominence. Lukierski is one of the original DSR people. Majid would talk Noncommutative Geometry, maybe also DSR. Harald Grosse and Harold Steinacker I think do noncommutative field theory. They may connect with what Rivasseau's abstract says he is going to talk about. Jerzy Lewandowski is a longtime collaborator of Ashtekar who has been a major figure in developing Loop Quantum Cosmology. Judging from his recent papers he might discuss Quantum Field Theory in Expanding Space Time.
He gave a very interesting talk about that at the Planck Scale conference in Wroclaw early July.
PDF slides are now available for some of the plenary talks given at Marcel 12 in early July.
http://www.icra.it/MG/mg12/en/
just click on plenary and select a speaker, to see if a PDF file is available.
Laurent Freidel:
http://www.icra.it/MG/mg12/talks_plenary/Freidel.pdf
Herbert Hamber:
http://www.icra.it/MG/mg12/talks_plenary/Hamber.pdf
Juan Maldacena (a string theorist, included for comparison sake)
http://www.icra.it/MG/mg12/talks_plenary/Maldacena.pdf
The Marcel Grossmann is a major international conference which is held every three years. Marcel Eleven was in Berlin 2006, Marcel Twelve was in Paris.
The theme is "recent developments in theoretical and experimental general relativity, astrophysics, and relativistic field theories." (See main page for overview and more links.)
MG12 was attended by 886 scientists:
http://www.icra.it/MG/mg12/en/participants_list.htm
The past 3 years have been an especially active period for Spin Foam and Loop QG with a wealth of new results. Freidel's talk reflects this: it is essentially a "Spin foam: current status and directions" talk. The comparison between Freidel and Maldacena's talk is revealing.
The timetable of talks at Loop 09 is up:
http://www.mighty-security.com/loop/timetable1.htm
The timetable of talks at Loop 09 is up:
http://www.mighty-security.com/loop/timetable1.htm
Thanks for spotting that! We can get the titles of the plenary talks.
Monday 3 August
Thiemann: Loop Quantum Gravity-A Status Report
Sahlmann: The Mathematics of Canonical LQG
Giesel: Reduced Phase Space Quantization of Loop Quantum Gravity
Dittrich: Diffeomorphism Symmetry and Discreteness in Quantum Gravity
Tuesday 4 August
Ashtekar: Introduction to Loop Quantum Cosmology
Singh: On the Abscence of Singularities in Loop Quantum Cosmology
Bojowald: Loop Quantum Gravity and Cosmology
Maartens: Key Issues in Cosmology and Challenges for LQC
Wednesday 5 August
Rovelli: Loops, Foams and Scattering
Engle: Loop Quantum Gravity Spin-Foam Models
Speziale: A Geometric Quantization of SU(2) Phase Space
Evening public lecture by Rovelli: What is space? What is time? Quantum gravity and the beginning of the universe.
Thursday 6 August
Corichi: Black Holes in Loop Quantum Gravity
Perez: Black Hole Entropy and SU(2) Chern-Simon Theory
Pullin: Midi-superspace Loop Quantum Gravity
Varadarajan: Quantum Gravity and the Information Loss Problem
Friday 7 August
Oriti: Group Field Theory for Quantum Gravity
Rivasseau: Renormalization and Loop Gravity
H-Y Guo: Special Relativity Triple and Triply Special Relativity
Closing Session chaired by Ashtekar
In addition to the approximately 20 plenary session talks the titles of 72 other talks are listed to be given in the parallel sessions--two of which are being run simultaneously.
I am proud to say that 7 of the people giving papers at this conference in Beijing have been members here at PF Beyond forum. This includes three of those giving invited plenary talks---they have posted on rare occasions and/or a long time ago (one doesn't even post, just checks in and reads now and then)---and four others among those giving parallel session talks, who have posted here more often and been of considerable benefit to us.
This is the schedule of George Ellis conference:
http://www.mth.uct.ac.za/~jeff/Quantum_Gravity/Schedule.html
Thanks! And also for posting the talks from the FQXi Azores conference that was held just a month or so ago.
I'm glad they put PDF slide sets on line, so we can check them out.
Just to have the handy, I will add it to this thread:
http://www.fqxi.org/conference/talks
Oriti's talk:
http://www.fqxi.org/data/documents/Oriti%20Azores%20Talk.pdf
I see that Daniele Oriti was in the final lineup of invited plenary talks at the Beijing conference. In fact he spoke today, 7 August. Probably essentially the same talk, giving the motivation, introduction and basics of Group Field Theory----plus its overlap (potentially as a kind of unifying framework) with Loop/Spinfoam, Simplicial (Regge) QG, CDT.
So much going on it is hard to keep proper account of it. The Planck Scale conference in Wroclaw was a really major event and now we have the Beijing, and the Marcel 12 in Paris, and the Azores conferences.
Just to keep it handy here are links for Wroclaw:
http://www.ift.uni.wroc.pl/~planckscale/movie/
Someone just asked me about the subject of Oriti's talk---which was on Day 4 in Wroclaw, and there is a video.
That thread on the Planck Scale conference is:
http://physicsforums.com/showthread.php?t=325794
Also an alternative link for the videos of the lectures is at Remi Durka's website:
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php
Here, for example is Oriti's Wroclaw talk slides:
http://www.ift.uni.wroc.pl/~planckscale/lectures/4-Thursday/1-Oriti.pdf
and video:
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php?plik=http://panoramix.ift.uni.wroc.pl/~planckscale/video/Day4/4-1.flv&tytul=4.1%20Oriti
The ILQGS schedule for the Fall 2009 is now posted
http://relativity.phys.lsu.edu/ilqgs/schedulefa09.html
It is a conference-call type hookup so people participate in several parts of the world.
you download the lecture slides in advance and the speaker tells you what slide.
International LQG Seminar
Sept 8 TBA
Sept 22 Vistas from perturbative quantum gravity
Richard Woodard University of Florida
Oct 6 Aharonov-Bohm and LQG
Eugenio Bianchi SNS Pisa
Oct 20 Spin foams from loop quantum gravity perspective
Jerzy Lewandowski Warszaw University
Nov 3 Group field theory and all that
Daniele Oriti Albert Einstein Institute
Nov 17 Asymptotics of the new vertex
Frank Hellmann University of Nottingham
Dec 1 Polymer parameterized field theory
Alok Laddha Raman Research Institute
Go here to see a list of all the past seminars and who gave them:
http://relativity.phys.lsu.edu/ilqgs/
For each past seminar there is an audio file, so you can listen
and a PDF file of the speaker's slides which you can download.
To keep some links handy for reference
Corfu QG School:
http://www.physics.ntua.gr/corfu2009/qg.html
Ellisfest speakers:
http://www.mth.uct.ac.za/~jeff/Quantum_Gravity/Participants.html
PlanckScale conference video and slides:
http://www.ift.uni.wroc.pl/~planckscale/
http://www.ift.uni.wroc.pl/~planckscale/movie/
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php
Marcel Twelve (886 participants):
http://www.icra.it/MG/mg12/en/
http://www.icra.it/MG/mg12/talks_plenary/Freidel.pdf
Loops 2009 (~230 part.) schedule of talks:
http://www.mighty-security.com/loop/timetable1.htm
June school for Nonperturbative Gravity and QCD at Zakopane.
http://th-www.if.uj.edu.pl/school/2009/
http://th-www.if.uj.edu.pl/school/2009/lectures.html
Asymptotic safety conference:
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
Abhayfest:
http://igc.psu.edu/events/abhayfest/program.shtml
GRG 19 (Mexico City 5-9 July 2010):
http://www.gr19.com/index.php
Links to check for new announcements:
http://www.maths.nottingham.ac.uk/qg/
http://grg.maths.qmul.ac.uk/hyperspace/conference/
http://grg.maths.qmul.ac.uk/hyperspace/conference/latest.html
Topcited Loop/Foam papers since 2006:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+GRAVITY+AND+DK+LOOP+SPA CE+AND+DATE+%3E+2006+or+%28k+spin%2C+foam+and+date +%3E+2006%29&FORMAT=www&SEQUENCE=citecount%28d%29
Rovelli's talk at Strings 2008:
Video
http://cdsweb.cern.ch/record/1121957?ln=en
Slides
http://indico.cern.ch/getFile.py/acc...s&confId=21917
2003 draft of Rovelli's book online:
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
Rovelli's chapter in Oriti's book:
http://arxiv.org/abs/gr-qc/0604045
Review of LQG as of May 2008:
http://relativity.livingreviews.org/Articles/lrr-2008-5/
Steven Weinberg's 6 July talk, main CERN link:
http://indico.cern.ch/conferenceDisplay.py?confId=57283
Weinberg video:
http://cdsweb.cern.ch/record/1188567/
To save time jump to minute 58, the last 12 minutes.
Ted Jacobson's 2007 paper on renormalization as it affects LQG:
http://arXiv.org/abs/0707.4026
more links to keep handy for reference:
Photos from the first Loops conference, at Marseille 2004
http://math.ucr.edu/home/baez/marseille/
2006 video lecture by Krasnov:
http://pirsa.org/06110041/
2006 audio+pdf talk at the ILQGS:
http://relativity.phys.lsu.edu/ilqgs/krasnov032007.pdf
http://relativity.phys.lsu.edu/ilqgs/krasnov032007.aif
2009 paper Gravity as BF theory plus potential
http://arxiv.org/abs/0907.4064
Ancillary papers
http://arxiv.org/abs/0811.3147
http://arxiv.org/abs/0812.3603
Intro to Plebanski
http://arxiv.org/abs/0904.0423
Comment by Bengtsson:
http://arxiv.org/abs/gr-qc/0703114
The programme for the Corfu QG school, listing the other talks besides the main lecture series, is now posted:
http://www.physics.ntua.gr/corfu2009/Program/3rdWeekSchool.pdf
http://www.physics.ntua.gr/corfu2009/Program/3rdWeekSchool.html
The main link for the Corfu QG school with abstracts of the five lecture series is still this:
http://www.physics.ntua.gr/corfu2009/qg.html
Check here for recordings of the EG4 talks as they become available:
http://www.emergentgravity.org/index.php?main=main_EGIV_programme.php
Next summer, 2010, there will be another QG school. This time in Mexico at Uni Morelia (which hosted the Loops 2007 conference). It will last 10 days: 23 June-3 July.
The organizers are:
Don Marolf
Abhay Ashtekar
Alejandro Corichi
Maximo Banados
More info at
http://www.physics.ucsb.edu/~pasi/
The school will be aimed at advanced PhD students and postdocs to enable them to get started in QG research.
It sounds similar to the two European QG schools funded by the European agency ESF---in Zakopane 2007 and in Corfu 2009.
But this time the corresponding USian agency NSF is getting into the act and funding the school.
Immediately the school is finished, the big GR 19 conference will commence in Mexico City. It runs 5 July thru 9 July.
http://www.gr19.com/
The international conference on General Relativity and Gravitation ("GR") is held every three years. The previous one was GR 18, held at Sydney in 2007.
Here is part of the programme of parallel sessions from the GR 19 website:
==quote==
D1 Loop Quantum Gravity and Spin Foams
Chair: Alejandro Corichi
D2 Strings, branes and M-theory
Chair: (to be announced)
D3 Causal sets, Causal dynamical triangulations, Non-commutative geometry, and other approaches to quantum gravity
Chair: Fay Dowker
D4 Quantum fields in curved space-time, semiclassical gravity, quantum gravity phenomenology, and analog models
Chair: Bill Unruh
==endquote==
Do you know when the slides from Loops 09 will be released? :eek: I am loosing hope. Also, won't you comment about http://arxiv.org/abs/0909.0939 "Spin-Foams for All Loop Quantum Gravity". I thought it was a great paper.
Do you know when the slides from Loops 09 will be released?
No I don't! And you remember that the original website was hacked, so they had to move everything to an ultra-secure host site. To me this indicates serious unexplained web-problems, and I stopped having any expectations at all.
Let's have our discussions in another thread. This thread is convenient for links that constantly get used, to check for current developments like the Corfu School. Let's make a separate thread to comment on the Lewandowski paper, if you would like.
4D quantum gravity links to keep handy for reference:
Fall 2009 schedule for International LQG Seminar, online.
http://relativity.phys.lsu.edu/ilqgs/schedulefa09.html
Upcoming talks by Woodard, Bianchi, Lewandowski, Oriti, Hellmann...
Past ILQGS talks.
http://relativity.phys.lsu.edu/ilqgs/
September 2009 Corfu QG School:
http://www.physics.ntua.gr/corfu2009/qg.html
http://www.physics.ntua.gr/corfu2009/Program/3rdWeekSchool.html
June 2009 school for Nonperturbative Gravity and QCD at Zakopane. No online media, proceedings will be published later.
http://th-www.if.uj.edu.pl/school/2009/
http://th-www.if.uj.edu.pl/school/2009/lectures.html
June 2009 PlanckScale conference video and slides:
http://www.ift.uni.wroc.pl/~planckscale/
http://www.ift.uni.wroc.pl/~planckscale/movie/
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php
July 2009 Marcel Twelve conference in Paris (886 participants):
http://www.icra.it/MG/mg12/en/
http://www.icra.it/MG/mg12/talks_plenary/Freidel.pdf
Loops 2009 in Beijing (~230 participants)
http://www.mighty-security.com/loop/timetable1.htm
August 2009 EG4 at Vancouver
http://www.emergentgravity.org/index.php?main=main_EGIV_programme.php
November 2009 Asymptotic safety conference at Perimeter:
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
June 2010 Americas QG school at Morelia
http://www.physics.ucsb.edu/~pasi/
July 2010 GR19 conference in Mexico City
http://www.gr19.com/index.php
Links to check for new announcements:
http://www.maths.nottingham.ac.uk/qg/
http://grg.maths.qmul.ac.uk/hyperspace/conference/
http://grg.maths.qmul.ac.uk/hyperspace/conference/latest.html
Topcited Loop/Foam papers since 2006:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+GRAVITY+AND+DK+LOOP+SPA CE+AND+DATE+%3E+2006+or+%28k+spin%2C+foam+and+date +%3E+2006%29&FORMAT=www&SEQUENCE=citecount%28d%29
Some classic online sources:
Rovelli's talk at Strings 2008 Video
http://cdsweb.cern.ch/record/1121957?ln=en
Slides
http://indico.cern.ch/getFile.py/acc...s&confId=21917
2003 draft of Rovelli's book online
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
Rovelli's chapter in Oriti's book
http://arxiv.org/abs/gr-qc/0604045
Review of LQG as of May 2008:
http://relativity.livingreviews.org/Articles/lrr-2008-5/
Steven Weinberg's 6 July talk, main CERN link:
http://indico.cern.ch/conferenceDisplay.py?confId=57283
Weinberg video:
http://cdsweb.cern.ch/record/1188567/
To save time jump to minute 58, the last 12 minutes.
Photos from the first Loops conference, at Marseille 2004
http://math.ucr.edu/home/baez/marseille/
Krasnov 2006 video lecture (because he takes a radical longshot.)
http://pirsa.org/06110041/
Krasnov 2006 audio+pdf talk at the ILQGS
http://relativity.phys.lsu.edu/ilqgs/krasnov032007.pdf
http://relativity.phys.lsu.edu/ilqgs/krasnov032007.aif
2009 paper Gravity as BF theory plus potential
http://arxiv.org/abs/0907.4064
http://arxiv.org/abs/0811.3147
http://arxiv.org/abs/0812.3603
http://arxiv.org/abs/0904.0423
Comment by Bengtsson:
http://arxiv.org/abs/gr-qc/0703114
http://www.perimeterinstitute.ca/en/Events/Gravity_at_a_Lifshitz_Point/Gravity_at_a_Lifshitz_Point/
Gravity at a Lifshitz Point
November 8 - 10, 2009
Perimeter Institute
The construction of a quantum theory of gravity might require us to give up one or more of the fundamental principles of standard quantum field theory. A recent proposal dispensing with Lorentz invariance builds upon an analogy with condensed matter systems characterized by a Lifshitz point. This proposal also seems to produce a theory which is well behaved in the ultraviolet regime.
This workshop intends to bring together researchers working on this or related ideas. The focus will be on the viability of the proposal (compatibility with large scale phenomenology and renormalizabilty) and its relation to other research directions, like causal dynamical triangulations and aether theories.
Scientific Organizers:
Dario Benedetti, Perimeter Institute
Robert Myers, Perimeter Institute
Petr Horava, University of California, Berkeley
******
Since the 1st day of this workshop will be in the last day of the Assymptotic Safety conference, maybe Weiberg will meet Horava, and something great will come out of that!
Another valuable resource is this collection of slides+audio from the summer 2009 Abhayfest
(celebrating the birthday of Abhay Ashtekar)
http://gravity.psu.edu/events/abhayfest/proceedings.shtml
Slides and audio available for talks by
Jim Hartle
Carlo Rovelli
Jerzy Lewandowski
Laurent Freidel
Lee Smolin
Gary Horowitz
Rodolfo Gambini
Robert Wald
Thomas Thiemann
Roger Penrose
Klaus Fredenhagen
(in no special order) and a bunch more.
Resources for conformal symmetry:
http://physicsforums.com/showthread.php?t=172461
(Sam Alkhaiat tutorial)
http://en.wikipedia.org/wiki/Conformal_symmetry
(very brief Wiki article with a picture)
Reflections on spontaneous symmetry breaking by Steven Weinberg
http://cerncourier.com/cws/article/cern/32522
't Hooft Erice talk (September 2009) quantum gravity should incorporate conformal symmetry in some fashion
http://arxiv.org/abs/0909.3426
Nicolai Planck Scale talk (July 2009) quantum gravity should incorporate conformal symmetry at least in the limit (and should learn certain other things from QFT and the Standard Model)
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php?plik=http://panoramix.ift.uni.wroc.pl/~planckscale/video/Day1/1-3.flv&tytul=1.3%20Nicolai
Brief Wikipedia article relating to Coleman Weinberg mechanism by which masses can be generated. C-W symmetry breaking invoked in the Meissner Nicolai extension of the Standard Model.
http://en.wikipedia.org/wiki/Coleman–Weinberg_potential
MTd2 found how to get the videos of the talks at Loops 2009, the big Loops conference at Beijing this summer.
You go to this catalog
http://www.mighty-security.com/loop/resource.htm
and you copy down the item number of the talk you want
and go to another site and request that number.
For example to get Ashtekar's talk, get the plenary session video for August 4 (8-4)
For Rovelli's, the plenary session for August 5.
Looking at the catalog, this means for Ashtekar it is serial number
8953789510079792
For Rovelli it would be
8605657721191707
For, say, Dan Oriti talking about Group Field Theory, it would be the August 7 plenary session
5570901362601769
==========================
Now suppose the video file can't be handled or there is some computer problem, they also have audio-only
And in that case the serial numbers for the same three plenary sessions are
8350111663470163
1930906596035020
1769207291471637
Let's hope some of these work. I'm going to give them a try.
It says: "go to http://file.mofile.com and enter the “pickup code” in the box at the top of the page."
So I'm going to mofile.com and entering the number 8605657721191707 which is the one for the Wednesday August 5 morning plenary session.
For more listings of the program timetable:
http://www.mighty-security.com/loop/timetable1.htm
http://www.mighty-security.com/loop/timetable2.htm
http://www.mighty-security.com/loop/timetable3.htm
http://www.mighty-security.com/loop/timetable4.htm
and so forth.
Well it didn't work for me! I went to mofile.com and put in the correct number 8605657721191707 in the right box
and things started to happen, but the screens were in Chinese! It wanted me to click on a button to continue but I couldn't read what I was agreeing to if I clicked. So being a cautious person, I bailed out.
Maybe it was working OK and I just should have clicked and continued. But it just wasn't "wai-gwo-ren" friendly, so I bailed. I think wai-gwo means foreign and ren means person.
Maybe someone who reads Chinese will try the mofile.com site out and give us a little coaching on how to proceed.
The Asymptotic Safety conference starts 5 November, less than 2 weeks away. It's an important landmark, perhaps a turning point. Interest in AsymSafe QG has revived some 30 years after Weinberg presented the idea at Erice (Sicily) in 1976.
Weinberg is working on it again and takes a sober cautious attitude. Not a sure bet, but deserves to be worked on. An alternative to string, as a way to arrive at unified fundamental description of the world. Also the running of constants like Newton G and the cosmo Lambda could provide natural mechanisms to explain cosmological phenomena such as inflation.
So AsymSafe has a key resonance with the currently hot field of cosmology---early universe in particular.
We might want to study the lineup of conference speakers and what they are talking about:
==excerpts from Perimeter host page, edited for compactness==
Thursday, November 5, 2009
8:30 - 9:20 AM Registration
9:20-9:30 AM Introductory Remarks
9:30 - 10:30 AM Steven Weinberg, University of Texas Prospects for Asymptotic Safety
11:00 AM – 12:00 PM Martin Reuter, Mainz University TBA
2:00 – 3:00 PM Jean Zinn-Justin, CEA, Saclay TBA
3:00 - 4:00 PM Holger Gies, ITP, Jena University Mechanisms of Asymptotic Safety
4:30 - 5:30 PM B.F.L. Ward, Baylor University Asymptotic Safety and Resummed Quantum Gravity
Friday, November 6, 2009
9:30-10:30 AM Lee Smolin, Perimeter Institute Asymptotic safety in the light of our modern understanding of quantum geometry
11:00AM – 12:00 PM Renate Loll, Utrecht University TBA
2:00 – 3:00 PM Max Niedermaier, Tours University Gravitational fixed points and asymptotic safety from perturbation theory
3:00-4:00 PM Frank Saueressig, Mainz University TBA
4:30-6:00 PM TBA
6:00PM Banquet Dinner
Saturday, November 7, 2009
9:30-10:30 AM Arkady Tseytlin, Imperial College, London Comments on UV divergences in quantum gravity
11:00AM – 12:00 PM Vincent Rivasseau, Universite Paris-Sud XI, Orsay TBA
2:00 – 3:00 PM Alfio Bonanno, INAF, Catania The mass-inflation phenomenon in the asymptotic safety scenario
3:00-4:00 PM John Joseph M. Carrasco, UCLA Perturbative cancellations in gravity theories
4:30-6:00PM TBA
Sunday, November 8, 2009
9:30 - 10:30 AM Jan Ambjorn, Utrecht University TBA
11:00AM – 12:00 PM Daniel Litim, University of Sussex TBA
2:00 PM "Gravity at a Lifshitz Point" workshop begins at 2:00pm
(Please note: Participants from the "Asymptotic Safety" workshop are welcome to stay for this afternoon's talks during the "Gravity at a Lifshitz Point" workshop.)
==endquote==
Another talk has been listed, but not yet assigned a time-slot:
Michael Scherer Friedrich-Schiller-Universität A mechanism for Asymptotic Safety of chiral Yukawa systems
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
I have edited out much of the nonessential detail such as coffeebreaks, discussion, lunch, and room locations. I expect, since it is Perimeter, video of talks will appear online.
I note that Lee Smolin authored some of the early papers on AsymSafety, back in the 1980s, while postdoc at Princeton IAS, so it's not an unfamiliar topic for him. I'm especially curious to hear what both he and Renate Loll have to say. Also Bonanno in his talk on Saturday, because he has worked a lot on the connection between AsymSafe QG and early universe cosmology--some potentially elegant connections.
The chief organizer of the conference is Roberto Percacci
http://www.perimeterinstitute.ca/index.php?option=com_content&task=view&id=30&Itemid=72&pi=Roberto_Percacci
Often the organizer will act as host and not present a paper of his own, but will instead introduce the others. However in this case, since Percacci is one of the most active researchers and has contributed significantly to the field, one might hope that he doubles as a participant.
Percacci gave a talk at Zakopane in June 2009 which covered recent developments in AsymSafe, focusing on evidence for the UV fixed point. The PDF of his slides is here
http://th-www.if.uj.edu.pl/school/2009/lectures/percacci.pdf
He has a FAQ and bibliography on AsymSafe here
http://www.percacci.it/roberto/physics/as/
Here is the AsymSafe FAQ:
http://www.percacci.it/roberto/physics/as/faq.html
Jerzy Lewandowski has essentially codified Loop Foam gravity for us.
This had to happen, and there had to be a definitive 2009 exposition of the basics.
So far the best I know of is Jerzy's
http://arxiv.org/abs/0909.0939
Spin-Foams for All Loop Quantum Gravity
and the audio+slides version is at ILQGS
http://relativity.phys.lsu.edu/ilqgs/lewandowski102009.pdf
http://relativity.phys.lsu.edu/ilqgs/lewandowski102009.wav
http://relativity.phys.lsu.edu/ilqgs/
Something that impressed me, that may seem irrelevant, is how strongly Jerzy stressed the seminal importance of work by Michael Reisenberger done around 1994-1998. Here is a 1990 photo of MR at the Vatican Observatory
http://www34.homepage.villanova.edu/robert.jantzen/drbob/graphics/g9/halpern/photos/reisenberger-leopold1990.jpg
Now Reisenberger is senior faculty at the Montevideo Instituto de Fisica. He and Rodolfo Gambini are the two top QG people at University of Montevideo.
Reisberger's 1994 paper was called Worldsheet formulations of gauge theories and gravity http://arxiv.org/abs/gr-qc/9412035 It was written while he was still at Utrecht, at Gerard 't Hooft's ITP.
His 1997 paper with Carlo Rovelli was called "Sum over Surfaces'' form of Loop Quantum Gravity http://arxiv.org/abs/gr-qc/9612035 This was written while he was at the Schrödinger Institute in Vienna, and also at Montevideo.
A 1998 paper that Jerzy says should still be studied more (still has germinal undeveloped ideas) is called On relativistic spin network vertices http://arxiv.org/abs/gr-qc/9809067
Jerzy points to these as the founding papers of the spinfoam approach, the genesis of the idea. He also acknowledges learning a lot from John Baez clear 2000 exposition, and the review paper by Perez.
Jerzy presents a development of the spinfoam concept that appears in a certain sense natural. He defines the vertex formula for the foam using an enclosing spinnetwork---without invoking terms like "10j symbol" or "15j symbol". If you accept the idea of cylinder function (basic to the uniqueness theorem of "L.O.S. & T.") then the spinnetwork idea is not ad hoc---it flows naturally from the cylinderfunctions on the space of connections. And then the spinfoam idea flows naturally from the spinnetwork idea. He avoids all disconnects between the ideas.
And he seems to be saying that he was helped to re-understand the spinfoam concept by going back to Reisenberger's initial vision of it, or his preliminary glimpse. After he has finished the development, he can derive the current spinfoam vertex formulas, such as the Engle-Livine- Pereira-Rovelli, and see how the technical numbers like the angular momentum "j" symbols arise.
Lewandowski has been a major force in making Loop-and-related physics mathematically rigorous. His long collaboration with Ashtekar, spanning many years and many papers, had this main thrust.
If the organizers of the September 2009 Corfu School eventually succeed in putting online the 5-hour series of lectures by Carlo Rovelli, this would be what I'd say was the current definitive version of Loop Foam gravity. But we don't have those lectures as online media yet. At least for time being, Jerzy's paper and talk will fill the bill.
Here's a current photo of Reisenberger, one of 9 snapshots of Theiss scientists.
http://www.theissresearch.org/scientists/
It's alphabetical so scroll down.
If anyone wants to google more information about the University of Montevideo, the official name is UDELAR universita de la republica. Montevideo is capital of Uruguay, which is a Republic, so the main Uni is the University of the Republic. Here is the Montevideo Institute of Physics page:
http://www.fisica.edu.uy/
and here's the faculty list:
http://www.fisica.edu.uy/integrantes.html
http://arxiv.org/abs/0909.0939
v1. The second paper we appreciate so much is the derivation of the new spin-foam model from the Holst action by Engle, Livine, Pereira and Rovelli [6]. Those two excellent works brought spin-foams closer to LQG. On the other hand, we regret have not considered here closer the Freidel-Krasnov model [12].
v2. The second paper we appreciate so much is the derivation of the new spin-foam model from the Holst action by Engle, Livine, Pereira and Rovelli [6]. Those two excellent works brought spin-foams closer to LQG. On the other hand, the works that should be and will be considered closer in the spirit of the current paper, are the Freidel-Krasnov model [15] (especially in the range of γ in which that model does not overlap with EPRL). Also the pioneering works of Reisenberger [2, 11, 13] contain a lot of ideas that still have not been explored enough in the literature.
v2 is much better (sociologically :smile: for me) - I am quite suspicious of Rovelli unless Freidel or Reisenberger are coauthors.
The Asymptotic Safety conference starts 5 November, just a few days from now. Interest in AsymSafe QG has revived some 30 years after Weinberg presented the idea at Erice (Sicily) in 1976.
A more complete list conference speakers and topics is now available:
==excerpts from Perimeter host page, edited for compactness==
Thursday, November 5, 2009
8:30 - 9:20 AM Registration
9:20-9:30 AM Introductory Remarks
9:30 - 10:30 AM Steven Weinberg, University of Texas Prospects for Asymptotic Safety
11:00 AM – 12:00 PM Martin Reuter, Mainz University Gravitational average action and asymptotic safety: past and future
2:00 – 3:00 PM Jean Zinn-Justin, CEA, Saclay Asymptotic safety: a review
3:00 - 4:00 PM Holger Gies, ITP, Jena University Mechanisms of Asymptotic Safety
4:30 - 5:30 PM B.F.L. Ward, Baylor University Asymptotic Safety and Resummed Quantum Gravity
Friday, November 6, 2009
9:30-10:30 AM Lee Smolin, Perimeter Institute Asymptotic safety in the light of our modern understanding of quantum geometry
11:00AM – 12:00 PM Renate Loll, Utrecht University TBA
2:00 – 3:00 PM Max Niedermaier, Tours University Gravitational fixed points and asymptotic safety from perturbation theory
3:00-4:00 PM Frank Saueressig, Mainz University Exploring the Theory Space of Asymptotically Safe Quantum Gravity
4:30-5:00 PM Elisa Manrique, Mainz University TBA
5:00-5:30 PM Christophe Rahmede, University of Sussex TBA
Saturday, November 7, 2009
9:30-10:30 AM Arkady Tseytlin, Imperial College, London Comments on UV divergences in quantum gravity
11:00AM – 12:00 PM Vincent Rivasseau, Universite Paris-Sud XI, Orsay TBA
2:00 – 3:00 PM Alfio Bonanno, INAF, Catania The mass-inflation phenomenon in the asymptotic safety scenario
3:00-4:00 PM John Joseph M. Carrasco, UCLA Perturbative cancellations in gravity theories
4:30-5:00PM Gian Paolo Vacca, INFN, Bologna TBA
5:00-5:30PM Michael Scherer ITP, Jena University A mechanism for Asymptotic Safety of chiral Yukawa systems
Sunday, November 8, 2009
9:30 - 10:30 AM Jan Ambjorn, Utrecht University CDT and asymptotic safety
11:00AM – 12:00 PM Daniel Litim, University of Sussex TBA
2:00 PM "Gravity at a Lifshitz Point" workshop begins at 2:00pm
(Please note: Participants from the "Asymptotic Safety" workshop are welcome to stay for this afternoon's talks during the "Gravity at a Lifshitz Point" workshop.)
==endquote==
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
I have edited out nonessential detail such as coffeebreaks, discussion sessions, meals, and room locations. Since it is Perimeter, video of talks might appear online.
The chief organizer of the conference is Roberto Percacci
http://www.perimeterinstitute.ca/index.php?option=com_content&task=view&id=30&Itemid=72&pi=Roberto_Percacci
Percacci gave a talk at Zakopane in June 2009 which covered recent developments in AsymSafe, focusing on evidence for the UV fixed point. The PDF of his slides is here
http://th-www.if.uj.edu.pl/school/2009/lectures/percacci.pdf
He has a FAQ and bibliography on AsymSafe here
http://www.percacci.it/roberto/physics/as/
Here is the AsymSafe FAQ:
http://www.percacci.it/roberto/physics/as/faq.html
The AsymSafe conference starts tomorrow. Some new titles of talks have been added to the list, and some of the speakers have posted abstracts. Smolin's was interesting, I thought. I'm curious to know what Rivasseau is proposing as a mechanism that could underlie and cause Asymptotic Safety.
I have highlighted Rahmede's talk because he is reporting joint work with Roberto Percacci and others. The corresponding papers have just been posted on arxiv. It is possible that Rahmede's talk will cover among the most valuable recent results reported at the conference. So I highlighted those three.
Here's an updated list that includes abstracts of some talks:
Jan Ambjorn, Utrecht University
CDT and asymptotic safety
CDT is a lattice regularization of quantum gravity. The phase structure of the lattice theory is discussed and a candidate UV fixed point located.
Alfio Bonanno, INAF, Catania
The mass-inflation phenomenon in the asymptotic safety scenario
John Joseph M. Carrasco, UCLA
Perturbative cancellations in gravity theories
I will present recent results through four loops demonstrating that the maximally supersymmetric (N=8) generalization of gravity is surprisingly well behaved in the ultraviolet as a result of unexpected cancellations between contributing terms. These cancellations first manifest at one loop in the form of the "no-triangle property," with all-loop order implications through unitarity. I will conclude by discussing similar novel cancelations identified in pure Einstein gravity, at one loop, which suggest a possible explanation for the unexpectedly tame high energy behavior of N=8 supergravity beyond the limited UV protection of supersymmetry.
Holger Gies, ITP, Jena University
Mechanisms of Asymptotic Safety
Renate Loll, Utrecht University
Nonperturbative Insights from Causal Dynamical Triangulations
Max Niedermaier, Tours University
Gravitational fixed points and asymptotic safety from perturbation theory
Christoph Rahmede, Jena University
Renormalization Group Flow in Scalar-Tensor Theories
Martin Reuter, Mainz University
Gravitational average action and asymptotic safety: past and future
Vincent Rivasseau, Université Paris-Sud XI, Orsay
A New Mechanism for Asymptotic Safeness
Frank Saueressig, Mainz University
Exploring the Theory Space of Asymptotically Safe Quantum Gravity
Michael Scherer, ITP, Jena University
A mechanism for Asymptotic Safety of chiral Yukawa systems
We will discuss Weinberg's idea of asymptotic safety for a chiral Yukawa system with a U(N_L)_L x U(1)_R symmetry in a leading-order derivative expansion using nonperturbative functional RG equations. As a toy model sharing important features with the standard model we explicitely discuss N_L=10 for which we find a non-Gaussian fixed point and compute its critical exponents. We observe a reduced hierarchy problem and obtain predictions for the toy Higgs and the toy top mass.
Lee Smolin, Perimeter Institute
Asymptotic safety and deformed symmetry
I review work on asymptotic safety in quantum gravity in a 1/N expansion. I highlight the result that the scaling behavior governed by the non-trivial fixed point must be characterized by a scaling dimension less than four. Otherwise a Weyl curvature squared counterterm is required, that renders the theory unstable. This reduced scaling dimension then implies that Lorentz invariance is either broken or deformed, and this is transmitted to the matter sector. However, there are strong constraints on breaking of Lorentz invariance at the Planck scale due to the absence of birefringence of photons. The present constraints on deforming Lorentz invariance are, however, just at the Planck scale. I will then review semiclassical quantum gravity arguments that Lorentz symmetry is deformed.
Arkady Tseytlin, Imperial College, London
Comments on UV divergences in quantum gravity
Gian Paolo Vacca, Bologna University
Quantum Gravitational Corrections to Matter: A Running Controversy
B.F.L. Ward, Baylor University
Asymptotic Safety and Resummed Quantum Gravity
In Weinberg’s asymptotic safety approach to quantum gravity, one has a finite dimensional critical surface for a UV stable fixed point to generate a theory of quantum gravity with a finite number of physical parameters. The task is to demonstrate how this fixed point behavior actually arises. We argue that, in a recently formulated extension of Feynman’s original formulation of the theory, which we have called resummed quantum gravity, we recover this fixed-point UV behavior from an exact re-arrangement of the respective perturbative series. We argue that the results we obtain are consistent both with the exact field space Wilsonian renormalization group results of Reuter and Bonanno and with recent Hopf-algebraic Dyson-Schwinger renormalization theory results of Kreimer. We calculate the first "first principles" predictions of the respective dimensionless gravitational and cosmological constants and argue that they support the Planck scale cosmology advocated by Bonanno and Reuter as well. Comments on the prospects for actually predicting the currently observed value of the cosmological constant are also given.
Steven Weinberg, University of Texas, Austin
Prospects for Asymptotic Safety
Omar Zanusso, SISSA
Asymptotic safety in the nonlinear sigma models and gravity
Jean Zinn-Justin, CEA, Saclay
Asymptotic safety: a review
I shall review on field theory examples, the meaning of the concept of asymptotic safety in the context of low energy effective field theories.
---from the webpage http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Abstracts/
BTW, have you noticed what means to Carrasco go to this conference?
BTW, let me guess, the paper in which Vincent Rivasseau will base his talk is this one:
http://arxiv.org/abs/0906.5477
Horava Gravity conference starts in the same day Asymptotic Safety ends:
http://www.perimeterinstitute.ca/en/Events/Gravity_at_a_Lifshitz_Point/Gravity_at_a_Lifshitz_Point/
BTW, have you noticed what means to Carrasco go to this conference?
Yes, I'm very curious whether his results are at all related to AS. Gping by Percacci's GraviGUT, maybe we can soon have an AS landscape too. :wink:
BTW, time to include this guy, B.F.L Ward, on the thread of Rovelli's program:
Resumed gravity:
http://arxiv.org/find/gr-qc/1/au:+Ward_B/0/1/0/all/0/1
I didn't know this guy, but I got hints of this idea in other papers, and posted it here
http://www.physicsforums.com/showpost.php?p=2416009&postcount=20
"[...]it is not just the physicists' trying to dig something out of diagrams. It is the couplings of the theory dynamically cooperating and organizing somehow among themselves to find a point stable in a surface, all this which ends up causing the renormalization of the theory."
EDIT.: I guess I really did read about him, I just forgot, here's more of his papers:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=ea+Ward,+B+F+L
RUTA recently contributed another link to add to our list of 4D quantum gravity links to keep handy for reference.
Workshops at Ashtekar's Penn State IGC:
http://www.gravity.psu.edu/events/workshops.shtml
Past talks of the International LQG Seminar, online.
http://relativity.phys.lsu.edu/ilqgs/
September 2009 Corfu QG School (so far audio has been posted for only a small portion)
http://www.physics.ntua.gr/corfu2009/qg.html
http://www.physics.ntua.gr/corfu2009/Program/3rdWeekSchool.html
June 2009 school for Nonperturbative Gravity and QCD at Zakopane. Online media incomplete.
http://th-www.if.uj.edu.pl/school/2009/
http://th-www.if.uj.edu.pl/school/2009/lectures.html
June 2009 PlanckScale conference video and slides:
http://www.ift.uni.wroc.pl/~planckscale/
http://www.ift.uni.wroc.pl/~planckscale/movie/
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php
July 2009 Marcel Twelve conference in Paris (886 participants):
http://www.icra.it/MG/mg12/en/
http://www.icra.it/MG/mg12/talks_plenary/Freidel.pdf
Loops 2009 in Beijing (~230 participants)
http://www.mighty-security.com/loop/timetable1.htm
August 2009 EG4 at Vancouver. No online media so far.
http://www.emergentgravity.org/index.php?main=main_EGIV_programme.php
November 2009 Asymptotic safety conference at Perimeter:
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
AsymSafe videos:
http://pirsa.org/C09025
November 2009 Horava gravity videos:
http://pirsa.org/C09026
June 2010 Americas QG school at Morelia
http://www.physics.ucsb.edu/~pasi/
July 2010 GR19 conference in Mexico City
http://www.gr19.com/index.php
Links to check for new announcements:
http://www.maths.nottingham.ac.uk/qg/
http://grg.maths.qmul.ac.uk/hyperspace/conference/
http://grg.maths.qmul.ac.uk/hyperspace/conference/latest.html
Topcited Loop papers after 2006 (keywords SPIN FOAM, GROUP FIELD THEORY, LOOP QUANTUM COSMOLOGY, LOOP QUANTUM GRAVITY):
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+K+SPIN%2CFOAM+OR+DK+FIELD+THEORY%2 C+GROUP+OR+DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUA NTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29
Some classic online sources:
Rovelli's talk at Strings 2008 Video
http://cdsweb.cern.ch/record/1121957?ln=en
Slides
http://indico.cern.ch/getFile.py/acc...s&confId=21917
2003 draft of Rovelli's book online
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
Rovelli's chapter in Oriti's book
http://arxiv.org/abs/gr-qc/0604045
Review of LQG as of May 2008:
http://relativity.livingreviews.org/Articles/lrr-2008-5/
Steven Weinberg's 6 July talk, main CERN link:
http://indico.cern.ch/conferenceDisplay.py?confId=57283
Weinberg video:
http://cdsweb.cern.ch/record/1188567/
To save time jump to minute 58, the last 12 minutes.
Photos from the first Loops conference, at Marseille 2004
http://math.ucr.edu/home/baez/marseille/
Longshots:
Vincent Rivasseau at the 2009 Perimeter AsymSafe conference.
http://pirsa.org/09110049/
Ted Jacobson at the 2009 Perimeter HorGrav conference.
http://pirsa.org/09110066/
Krasnov 2006 video lecture
http://pirsa.org/06110041/
Krasnov 2008 audio+pdf talk at the ILQGS
http://relativity.phys.lsu.edu/ilqgs/krasnov020508.pdf
http://relativity.phys.lsu.edu/ilqgs/krasnov020508.aif
The list of upcoming conferences known as "hyperspace" has moved.
http://hyperspace.aei.mpg.de/category/Conferences/
Four authors have posted major papers since the last time I updated this short list of sources to keep handy. Steven Weinberg, Roberto Percacci, Kirill Krasnov, and Thomas Thiemann.
http://arxiv.org/abs/0911.3165
Asymptotically Safe Inflation
Steven Weinberg
Discussion: http://physicsforums.com/showthread.php?t=355757
http://arxiv.org/abs/0910.5167
Gravity from a Particle Physicist's perspective
R. Percacci
http://arxiv.org/abs/0911.0386
Renormalization Group Flow in Scalar-Tensor Theories. I
Gaurav Narain, Roberto Percacci
Discussion: http://physicsforums.com/showthread.php?t=349513
http://arxiv.org/abs/0911.3793
Gravity-Yang-Mills-Higgs unification by enlarging the gauge group
Alexander Torres-Gomez, Kirill Krasnov (University of Nottingham)
Discussion: http://physicsforums.com/showthread.php?t=356492
http://arxiv.org/abs/0911.3433
Canonical path integral measures for Holst and Plebanski gravity. I. Reduced Phase Space Derivation
Jonathan Engle, Muxin Han, Thomas Thiemann
Discussion: http://physicsforums.com/showthread.php?t=356264
Time to do some housekeeping on this list of 4D quantum gravity links to keep handy.
The list of upcoming conferences known as "hyperspace" has moved to the AEI site.
http://hyperspace.aei.mpg.de/category/Conferences/
June 2009 PlanckScale conference video and slides:
http://www.ift.uni.wroc.pl/~planckscale/
http://www.ift.uni.wroc.pl/~planckscale/movie/
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php
RUTA pointed out these workshops at Ashtekar's Penn State IGC:
http://www.gravity.psu.edu/events/workshops.shtml
Past talks of the International LQG Seminar, online:
http://relativity.phys.lsu.edu/ilqgs/
July 2009 Marcel Twelve conference in Paris (886 participants):
http://www.icra.it/MG/mg12/en/
http://www.icra.it/MG/mg12/talks_plenary/Freidel.pdf
Loops 2009 in Beijing (~230 participants):
http://www.mighty-security.com/loop/timetable1.htm
November 2009 Asymptotic safety conference at Perimeter:
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
AsymSafe videos:
http://pirsa.org/C09025
November 2009 Horava gravity videos:
http://pirsa.org/C09026
June 2010 Americas QG school at Morelia:
http://www.physics.ucsb.edu/~pasi/
July 2010 GR19 conference in Mexico City:
http://www.gr19.com/index.php
Nottingham QG network:
http://www.maths.nottingham.ac.uk/qg/
Topcited Loop papers after 2006
(keywords "spin, foam", "field theory, group", "quantum gravity, loop space", and "quantum cosmology, loop space"):
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+K+SPIN%2CFOAM+OR+DK+FIELD+THEORY%2 C+GROUP+OR+DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUA NTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29
Classic online sources.
Rovelli's talk at Strings 2008 Video:
http://cdsweb.cern.ch/record/1121957?ln=en
Slides:
http://indico.cern.ch/getFile.py/acc...s&confId=21917
2003 draft of Rovelli's book online:
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
Rovelli's chapter in Oriti's book:
http://arxiv.org/abs/gr-qc/0604045
Review of LQG as of May 2008:
http://relativity.livingreviews.org/Articles/lrr-2008-5/
Steven Weinberg's 6 July talk, main CERN link:
http://indico.cern.ch/conferenceDisplay.py?confId=57283
Weinberg video (historical overview up to minute 58 followed by
no-frills approach to unification in the last 12 minutes):
http://cdsweb.cern.ch/record/1188567/
Related Weinberg paper Asymptotically Safe Inflation:
http://arxiv.org/abs/0911.3165
Discussion thread http://physicsforums.com/showthread.php?t=355757
Roberto Percacci's Gravity from a Particle Physicist's Perspective:
http://arxiv.org/abs/0910.5167
Narain and Percacci Renormalization Group Flow in Scalar-Tensor Theories. I:
http://arxiv.org/abs/0911.0386
Discussion thread http://physicsforums.com/showthread.php?t=349513
Photos from the first Loops conference, at Marseille 2004:
http://math.ucr.edu/home/baez/marseille/
Selected longshots.
Vincent Rivasseau at the 2009 Perimeter AsymSafe conference:
http://pirsa.org/09110049/
Ted Jacobson at the 2009 Perimeter HorGrav conference:
http://pirsa.org/09110066/
Krasnov 2006 video lecture:
http://pirsa.org/06110041/
Krasnov 2008 audio+pdf talk at the ILQGS:
http://relativity.phys.lsu.edu/ilqgs/krasnov020508.pdf
http://relativity.phys.lsu.edu/ilqgs/krasnov020508.aif
Krasnov and Gomez Gravity-Yang-Mills-Higgs unification by enlarging the gauge group:
http://arxiv.org/abs/0911.3793
It could be that there will be no Loops 2010 conference, no big international QG meeting.
I've heard nothing about one being organized. On the other hand, I have heard of other comparable or related events:
Sabine Hossenfelder is organizing a Stockholm workshop on the experimental search for QG.
http://backreaction.blogspot.com/2009/11/experimental-search-for-quantum-gravity.html
Here's the website:
http://th.physik.uni-frankfurt.de/~hossi/ESQG10/
This will take place 12-16 July.
Then there is this two-week-long PASI QG school, with lecture-series by Abhay Ashtekar, Carlo Rovell, Laurent Freidel, Renate Loll...
PASI stands for "Panamerican Advanced Studies Institute". The school will be supported by the US National Academy of Sciences. In a way that is even better than having a Loops conference (in terms of some obvious practical goals.) Here is the 2010 QG School website:
http://www.physics.ucsb.edu/~pasi/
This will take place 23 June-3 July.
Thanks to 'Sabah for mentioning the Experimental QG Search workshop. The website already shows an impressive list of QG people who will be participating.
Also being held in 2010 is the 19th international General Relativity and Gravitation conference, GR19. This is a major conference held every three years, bringing all gravity related research programs together. One of the parallel sessions will be devoted to Loop.
http://www.gr19.com/index.php
This will take place 5-9 July.
So things will be happening with some resemblance to an annual meeting, but as far as I know no official Loops 2010 has been announced.
Here's the website for Strings 2010, in case anyone is interested.
http://mitchell.physics.tamu.edu/Conference/string2010/
It will take place 15-19 March.
I think it's good to point out the upcoming Quantum Gravity school held in Zakopane taking place 28 February - 4 March. This year the main topic is Open problems in Loop Quantum Gravity and it seems to be quite interesting as a way to settle future directions. The programme (and registration - still opened!) here:
http://www.fuw.edu.pl/~jpa/qgqg3/
*Notice*
At the end of the Loops'09 conference it was announced that there won't be any Loops'10 precisely because of GR19. And so, the next one is Loops'11 to be held in Madrid, Spain.
It's often informative to note the focus of the year's workshops, conferences and schools. Can give an idea about the direction things are going. This year there will be two QG schools (when I started watching in 2003 there were no annual Loop conferences and no QG schools at all.) This year there will also be a workshop on search for observable effects--QG phenomena.
The programs for the year's meetings are mosty not posted yet, but here are links to the websites that we can watch for information as it appears.
QGQG3, The third European QG school, 28 February - 4 March
http://www.fuw.edu.pl/~jpa/qgqg3/
Panamerican QG School, the first such supported by the US, 23 June - 3 July
http://www.physics.ucsb.edu/~pasi/
GR19, the triennial international meeting on General Rel and Gravitation, 5 - 9 July
http://www.gr19.com/index.php
Workshop on the Experimental Search for Quantum Gravity, 12 - 16 July
http://th.physik.uni-frankfurt.de/~hossi/ESQG10/
There will be a session of GR19 devoted to loop and spinfoam quantum gravity. This will serve as the main international LQG conference this year so there will be no separate Loops 2010, as Guedes tells us. He also says Loops 2011 will be held in Madrid.
In an earlier post I had a bad link to the slides for Rovelli's Strings 2008 talk.
Here are the (in one case repaired) links
Video:
http://cdsweb.cern.ch/record/1121957?ln=en
Slides:
http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917
An undergraduate course in Loop Quantum Gravity:
http://www.phys.lsu.edu/classes/spring2010/phys4750/
Professor Jorge Pullin has already posted the first two problem sets online. The second set is due 15 February.
Instead of a text, he is distributing his own lecture notes--but so far these are only for the students taking the course: they have not been posted on line.
==quote==
PHYS 4750: Introduction to loop quantum gravity
...
This course will be an introduction for undergraduates to loop quantum gravity. To our knowledge, this is the first time such a course is offered in the world. We will assume minimal prerequisites: some knowledge of Lagrangian mechanics, some quantum mechanics and special relativity.
Topics:
1. Introduction: quantum gravity, why, what?
2. Special relativity and electromagnetism.
3. Some elements of general relativity.
4. Hamiltonian mechanics including constraints and fields.
5. Quantum mechanics and elements of quantum field theory.
6. Yang-Mills theories.
7. General relativity in terms of Ashtekar’s new variables.
8. Loop representation for general relativity.
9. An application: loop quantum cosmology.
10. Further developments.
11. Open issues and controversies.
Grades for the course will consist 50% on homework (graded pass/fail) and a final presentation of a paper. A list of possible topics will be given later in the semester. ...
==endquote==
Prof. Pullin is also a proficient player of the Scottish bagpipes. In case you do not believe this, his website has a link enabling you to hear him perform on the melancholy and belligerent instrument of his Scottish ancestors.
http://www.phys.lsu.edu/faculty/pullin/
The schedule of talks to be held at the main annual Strings conference has been partially posted.
http://mitchell.physics.tamu.edu/Conference/string2010/Conference.html#
So far the titles of the talks are not included in the schedule.
The conference begins in slightly less than one month, on 15 March.
http://mitchell.physics.tamu.edu/Conference/string2010/
By watching the titles of the talks and comparing Strings 2010 with the same conference in past years we can hopefully learn something about trends and shifts of focus in this collection of research fields.
It has been over two months, time to update this list of handy 4D quantum gravity links.
The list of upcoming conferences known as "hyperspace" has moved to the AEI site:
http://hyperspace.aei.mpg.de/category/Conferences/
The Nottingham QG network:
http://www.maths.nottingham.ac.uk/qg/
June 2009 PlanckScale conference video and slides:
http://www.ift.uni.wroc.pl/~planckscale/
http://www.ift.uni.wroc.pl/~planckscale/movie/
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php
RUTA pointed out these workshops at Ashtekar's Penn State IGC:
http://www.gravity.psu.edu/events/workshops.shtml
Past talks of the online International LQG Seminar, run by Prof. Jorge Pullin:
http://relativity.phys.lsu.edu/ilqgs/
July 2009 Marcel Twelve conference in Paris (886 participants):
http://www.icra.it/MG/mg12/en/
http://www.icra.it/MG/mg12/talks_plenary/Freidel.pdf
November 2009 Asymptotic safety conference at Perimeter:
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
AsymSafe videos:
http://pirsa.org/C09025
November 2009 Horava gravity videos:
http://pirsa.org/C09026
28 February - 4 March 2010, The third European QG school (QGQG3, quantum geometry/gravity)
http://www.fuw.edu.pl/~jpa/qgqg3/
15-19 March 2010 Strings 2010
http://mitchell.physics.tamu.edu/Conference/string2010/
23 June-3 July 2010, Americas QG school at Morelia:
http://www.physics.ucsb.edu/~pasi/
5-9 July 2010, GR19 conference in Mexico City
http://www.gr19.com/index.php
(LQG will have a session of GR19 which will serve as this year's "Loops 2010"
12-16 July 2010, Sabine Hossenfelder's Stockholm workshop on the experimental search for QG
http://th.physik.uni-frankfurt.de/~hossi/ESQG10/
http://backreaction.blogspot.com/2009/11/experimental-search-for-quantum-gravity.html
Loops 2011 will be held in Madrid.
Topcited Loop papers after 2006
(keywords "spin, foam", "field theory, group", "quantum gravity, loop space", and "quantum cosmology, loop space"):
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+K+SPIN%2CFOAM+OR+DK+FIELD+THEORY%2 C+GROUP+OR+DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUA NTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29
Classic online sources.
Rovelli's talk at Strings 2008 Video:
http://cdsweb.cern.ch/record/1121957?ln=en
Slides: http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917
2003 draft of Rovelli's book online:
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
Rovelli's chapter in Oriti's book:
http://arxiv.org/abs/gr-qc/0604045
Review of LQG as of May 2008:
http://relativity.livingreviews.org/Articles/lrr-2008-5/
Steven Weinberg's 6 July 2009 talk, main CERN link:
http://indico.cern.ch/conferenceDisplay.py?confId=57283
Weinberg video (historical overview up to minute 58 followed by
no-frills approach to unification in the last 12 minutes):
http://cdsweb.cern.ch/record/1188567/
Related Weinberg paper Asymptotically Safe Inflation:
http://arxiv.org/abs/0911.3165
Discussion thread http://physicsforums.com/showthread.php?t=355757
Etera Livine's 17 February 2010 talk, A review of Spinfoams and Group Field Theory
http://pirsa.org/10020079/
Related paper by Girelli Livine Oriti, 4d Deformed Special Relativity from Group Field Theories
http://arxiv.org/abs/0903.3475
Photos from the first Loops conference, at Marseille 2004:
http://math.ucr.edu/home/baez/marseille/
Selected longshots.
Vincent Rivasseau at the 2009 Perimeter AsymSafe conference:
http://pirsa.org/09110049/
Ted Jacobson at the 2009 Perimeter HorGrav conference:
http://pirsa.org/09110066/
Ted Jacobson Thermodynamics of Spacetime: The Einstein Equation of State
http://arXiv.org/abs/gr-qc/9504004
Ted Jacobson Introduction to Quantum Fields in Curved Spacetime and the Hawking Effect
http://arxiv.org/abs/gr-qc/0308048
Erik Verlinde On the Origin of Gravity and the Laws of Newton
http://arxiv.org/abs/1001.0785
Lee Smolin, Newtonian gravity in loop quantum gravity
http://arxiv.org/abs/1001.3668
Jerzy Kowalski-Glikman, Note on gravity, entropy, and BF topological field theory
http://arxiv.org/abs/1002.1035
Easson Frampton Smoot, Entropic Accelerating Universe
http://arxiv.org/abs/1002.4278
Renate Loll 3-week course at Perimeter, Intro to Quantum Gravity:
Lecture 1: http://pirsa.org/10010094/ (25 January 2010)
Lecture 2: http://pirsa.org/10010095/ (26 January)
Lecture 3: http://pirsa.org/10010096/ (27 January)
Lecture 4: http://pirsa.org/10010097/ (28 January)
Lecture 5: http://pirsa.org/10010098/ (29 January)
Lecture 6: http://pirsa.org/10020060/ (1 February)
Lecture 7: http://pirsa.org/10020061/ (2 February)
Lecture 8: http://pirsa.org/10020062/ (3 February)
Lecture 9: http://pirsa.org/10020063/ (4 February)
Lecture 10: http://pirsa.org/10020064/ (5 February)
Lecture 11: http://pirsa.org/10020065/ (8 February)
Lecture 12: http://pirsa.org/10020066/ (9 February)
Lecture 13: http://pirsa.org/10020067/ (10 February)
Lecture 14: http://pirsa.org/10020068/ (11 February)
Lecture 15: http://pirsa.org/10020069/ (12 February)
Undergrad LQG course at Louisiana State taught by Jorge Pullin. Some material online:
http://www.phys.lsu.edu/classes/spring2010/phys4750/
http://www.phys.lsu.edu/faculty/pullin/
List of Strings 2010 talks, for comparison or trend-spotting:
http://mitchell.physics.tamu.edu/Conference/string2010/TitleofTalks.html
Erik Verlinde's two blog entries about his entropic force explanation of gravity.
http://staff.science.uva.nl/%7Eerikv/page20/page18/page18.html
The informal blog discussion is a helpful addition to the paper.
Sabine Hossenfelder's notes commenting on Verlinde's paper.
http://prime-spot.de/Physics/notes6.pdf
Her blog entry summarizing what she said in the notes:
http://backreaction.blogspot.com/2010/03/gravity-is-entropy-is-gravity-is.html
Another insightful Jacobson paper on causal horizon entropy to keep in the top drawer.
http://arxiv.org/abs/gr-qc/0302099
thanks to MTd2 for the reference linking to it.
It was already pointed out that this year's LOOPS 2010 is planned as the Loops section of a major international conference that happens every three years, the General Relativity and Gravitation (abbr. GRG, or simply GR) triennial.
This time it's the 19th GR triennial, so you google "GR19"
Then you click on "scientific program" and within that, click on Parallel Sessions.
===quote from GR19 website about some parallel sessions===
D1 Loop Quantum Gravity and Spin Foams
Chair: Alejandro Corichi
Partial list of speakers:
Abhay Ashtekar
Bianca Dittrich
Laurent Freidel
Parampeet Singh
D2 Strings, branes and M-theory
Chair: Shiraz Minwalla
Partial list of speakers:
Petr Horava
Xi Yin
Wei Song
D3 Causal sets, Causal dynamical triangulations, Non-commutative geometry, and other approaches to quantum gravity
Chair: Fay Dowker
Partial list of speakers:
Renate Loll
David Rideout
Steve Carlip
Daniel Litim
==endquote==
Carlo Rovelli will be giving a plenary survey talk Tuesday 6 July 11:30-12:30 titled
Progress in loop gravity and spin foams
http://www.gr19.com/index.php
Wei Song is one of the guys from the Fermi Sea paper: http://arxiv.org/abs/0912.4265
Xi Yin is a guy that has worked recently with Davide Gaiotto, and he is pretty mainstream string theory.
So, I don't think these qualify as something that would belong to a Loops conference.
Maybe Petr Horava, but he should present his recent work with Cenke Xu to look like more loopy: http://arxiv4.library.cornell.edu/abs/1003.0009
Wei Song is one of the guys from the Fermi Sea paper: http://arxiv.org/abs/0912.4265
Xi Yin is a guy that has worked recently with Davide Gaiotto, and he is pretty mainstream string theory.
So, I don't think these qualify as something that would belong to a Loops conference.
Maybe Petr Horava, but he should present his recent work with Cenke Xu to look like more loopy: http://arxiv4.library.cornell.edu/abs/1003.0009
The Loop session of GR19 is the session chaired by Alejandro Corichi.
The papers by Horava, and by Xi Yin are not supposed to be Loop papers! :biggrin:
They are not being given in the Loop session, they are being given in the STRING THEORY session of GR19. There is no reason for Horava to "look loopy".
I just threw in some extra information. Including some about the CAUSAL SETS/DYNAMICAL TRIANGULATIONS ETC session, chaired by Dowker. That's looking good already:
with Loll, and Steve Carlip.
These sessions will be getting a lot more speakers as time goes on. It is still very early. But already they are beginning to take shape.
Let's not start discussion here in this thread. Keep it for selected links. If you want to discuss GR19, could we start a discussion thread about it?
The international GRG (general relativity and gravitation) society holds a big conference every three years. The upcoming one is GR19 Mexico City starting 5 July 2010:
http://www.gr19.com/index.php
They typically draw some 600 or more participants talking on every aspect of the cosmos' geometry: numerical sims, gravitational waves, lensing, cosmology, quantum gravity/geometry, loop-string-triangulations, analog black hole models, etc etc.
This year there will be, in addition to all the technical talks in-conference, a plenary public lecture for everybody, not just for conference participants.
This pubic lecture will be on the evening of 6 July, and it will be given by George F. Smoot.
:biggrin:
Smoot gives a dynamite talk
http://www.ted.com/talks/george_smoot_on_the_design_of_the_universe.html
Rovelli is giving a plenary (in-conference) talk on current progress in LQG.
When you put the various conference elements together with mariachi music it augurs well--promises a lively mix.
====================================
Parampreet Singh has started a crash course at Perimeter in cosmo perturbation theory---techniques critical in studying the early universe.
James Bardeen wrote the closest thing to a textbook on this--a 1988 review paper. Param is using the Bardeen paper as text.
Try this link:
http://adsabs.harvard.edu/abs/1988gsjs.conf.....B
Cosmological perturbations from quantum fluctuations to large scale structure
There is the first Param lecture video:
http://pirsa.org/10040058/
You may notice some minor file mis-labeling if you play it. But that is Param doing his first lecture (not somebody else Anders Sandvik)
He's good. Neil Turok, director of Perimeter is supposed to be giving some of the lectures in this course. It looks like they are doing one lecture a day. Maybe for a total of 15 lectures. (The typical Perimeter crash course format.)
The course is called Explorations in Cosmology 2,
because Perimeter just concluded a 15 lecture crash course called "Explorations in Cosmology 1". This is the follow-up to that first course. It was taught by Tolley and Sandera
All the 15 videos are available for that too, if you want.
Param is a many times co-author with top people in LQC (loop quantum cosmology) including Abhay Ashtekar. He was postdoc at Penn State. It is to be expected that what he is teaching now is relevant to testing LQC because quantum fluctuations are theory and largescale structure are observation and Bardeen's cosmo perturbation math is the bridge from the theory (you want to test) to the structure (you can observe.)
Time to update this list of handy QG links. Last time I updated was February 2010. We can add Mathilde Marcolli's paper and also Kirill Krasnov's exciting Perimeter video.
To find out about conferences and workshops, "hyperspace" at the AEI site:
http://hyperspace.aei.mpg.de/category/Conferences/
The Nottingham QG network:
http://www.maths.nottingham.ac.uk/qg/
Introductory courses:
Renate Loll 3-week course at Perimeter, Intro to Quantum Gravity:
Lecture 1: http://pirsa.org/10010094/ (25 January 2010)
for all 15 lectures, see
http://pirsa.org/index.php?p=speaker&name=Renate_Loll
Undergrad LQG course at Louisiana State taught by Jorge Pullin. Some material online:
http://www.phys.lsu.edu/classes/spring2010/phys4750/
http://www.phys.lsu.edu/faculty/pullin/
June 2009 PlanckScale conference video and slides:
http://www.ift.uni.wroc.pl/~planckscale/
http://www.ift.uni.wroc.pl/~planckscale/movie/
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php
RUTA pointed out these workshops at Ashtekar's Penn State IGC:
http://www.gravity.psu.edu/events/workshops.shtml
Past talks of the online International LQG Seminar, run by Prof. Jorge Pullin:
http://relativity.phys.lsu.edu/ilqgs/
November 2009 Asymptotic safety conference at Perimeter:
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
AsymSafe videos:
http://pirsa.org/C09025
7-13 February 2010, Oberwolfach workshop on Noncommutative Geometry and LQG ("Loops, Algebras, Spectral Triples")
http://www.mfo.de/programme/schedule/2010/06b/OWR_2010_09.pdf
28 February - 4 March 2010, The third European QG school (QGQG3, quantum geometry/gravity)
http://www.fuw.edu.pl/~jpa/qgqg3/
23 June-3 July 2010, Americas QG school at Morelia:
http://www.physics.ucsb.edu/~pasi/
5-9 July 2010, GR19 conference in Mexico City
http://www.gr19.com/index.php
(LQG will have a session of GR19 which will serve as this year's "Loops 2010", Loops 2011 will be in Madrid).
12-16 July 2010, Sabine Hossenfelder's Stockholm workshop on the experimental search for QG
http://th.physik.uni-frankfurt.de/~hossi/ESQG10/
http://backreaction.blogspot.com/2009/11/experimental-search-for-quantum-gravity.html
Topcited Loop papers after 2006
(keywords "spin, foam", "field theory, group", "quantum gravity, loop space", and "quantum cosmology, loop space"):
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+K+SPIN%2CFOAM+OR+DK+FIELD+THEORY%2 C+GROUP+OR+DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUA NTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29
Classic online sources.
Rovelli's talk at Strings 2008 Video:
http://cdsweb.cern.ch/record/1121957?ln=en
Slides: http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917
2003 draft of Rovelli's book online:
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
Rovelli's chapter in Oriti's book:
http://arxiv.org/abs/gr-qc/0604045
Review of LQG as of May 2008:
http://relativity.livingreviews.org/Articles/lrr-2008-5/
Rovelli, A new look at loop quantum gravity
http://arxiv.org/abs/1004.1780
Steven Weinberg's 6 July 2009 talk, main CERN link:
http://indico.cern.ch/conferenceDisplay.py?confId=57283
Weinberg video (historical overview up to minute 58 followed by
no-frills approach to unification in the last 12 minutes):
http://cdsweb.cern.ch/record/1188567/
Related Weinberg paper Asymptotically Safe Inflation:
http://arxiv.org/abs/0911.3165
Discussion thread http://physicsforums.com/showthread.php?t=355757
Recent progress in core Lqg:
Etera Livine's 17 February 2010 talk, A review of Spinfoams and Group Field Theory
http://pirsa.org/10020079/
Related paper by Girelli Livine Oriti, 4d Deformed Special Relativity from Group Field Theories
http://arxiv.org/abs/0903.3475
Alesci Rovelli, A regularization of the hamiltonian constraint compatible with the spinfoam dynamics
http://arxiv.org/abs/1005.0817
Bianchi Regoli Rovelli, Face amplitude of spinfoam quantum gravity
http://arxiv.org/abs/1005.0764
Bianchi Rovelli Vidotto, Towards Spinfoam Cosmology
http://arxiv.org/abs/1003.3483
Photos from the first Loops conference, at Marseille 2004:
http://math.ucr.edu/home/baez/marseille/
Selected longshots.
Mathilde Marcolli et al, Spin Foams and Noncommutative Geometry
http://arxiv.org/abs/1005.1057
Kirill Krasnov Deformations of General Relativity
http://pirsa.org/10050002/
Lisi Smolin Speziale, Unification of gravity, gauge fields, and Higgs bosons
http://arxiv.org/abs/1004.4866
Vincent Rivasseau at the 2009 Perimeter AsymSafe conference:
http://pirsa.org/09110049/
Ted Jacobson at the 2009 Perimeter HorGrav conference:
http://pirsa.org/09110066/
Ted Jacobson Thermodynamics of Spacetime: The Einstein Equation of State
http://arXiv.org/abs/gr-qc/9504004
Ted Jacobson Introduction to Quantum Fields in Curved Spacetime and the Hawking Effect
http://arxiv.org/abs/gr-qc/0308048
Erik Verlinde On the Origin of Gravity and the Laws of Newton
http://arxiv.org/abs/1001.0785
Lee Smolin, Newtonian gravity in loop quantum gravity
http://arxiv.org/abs/1001.3668
Jerzy Kowalski-Glikman, Note on gravity, entropy, and BF topological field theory
http://arxiv.org/abs/1002.1035
Easson Frampton Smoot, Entropic Accelerating Universe
http://arxiv.org/abs/1002.4278
Chamseddine Connes, Noncommutative Geometry as a Framework for Unification of all Fundamental Interactions including Gravity. Part I
http://arxiv.org/abs/1004.0464
Francesca's LQG world map:
http://maps.google.com/maps/ms?ie=UTF8&hl=en&msa=0&msid=106449985216139270436.0004843830d27f3e6c50e&t=h&z=0
To add to our list of this year's conferences on QG and unification:
Regensburg Conference on Quantum Field Theory and Gravity: Conceptual and Mathematical Advances in the Search for a Unified Framework (28 September - 1 October)
http://www.uni-regensburg.de/qft2010/qftgravity2010program.html
"...the aim of this conference is to bring together physicists and mathematicians working in quantum field theory and general relativity, and to encourage scientific discussions on fundamental and conceptual issues. Selected talks will introduce different directions of research, in a way as non-technical and easily accessible as possible. The conference is also intended for young researchers on the graduate and post-graduate level."
Confirmed invited participants:
Christian Bär (Potsdam)
Helga Baum (Berlin)
Andreas Doering (Oxford)
Michael Dütsch (Göttingen)
Thomas Elze (Pisa)
Bertfried Fauser (Birmingham)
Chris Fewster (York)
Christian Fleischhack (Paderborn)
Klaus Fredenhagen (Hamburg)
Claus Gerhardt (Heidelberg)
Domenico Giulini (Hannover)
Dietrich Häfner (Grenoble)
Christian Hainzl (Tübingen)
Stefan Hollands (Cardiff)
Ines Kath (Greifswald)
Claus Kiefer (Köln)
Michael Kiessling (Rutgers)
Jerzy Kijowski (Warszawa)
Philippe LeFloch (Paris)
Renate Loll (Utrecht)
Dieter Lüst (München)
Robert Oeckl (Morelia)
Daniele Oriti (Golm)
Gerd Rudolph (Leipzig)
Miguel Sánchez (Granada)
Alexander Strohmaier (Loughborough)
Blake Temple (Davis)
Stefan Teufel (Tübingen)
Shing-Tung Yau (Harvard)
Matilde Marcolli and two others organized a Noncommutative Geometry and LQG workshop at Oberwolfach in February.
http://www.mfo.de/programme/schedule/2010/06b/OWR_2010_09.pdf
15 talks, including these:
Hanno Sahlmann
Introduction to Loop Quantum Gravity – physics background, and kinematics
Johannes Aastrup
On spectral triples in Quantum gravity
Klaus Fredenhagen
Perturbative Algebraic Quantum Field theory
Thomas Thiemann
Reduced phase-space quantisation in Loop Quantum Gravity
Jesper Møller Grimstrup
On Spectral Triples of Holonomy Loops II
Matilde Marcolli
Spin foams and noncommutative geometry
Fedele Lizzi
Noncommutative Lattices
Jurek Lewandowski (with Andrzej Okolow)
Quantum Group Connections
Raimar Wulkenhaar
Quantum field theory on noncommutative geometries
Marcolli's two co-organizers were Ryszard Nest and Christian Fleischhack. Nest (b. 1950) is director of the NCG group at Uni Copenhagen. He has co-authored with Aastrup and Grimstrup, who have been known to us since around 2006 when they initiated an effort to combine LQG and NCG (with its realization of the standard particle physics model.) Fleischhack has published a number of LQG papers--I particularly remember his work on black hole entropy in association with Jerzy Lewandowski, but see his publication list here: http://www.math.uni-hamburg.de/home/fleischhack/ .
=======================
Another workshop. John Barrett and Daniele Oriti each give presentations here.
14-17 May 2010 at Bayrischzell (picturesque town in the mountains some 50 miles south of Munich)
Noncommutativity and Physics: Spacetime Quantum Geometry
Program consisted of 21 talks:
http://hep.itp.tuwien.ac.at/~miw/bzell2010/program2010.html
Some samples of the 21 talks:
John Barrett State sum models, induced gravity and the spectral action
Fedele Lizzi Bosonic spectral action induced from anomaly cancellation
Catherine Meusburger Observables for quantum gravity from higher categories
Daniele Oriti The microscopic dynamics of quantum space as a group field theory
Oriti's slides as sample of the available PDF:
http://hep.itp.tuwien.ac.at/~miw/bzell2010/Oriti-2010.pdf
Another sample, Fedele Lizzi's slides:
http://hep.itp.tuwien.ac.at/~miw/bzell2010/Lizzi-2010.pdf
Scenery and list of speakers:
http://hep.itp.tuwien.ac.at/~miw/bzell2010/
==================
Perimeter Laws of Nature conference:
http://www.perimeterinstitute.ca/en/Events/Laws_of_Nature/Schedule/
All the videos:
http://pirsa.org/C10001
Smolin and Unger presentation:
http://pirsa.org/10050053/
Related Ariel Caticha talk on getting quantum theory from Entropic Dynamics:
http://pirsa.org/10050021/
(What Ariel calls entropic dynamics looks like a nice mathematical generalization of bayes inference to me, not sure of value but interesting...good questions from Rafael Sorkin.)
GR19 is shaping up. Parallel session timeslots have been assigned. Sessions D1 thru D4 are of special interest to us here.
This is a major international conference on General Relativity and Gravitation which takes place every three years. This time it will be in Mexico City, July 5-9.
Parallel Session D1, Loop and Spin Foam (chair=Corichi) has been assigned a total of 6 hours.
D2, Strings Branes and M (Minwalla) has been assigned 3 hours.
D3, Causal Sets, CDT, NCG (Dowker) has been assigned 4 hours.
D4, curved space QFT (Unruh) has been assigned 8 hours.
The full title of Bill Unruh's session is "Quantum fields in curved space-time, semiclassical gravity, quantum gravity phenomenology, and analog models."
I think it is significant that they got a famous top physicist (of the Unruh effect) to chair and that there is a lot of activity in things like effective field theory, phenomenology, analog lab models of black hole horizons, and field theory on curved spacetime.
It seems like a healthy development to me, and the Mexico GR19 is signaling this development.
http://www.gr19.com/paralsec.php
BTW when I first came to PF Beyond Forum, Alejandro Corichi was posting here a lot*. Not for years now, but it goes to show----shows something, doesn't it? Not quite sure what. Anyway since those days he has put together a strong LQG/Spinfoam program at UNAM Morelia, and now he chairs the Loop session at the triennial GR conference. Good luck with it.
*Under some pseudonym which out of respect for anonymity I have completely forgotten :biggrin:
Thought Grind
Jun3-10, 07:56 PM
Hello,
Just wondering if it would be OK for a self-taught physicist to take a poke at LQG, its design, function and context. There are many aspects I find questionable and figure that if it is the unification of the General Theory of Relativity and Quantum Mechanics then you could withstand the prodding of one such as I. I hold no ill will and greatly respect the efforts that went into the creation of LQG but that alone doesn't justify the fundaments of the relative truths involved that seem ... misconstrued?
If not then thank-you for your time,
Sean B.
Sean, not in this thread please. Just start your own thread to challenge and/or ask questions about LQG. Others have done so and have gotten a number of people involved in answering!
This thread has settled down into a concise regularly updated reading list of key papers, reviews, conferences. Source material that has proven useful to keep handy. I don't want to mess up that function by having a discussion in the middle of it. :biggrin:
I hope you understand, and are successful in starting a separate "Questions about LQG" or a "Things wrong with LQG" thread that you find satisfactory.
Thought Grind
Jun8-10, 09:52 AM
Thank you, I may do just that.
To add to the main list of links, next time it is updated:
A list of QG researchers, mostly involved in LQG
http://en.wikipedia.org/wiki/List_of_loop_quantum_gravity_researchers
Popularization of science at frontiers of research is often misleading---creating more confusion than understanding---but it can still be helpful to keep handy some selected public outreach links:
http://gravity.psu.edu/outreach/index.shtml
This list is organized by date, so there is a section of recent (2006-2010) material---illustrated magazine articles, video clips. Links to about 15 recent items, many from European media instead of Usa. There is also a section with older outreach stuff.
The list of lectures has been posted for the Morelia QG school.
The school begins in less than a week---on Wednesday 23 June.
Some reading lists have been provided, and some links to online papers.
http://www.physics.ucsb.edu/~pasi/lectures.html
Rovelli is scheduled to give three 90-minute lectures based on his "New LQG" paper of April 2010 (Arxiv 1004.1780).
I see that each speaker is scheduled to give three 90-minute lectures.
The title of Freidel's talks has not been posted.
The title of Renate Loll's talks has not been posted
Ashtekar has posted an extensive reading list for his talks on Loop Quantum Cosmology.
http://www.physics.ucsb.edu/~pasi/index.html
The 2010 QG School at Morelia is currently in session.
I believe the main organizer is Alex Corichi:
http://www.matmor.unam.mx//index.php?option=com_content&task=view&id=48&Itemid=58
Today I read that the organizers plan to post video of the lectures on line.
This could eventually be a useful resource. Rovelli will give three 90-minute lectures, as will Ashtekar, Laurent Freidel, and others. Again, the links are:
http://www.physics.ucsb.edu/~pasi/index.html
http://www.physics.ucsb.edu/~pasi/lectures.html
If I am not mistaken, Freidel's series of 3 lectures will start on Monday 28 June and Rovelli's on Wednesday 30 June.
The international GR conference (General Relativity and Gravitation), held every three years, starts in Mexico City a couple of days from now.
Rovelli will give a one-hour plenary talk, Tuesday July 6, 11:30-12:30. Corichi is chairing the following:
LQG and Spin Foam sessions
Tuesday July 6th
Freidel 14:00 - 14:30
Kisielowski 14:30 - 14:45
Kaminski 14:45 - 15:00
Singh 15:00 - 15:30
Pawlowski 15:30 - 15:45
Wilson 15:45 - 16:00
Thursday, July 8th
Dittrich 16:30 - 17:00
Perez 17:00 - 17:15
Dziendzikowski 17:15 - 17:25
Zapata 17:25 - 17:35
Perini 17:35 - 17:50
Pullin 17:50 - 18:10
Tsobanjan 18:10 - 18:20
Mangliaro 18:20 - 18:30
Friday, July 9th
Ashtekar 16:30 - 17:00
Campiglia 17:00 - 17:15
Vidotto 17:15 - 17:30
Bianchi 17:30 - 17:45
Lewandowski 17:45 - 18:05
Husain 18:05 - 18:20
Ma 18:20 - 18:30
http://www.gr19.com/parallels/d1_program.php
http://www.gr19.com/
Rovelli's talk will give a survey "Progress in loop gravity and spin foams". For the complete list see
http://www.gr19.com/scipro.php
===============================
Fay Dowker is chairing session D3 Causal sets, Causal dynamical triangulations, Non-commutative geometry, and other approaches to quantum gravity
Monday July 5
14:00 - 14:30 Loll
14:30 - 15:00 Litim
15:00 - 15:20 Satz
15:20 - 15:35 Oeckl
15:35 - 15:55 Sakellariadou
15:55 - 16:00 Nelson
16:30 - 17:00 Carlip
17:00 - 17:30 Rideout
17:30 - 17:50 Craig
17:50 - 18:00 Bonder
18:00 - 18:10 Magdaleno
18:10 - 18:20 Tafoya
18:20 - 18:30 Nesterov
17.00-17.30 Amsel,
17.30-17.45 Gorbonos
17.45-18.00 Rodriguez
18.00-18.15 Chirco
αβγδεζηθικλμνξοπρσςτυφχψω...ΓΔΘΛΞΠΣΦΨΩ...∏∑∫∂√ ...± ÷...←↓→↑↔~≈≠≡≤≥...½...∞...(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
Rovelli gave a brief 10-slide presentation back in May of 2009 which makes some simple points worth recalling. Rovelli recently gave a thumbnail sketch of LQG. Around 10 slides illustrated by drawings. You can look at the original slides and listen to the audio here:
http://relativity.phys.lsu.edu/ilqgs/panel050509.pdf
http://relativity.phys.lsu.edu/ilqgs/panel050509.mp3
It is a 3-way discussion and Rovelli is the second in line, so when you open the slides PDF you must scroll down about 10 slides first to come to Rovelli's section, likewise with the Audio mp3 you have to fast forward to about one third of the way, and just get the middle third of the recording. He will tell you in the audio which slide, when to switch slides and so forth. The other presentations, by Ashtekar and Freidel, are also good. But here I am focusing just on this very short 20 minute sequence by Rovelli....
...
...
Here I won't transcribe all 10-or-so slides. Just a few selected ones. If you want to see more you can go back to the original post, or use the LSU.EDU link. I was reminded of this seminar presentation by some questions that Naty was asking on several occasions this week. Maybe the best would be to listen to the AUDIO that goes with the slides. It is also available from that lsu.edu link. But FWIW here are just a few slides.
== a few of Rovelli's slides transcribed verbatim, without the illustrations==
Some questions
1. Is quantum space made out of loops and spin-networks or tetrahedra and 4-simplices?
2. Is flat space formed by many small tetrahedra with low-spin, or by few large tetrahedra with with high-spin?
3. Is low-energy physics given by quantum gravity on a single 4-simplex? Or by an infinite triangulation limit?
4. How do we study the the continuum limit from Planck scale discretness to the macroscopic continuum?
5. A spinfoam model is like a new version of quantum Regge calculus. So, why it should work better than quantum Regge calculus?
Claim: these questions are ill posed.
***
1. Is quantum space made out of loops and spin-networks or tetrahedra and 4-simplices?
The meaningful question in quantum theory is not how something is, but how it responds to a measurement.
There is no space “between” quanta of space, and it makes no sense to ask what is the geometry between one quantum and another, or inside a quantum, or what is the “geometry of quantum”. It is like asking for the “shape of a photon”. Or “What do I measure if I measure the energy in the space occupied by half a photon?”
***
2. Is flat space formed by few tetrahedra with high spin, or by many tetrahedra (or loops) with low spin?
How many particles are there in the Fock vacuum?
How many particles are invoved in a two-particle interaction?
Quantum theory gives the probability for measurement outcomes: it does not describe “what is between measurements”.
“In between pictures” are just descriptions of the ways I decide to do calculations. They are different for different measurements, and at different orders in perturbation theory.
[my comment. Rov sometimes like Feyn has flashes of unusual common sense. they illuminate.]
***
The good question, I think, is:
What can we compute that makes sense?
and
How can we compute it?
***
...
...[SNIP. SLIDES OMITTED HERE]
...
***
Summary
1. “Loopy, polymer, triangulated” spaces are helps for intuition, not descriptions of reality. No incompatibility between them.
2. In quantum gravity, flat space is neither many small planck scale things not few big large-spin 4 simplices. It is a process with a transition amplitudes. We can represent it with different pictures, according to the measurements we are considering, the calculation scheme, and the approximation scheme.
3. We must compute diff-invariant amplitudes, including when dealing with excitations over a flat space. The only way of doing so that I know is to code the background into the boundary space. (Boundary formalism.)
4. We need an approximation scheme. For scattering amplitudes, we can truncate degrees of freedom to a finite number, very much like is done in computing in QED and QCD. (Vertex expansion.)
5. Regime of validity of the vertex expansion: processes whose size L is not much larger than the minimal relevant wavelength λ. Includes the large distance behavior of the scattering amplitudes in coordinate space.
6. At given ratio λ/L, the Large-spin Limit captures processes at scales larger than the Planck length. It gives the semiclassical limit.
→ This does not mean that flat space is “made out of large 4-simplices”!
→ It means that we describe measurements performed at scales larger that the
Planck scale, at low order.
==end quote==
What comes through to me is that LQG and allied types of QG are not saying what space is made of. They are talking about geometry---measurement of spatial relationships between events. Just like in ordinary QM, a particle has no trajectory, we do not make claims about what is "in between measurements."
The meaningful question in quantum theory is not how something is, but how it responds to a measurement.
These same concerns came up in a recent discussion (with Naty and others) of Rovelli's April 2010 paper. http://arxiv.org/abs/1004.1780
...
Bohr expressed the essential about any quantum theory when he said "Physics is concerned not with how Nature is, but with what we can say about it." Some words to that effect.
There are always going to be alternative ways to picture the relation between measurements. And there will be some ways to picture that are very much better than others.
...
...
==quote Rovelli page 4==
This physical picture admits variants. In the case Γ is the two-skeleton dual to a triangulation of a 3d space, one can view the individual grains as flat tetrahedra. In some cases, namely for some states, these tetrahedra can be viewed as forming a 3d Regge geometry. (For this, matching conditions between the length of triangles must be satisfied [6].) In the general case, one can associate them a “twisted geometry” [6].
Such geometrical pictures are helps for the intuition, but there is no microscopic geometry at the Planck scale and these pictures should not be taken too literally in my opinion. They are choices of classes of continuous geometries interpolating finite sets of geometrical data. It is clear that many such choices are possible. They are analogous to choices of interpolating functions to visualize or describe sets of data points. For instance, we can interpolate a set of data points by means of an interpolating polynomial, or a piecewise linear function, or a piecewise constant functions... As we will better see below, these choices have strict analogs for quantum geometry.
These geometrical pictures can play a very useful role in various situations, but what the theory is about is expectation values of physical observables, not mental pictures of the geometry of individual states.
==endquote==
Essentially just echoing Bohr and reminding us of what has always been the basic quantum philosophy.
Feynman pointed out that pictures of the microscopic quantum world merely show how you plan to calculate. They don't show the world. Different ways to diagram the same thing correspond to different ways of calculating---conceivably these can be consistent: lead to the same answers.
So in LQG there are different formulations (plus others listed in 1004.1780) :
embedded spin networks
combinatorial (not embedded) spin networks
canonical formulation (no spin foams)
spin foam formulation (embedded or combinatorial)
The tendency is for these to be consistent, give the same results. Besides LQG there are also simplicial approaches, like Regge or CDT: triangulations instead of networks. Some use massive computer simulation in place of mathematical analysis.
I suppose that some non-LQG approaches could end up leading to the same answers. I don't know how likely that is, but it's possible.
Here are some QG links that are useful to have handy. Last time I updated was in May 2010. You can look back a few posts to the May list to find some which for brevity's sake I have omitted here.
To find out about conferences and workshops, "hyperspace" at the AEI site:
http://hyperspace.aei.mpg.de/category/Conferences/
The Nottingham QG network:
http://www.maths.nottingham.ac.uk/qg/
Some links to conferences etc.
June 2009 PlanckScale conference video and slides:
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php
Workshops at Ashtekar's Penn State IGC:
http://www.gravity.psu.edu/events/workshops.shtml
Online International LQG Seminar:
http://relativity.phys.lsu.edu/ilqgs/
November 2009 Asymptotic safety conference at Perimeter:
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
AsymSafe conference videos:
http://pirsa.org/C09025
February 2010 Oberwolfach workshop on Noncommutative Geometry and LQG ("Loops, Algebras, Spectral Triples"):
http://www.mfo.de/programme/schedule/2010/06b/OWR_2010_09.pdf
March 2010, Zakopane QG workshop (QGQG = quantum geometry/gravity):
http://www.fuw.edu.pl/~jpa/qgqg3/
July 2010 Stockholm workshop on the experimental search for QG:
http://th.physik.uni-frankfurt.de/~hossi/ESQG10/
Renate Loll 3-week course at Perimeter, Intro to Quantum Gravity:
http://pirsa.org/index.php?p=speaker&name=Renate_Loll
Photos from the first Loops conference, at Marseille 2004:
http://math.ucr.edu/home/baez/marseille/
Loop papers from 2007-present (currently 500 or more papers) ranked by citation count:
(keywords "spin, foam", "field theory, group", "quantum gravity, loop space", and "quantum cosmology, loop space"):
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+K+SPIN%2CFOAM+OR+DK+FIELD+THEORY%2 C+GROUP+OR+DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUA NTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29
Classic online sources.
Review of LQG as of May 2008:
http://relativity.livingreviews.org/Articles/lrr-2008-5/
Rovelli April 2010 paper, A new look at loop quantum gravity:
http://arxiv.org/abs/1004.1780
Rovelli's talk at Strings 2008 Video:
http://cdsweb.cern.ch/record/1121957?ln=en
Slides: http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917
2003 draft of Rovelli's book online:
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
Rovelli's chapter in Oriti's book:
http://arxiv.org/abs/gr-qc/0604045
Weinberg on Asymptotic Safety and general overview.
Weinberg's 6 July 2009 talk, main CERN link:
http://indico.cern.ch/conferenceDisplay.py?confId=57283
Weinberg video (historical overview up to minute 58 followed by
no-frills approach to unification in the last 12 minutes):
http://cdsweb.cern.ch/record/1188567/
Related Weinberg paper Asymptotically Safe Inflation:
http://arxiv.org/abs/0911.3165
Discussion thread http://physicsforums.com/showthread.php?t=355757
Recent progress in core Lqg:
Etera Livine's 17 February 2010 talk, A review of Spinfoams and Group Field Theory:
http://pirsa.org/10020079/
Related paper by Girelli Livine Oriti, 4d Deformed Special Relativity from Group Field Theories:
http://arxiv.org/abs/0903.3475
Bianchi Rovelli Vidotto, Towards Spinfoam Cosmology:
http://arxiv.org/abs/1003.3483
Rovelli, A new look at LQG:
http://arxiv.org/abs/1004.1780
Bianchi Regoli Rovelli, Face amplitude of spinfoam QG:
http://arxiv.org/abs/1005.0764
Alesci Rovelli, A regularization of the hamiltonian constraint compatible with the spinfoam dynamics:
http://arxiv.org/abs/1005.0817
Rovelli Speziale, On the geometry of LQG on a graph:
http://arxiv.org/abs/1005.2927
Ding Rovelli, Physical boundary Hilbert space and volume operator in the Lorentzian new spin-foam theory:
http://arxiv.org/abs/1006.1294
Selected longshots.
Rovelli Smerlak, Thermal time and the Tolman-Ehrenfest effect: temperature and the "speed of time":
http://arxiv.org/abs/1005.2985
Mathilde Marcolli et al, Spin Foams and Noncommutative Geometry:
http://arxiv.org/abs/1005.1057
Kirill Krasnov Deformations of General Relativity:
http://pirsa.org/10050002/
Lisi Smolin Speziale, Unification of gravity, gauge fields, and Higgs bosons:
http://arxiv.org/abs/1004.4866
Vincent Rivasseau at the 2009 Perimeter AsymSafe conference:
http://pirsa.org/09110049/
Ted Jacobson at the 2009 Perimeter HorGrav conference:
http://pirsa.org/09110066/
Ted Jacobson Thermodynamics of Spacetime: The Einstein Equation of State:
http://arXiv.org/abs/gr-qc/9504004
Ted Jacobson Introduction to Quantum Fields in Curved Spacetime and the Hawking Effect:
http://arxiv.org/abs/gr-qc/0308048
Erik Verlinde On the Origin of Gravity and the Laws of Newton:
http://arxiv.org/abs/1001.0785
Lee Smolin, Newtonian gravity in loop quantum gravity:
http://arxiv.org/abs/1001.3668
Jerzy Kowalski-Glikman, Note on gravity, entropy, and BF topological field theory:
http://arxiv.org/abs/1002.1035
Easson Frampton Smoot, Entropic Accelerating Universe:
http://arxiv.org/abs/1002.4278
Chamseddine Connes, Noncommutative Geometry as a Framework for Unification of all Fundamental Interactions including Gravity. Part I:
http://arxiv.org/abs/1004.0464
Smolin and Unger presentation at Laws of Nature workshop{ http://pirsa.org/C10001 }:
http://pirsa.org/10050053/
A list of QG researchers worldwide, mostly LQG but some other:
http://en.wikipedia.org/wiki/List_of_loop_quantum_gravity_researchers
Francesca's LQG world map:
http://maps.google.com/maps/ms?ie=UTF8&hl=en&msa=0&msid=106449985216139270436.0004843830d27f3e6c50e&t=h&z=0
Selected outreach links from IGC (Institute for Gravitation and the Cosmos) with a section of recent (2006-2010) popular articles:
http://gravity.psu.edu/outreach/index.shtml
The organizers of GR19 intend to make certain talks available online in some form.
As yet the links posted to various plenary talks do not work for me. If you wish you can try, for example:
http://www.gr19.com/public_html/compres_lecturas/rovelli.key.zip
If there are some bugs at the UNAM Morelia site we simply need to wait for them to be worked out.
Here is the plenary lecture menu:
http://www.gr19.com/plenlect.php
================
The next update of selected LQG links may include one or more papers realizing LQG in Group Field Theory
http://arxiv.org/abs/1008.0354
EPRL/FK Group Field Theory
Joseph Ben Geloun, Razvan Gurau, Vincent Rivasseau
http://arxiv.org/abs/1007.3150
Quantum Corrections in the Group Field Theory Formulation of the EPRL/FK Models
Thomas Krajewski, Jacques Magnen, Vincent Rivasseau, Adrian Tanasa, Patrizia Vitale
Recently I updated the list of Lqg links that are especially useful to keep handy.
See post #240, from 24 July.
So the list won't get updated again for a while, but, when that happens, two important paper to be included will be these by Eugenio Bianchi, Elena Magliaro, Claudio Perini:
http://arxiv.org/abs/0912.4054 Coherent spin-networks
http://arxiv.org/abs/1004.4550 Spinfoams in holomorphic representation
Francesca and others have compiled a list of people and places where LQG-and-allied research is in progress, or where a PhD student interested in LQG might connect with an advisor. I want to re-organize and edit the list to the best of my knowledge, and bring it up to date as well as I can. (In some cases I can't independently verify but just have to go along with the Google list.)
Here is the original:http://maps.google.com/maps/ms?ie=UTF8&hl=en&msa=0&msid=106449985216139270436.0004843830d27f3e6c50e&t=h&z=0
Australia
University of Sydney/Macquarie University
Permanent: Daniel Terno http://www.qscitech.info/ Postdoc: Florian Girelli
Britain
QG Nottingham
Permanents: John Barrett, Kirill Krasnov, Jorma Louko. http://www.maths.nottingham.ac.uk/research/applied_mathematics/quantum_gravity/
(Affiliated: Ed Copeland http://www.nottingham.ac.uk/physics/research/particles/)
Cambridge
Permanent: Ruth M. Williams
King's College London
Permanent: Mairi Sakellariadou.
http://www.kcl.ac.uk/schools/nms/physics/people/academic/sakellariadou/
Canada
Perimeter Institute for Theoretical Physics
Permanent: Laurent Freidel, Fotini Markopoulou, Lee Smolin.
Western Ontario
Permanent: Daniel Christensen
McMaster University
Permanent: Seth Major. http://academics.hamilton.edu/physics/smajor/
New Brunswick
Permanent: Viqar Husain http://www.math.unb.ca/~husain/
Denmark
Niels Bohr Instituttet
Permanent: Jan Ambjorn http://www.nbi.ku.dk/english/
France
CPT Marseille
Permanent: Alejandro Perez, Carlo Rovelli, Simone Speziale. http://www.cpt.univ-mrs.fr/~quantumgravity/ Postdocs: Eugenio Bianchi, Muxin Han, Christian Roeken, Antonino Marcianò, Marco Valerio Battisti... Students: Roberto Pereira, Valentin Bonzom, Daniele Pranzetti, You Ding, Matteo Smerlak.
École normale supérieure de Lyon
Permanent: Etera Livine. Postdoc: Johannes Tambornino
Universite De Paris XI Paris Sud
Permanent: Vincent Rivasseau http://www.rivasseau.com/index.html
Tours
Permanent: Karim Noui
Universite Montpellier II
Permanent: Sergei Alexandrov
Grenoble
Permanent: Aurelien Barreau http://lpsc.in2p3.fr/ams/aurelien/
Germany
AEI Berlin
Permanent: Bianca Dittrich, Daniele Oriti, Hermann Nicolai. http://www.aei.mpg.de/english/research/teams/
Erlangen
Permanent: Thomas Thiemann and one more faculty soon! Postdocs: Emanuele Alesci, Enrique Fernandez Borja, Derek Wise,...PhD students: Christian Boehmer,...
Universität Hamburg
Permanent: Catherine Meusburger. http://www.math.uni-hamburg.de/home/meusburger/ Postdoc: Winston Fairbairn.
Rheinische Friedrich-Wilhelms-Universität
Permanent: Klaus Kiefer
Universität Paderborn
Permanent: Christian Fleischhack
India
Raman Research Institute
Permanent: Madhavan Varadarajan
IUCAA Pune
Permanent: Naresh Dadhich
Italy
Pavia
Permanent: Mauro Carfora and Annalisa Marzuoli. Students: Hal Haggard and Francesca Vidotto (2011)
Torino
Permanent: Lorenzo Fatibene http://www.dm.unito.it/personalpages/fatibene/index.htm
Sapienza University of Rome
Permanent: Giovanni Montani, Giovanni Amelino Camelia. Giovanni Montani http://www.icra.it/cgm/welcome.htm http://www.roma1.infn.it/~amelino/
Korea
Asia Pacific Center for Theoretical Physics
Permanent: Hanno Sahlmann
Lebanon
American University of Beirut
Permanent: Tamer Tlas.
Mexico
Morelia
Permanent: Alejandro Corichi, Robert Oeckl, José Zapata. http://www.matmor.unam.mx/~corichi/lqgindex.html
Cinvestav Zacatenco
Permanent: Merced Montesinos
Netherlands
University of Utrecht
Permanent: Renate Loll http://www.phys.uu.nl/~loll/Web/title/title.html
People's Republic of China
Beijing Normal University
Permanent: Yongge Ma http://physics.bnu.edu.cn/application/research/gravity/LQG/eng/research.html
Academia Sinica
Permanent: Hoi-Lai Yu
Poland
University of Warsaw
Permanent: Jerzy Lewandowski. http://www.fuw.edu.pl/~lewand/homepage.html
Uniwersytet Wrocławski (University of Wroclaw)
Permanent: Jerzy Kowalski-Glikman.
Uniwersytet Jagielloński (Jagelonian University)
Permanent: Marek Szydlowski.
Spain
IEM-QFT Madrid
Permanent: Fernando Barbero, Guillermo Mena Marugán. Postdoc: Tomasz Pawlowski. http://www.iem.csic.es/departamentos/qft/index.html
Taiwan
National Cheng Kung University
Permanent: Chopin Soo
United States
PennState
Permanent: Abhay Ashtekar, Martin Bojowald. Postdocs: Andy Randono, Claudio Perini, Elena Magliaro, Jacobo Diaz Polo, William Nelson, Simone Mercuri. PhD:Miguel Campiglia, Adam Henderson, Artur Tsobanjan, Edward Wilson...
Louisiana State University
Permanent: Kristina Giesel, Jorge Pullin, Parampreet Singh. http://relativity.phys.lsu.edu/
Florida Atlantic University
Permanent: Jonathan Engle, Warner Miller
Haverford College
Permanent: Stephon Alexander.
Kansas State University
Permanent: Louis Crane. http://www.math.ksu.edu/main/contact_info/personnel_detail?person_id=1330
Riverside
Permanent:John Baez. http://math.ucr.edu/home/baez/README.html
Caltech
Permanent: Matilde Marcolli. http://www.its.caltech.edu/~matilde/
Uruguay
Montevideo
Permanent: Rodolfo Gambini, Michael Reisenberger
===================
Another candidate for the list of links to keep handy. John Norton's discussion of diff-invariance and the hole argument.
http://www.pitt.edu/~jdnorton/papers/decades.pdf
In the previous post's listing, Erlangen should have this link:
http://theorie3.physik.uni-erlangen.de/people.html
=========
Links for a short course in LQG as per request in http://physicsforums.com/showthread.php?p=2868346#post2868346
Suggested Prep:
Rovelli Upadhya http://arxiv.org/abs/gr-qc/9806079 (easy)
Rovelli Gaul http://arxiv.org/abs//gr-qc/9910079 (just relevant parts, short spinfoam section pp 43-46)
Baez on spinfoams http://arxiv.org/abs/gr-qc/9709052 (see especially pages 1-4 and 33,34)
Lewandowski et al on spinfoams http://arxiv.org/abs/0909.0939 (hard, but skim to know it's there)
Suggested Target:
Bianchi Rovelli Vidotto http://arxiv.org/abs/1003.3483
Rovelli http://arxiv.org/abs/1004.1780
References (there is no up-to-date reference but these are useful):
http://www.livingreviews.org/lrr-2008-5
www.cpt.univ-mrs.fr/~rovelli/book.pdf
==quote from Baez 1997 pages 33 and 34==
Quantum gravity without a background spacetime
As we have seen, the heart of ...[a spin foam] model is the following formula for the amplitude Z(F) of a spin foam F......Since this formula does not depend on the ambient spacetime manifold, but only on the spin foam itself, we may consider it more generally as a formula for evaluating the amplitude of any Spin(4) spin foam with ...[restrictions since removed]...
This gives an ‘abstract’ spin foam model, where there is no picture of spacetime other than that provided by the spin foam itself. Using the formula described in Section 3, we may think of each face of κ as ‘carrying’ a certain area, which it would give to any imagined surface it intersected transversely. Similarly, we may think of each edge as carrying a certain volume...The main point, however, is that if we think of an abstract spin foam as a kind of quantum 4-geometry, the above formula serves as a rule for computing the amplitude of any such quantum 4-geometry.
There are, of course, very serious problems in extracting physics from such a model. Most obviously, it is difficult to sum over all spin foams. Nonetheless it seems worth investigating such models.
==endquote==
[Note that several of the problems Baez mentioned have been addressed over the past 10 years.]
I think this Baez 1997 passage pointed in the right direction. The 'abstract' or manifoldless spinfoam turned out to be a good idea. Pedagogically, the whole Baez 1997 spinfoam tutorial has things to recommend it, in spite of being obviously out of date on some points.
There's a longish list of LQG resource links in post #240 of this thread.
The list of resource links (see post #240) when it gets updated should include this one mentioned by Sheaf:
http://math.ucr.edu/home/baez/penrose/
which has a couple of circa-1970 papers by Penrose where he introduced the idea of spin-network.
Two posts back, #245, I tried to work out a brief syllabus or self-teaching course plan for a graduate student to learn LQG. The preparation included looking at some earlier pedagogical introductions to canonical (old) LQG---by Rovelli Upadhya, and by Rovelli Gaul.
Now I would add a new introductory paper to the "beginning textbook" list:
http://arXiv.org/abs/1007.0402
Introductory lectures to loop quantum gravity
Pietro Doná, Simone Speziale
This paper derives from a series of lectures given last year. It was posted July 2010.
αβγδεζηθικλμνξοπρσςτυφχψω...ΓΔΘΛΞΠΣΦΨΩ...∏∑∫∂√ ...± ÷...←↓→↑↔~≈≠≡≤≥...½...∞...(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
ssivark007
Sep24-10, 07:08 AM
Hi Marcus, I just discovered this gem of a resource you've been compiling. Great work!
A couple of posts back, you had put up a list of places around the world where people work in LQG. I'd like to ad another Indian place to the list : Institute of Mathematical Sciences, Chennai, India. Prof. Ghanashyam Date, and a few of his colleagues there work on LQG. Right now, there are also a few PhD students working with them.
Further, right now, an LQG school is being held in IMSc(for 8 days) which I'm attending. I'm a senior year undergrad student, and this is my first exposure to the field. Here's the link to school's website : http://www.imsc.res.in/~shyam/LQGSchool/
Cheers,
Siva
Siva, that was a major omission! I know of Gananshyam Date by reputation and have read several of his papers. The Institute for Mathematical Sciences (IMSc Chennai) should have been on the list all along. Someone who knows how to do that should add it to the list at "google maps" which I was using as my source.
Thanks for letting us know about the LQG school that is currently in progress at Chennai.
... (... to go along with the Google list.)
Here is the original:http://maps.google.com/maps/ms?ie=UTF8&hl=en&msa=0&msid=106449985216139270436.0004843830d27f3e6c50e&t=h&z=0
...
...
India
Raman Research Institute
Permanent: Madhavan Varadarajan
IUCAA Pune
Permanent: Naresh Dadhich
...
...
IMSc Chennai
Permanent: Ganashyam Date
I can't edit post #243 but if/when I recopy it I will make the addition.
ssivark007
Sep24-10, 02:17 PM
Here is a (partial) list. I guess this wiki page will be updated once in a while by some maintainers.
http://en.wikipedia.org/wiki/List_of_loop_quantum_gravity_researchers
Here are some QG links that have been useful to have handy. Last time I updated the list was in July 2010. You can look back a few posts to the July list to find some which for brevity's sake have been omitted here.
Possible "textbook" resources:
Rovelli Upadhya http://arxiv.org/abs/gr-qc/9806079 (easy)
Rovelli Gaul http://arxiv.org/abs//gr-qc/9910079 (just relevant parts, short spinfoam section pp 43-46)
Baez handwritten lecture notes on spin networks/foams
http://math.ucr.edu/home/baez/foam/
Doná Speziale Introductory lectures to loop quantum gravity
http://arXiv.org/abs/1007.0402
Bojowald textbook (to be released) "Canonical GR and applications"
http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521195751
Renate Loll 3-week course at Perimeter, Intro to Quantum Gravity:
http://pirsa.org/index.php?p=speaker&name=Renate_Loll
Baez on spinfoams http://arxiv.org/abs/gr-qc/9709052 (see especially pages 1-4 and 33,34)
Lewandowski et al on spinfoams http://arxiv.org/abs/0909.0939
To find out about conferences and workshops, "hyperspace" at the AEI site:
http://hyperspace.aei.mpg.de/category/Conferences/
The Nottingham QG network:
http://www.maths.nottingham.ac.uk/qg/
Some links to conferences etc.
May 23-28, 2011: Loops 11 conference in Madrid
http://www.iem.csic.es/loops11/
June 2009 PlanckScale conference video and slides:
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php
Workshops at Ashtekar's Penn State IGC:
http://www.gravity.psu.edu/events/workshops.shtml
Online International LQG Seminar:
http://relativity.phys.lsu.edu/ilqgs/
November 2009 Asymptotic safety conference at Perimeter:
http://www.perimeterinstitute.ca/en/Events/Asymptotic_Safety/Asymptotic_Safety_-_30_Years_Later/
AsymSafe conference videos:
http://pirsa.org/C09025
February 2010 Oberwolfach workshop on Noncommutative Geometry and LQG ("Loops, Algebras, Spectral Triples"):
http://www.mfo.de/programme/schedule/2010/06b/OWR_2010_09.pdf
March 2010, Zakopane QG workshop (QGQG = quantum geometry/gravity):
http://www.fuw.edu.pl/~jpa/qgqg3/
July 2010 Stockholm workshop on the experimental search for QG:
http://th.physik.uni-frankfurt.de/~hossi/ESQG10/
Photos from the first Loops conference, at Marseille 2004:
http://math.ucr.edu/home/baez/marseille/
Loop papers from 2007-present (currently 500 or more papers) ranked by citation count:
(keywords "spin, foam", "field theory, group", "quantum gravity, loop space", and "quantum cosmology, loop space"):
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+K+SPIN%2CFOAM+OR+DK+FIELD+THEORY%2 C+GROUP+OR+DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+OR+QUA NTUM+COSMOLOGY%2C+LOOP+SPACE+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29
Classic online sources.
Review of LQG as of May 2008:
http://relativity.livingreviews.org/Articles/lrr-2008-5/
Bianchi Rovelli Vidotto, Towards Spinfoam Cosmology:
http://arxiv.org/abs/1003.3483
Rovelli April 2010 paper, A new look at loop quantum gravity:
http://arxiv.org/abs/1004.1780
Rovelli's talk at Strings 2008 Video:
http://cdsweb.cern.ch/record/1121957?ln=en
Slides: http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&materialId=slides&confId=21917
2003 draft of Rovelli's book online:
http://www.cpt.univ-mrs.fr/%7Erovelli/book.pdf
Rovelli's chapter in Oriti's book:
http://arxiv.org/abs/gr-qc/0604045
Penrose circa-1970 papers introducing spin-networks
http://math.ucr.edu/home/baez/penrose/
Baez notes on spin networks and spinfoams
http://math.ucr.edu/home/baez/foam/
Weinberg's 6 July 2009 talk, main CERN link:
http://indico.cern.ch/conferenceDisplay.py?confId=57283
Weinberg video (historical overview up to minute 58 followed by
no-frills approach to unification in the last 12 minutes):
http://cdsweb.cern.ch/record/1188567/
Recent progress in Lqg and Gft:
Livine's 17 February 2010 talk, A review of Spinfoams and Group Field Theory:
http://pirsa.org/10020079/
Related paper by Girelli Livine Oriti, 4d Deformed Special Relativity from Group Field Theories:
http://arxiv.org/abs/0903.3475
Bianchi Magliaro Perini Coherent spin-networks
http://arxiv.org/abs/0912.4054
Bianchi Magliaro Perini Spinfoams in holomorphic representation
http://arxiv.org/abs/1004.4550
Bianchi Regoli Rovelli, Face amplitude of spinfoam QG:
http://arxiv.org/abs/1005.0764
Alesci Rovelli, A regularization of the hamiltonian constraint compatible with the spinfoam dynamics:
http://arxiv.org/abs/1005.0817
Rovelli Speziale, On the geometry of LQG on a graph:
http://arxiv.org/abs/1005.2927
Ding Rovelli, Physical boundary Hilbert space and volume operator in the Lorentzian new spin-foam theory:
http://arxiv.org/abs/1006.1294
Geloun Gurau Rivasseau on LQG Spinfoam Group Field Theory
http://arxiv.org/abs/1008.0354
Lewandowski et al Gravity quantized
http://arxiv.org/abs/1009.2445
Bianchi Doná Speziale Polyhedra in LQG (quantum polyhedra as intertwiners)
http://arxiv.org/abs/1009.3402
Thermal time
Rovelli Smerlak, Thermal time and the Tolman-Ehrenfest effect: temperature and the "speed of time":
http://arxiv.org/abs/1005.2985
Connes Rovelli 1994 Thermal time paper
http://arxiv.org/abs/gr-qc/9406019
Rovelli 2009 Time essay
http://arxiv.org/abs/0903.3832
Unimodular Gravity
Smolin Unimodular loop quantum gravity and the problems of time
http://arxiv.org/abs/1008.1759
Ellis Murugan van Elst The gravitational effect of the vacuum
http://arxiv.org/abs/1008.1196
Smolin's Abhayfest talk
http://gravity.psu.edu/events/abhayfest/talks/Smolin.pdf
Chiou Geiller Unimodular Loop Quantum Cosmology
http://arxiv.org/abs/1007.0735
Smolin The quantization of unimodular gravity and the cosmological constant problem
http://arxiv.org/abs/0904.4841
Bianchi Rovelli Why all these prejudices against a constant? (contrasting viewpoint)
http://arxiv.org/abs/1002.3966
Selected longshots:
Julian Barbour Conformal superspace: configuration space of GR
http://arxiv.org/abs/1009.3559
Matilde Marcolli et al, Spin Foams and Noncommutative Geometry:
http://arxiv.org/abs/1005.1057
Kirill Krasnov Deformations of General Relativity:
http://pirsa.org/10050002/
Lisi Smolin Speziale, Unification of gravity, gauge fields, and Higgs bosons:
http://arxiv.org/abs/1004.4866
Vincent Rivasseau at the 2009 Perimeter AsymSafe conference:
http://pirsa.org/09110049/
Ted Jacobson at the 2009 Perimeter HorGrav conference:
http://pirsa.org/09110066/
Ted Jacobson Thermodynamics of Spacetime: The Einstein Equation of State:
http://arXiv.org/abs/gr-qc/9504004
Ted Jacobson Introduction to Quantum Fields in Curved Spacetime and the Hawking Effect:
http://arxiv.org/abs/gr-qc/0308048
Erik Verlinde On the Origin of Gravity and the Laws of Newton:
http://arxiv.org/abs/1001.0785
Lee Smolin, Newtonian gravity in loop quantum gravity:
http://arxiv.org/abs/1001.3668
Modesto Randono Entropic corrections to Newton's law
http://arxiv.org/abs/1003.1998
Jerzy Kowalski-Glikman, Note on gravity, entropy, and BF topological field theory:
http://arxiv.org/abs/1002.1035
Easson Frampton Smoot, Entropic Accelerating Universe:
http://arxiv.org/abs/1002.4278
Chamseddine Connes, Noncommutative Geometry as a Framework for Unification of all Fundamental Interactions including Gravity. Part I:
http://arxiv.org/abs/1004.0464
Smolin and Unger presentation at Laws of Nature workshop{ http://pirsa.org/C10001 }:
http://pirsa.org/10050053/
A list of QG researchers worldwide, mostly LQG but some other:
http://en.wikipedia.org/wiki/List_of_loop_quantum_gravity_researchers
Francesca's LQG world map:
http://maps.google.com/maps/ms?ie=UTF8&hl=en&msa=0&msid=106449985216139270436.0004843830d27f3e6c50e&t=h&z=0
Selected outreach links from IGC (Institute for Gravitation and the Cosmos) with a section of recent (2006-2010) popular articles:
http://gravity.psu.edu/outreach/index.shtml
αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔~≈≠≡ ≤≥½∞(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
Xristy helpfully assembled the links to the chapters of a new book which are available in preprint form online.
http://physicsforums.com/showthread.php?p=2899654#post2899654
The book is a collection of talks given at George Ellis' 70th birthday celebration, called The Foundations of Space and Time. A gathering of people from Loop, CDT, String, Cosmology communities comparing notes on basic issues and each other's approaches. Ellis co-edited the book and it is to be published by Cambridge Press.
http://www.cambridge.org/uk/catalogue/catalogue.asp?isbn=9780521114400
Some information is posted about Loops 11. It can be interesting to look down the list of plenary speakers at a major conference--it may give some idea of where the field is or where it's going. The Loops conference is held approximately biannually (once every two years) with other related conferences sometimes filling in on off-years. Here's the plenary speakers list:
Abhay Ashtekar (Penn State University, USA).
Martin Bojowald (Penn State University, USA).
Alejandro Corichi (UNAM-Morelia, Mexico).
Bianca Dittrich (Albert Einstein Institute, Germany).
Kristina Giesel (TU Munich, Germany).
Jerzy Lewandowski (Warsaw University, Poland).
Renate Loll (Utrecht University, Netherland).
Yongge Ma (Beijing Normal University, China).
Don Marolf (Univ. California-Santa Barbara, USA).
Daniele Oriti (Albert Einstein Institute, Germany).
Tomasz Pawlowski (University of New Brunswick, Canada).
Alejandro Pérez (Univ. Méditerranée, Marseille, France).
Jorge Pullin (Louisiana State University, USA).
Carlo Rovelli (Univ. Méditerranée, Marseille, France).
Hanno Sahlmann (Karslruhe University, Germany).
Parampreet Singh (Perimeter Institute, Canada).
Lee Smolin (Perimeter Institute, Canada).
Thomas Thiemann (Univ. Erlangen-Nurnberg, Germany).
Madhavan Varadarajan (Raman Research Institute, India).
The Loops 11 conference will be held 23-28 May, in Madrid:
http://www.iem.csic.es/loops11/
for comparison, here are the plenary speakers and talks of Loops 09 and Loops 07:
http://physicsforums.com/showthread.php?p=2296306#post2296306
http://www.matmor.unam.mx/eventos/loops07/ (links to plenary talks/abstracts)
Christine's thread about the forthcoming Hamiltonian GR textbook (applications to LQG cosmology) by Penn State's Martin Bojowald
http://physicsforums.com/showthread.php?t=432381
Atyy called attention to an interesting January 2010 paper by Madhavan Varadarajan
which was cited in Thiemann's latest (October 2010). This gives a good idea of what some of the plenary talks will be about at Loops 11.
Some information is posted about Loops 11... Here's the plenary speakers list:
...
...
Lee Smolin (Perimeter Institute, Canada).
Thomas Thiemann (Univ. Erlangen-Nurnberg, Germany).
Madhavan Varadarajan (Raman Research Institute, India).
The Loops 11 conference will be held 23-28 May, in Madrid:
http://www.iem.csic.es/loops11/
Rovelli's talk could draw from the October "Simple Model" paper http://arxiv.org/abs/1010.1939
Lewandowski's from his September "Gravity Quantized" http://arxiv.org/abs/1009.2445
Smolin could conceivably talk about Unimodular Gravity (and the problem of time? http://arxiv.org/abs/1008.1759 )
Thiemann's talk could draw from http://arxiv.org/abs/1010.2426
Varadarajan's from http://arxiv.org/abs/1001.3505
LQG-RELATED TEXTBOOKS etc. scheduled for release:
Christine's thread about Bojowald's Hamiltonian GR textbook (applications to LQG cosmology)
http://physicsforums.com/showthread.php?t=432381
Cambridge Press page about Canonical Gravity and Applications
http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521195751
Amazon page about Once Before Time, Bojowald's forthcoming Loop cosmology popularization
http://www.amazon.com/Once-Before-Time-Whole-Universe/dp/0307272850
World Scientific press page about Montani's textbook Primordial Cosmology:
http://www.worldscibooks.com/physics/7235.html
Cambridge Press page about Foundations of Space and Time (Ellisfest collection)
http://www.cambridge.org/uk/catalogue/catalogue.asp?isbn=9780521114400
Chennai basic LQG/LQC Lectures http://arxiv.org/pdf/1004.2952
(Ganashyam Date gave a series of beginning lectures on LQG which explain certain things most clearly--only 72 pages, not a textbook but could be used as supplemental reading.)
Xristy's links to draft chapters of the Ellisfest book:
http://physicsforums.com/showthread.php?p=2899654#post2899654
Eugenio Bianchi will give a talk soon at Perimeter, about Loop Quantum Gravity, and it will go on the PIRSA online lecture archive
http://pirsa.org/10110052/
9 November
A newcomer was asking about math prep for LQG--here are some online notes on group representation theory---if you know better online notes please say. There is quite a variety here to pick and choose from:
http://www.math.columbia.edu/~woit/RepThy/
A one-year masters (MSc) program is being set up by John Barrett and colleagues at Nottingham. The first year of operation will start September 2011. We may be able to pick up some information about their curriculum, lecture notes, textbooks---get some clues from this.
http://johnwbarrett.wordpress.com/
==quote==
New MSc course
Here at Nottingham we are starting an MSc in Gravity, Particles and Fields. This is very specifically aimed at students interested in getting into relativity and particle physics research, in areas such as quantum gravity, cosmology, quantum information, etc.
The first run starts in September 2011, so we are open for applications now.
==endquote==
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx
==quote==
Gravity, Particles and Fields Masters (MSc)
Duration: 1 year full-time
The course provides an introduction to the physical principles and mathematical techniques of current research in general relativity, quantum gravity, particle physics, quantum field theory, quantum information theory, cosmology and the early universe.
The programme of study includes a taught component of closely-related modules in this popular area of mathematical physics. The course also includes a substantial project that will allow students to develop their interest and expertise in a specific topic at the frontier of current research, and develop their skills in writing a full scientific report.
The course will provide training in advanced methods in mathematics and physics which have applications in a wide variety of scientific careers and provide students with enhanced employability compared with undergraduate Bachelors degrees. In particular, it will provide training appropriate for students preparing to study for a PhD in the research areas listed above. For those currently in employment, the course will provide a route back to academic study.
Key facts
• The course is taught jointly by the School of Mathematical Sciences and the School of Physics and Astronomy.
• Dissertation topics are chosen from amongst active research themes of the Particle Theory group, the Quantum Gravity group, and the Quantum Information group
• In addition to the lectures on the course, there are several related series of research-level seminars to which Masters students are welcomed.
• The University of Nottingham is ranked in the top 1 per cent of all universities worldwide.
...
==endquote==
QGravity
Nov24-10, 06:04 PM
Does LHC Can test Loop quantum gravity or other approaches to QG?
Does LHC Can test Loop quantum gravity or other approaches to QG?
I haven't thought much about it. It seems to me that in this period of history new physics is often going to be revealed by the huge river of data coming from the sky---astrophysical observations by new types of instruments (many in space but also on ground.)
The importance of LHC may have been exaggerated relative to other less expensive instruments. I really don't know, it's hard to judge. But I'll mention a few things to think about besides the LHC. Some might be relevant to testing LQG and others not.
Things to be investigated include: dark energy or cosmological constant, dark matter, Gammaray Bursts, high-energy cosmic rays, early universe neutrinos, polarization and other features of Microwave Backgound, gravitational wave imprint in CMB, signals from black hole formation (unusual stellar explosions). Largescale structure of universe.
Instruments: interferometers including spaceborn, synthetic aperture telescopes, atmospheric Cherekov gammaray telescopes, CMB-mapping spacecraft beyond COBE and WMAP, X-ray astronomy using spacecraft, gravitational wave detectors, neutrino detectors like IceCube in Antarctica, Cosmic Ray detector arrays like the Auger, gammaray astronomy in space as with FermiLAT or combining orbital and ground as with SWIFT.
This is a quick impromptu list bound to leave stuff out. I'd guess that LQG testing comes in here somewhere with CMB early universe astronomy, and maybe somehow with some of the ways of gathering information.
In a sense cosmology is the "collider" for quantum gravity and unification. The main arena for testing models is going to be the early universe. It's is where the energy is, and the phenomena we have to make sense of.
So when Weinberg talked to Strings 2010 (about his "Plan B" in case string although great mathematics proved physically disappointing) he focused on applying his Plan B idea to cosmology. Its where everything has to go eventually, not just hobble on to the next particle accelerator.
So we have to watch developments in quantum cosmology and related areas. Here is a unique resource. Penrose June 2009 talk at the Institute for Gravitation and Cosmology:
The title was "Fashion, Faith, and Fantasy in the New Science of the Universe"
1. http://www.youtube.com/watch?v=iPnXsI5DUDY
2. http://www.youtube.com/watch?v=andTUow31eE
3. http://www.youtube.com/watch?v=4BtYn2Wde4o&NR=1
4. http://www.youtube.com/watch?v=zVTCaaP5Y0s&feature=related
5. http://www.youtube.com/watch?v=bQNUwHnQzvA&feature=related
6. http://www.youtube.com/watch?v=DvfRYzRgqWE&feature=related
7. http://www.youtube.com/watch?v=afsd3_PJais&feature=related
8. http://www.youtube.com/watch?v=UMi_QB0vWC0&feature=related
9. http://www.youtube.com/watch?v=tiRy07yweA0&feature=related
10. http://www.youtube.com/watch?v=5jXj1TwiFys&feature=related
http://gravity.psu.edu/events/abhayfest/
=======================================
Weinberg on Asymptotic Safe gravity/cosmology, at Strings 2010:
https://mediamatrix.tamu.edu/streams/327756/PHYS_Strings_2010_3-18-10C
A recent Asyptotic Safe gravity paper that I think will prove important (sometimes computational power enables progress as much as a new idea, it's happened before in other fields.)
http://arxiv.org/abs/1012.3081
The Universal RG Machine
Dario Benedetti, Kai Groh, Pedro F. Machado, Frank Saueressig
38 pages
(Submitted on 14 Dec 2010)
"Functional Renormalization Group Equations constitute a powerful tool to encode the perturbative and non-perturbative properties of a physical system. We present an algorithm to systematically compute the expansion...
... In a first illustrative example, we re-derive the gravitational beta-functions of the Einstein-Hilbert truncation, demonstrating their background-independence. As an additional result, the heat-kernel coefficients for transverse vectors and transverse-traceless symmetric matrices are computed to second order in the curvature."
Here is Roberto Percacci's website index page for AsymSafe gravity.
http://www.percacci.it/roberto/physics/as/index.html
Thanks to Atyy for pointing out the new picture (Benedetti, Machado, Rahmede collaborating at the blackboard)
Percacci has a FAQ for AsymSafe, and useful links to stuff.
Someone was asking if Pedro is from Brazil or Portugal--here's his current page:
http://www.gen.cam.ac.uk/research/AMA/members/Pedro.html
The previous post mentioned some Asymptotic Safe gravity stuff (from Weinberg, Percacci, Benedetti et al...). On the same subject, one of the major figures in AS gravity, Martin Reuter, just came out with a paper formulating AS in a way that looks compatible with LQG. The Holst action, which LQG uses, and its Immirzi parameter. This could serve as a bridge between the two QG approaches.
http://arxiv.org/abs/1012.4280
Another Loop textbook coming out.
http://www.springer.com/physics/theoretical,+mathematical+%26+computational+physic s/book/978-1-4419-8275-9
This will be in the Springer Lecture Series, planned release date March 2011.
Quantum Cosmology, by Martin Bojowald
approx. 250 pages
This might serve as a companion to another textbook which Cambridge Press is bringing out
http://www.cambridge.org/gb/knowledge/isbn/item5692826/?site_locale=en_GB
Canonical Gravity and Applications: Cosmology, Black Holes, and Quantum Gravity, by the same author
approx. 310 pages
The UK Amazon says it is temporarily out of stock:
http://www.amazon.co.uk/Canonical-Gravity-Applications-Cosmology-Quantum/dp/0521195756
US Amazon says you can pre-order, available January 2011.
It's interesting to see QG and QC take shape as academic subjects. When I started watching the field in 2003 there were, as far as I know, no textbooks. At least not for quantum *cosmology*, which (because we have so much data on the early universe) seems to be the key to the whole business.
John Baez *Week 280* has a valuable discussion of the 2009 Corfu QG school and workshop:
http://math.ucr.edu/home/baez/week280.html
Also interesting was the lively discussion at the nCategory Cafe which followed.
http://golem.ph.utexas.edu/category/2009/09/this_weeks_finds_in_mathematic_41.html
(MTd2 took active part, exotic smooth structures came up, and Torsten A-M who has posted some at PF Beyond also got into it.)
piareround
Jan6-11, 03:54 PM
So I while back I asked about the relationship between quantum foam, Quantum Loop Gravity theory, string theory, and how many dimensions each theory requires in this link here (http://www.physicsforums.com/showthread.php?t=432962). As you may note nismaratwork helped me to understand how string theory would smear out quantum foam. He also helped remind me that String Theory require multiple dimensions but quantum foam requires only four.
However, I as I was reading your thread I realized that I assumed two things:
First, quantum loop gravity only requires 4 dimensional Minkowski Space
Second, that quantum foam actually plays a role in quantum loop gravity.
So I was hoping you could help me with the following questions:
Are there any limits, such as a minimum or maximum, on the number of dimensions that quantum loop gravity, independent of string theory, would require?
Is their a relationship between quantum foam and quantum loop gravity? If so, what role exactly does quantum foam play in quantum loop gravity theory? If not, does quantum loop gravity, replace quantum foam with something analogous to quantum foam purpose in solution the Klein-Gordon Equation(*)?
So I while back I asked about the relationship between quantum foam, Quantum Loop Gravity theory, string theory, and how many dimensions each theory requires in this link here (http://www.physicsforums.com/showthread.php?t=432962). As you may note nismaratwork helped me to understand how string theory would smear out quantum foam. He also helped remind me that String Theory require multiple dimensions but quantum foam requires only four.
However, I as I was reading your thread I realized that I assumed two things:
First, quantum loop gravity only requires 4 dimensional Minkowski Space
Second, that quantum foam actually plays a role in quantum loop gravity.
So I was hoping you could help me with the following questions:
Are there any limits, such as a minimum or maximum, on the number of dimensions that quantum loop gravity, independent of string theory, would require?
Is their a relationship between quantum foam and quantum loop gravity? If so, what role exactly does quantum foam play in quantum loop gravity theory? If not, does quantum loop gravity, replace quantum foam with something analogous to quantum foam purpose in solution the Klein-Gordon Equation(*)?
Let's start a separate thread, for discussion/explanation. I try to use this thread just to provide selected links to useful source material for people following current LQG research.
It would get unwieldy to include discussion and explanation in addition to what it's doing already.
I will start a thread for you, with your questions about LQG.
This year (first two weeks March 2011) the best ever QG school will be held at the ski resort Zakopane. It is aimed at postdocs and advanced PhD students ready to enter QG research. The school is definitive of the field, so we can learn some things from examining the schedule.
Of the lectures on LQG, those I have colored bright blue will probably be more from the manifold-free perspective----no spacetime continuum manifold. That will be about half, I guess. Those I have colored dark or navy blue will probably use the older development which starts with a 4D manifold. Talks listed in black are on other types of QG, or neutral as regards this change in LQG.
So one thing we can learn by looking at the school line-up is how this reconstitution or reformulation of LQG is progressing. Another thing to gauge is how much the Loop people are looking towards Group Field Theory, Noncommutative Field Theory, and Noncommutative Geometry for additional inspiration. I think it has to do with a sense that LQG is ready to take on matter---to rebuild QFT on a quantum geometrical basis---and they are on the lookout for ideas.
In any case here is the schedule color-coded as I described earlier:
Mar 1
A. Ashtekar 2h — Opening lecture
C. Rovelli 2h — Spin foams
K. Giesel 2h — Loop quantum gravity
H. Sahlmann 2h — Loop quantum gravity
Mar 2
K. Giesel 2h — Loop quantum gravity
H. Sahlmann 2h — Loop quantum gravity
C. Rovelli 2h — Spin foams
Mar 3
K. Giesel 1h — Loop quantum gravity
H. Sahlmann 1h — Loop quantum gravity
J. Brunnemann 2h — Volume operator
C. Rovelli 2h — Spin foams
Mar 4 Break (Friday)
Mar 5
C.Rovelli 2h — Spin foams
W. Kamiński 2h — EPRL map: SO(4) and SO(1,3), integrability
P. Singh 2h — Loop quantum cosmology
Mar 6
S. Hollands 2h — Exact QFT in curved backgrounds
C. Rovelli 2h — Spin foams
P. Singh 2h — Loop quantum cosmology
Mar 7
S. Hollands 2h — Exact QFT in curved backgrounds
S. Speziale 2h— LQG and twisted geometries
C. Perini 1h — Graviton propagator
E. Bianchi 1h — Friedmann equation from the EPRL vertex amplitude
Mar 8
T. Krajewski 2h — Group field theories
S. Hollands 2h — Exact QFT in curved backgrounds
J.B. Geloun/V. Rivasseau 2h — EPRL GFT
Mar 9 Break (Wednesday)
Mar 10
H. Steinacker 2h — Non-commutative geometry and matrix models
J. Barrett 2h — Large j limit of spin foam amplitudes
T. Krajewski 2h — Group field theories
Mar 11
H. Steinacker 2h — Non-commutative geometry and matrix models
H. Grosse 2h — Renormalisation of the Grosse-Wulkenhaar model
M. Burić 2h — Renormalisation of the Grosse-Wulkenhaar model
Mar 12
H. Steinacker 2h — Non-commutative geometry and matrix models
K. Noui 2h — SLq(2,C)
W. Fairbairn 2h — SLq(2,C) EPRLK model
Mar 13
B. Dittrich 2h — Diffeomorphisms, renormalisation and perfect action in discrete theories
J. Jurkiewicz 2h — Causal dynamical triangulations
C. Meusburger 2h — 2+1 gravity
Offhand it seems like the school lineup is about evenly balanced in respect to manifoldy/manifoldless or however you want to imagine the shifting reconstitution going on.
http://www.fuw.edu.pl/~kostecki/school3/
Stanford-SLAC has a new physics database called Inspire. It improves on Spires, which has been in use for over a decade. Inspire is still in beta and being worked-on.
Here, in effect, is a history of Loop Gravity from 2005 onwards obtained simply by finding each year's papers and listing them ranked by cite count. The cites reflect the interest of the research community, so you can see what were considered (roughly speaking) the most interesting/valuable Loop papers of each year. These leading papers influence the direction that research in the field moves. You will see the focus and makeup of the top papers change over time.
(To learn more about any paper click on the corresponding "detailed record" link.)
The number of papers which appeared each year are given in parenthesis.
2005: (42)
http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+gravity%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2005&d2d=&d2m=&d2y=2005&sf=&so=a&rm=citation&rg=25&sc=0&of=hb
2006: (77)
http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+gravity%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2006&d2d=&d2m=&d2y=2006&sf=&so=a&rm=citation&rg=25&sc=0&of=hb
2007: (120)
http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+gravity%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2007&d2d=&d2m=&d2y=2007&sf=&so=a&rm=citation&rg=25&sc=0&of=hb
2008: (142)
http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+gravity%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2008&d2d=&d2m=&d2y=2008&sf=&so=a&rm=citation&rg=25&sc=0&of=hb
2009: (145)
http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+gravity%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2009&d2d=&d2m=&d2y=2009&sf=&so=a&rm=citation&rg=25&sc=0&of=hb
2010: (153)
http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+gravity%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+cosmology%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2010&d2d=&d2m=&d2y=2010&sf=&so=a&rm=citation&rg=25&sc=0&of=hb
The keywords used are "quantum gravity: loop space", "quantum cosmology: loop space", "spin: foam".
I will try to assemble here links which can help assess the current status of LQG and LQC (loop gravity and loop cosmology)---as well as provide an introduction to the modern formulation of loop gravity using combinatorial spinfoam dynamics. This spinfoam formulation is sometimes referred to as the "full theory" as contrasted with loop cosmology which has been developed as a symmetry reduced version: made simpler by assuming some degree of uniformity in the universe. There are several points to be made about current developments, for which corresponding source links will be given.
Quantum cosmology has become observational. Here are articles mostly by early universe phenomenologists about ways of testing LQC against CMB data. Since LQC derives from LQG, this turns out to be the most accessible route to testing LQG.
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+QUANTUM+GRAVITY%2C+LOOP+SPAC E+OR+DK+QUANTUM+COSMOLOGY%2C+LOOP+SPACE%29+AND+%28 DK+POWER+SPECTRUM+or+dk+cosmic+background+radiatio n%29+AND+DATE+%3E+2008&FORMAT=www&SEQUENCE=citecount%28d%29
Loop cosmology connects with the full (spinfoam) theory:
http://arxiv.org/abs/1003.3483
Towards Spinfoam Cosmology
The distinctive prediction of a bounce carries over:
http://arxiv.org/abs/1010.1258
Big Bounce in Dipole Cosmology
LQC bounce naturally initiates a period of superinflation even without the usual scalar ("inflaton") field. If the usual scalar field is present as well, the bounce ensures ample inflation without any further adjustments.
http://arxiv.org/abs/1103.2475
Probability of Inflation in Loop Quantum Cosmology
This is a kind of observational confirmation because it shows that LQC makes observed features of the universe associated with inflation more likely.
A definitive presentation of LQG, with some math prerequisites:
http://arxiv.org/abs/1102.3660
Lectures on Loop Gravity
A definitive presentation of LQC, as of mid-2010:
http://arxiv.org/abs/1005.5491.
The Big Bang and the Quantum
A comparatively non-technical presentation of LQG, including its historical development and evidence suggesting the theory recovers classical GR.
http://arxiv.org/abs/1012.4707
Loop quantum gravity: the first twenty five years
http://arxiv.org/abs/1101.4049
Cosmological constant in spinfoam cosmology
http://arxiv.org/abs/1101.3264
Spinfoam Fermions: PCT Symmetry, Dirac Determinant, and Correlation Functions
http://arxiv.org/abs/1012.1739
Lorentz covariance of loop quantum gravity
Formation of an inclusive research community of Quantum Gravity/Geometry/Cosmology is being helped by European Science Foundation "QG" events such as this year's conference at the Zurich ETH:
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:start
Quantum Theory and Gravitation
Topics to be covered include:
General quantum theory, relativistic quantum theory, emergence of space(-time)
General quantum field theory, including deformations of QFTs
QFT on curved and NC space-times
Canonical quantum gravity and supergravity
Regge calculus
String theory and M-theory
Loop gravity, spin foam
Quantum cosmology
International Advisory Board
John Barrett
Harald Grosse
Hermann Nicolai
Carlo Rovelli
Roger Picken
mehul ahir
Mar18-11, 02:02 AM
sir my question is that is it literally impossible to prdict the volume f the previous universe or it can be pradicted with accurate theorues?please tell me sir
Mehul Ahir, sir, that is a helpful question because it reminds us of how little we know. There are several different approaches to Quantum Cosmology, and on the whole they are young unformed theories. We do not know which, if any, is to be trusted.
Loop cosmology is only just beginning to be compared with real observational data. You can see in the recent Ashtekar-Sloan paper how they confront the theory with WMAP data. http://arxiv.org/abs/1103.2475 So far there are some pretty nice agreements with data but further testing could prove the theory wrong!
And even if the theory survives a number of tests and begins to be tentatively trusted, it still says very little definite about the contracting phase of the universe, before the bounce. Even if we believed the LQC theory we could still say almost nothing about the spatial volume. Only that distances were contracting in the same sense that they are now expanding.
We do not know the total spatial volume the universe has even today. We only can estimate how far away the most distant material is that we can see.
The great thing, as I see it, is that scientists are doing their job. They are supposed to construct simple TESTABLE theories that fit the data. And then their job is to derive predictions from theory that can be checked by observation---and if those predictions are not observed then the theory is disproved and one must construct a better one. The good news is not that Loop Cosmology is right (we don't know that) but that it is testable. It replaces the former singularity with a particular kind of bounce that has measurable consequences to look for in the cosmic microwave background (CMB, the ancient light).
The next biannual Loops conference, Loops 2011, will be held in Madrid the last week of May.
To date about 150 people have registered to partciipate:
http://www.iem.csic.es/loops11/
Strings 2011 will be held one month later, at the end of June, in Uppsala, Sweden.
http://www-conference.slu.se/strings2011/
The registered participants include Stephen Hawking, Juan Maldacena, John Schwarz, Michael Green, and Edward Witten:
https://www.akademikonferens.se/list.jsf?conf=strings2011
Loop cosmology linking up with early universe phenomenology is a recent development that has changed the QG picture somewhat. Here are 29 early U. phenom. papers that appeared 2009 or later:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+QUANTUM+GRAVITY%2C+LOOP+SPAC E+OR+DK+QUANTUM+COSMOLOGY%2C+LOOP+SPACE%29+AND+%28 DK+primordial%2C+fluctuation+OR+DK+INFLATION+OR+DK +COSMIC+BACKGROUND+RADIATION%29+AND+DATE+%3E+2008&FORMAT=www&SEQUENCE=citecount%28d%29
The Spires search is:
IND (DK QUANTUM GRAVITY, LOOP SPACE OR DK QUANTUM COSMOLOGY, LOOP SPACE) AND (DK PRIMORDIAL, FLUCTUATION OR DK INFLATION OR DK COSMIC BACKGROUND RADIATION) AND DATE > 2008
====================
The next biannual Loops conference, Loops 2011, will be held in Madrid the last week of May.
We can get an idea of where in the US you can study Loop gravity/cosmology by looking at the list of 170 registered participants.
Only 25 are from US institutions---the US lags Europe in QG.
http://www.iem.csic.es/loops11/
Here's where the US participants come from
PSU (Penn State) 13
LSU (Louisiana) 4
UC Berkeley 2
Hamilton 1
FAU (Florida Atlantic, Boca Raton) 1
FSU (Florida State, Talahassee) 1
Utah State 1
Dartmouth College 1
Le Moyne College 1
Chris Duston, the guy coming from FSU, is doing his PhD in quantum gravity/cosmology under Matilde Marcolli (Caltech). So Caltech has a kind of spectral presence in this listing as well.
==================================
Strings 2011 will be held one month later, at the end of June, in Uppsala, Sweden.
http://www-conference.slu.se/strings2011/
https://www.akademikonferens.se/list.jsf?conf=strings2011
The three public lectures (by Stephen Hawking, Brian Greene, Andrei Linde) will feature the stringy Landscape and the Multiverse.
===================================
In between these two, in mid June, there's the Zurich conference
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:start
Quantum Theory and Gravitation
87 registered participants so far, ecumenical (brings together prominent people from various different approaches to QG) interesting lineup of speakers. 30 from some 5 or 6 different lines of research.
Here is a page about the new one-year MSc program at Nottingham, in Gravity, Particles and Fields
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx
==quote==
The course provides an introduction to the physical principles and mathematical techniques of current research in general relativity, quantum gravity, particle physics, quantum field theory, quantum information theory, cosmology and the early universe.
The programme of study includes a taught component of closely-related modules in this popular area of mathematical physics. The course also includes a substantial project that will allow students to develop their interest and expertise in a specific topic at the frontier of current research, and develop their skills in writing a full scientific report.
The course will provide training in advanced methods in mathematics and physics which have applications in a wide variety of scientific careers and provide students with enhanced employability compared with undergraduate Bachelors degrees. In particular, it will provide training appropriate for students preparing to study for a PhD in the research areas listed above. For those currently in employment, the course will provide a route back to academic study.
Entry requirements: At least a second class honours (2:2) BSc degree (or equivalent from other countries) in Physics, Mathematical Physics or Mathematics, or joint degrees containing substantial elements of physics or mathematics.
Other requirements: Previous knowledge of mechanics, quantum mechanics, special relativity and methods of mathematical physics (all as taught typically at BSc level 2) is required.
IELTS: 6.0 (with no less than 5.0 in any element)
TOEFL paper based: 550 (with at least 4.0 on the TWE)
TOEFL IBT: 79 (with no less than 17 in any element)
==endquote==
The main person responsible for the new program is John Barrett. His research is in several QG areas including Loop and NC-geometry. He's also director of ESF-QG the European Science Foundation setup for funding quantum gravity and quantum geometry.
Here's Barrett's Nottingham faculty page:
http://www.nottingham.ac.uk/mathematics/people/john.barrett
and personal homepage
http://johnwbarrett.wordpress.com/
http://johnwbarrett.wordpress.com/talks/
Exemplifying directions in the European QG community, here's the website of a conference that Barrett's ESF-QG agency is sponsoring this summer in Zurich.
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:start
It brings together Loop, NCG, String, SUGRA, QFT on Curved space---speakers chosen who the organizers consider able to talk to each other and exchange ideas. Amazing conference, first of its kind. Barrett is one of the organizers, with Carlo Rovelli, Hermann Nicolai* and some other top people.
*director of the QG+unification wing at MPI Potsdam
=================
I have some more stuff related to the Loop academic terrain and entry to the field in this other thread:
http://physicsforums.com/showthread.php?p=3229102#post3229102
which was started by Barak (about doing one's PhD in Loop).
==================
Incidental information about the annual Strings conference (late June, Uppsala).
http://www-conference.slu.se/strings2011/
Preliminary list of confirmed speakers (sorted by type):
OPENING TALK
David Gross (KITP, Santa Barbara) opening talk
REVIEWS and other talks
Henriette Elvang (University of Michigan) review talk
Michael Green (Cambridge University)
Juan Maldacena (IAS, Princeton)
Liam McAllister (Cornell University) review talk
Greg Moore (Rutgers University) review talk
Subir Sachdev (Harvard University) review talk
Nathan Seiberg (IAS, Princeton) review talk
Ashoke Sen (Harish-Chandra Research Institute, Allahabad)
Samson Shatashvili (Trinity College, Dublin and IHES)
Gerard `t Hooft (University of Utrecht)
Erik Verlinde (University of Amsterdam)
Edward Witten (IAS, Princeton)
Fabio Zwirner (University of Padua) review talk
SUMMARY TALK AT END
Jeff Harvey (University of Chicago) summary talk
PUBLIC LECTURES (inflation, landscape of multiverses...)
Brian Greene (Columbia University)
Andrei Linde (Stanford University)
Stephen Hawking (TBC)
Thanks to Barak for this item from Oxford University Press catalogue:
http://ukcatalogue.oup.com/product/academic/physics/9780199590759.do
A First Course in Loop Quantum Gravity
Rodolfo Gambini and Jorge Pullin
280 pages | 18 b/w line figures | 246x171mm
to be released: August 2011
TOC
1: Why quantize gravity
2: Special relativity and electromagnetism
3: Some elements of general relativity
4: Hamiltonian mechanics including constraints and fields
5: Yang-Mills theories
6: Quantum mechanics and elements of quantum field theories
7: General relativity in terms of Ashtekar's variables
8: Loop representation for general relativity
9: An application: loop quantum cosmology
10: Further developments
11: Open issues and controversies
Publisher's decription:
"First book on the subject at the undergraduate level
Quick introduction to many major topics in fundamental theoretical physics suitable for undergraduate courses
High interest currently in quantum gravity among physicists worldwide
Controversial subject which needs good, impartial introduction from respected scientists
This book provides an accessible introduction to loop quantum gravity and some of its applications, at a level suitable for undergraduate students and others with only a minimal knowledge of college level physics. In particular it is not assumed that the reader is familiar with general relativity and only minimally familiar with quantum mechanics and Hamiltonian mechanics. Most chapters end with problems that elaborate on the text, and aid learning. Applications such as loop quantum cosmology, black hole entropy and spin foams are briefly covered. The text is ideally suited for an undergraduate course in the senior year of a physics major. It can also be used to introduce undergraduates to general relativity and quantum field theory as part of a 'special topics' type of course.
Readership: Undergraduates and beginning graduate physics students, lecturers in physics."
This forthcoming undergrad Loop gravity text came up in Barak's thread here:
http://physicsforums.com/showthread.php?p=3226419#post3226419
http://physicsforums.com/showthread.php?p=3232530#post3232530
First undergraduate textbook could appear this year. Scheduled for September 2011. Oxford U Press:
http://ukcatalogue.oup.com/product/academic/physics/9780199590759.do
EDIT: Atyy points out that Bojowald has already published a textbook in LOOP COSMOLOGY
and also one in the CANONICAL APPROACH TO GENERAL RELATIVITY.
Neither is explicitly an undergrad text in LQG, but the former treats the application of LQG to cosmo which is pretty close.
And the latter although mainly it is not about QG it has a chapter at the end, I recall.
======================
The question is: should we call the Oxford Press book the "First undergrad LQG text"?
I think yes, because for one thing that is what OUP calls it:
==quote==
Publisher's decription:
First book on the subject at the undergraduate level
Quick introduction to many major topics in fundamental theoretical physics suitable for undergraduate courses
High interest currently in quantum gravity among physicists worldwide
==endquote==
And for another thing Bojo book about Hamiltonian formulation of GR is not directly aimed at LQG. It does not start out talking QG. It puts it in as a last chapter.
The Gambini Pullin is explicitly aimed. It starts out with chapter 1 "Why quantized gravity?"
And it is TITLED as a textbook for LQG, not just as a GR text with apps.
First undergraduate textbook could appear this year. Scheduled for September 2011. Oxford U Press:
http://ukcatalogue.oup.com/product/academic/physics/9780199590759.do
Not Bojowald's, or is that not undergarduate? http://www.physicsforums.com/showthread.php?t=432381
First undergraduate textbook could appear this year. Scheduled for September 2011. Oxford U Press:
http://ukcatalogue.oup.com/product/academic/physics/9780199590759.do
Not Bojowald's, or is that not undergarduate? http://www.physicsforums.com/showthread.php?t=432381
Atyy, good question! I edited so as to respond in the appropriate place, right after the OUP publisher's blurb. I think in fact that the Gambini IS the first explicitly LQG undergrad text!
The Bojo text is on Canonical GR, with several applications. It could be used as a text but doesn't have the clear focus on LQG.
Oxford press says Gambini is the first LQG text for undergrads. And they are right. If you look at the title and TOC of the Bojo books you will see what I mean.
New page, so I will make the update post here for easy reference:
It hasn't been done for over a month so it's probably time to redo the regularly updated links post to give an introductory overview of the Loop program.
==================================
BRIEF OVERVIEW OF THE LOOP QG PROGRAM
Loop Gravity is a small growing field. It has had regular biannual conferences only since 2005 (Loops '05 was held at Potsdam.) Attendance at the biannual (Loops '11 Madrid) is now up to about 170.
Because centers of LQG research are spreading rather rapidly, jobs and postdoc positions seem currently to be ample compared to the number of new PhDs. It's hard to predict the future, but at least for now job prospects seem pretty good. Most new PhDs are out of Marseille,Penn State, AEI-Potsdam, and they all get placed. There are starting to be more PhDs now out of other places: Nottingham, Erlangen, Lyon, Cambridge, London...hard to give an exhaustive list.
First undergraduate textbook could appear this year. Scheduled for September 2011. Oxford U Press:
http://ukcatalogue.oup.com/product/academic/physics/9780199590759.do
Newly established Masters program aimed at Loop and other QG research (among other paths) starting at Nottingham in 2011:
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx
Survey for non-specialists, historical development and indications the theory recovers classical GR.
http://arxiv.org/abs/1012.4707
Loop quantum gravity: the first twenty five years
Definitive presentation of Loop gravity, with some math prerequisites:
http://arxiv.org/abs/1102.3660
Lectures on Loop Gravity
Loop cosmology, as of mid-2010:
http://arxiv.org/abs/1005.5491.
The Big Bang and the Quantum
Since Loop cosmology derives from LQG, this turns out to be the most accessible route to testing LQG. Here are 32 or more articles mostly by early universe phenomenologists about ways of testing LQC against CMB data,
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+QUANTUM+GRAVITY%2C+LOOP+SPAC E+OR+DK+QUANTUM+COSMOLOGY%2C+LOOP+SPACE%29+AND+%28 DK+PRIMORDIAL%2C+FLUCTUATION+OR+DK+INFLATION+OR+DK +COSMIC+BACKGROUND+RADIATION%29+AND+DATE+%3E+2008&FORMAT=www&SEQUENCE=citecount%28d%29
which have appeared since 2009.
Some other papers of possible interest:
http://arxiv.org/abs/1101.3264
Spinfoam Fermions: PCT Symmetry, Dirac Determinant, and Correlation Functions
http://arxiv.org/abs/1012.1739
Lorentz covariance of loop quantum gravity
The European Science Foundation "QG" network is encouraging development of a broad-base research community by events such as this year's QG 2011 conference in Zurich:
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:start
Topics to be covered include:
General quantum theory, relativistic quantum theory, emergence of space(-time)
General quantum field theory, including deformations of QFTs
QFT on curved and NC space-times
Canonical quantum gravity and supergravity
Regge calculus
String theory and M-theory
Loop gravity, spin foam
Quantum cosmology
===============================
The biannual Loops conference starts 23 May: Loops 2011 in Madrid.
http://www.iem.csic.es/loops11/
Click on "scientific program" in the menu on the left to see the list of talks. Abstracts of most talks are now available, just click on the title.
Many of the talks are about early universe pheno---the prospects for testing/constraining the theory.
Emerging challenges to the current formulation of Loop gravity are also represented at the conference and include "Shape dynamics" (see the session devoted to that on 23 May) and "Relative locality" (see talks by Laurent Freidel and Lee Smolin).
One of the signs of growth is the number of "parallel session" talks scheduled for Loops 2011, last time I checked there were 99 such. Younger researchers and newcomers to the field normally give talks in these parallel sessions.
=========================
Other signs of growth in the field:
the number of institutions now hosting Loop gravity (+ related phenomenology) research, and where one can do a Loop PhD
citations in the relevant categories (gr-qc, quantum cosmology, e.g. a growing share of "top 10 or top 30" papers)
simply the increased number of research papers coming out. Approximately doubled since 2006.
Loop gravity papers, by year
2005 41
2006 81
2007 121
2008 142
2009 141
2010 154
Loop cosmology papers, by year
2006 21
2007 39
2008 46
2009 45
2010 57
The current Loop cosmo formulation (Ashtekar et al) only appeared in 2006 so I start with that year.
Here are the relevant Spires searches, and links, if anyone wishes to see how the listing looks.
FIND DK SPIN,FOAM OR QUANTUM GRAVITY, LOOP SPACE OR QUANTUM COSMOLOGY, LOOP SPACE AND DATE = 2005
FIND DK QUANTUM COSMOLOGY, LOOP SPACE AND DATE = 2006
2005:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY% 2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+A ND+DATE+%3D+2005+&FORMAT=WWW&SEQUENCE=citecount%28d%29
2006:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY% 2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+A ND+DATE+%3D+2006+&FORMAT=WWW&SEQUENCE=citecount%28d%29
2007:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY% 2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+A ND+DATE+%3D+2007+&FORMAT=WWW&SEQUENCE=citecount%28d%29
2008:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY% 2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+A ND+DATE+%3D+2008+&FORMAT=WWW&SEQUENCE=citecount%28d%29
2009:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY% 2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+A ND+DATE+%3D+2009+&FORMAT=WWW&SEQUENCE=citecount%28d%29
2010:
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+DK+SPIN%2CFOAM+OR+QUANTUM+GRAVITY% 2C+LOOP+SPACE+OR+QUANTUM+COSMOLOGY%2C+LOOP+SPACE+A ND+DATE+%3D+2010+&FORMAT=WWW&SEQUENCE=citecount%28d%29
A new PF member asked "what exactly is LQG?" and requested a non-mathematical (effectively highschool level, I think) answer. Tom Stoer supplied the following which then got some editorial attention from Ben Crowell and Redbelly (who suggested copying it here.) I think it's an unbiased informative account:
==quote tom.stoer post==
What exactly is LQG?
It's difficult w/o math.
The problem with quantum gravity is that naive mechanisms to quantize gravity (which have been applied successfully to other fields) fail for gravity. That means that something fundamental has to be changed for quantum gravity.
There are different approaches to solve these problems, e.g.
a) string theory
b) asymptotic safety
c) loop quantum gravity (LQG)
I don't want to comment on a) and b) here.
Essentially LQG does the following: it introduces new variables which replace the (in GR) well-known metric that describes spacetime + curvature. This is pure math, so I don't want to go into details here, but what happens is that these new variables are rather close to fields that we know from gauge theory like QED and QCD. Indeed in a certain sense gravity looks rather similar to QCD, but there is one additional property of gravity that allowes one to apply a second mathematical trick which essentially replaces the fundamental fields with something like "fluxes through surfaces" or "fluxes along circles". These surfaces and circles are embedded into spacetime.
The next step is again rather technical and it becomes possible due to so-called diffeomorphism invariance: one can get rid of the the embedding of circles and surfaces into spacetime. Instead one replaces these entities with a so-called spin network, i.e. a graph with nodes and links between nodes where each link and each node carries some numbers which represent abstract entities from which certain properies of spacetime can be reconstructed. You can think about spacetime as made of cells (I will soon tell you that you can't :-); each cell has a certain volume carried by a node; each cell has certain surfaces and the link between different nodes (sitting inside these cells) carry the areas of the surfcaes.
The problem with this picture is that one might think about these cells as sitting in spacetime - but this is fundamentally wrong: this picture is only due to the construction, but basically there is no spacetime anymore; all there is are nodes and links (and certain numbers attributed to nodes and links). Spacetime is no longer fundamental but becomes an entity emerging from the more fundamental graphs with their nodes and links. The graphs are called spin networks b/c the numbers they are carrying have properties well-known from spins. But this is a mathematical property only, it does not means that there are real spinning objects.
Compare this emerging spacetime to a water surface of a lake. We know that it consists of atoms, and as soon as we get this picture it is clear that there is no water between the atoms; the surface is only an emerging phenomenon, the true fundamental objects are the atoms. In the same sense the spin networks are the fundametal entities from which spacetime, surfaces etc. and their properties like volume, area, curvature etc. can be constructed. Dynamics of spacetime (which was curvature, gravitational waves etc. in GR) is replaced by dynamics of spin networks: within a given graph new nodes with new links can appear (there are mathematical rules, but I don't want to go into detail here).
The last puzzle I have for you is the fact that such a spin network is not a mechanical object which "is" spacetime. Instead quantized spacetime is a superposition of (infinitly many) spin networks. This is well-known in quantum mechanics; there is no reason why an atom should be in a certain state; we can achieve that via preparation or measurement, but in principle a single atom can be in an arbitrary complex quantum state which is a superposition of "an atom sitting here, an atom moving in a certain direction over there, an atom moving in this or that direction, ...".
So classical spacetime is recovered by two averaging process: first there seems to be a regime were this superposition of spin networks is peaked around a single classical spacetime, i.e. where one network dominates the superposition of infinitely many spin networks; second from this single spin network one can reconstruct spacetime in the same sense as one can reconstruct the water surface from the individual atoms. But there may be different regimes (e.g. in black holes or closed to the big bang) where is classical picture and this averaging does no longer work. It may be that in these regimes all there is are spin networks w/o any classical property like smooth spacetime, areas, volume etc. It's like looking at a single atom: there is no water surface anymore.
Eventually this is why one started with this stuff: the classical picture of spacetime seems to become inconsistent when one tries to quantize it, i.e. when one defines these superpositins etc. These inconsistencies do not bother us as long as we talk about spacetime here, in the solar system etc. But they become a pain in the a... when we talk about spacetime near a singularity like a black hole or like the big bang. In order to understand these new non-classical regimes of spacetime a fundamentally new picture is required. This is what LQG (and other approaches) are aiming for: construct a new mathematical model from which well-known classical spacetime (like in GR) can be reconstrcuted, but which does not break down in certain regimes but remains well-defined and consistent.
He must so to speak throw away the ladder, after he has climbed up on it - Ludwig Wittgenstein
=====endquote=====
Original post:
http://physicsforums.com/showthread.php?p=3319185#post3319185
The Loops 2011 conference in Madrid last month had 165 participants. The program of talks is posted at this site:
http://www.iem.csic.es/loops11/
The QG11 conference in Zurich starts 14 June. 120 participants have registered so far.
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:programme
I'm trying out this Spires search to keep track of Loop early universe phenomenology papers (studying ways to test Loop cosmology.)
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+LOOP+SPACE+AND+%28QUANTUM+GR AVITY+OR+QUANTUM+COSMOLOGY%29+%29+AND+%28GRAVITATI ONAL+RADIATION+OR+PRIMORDIAL+OR+inflation+or+POWER +SPECTRUM+OR+COSMIC+BACKGROUND+RADIATION%29+AND+DA TE%3E2008&FORMAT=www&SEQUENCE=citecount%28d%29
It is a reworking of a search I was using earlier--what gets typed into the search terms box is:
FIND (DK LOOP SPACE AND (QUANTUM GRAVITY OR QUANTUM COSMOLOGY) ) AND (GRAVITATIONAL RADIATION OR PRIMORDIAL OR INFLATION OR POWER SPECTRUM OR COSMIC BACKGROUND RADIATION) AND DATE>2008
Just now when I tried it, the search came up with 42 items--papers that appeared 2009 or later.
The proposal of ways to test LQG---in particular the effects of the bounce at the start of expansion (which is a robust feature)---is an important development, I think. Another development is represented by this year's Quantum Theory and Gravitation conference ("QG11") which brings several QG communities together for comparison, sharing ideas, and discussion.
It is a mixed QG conference. We will see if the idea catches on. I have color-coded the list of talks to give an idea of the mix.
Causal Dynamical Triangulations(CDT)
Spectral Action (Connes Noncommutative Geometry)
LQG (incl. Group Field Theory)
Asymptotic Safety
Foundations-general considerations
String
======
Ambjorn: CDT, a quantum theory of geometry
Arnlind: Poisson Algebraic Geometry and Matrix Regularizations
Ashtekar: Quantum Cosmology and the Very Early Universe
Bachas: The problem of localization of gravity
Baez: Higher gauge theory, division algebras and superstrings
Barrett: State sum models and the spectral action
Beisert: Symmetries and Integrability for Scattering Amplitudes in N=4 Super Yang-Mills Theory
Blau: String Theory as a Theory of Quantum Gravity: a Status Report
Bodendorfer: Towards Loop Quantum Supergravity
Bossard: Toward the consistency of N=8 supergravity as a quantum field theory
Chamseddine: The Spectral Action
Compere: The translation anomaly of asymptotically flat spacetimes
Craps: Cosmological singularities in string theory
de Goursac: Renormalizability of noncommutative quantum field theories
Dixon: Ultraviolet behavior of quantum (super)gravity through four loops
Elvang: Symmetry constraints on the UV behavior of N=8 supergravity
Freidel: The principle of relative locality
Giulini: Very basic issues concerning quantum mechanics and gravitation
Hollands: Quantum field theory correlators on manifolds at very large and very short distances
Hoppe: Fundamental Structures of M-brane Theory
Jacobson: How general is the generalized second law?
Lechner: Covariant and local deformations of quantum field theories
Lewandowski: Canonical LQG: soluble models and other advances
Litim: Renormalisation group and the Planck scale
Loll: Nonperturbative highlights on quantum gravity from CDT
Longo: Boundary Quantum Field Theory and Conformal Field Theory
Morton: Extended Field Theories and Higher Gauge Theories
Mukhanov: Massive Gravity
Nicolai: Infinite-dimensional symmetries and the Wheeler-DeWitt equation
Oriti: Group field theory: a brief survey of recent developments
Reiterer: A class of gauges for the Einstein equations
Reuter: Einstein-Cartan Theory and Asymptotic Safety
Rovelli: Loop quantum gravity: the covariant dynamics
Shaposhnikov: Scale-invariant alternatives to general relativity
Speziale: Spin networks as twisted geometries
Steinacker: Matrix models, noncommutative gauge theory and emergent geometry
Wulkenhaar: Ward identities in matrix models arising from noncommutative geometry
I I'm not sure what Nicolai's talk is going to be about but just as a guess classify it "foundations-general considerations"--a potentially important topic suggested on the front page by the organizers.
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:programme
Currently the best review of LQG is this video talk:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=76%3Acarlo-rovelli-the-covariant-version-of-loop-quantum-gravity-definition-of-the-theory-results-open-problems&catid=35%3Aplenary-lectures&Itemid=1
The talk was given 25 May 2011 in Madrid, at the biannual Loops conference.
For a printed journal-style review try http://arxiv.org/abs/1012.4707 which was posted in December 2010.
There is also the LQG tutorial http://arxiv.org/abs/1102.3660
Peter McKenna
Jul21-11, 11:14 AM
Marcus,
About Causal Dynamic Triangulation, there still hasn't been much published out in layman's land. In the above discussion of LQG those terms almost describe an engineering model using an element system (something like a hydraulic model using links and nodes). Does this suggest that LQG acts like a secondary field much like eddy currents within an electromagnetic field (solved using a matrice)?
When looking at spin states 2D respresentation seem like "Fractals" as you described previously. How does CDT model or resolve loop gravity?
Marcus,
About Causal Dynamic Triangulation, there still hasn't been much published out in layman's land.... How does CDT model or resolve loop gravity?
Have you seen the SciAm article on CDT? It's well-written as an introduction for wide audience, and it has links to further reading, some of which is pretty accessible. I keep the URL to the SciAm article in my signature (check the end of this post). It is the "signal lake" link.
http://www.signallake.com/innovation/SelfOrganizingQuantumJul08.pdf
In the above discussion of LQG those terms almost describe an engineering model using an element system (something like a hydraulic model using links and nodes). Does this suggest that LQG acts like a secondary field much like eddy currents within an electromagnetic field (solved using a matrice)?
When looking at spin states 2D respresentation seem like "Fractals" as you described previously...
I'm not sure I can respond adequately. Maybe one of us will start a separate thread specifically to discuss these ideas. This thread does not have much discussion--it is mainly used to provide quick access to selected source material on Lqg.
I try to use this thread primarily as a place to keep the best current source material on LQG, including its phenomenology (ways of testing) and application to cosmology.
It should provide quick access to the latest review articles and survey talks.
Here is a search intended to dig up LQG/LQC pheno papers. It now gets 44 articles
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+LOOP+SPACE+AND+%28QUANTUM+GR AVITY+OR+QUANTUM+COSMOLOGY%29+%29+AND+%28GRAVITATI ONAL+RADIATION+OR+PRIMORDIAL+OR+INFLATION+OR+POWER +SPECTRUM+OR+COSMIC+BACKGROUND+RADIATION%29+AND+DA TE%3E2008&FORMAT=www&SEQUENCE=ds%28d%29
To see the latest, change the ordering from "by cite count" to "by date" and repeat the search.
The May 2011 Loops conference in Madrid had some great review talks. Video and slides PDF are available online. It can be useful to download both because you can scan through the slides and then drag the timebutton of the video to a part of the talk where you wish to focus attention. Also the video shows both slide and speaker and may sometimes cut off a part of a slide you want to read. So it may work best to download both and do your own split-screen. Ashtekar and Rovelli gave great survey talks:
Ashtekar's talk (for a Loop cosmology review):
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=181
Rovelli's talk (for status and open problems of the full LQG theory):
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=76
Peter McK expressed an interest in Causal Dynamical Triangulations, and Renate Loll gave a CDT review at the same conference. It's a good way to hear the latest.
Loll's review of CDT:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=182
For the listing of all the talks (linked to an abstract for each):
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=75
I'll include Frank Wilczek's Uppsala talk because I think it is a reality-based view of particle physics unification prospects. He gives the most likely picture of matter's future--- that which LQG spacetime geometry is apt to join up with.
Wilczek video: http://media.medfarm.uu.se/flvplayer/strings2011/video24
Wilczek slides: http://www-conference.slu.se/strings2011/presentations/4%20Thursday/1140_Wilczek.pdf
I'm currently having difficulty getting some of the videos of the Madrid talks.
The link to Rovelli's talk is:
http://www.iem.csic.es/departamentos/qft/grupos/gravitacional/loops11/Archives/Plenary-Lectures/Videos/Carlo-Rovelli_The-covariant-version-of-Loop-Quantum-Gravity-definition-of-the-theory-results-open-problems.mp4
That works fine. And the link to video of Ashtekar's talk works:
http://www.iem.csic.es/departamentos/qft/grupos/gravitacional/loops11/Archives/Plenary-Lectures/Videos/Abhay-Ashtekar_Recent-Advances-in-Loop-Quantum-Cosmology.mp4
But I believe the link to, for example, Renate Loll's talk is currently broken.
You can try various ones and see what luck you have. Here is the program:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=75
If you click on a particular talk you get a one-page summary with further links to the slides and (in the case of plenary talks given in the morning session) a link to the video, or what looks like one.
For example here are two summary pages:
Ashtekar's talk (for a Loop cosmology review):
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=181
Rovelli's talk (for status and open problems of the full LQG theory):
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=76
Click on Loll's talk and you get the summary page all right:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=182
And you can get her slides PDF. But the link to the video is given as:
http://161.111.24.61/loops11/Archives/Plenary-Lectures/Videos/Renate-Loll_Nonperturbative-Highlights-on-Quantum-Gravity-from-Causal-Dynamical-Triangulation.mp4
And that doesn't work. My first guess was that the links to video which are broken are the ones that begin
"161.111.24.61". The talks seem to be archived at two separate locations and one of the systems might be down. But that guess was wrong. If you have any current experience with getting videos of the talks, please share it. I'd like to know what luck others have had. Fortunately I downloaded a number of the talks before this problem developed (but I didn't happen to do that with Renate Loll's)
Currently the best review of LQG is this video talk:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=76
The talk was given 25 May 2011 in Madrid, at the biannual Loops conference.
...
When I posted that, a few weeks ago, the new version of its written counterpart, Zakopane Lectures, had not yet appeared. Now the new version is out. It has been expanded by an additional 10 pages or so, and rewritten in parts. It's now an excellent tutorial, aimed at advanced grad students ready and wanting to get into Loop research.
http://arxiv.org/abs/1102.3660
The Loop people have introductory winter "schools" for grad students and postdocs. This year they had a two-week school at the Zakopane ski resort. This paper is a condensed version of the series of lectures Rovelli taught at that that school. It has examples and exercises to work out. It reviews the open research problems, some where progress has recently been made. It presents the theory concisely, and also gives an overview of the various approaches that converged to it from different directions.
For a printed journal-style review article, try http://arxiv.org/abs/1012.4707 which appeared December 2010. Ths is not as pedagogical as the other. It is more for nonspecialists who just want a general status report and overview, with some historical background. It is not aimed at people who want to get their hands on quantum geometry and do some research in it.
QG growth in France has been remarkable in the past few years. It's interesting to examine what shape this is taking and to try to figure out why.
There are now many active centers of QG research:
Marseille (Rovelli's group)
Paris-Sud (Rivasseau's Orsay group)
Lyon (Livine's group)
Montpellier (Alexandrov, Roche)
Tours (Noui)
Ecole Polytechnique (Gabriel Catren)
http://www.rivasseau.com/
http://en.wikipedia.org/wiki/École_Polytechnique
http://en.wikipedia.org/wiki/Paris-Sud_11_University
http://www.polytechnique.edu/home/about-ecole-polytechnique/awards-and-honors/erc-starting-grant-awarded-to-gabriel-catren-62493.kjsp?RH=1282806775110
Paris-Sud has 4 Fields Medalists and 2 Nobel prizewinners. By Usa standards it is "Ivy", I guess.
The Paris Ecole Poly is like the French MIT---a small elite tech school. These are distinguished places.
It's interesting that Gabriel Catren should get a 5 year European Research Council (ERC) grant to set up a QG research team at the Ecole Poly. The emphasis of that research is on the foundations---the ontology of space and time---a more philosophical approach to basic questions in physics. You can read what he has to say about it at the above link.
I didn't know of Catren. Here is a bit more information:
http://www.crea.polytechnique.fr/LeCREA/fiches/Catren.htm
Perimeter video lectures:
http://pirsa.org/index.php?p=speaker&name=Gabriel_Catren
A little over 3 months ago, in post #274, I reported that the job situation (if postdoc fellowships are included) looked fairly good for new loop PhDs from Marseille, Penn State, and AEI Potsdam. This needs to be corrected or qualified by reservations.
The job situation is difficult (as with other areas of theoretical physics). Permanent positions are scarce, so what we are keeping track of are postdoc and other temporary positions.
For one thing, the new PhDs used to be mostly out of Marseille and Penn State, and now several new centers have emerged (Erlangen, Lyon, Beijing Normal, Florida Atlantic, Asia Pacific CTP in Korea, Morelia, Louisiana State, Sydney...to name a few) so it is more difficult to keep track. And it adds to the potential competition.
About all I can do is keep an eye on two or three main centers (Marseille, Penn State, Potsdam AEI) and from those I see new PhDs continuing to be placed, for the most part, but in temporary positions. I'd be glad to get other people's impressions and more accurate assessments based on direct experience.
To hazard a guess just as a casual onlooker (and this could be completely wrong) at this point if you are a new loop PhD to have a good chance at a 2 year postdoc contract or better your advisor should be Ashtekar, Rovelli, or Thiemann. I would be delighted to be corrected on that score.
The journal General Relativity and Gravitation has published a special issue containing written versions of talks at the 2nd QG school and workshop held at Corfu.
http://www.springerlink.com/content/473t7416228530w1/fulltext.pdf
The editors were:
Konstantinos Anagnostopoulos · Paolo Aschieri · Martin Bojowald · Harald Grosse · Larisa Jonke · George Zoupanos
Much of the special issue is restricted access ("pay per view") but John Baez' article is open access ("free") and there may be other stuff like that.
I think the editorial I linked to just now is free.
The main lecture series at the Corfu school were given by Abhay Ashtekar, John Baez, John Barrett, Vincent Rivasseau, Carlo Rovelli. Some of these were lectures were written up and included, along with some of the individual talks.
Here is the TOC for GRG Volume 43 Number 9
http://www.springerlink.com/content/p513t4384471/
This has links to all the ABSTRACTS---just click on the title of the talk. But the full text is in general not freely available.
Editorial
Noncommutative quantum field theory and gravity
Konstantinos Anagnostopoulos, Paolo Aschieri, Martin Bojowald, Harald Grosse, Larisa Jonke & George Zoupanos
Review Article
An invitation to higher gauge theory
John C. Baez & John Huerta
Research Articles
Non-perturbative QEG corrections to the Yang–Mills beta function
J.-E. Daum, U. Harst & M. Reuter
Geometry and observables in (2+1)-gravity
C. Meusburger
Asymptotics of 4d spin foam models
John W. Barrett, Richard J. Dowdall, Winston J. Fairbairn, Henrique Gomes, Frank Hellmann & Roberto Pereira
Braided algebras and the kappa-deformed oscillators
Jerzy Lukierski & Mariusz Woronowicz
Equivariant dimensional reduction and quiver gauge theories
Brian P. Dolan & Richard J. Szabo
Open multiple M2-branes I: quantum geometry of the M5-brane in a C-field
Chong-Sun Chu & Douglas J. Smith
Noncommutative geometry in string and twisted Hopf algebra of diffeomorphism
Satoshi Watamura
Renormalizable noncommutative quantum field theory
Harald Grosse & Raimar Wulkenhaar
Gravitational anomaly and fundamental forces
J. J. van der Bij
UV/IR duality in noncommutative quantum field theory
André Fischer & Richard J. Szabo
Curved space (matrix) membranes
Jens Hoppe
The Coulomb solution as a coherent state of unphysical photons
Glenn Barnich
Gauge symmetry breaking in matrix models
Harald Grosse, Fedele Lizzi & Harold Steinacker
Bianca Dittrich has accepted a tenure-track position at Perimeter.
There's an interview with her in Physics Today:
http://www.physicstoday.org/daily_edition/singularities/searching_for_a_theory_of_quantum_gravity
In the course of conversation with Atyy and others, in the Current Status of LQG thread, we came up with four papers which taken together can serve as a review as of August 2011:
http://physicsforums.com/showthread.php?p=3485140#post3485140
==quote==
That would make the combined essential "current status" review be
1102.3660 + 1108.2258 +1105.2212 + 1108.0832
Zakopane lectures+Emergence of gravity+Cosmological constant + On the structure
Rovelli + Magliaro Perini + Han + Rovelli
33 pages +6 pages +6 pages + 7 pages
==endquote==
For a video lecture affording an overview of LQG as of May 2011:
http://loops11.iem.csic.es/loops11/index.php?option=com_content&view=article&id=76
For Loop Quantum Cosmology status report:
http://arxiv.org/abs/1108.0893
For an index of research activity:
LOOP RESEARCH BY YEAR (loop quantum gravity, loop quantum cosmology, spin foam)
2005 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2005&d2d=&d2m=&d2y=2005&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (42 found)
2006 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2006&d2d=&d2m=&d2y=2006&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (77 found)
2007 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2007&d2d=&d2m=&d2y=2007&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (120 found)
2008 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2008&d2d=&d2m=&d2y=2008&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (142 found)
2009 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2009&d2d=&d2m=&d2y=2009&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (145 found)
2010 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2010&d2d=&d2m=&d2y=2010&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (152 found)
2011 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2011&d2d=&d2m=&d2y=2011&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (134 as of 16 Sept, annualized > 180)
http://howlonguntil.net/ 258 since 1 January
The annualized rate in this case 134*365/258 = 189
========================
Two links I want to keep handy relating to the cosmological constant problem:
http://arxiv.org/abs/1002.3966
http://arxiv.org/abs/1103.4841
=========================
αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔ ~≈≠≡ ≤≥½∞(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
http://www.physics.ntua.gr/cosmo11/Naxos2011/sci_prog.html
Called a "Summer School" but from the looks of the program it was more a high level workshop. The list of participants was mostly experts already established in various fields, not grad students! Interesting mix of Loop gravity, String, Loop cosmology, Asymsafe gravity, Triangulations gravity.
Just concluded. It ran last week 12-17 September
The topic was "Quantum Gravity and Quantum Cosmology"
Morning hour lectures by the likes of Ashtekar and Rovelli (Loop) and Kelly Stelle (String) and
Joe Silk (Latest Obs. Dark Matter) and Robert Brandenberger (Unconventional Cosmology)
Reuter (AsymSafe) Woodard (QG and Inflation) Bachas (String) Tsujikawa (Latest on Dark Energy) Wetterich (Spinor gravity), and so on.
And then after lunch there were 30 minute and 15 minute presentations. Also covering a broad mix of active approaches to QG and QC. To me the program looks like people getting down to business. Cosmology is the ultimate testing ground and whether they struggle or join forces, the different teams have to know each other accurately in depth and confront observations together.
One can say that representative folks from Loop, String, and other innovative approaches to gravity/cosmology were FRATERNIZING on the Aegean island of Naxos. Including major people, leaders in various fields. Nice to see that.
BTW Munich is hosting Strings 2012 and they have already set up their website:
http://wwwth.mpp.mpg.de/members/strings/strings2012/strings.html
We will see if they move a bit in the ecumenical direction of acknowledging the competition (Strings 2008 at CERN had a talk by Rovelli, 2010 at TexasA&M had one by Weinberg on AsymSafe cosmology, 2011 Uppsala had talks by Frank Wilczek and Erik Verlinde)
Also in September there was a 3 week workshop about QG at CERN.
http://ph-dep-th.web.cern.ch/ph-dep-th/content2/THInstitutes/2011/QG11/QG11.html
Hermann Nicolai's talk was at 2PM on 21 September and was followed by a scheduled period of discussion that concluded the day. It was titled: Quantum Gravity: Where do we stand?
http://ph-dep-th.web.cern.ch/ph-dep-th/content2/THInstitutes/2011/QG11/talks/QGCERN.pdf
There were 28 slides, each normally repeating as points were added.
Slide 13(3 repeats) was Background Independence
Slide 14(6 repeats) was Canonical Quantization
Slide 15(5) was Geometrodynamics [i.e. original quantum grav. eqn. Wheeler-DeWitt]
Slides 16-18(7) was a sequence of "Numerous Questions..." in which slide 17 posed an unexpected question with some humor/mild shock value.
Slide 19(6) was Loop Quantum Gravity
Slide 20(1) Quantum geometry according to LQG
Slide 21(1) Spin Foams
Slide 22(1) Spin Foam Models
Slide 23(5) Quantum gravity and experiment?
Slide 24(8) A Key Issue: Non-Uniqueness
Slide 25(1) The future of quantum gravity? [humorous illustration]
Slide 26(9) Waiting for news from the LHC.
Slide 27(9) Prospects I
Slide 28(6) Prospect II
First introductory LQG textbook went on sale 1 November 2011.
I checked today to see how it's doing. Earier books have covered related topics: canonical GR, application to cosmology etc. this is first wholly devoted to intro Loop.
A First Course in Loop Quantum Gravity
Rodolfo Gambini, Jorge Pullin
Oxford University Press.
http://www.amazon.com/First-Course-Loop-Quantum-Gravity/dp/0199590753
I found several things---one is that you get to browse online. You can look inside the book.
Another is that at least at 7PM Pacific time 3 November it is doing rather well for a textbook:
Amazon Best Sellers Rank: #62,638 in Books
#26 in Books > Professional & Technical > Professional Science > Physics > Mathematical Physics
So it is #26 on the Mathematical Physics bestseller list.
Here's the Oxford Press description:
This book provides an accessible introduction to loop quantum gravity and some of its applications, at a level suitable for undergraduate students and others with only a minimal knowledge of college level physics. In particular it is not assumed that the reader is familiar with general relativity and only minimally familiar with quantum mechanics and Hamiltonian mechanics. Most chapters end with problems that elaborate on the text, and aid learning. Applications such as loop quantum cosmology, black hole entropy and spin foams are briefly covered. The text is ideally suited for an undergraduate course in the senior year of a physics major. It can also be used to introduce undergraduates to general relativity and quantum field theory as part of a 'special topics' type of course.
First book on the subject at the undergraduate level
Quick introduction to many major topics in fundamental theoretical physics suitable for undergraduate courses
High interest currently in quantum gravity among physicists worldwide
Controversial subject which needs good, impartial introduction from respected scientists
Readership: Undergraduates and beginning graduate physics students, lecturers in physics.
Masters program at Nottingham, including Loop and other QG research
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx
Some papers:
Loop quantum gravity: the first twenty five years
Survey for non-specialists, historical development and indications the theory recovers classical GR.
http://arxiv.org/abs/1012.4707
Lectures on Loop Gravity
Definitive presentation of Loop gravity, with some math prerequisites:
http://arxiv.org/abs/1102.3660
The Big Bang and the Quantum
Loop cosmology, as of mid-2010:
http://arxiv.org/abs/1005.5491.
Testing:
Loop cosmology derives from LQG and this provides the most accessible route to testing. Here are articles mostly by early universe phenomenologists about ways of testing LQC against CMB data,
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+LOOP+SPACE+AND+%28QUANTUM+GR AVITY+OR+QUANTUM+COSMOLOGY%29+%29+AND+%28GRAVITATI ONAL+RADIATION+OR+PRIMORDIAL+OR+inflation+or+POWER +SPECTRUM+OR+COSMIC+BACKGROUND+RADIATION%29+AND+DA TE%3E2008&FORMAT=www&SEQUENCE=citecount%28d%29
These articles appeared 2009 or later. As of 3 November there were 45 of them.
Loops 2011 the biannual Loops conference was held in Madrid.
http://www.iem.csic.es/loops11/
Click on "scientific program" in the menu on the left to see the list of talks. Abstracts and slides pdf of most talks are now available, just click on the title. Videos of the plenary session morning talks are online. There were about 100 parallel session talks.
=========================
Research trends, as of 3 November:
http://howlonguntil.net/ day 307
162*365/307 = 193
816*365/307 = 970
LOOP RESEARCH BY YEAR (loop quantum gravity, loop quantum cosmology, spin foam)
2005 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2005&d2d=&d2m=&d2y=2005&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (42 found)
2006 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2006&d2d=&d2m=&d2y=2006&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (77 found)
2007 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2007&d2d=&d2m=&d2y=2007&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (120 found)
2008 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2008&d2d=&d2m=&d2y=2008&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (142 found)
2009 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2009&d2d=&d2m=&d2y=2009&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (145 found)
2010 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2010&d2d=&d2m=&d2y=2010&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (152 found)
2011 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2011&d2d=&d2m=&d2y=2011&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (162 found, annualized 193)
STRING,MEMBRANE,AdS/CFT RESEARCH BY YEAR
(search terms "string model", "membrane model" and "AdS/CFT correspondence")
2005 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2005&d2d=&d2m=&d2y=2005&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (988 found)
2006 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2006&d2d=&d2m=&d2y=2006&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1029 found)
2007 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2007&d2d=&d2m=&d2y=2007&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1050 found)
2008 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2008&d2d=&d2m=&d2y=2008&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1128 found)
2009 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2009&d2d=&d2m=&d2y=2009&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1132 found)
2010 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2010&d2d=&d2m=&d2y=2010&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1046 found)
2011 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2011&d2d=&d2m=&d2y=2011&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (816 found, annualized 970)
There is currently a broken link in the Nottingham webpage given in the previous post:
Masters program at Nottingham, including Loop and other QG research
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx
The link to "the Quantum Gravity group" near the bottom of the page should be to:
http://www.nottingham.ac.uk/mathematics/research/groups/mathematical-physics/quantum-gravity.aspx
=======================================
Francesca has created a world map of places where LQG research is being done or where you can do a PhD in Loop.
http://maps.google.com/maps/ms?ie=UTF8&hl=en&msa=0&msid=106449985216139270436.0004843830d27f3e6c50e&t=h&z=0
It does not have UC Davis but on the whole it is remarkably complete. It's hard to keep such a map up to date.
As confirmation that Carlip is advising LQG research as well as other QG, see:
http://arxiv.org/pdf/1111.2107v1
I want to assemble some information and links about the Quantum Geometry/Gravity program at Erlangen. It is getting to be quite a strong program. They have TWO QG groups, one in the Physics department led by Thiemann and now a second group in the Math department led by Meusburger. The intent is to have several postdocs in each, plus PhD students.
Here is about Meusburger:
http://www.algeo.math.uni-erlangen.de/people/meusburger-catherine/prof-dr-catherine-meusburger/research-group.html
A postdoc in Meusburger's group is Winston Fairbairn whom we know of as a Rovelli PhD and co-author. There is another postdoc opening. Prof Meusburger recently sent out this email announcement:
==excerpt==
A postdoc position will be available in the quantum gravity group within the algebra and geometry group at the Department of Mathematics, University of Erlangen-Nürnberg in Erlangen, Germany...
==endquote==
for more information:
http://www.algeo.math.uni-erlangen.de/people/meusburger-catherine/prof-dr-catherine-meusburger/positions.html
Here is about the quantum gravity group in the Physics Department led by Thiemann:
http://theorie3.physik.uni-erlangen.de/people.html
This group has grown by the addition of some strong people who have had experience with various "new models" approaches. Maïté Dupuis comes there from Lyon, for example.
She has co-authored a lot with Etera Livine, who was her PhD advisor, and also one paper with Freidel.
Enrique Borja, who has co-authored with Etera Livine (several) and Freidel (one)
Emanuele Alesci, a Rovelli PhD and coauthor.
It's also interesting that John Baez' student Derek Wise is there.
αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔ ~≈≠≡ ≤≥½∞(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
Here are results of an InSpire search is designed to turn up observational test-related Loop gravity/cosmology papers. In conjunction with LQG/LQC, the DESY search categories are gravitational radiation, inflation, power spectrum, cosmic background radiation, primordial.
Loop pheno papers (increasingly observational test-related)
2000-2003 2004-2007 2008-2011
6 27 46
Here's for the 4-year stretch (2008-2011)---as of today we get 46 papers.
http://inspirehep.net/search?ln=en&ln=en&p=find+d+%3C+2011+and+d+%3E+2008+and+k+loop+space+ and+%28quantum+gravity+or+quantum+cosmology%29+and +%28gravitational+radiation+or+inflation+or+power+ spectrum+or+cosmic+background+radiation+or+primord ial%29&action_search=Search&sf=&so=d&rm=citation&rg=100&sc=0&of=hb
If we look at the earlier 4-year stretch (2004-2007) using the same categories, we get 27 papers.
http://inspirehep.net/search?ln=en&ln=en&p=find+d+%3C+2007+and+d+%3E+2004+and+k+loop+space+ and+%28quantum+gravity+or+quantum+cosmology%29+and +%28gravitational+radiation+or+inflation+or+power+ spectrum+or+cosmic+background+radiation+or+primord ial%29&action_search=Search&sf=&so=d&rm=citation&rg=100&sc=0&of=hb
Here's the same search for the previous 4 years (2000-2003 inclusive), 6 papers found.
http://inspirehep.net/search?ln=en&ln=en&p=find+d+%3C+2003+and+d+%3E+2000+and+k+loop+space+ and+%28quantum+gravity+or+quantum+cosmology%29+and +%28gravitational+radiation+or+inflation+or+power+ spectrum+or+cosmic+background+radiation+or+primord ial%29&action_search=Search&sf=&so=d&rm=citation&rg=100&sc=0&of=hb
There is a small amount of overlap in the time segments because InSpire counts a paper as having appeared in a certain year, say 2006, if either it was published in professional journal in 2006 or posted as a preprint on arxiv in 2006.
αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔ ~≈≠≡ ≤≥½∞(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
Research trends, updated as of 25 November:
http://howlonguntil.net/ day 329/365
180*365/329 = 200
855*365/329 = 949
LOOP RESEARCH BY YEAR (loop quantum gravity, loop quantum cosmology, spin foam)
2005 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2005&d2d=&d2m=&d2y=2005&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (42 found)
2006 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2006&d2d=&d2m=&d2y=2006&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (77 found)
2007 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2007&d2d=&d2m=&d2y=2007&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (120 found)
2008 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2008&d2d=&d2m=&d2y=2008&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (142 found)
2009 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2009&d2d=&d2m=&d2y=2009&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (145 found)
2010 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2010&d2d=&d2m=&d2y=2010&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (152 found)
2011 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2011&d2d=&d2m=&d2y=2011&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (200 annualized, from 180 found)
STRING,MEMBRANE,AdS/CFT RESEARCH BY YEAR
(search terms "string model", "membrane model" and "AdS/CFT correspondence")
2005 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2005&d2d=&d2m=&d2y=2005&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (988 found)
2006 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2006&d2d=&d2m=&d2y=2006&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1029 found)
2007 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2007&d2d=&d2m=&d2y=2007&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1050 found)
2008 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2008&d2d=&d2m=&d2y=2008&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1128 found)
2009 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2009&d2d=&d2m=&d2y=2009&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1132 found)
2010 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2010&d2d=&d2m=&d2y=2010&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1046 found)
2011 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2011&d2d=&d2m=&d2y=2011&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (949 annualized, from 855 found)
αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔ ~≈≠≡ ≤≥½∞⇐⇑⇒⇓⇔∴∃⋅ℝℤℕℂ
One way to keep track of current developments in LQG is to watch the ILQGS online seminar list. I've shortened some titles for brevity.
ILQGS SEMINAR SCHEDULE SPRING 2012
(All seminars will held at 9:00 AM Central Time)
DATE Seminar Title Speaker(Institution)
1/31 Physics of Bianchi models in LQC Parampreet Singh(LSU)
2/14 Classical limit of SF on arbitrary triangulation Claudio Perini(PennState)
2/28 Continuous formulation of the LQG phase space Marc Geiller(Paris-Diderot)
3/13 Black hole evaporation in LQG Jacobo Diaz-Polo(LSU)
3/27 BH entropy in LQG new insight from local perspective A.Perez(Marseille)
4/10 Effective Field Theory QG from Shape Dynamics Tim Koslowski(Perimeter)
4/24 Path integral measure and triangulation independence S.Steinhaus(AEI)
5/8 TBA
http://relativity.phys.lsu.edu/ilqgs/schedulesp12.html
Audio files and slides PDF are made availble online at the ILQGS website.
http://relativity.phys.lsu.edu/ilqgs/
The site's blog has commentary by other LQG researchers and background notes.
Note that the 2/28 topic is the Freidel Geiller Ziprick paper, currently leading in our MIP poll. The 4/10 talk is on the topic of the current MIP runner-up.
Two of the talks are concerned with triangulation independence, an important issue, and one deals with the classical limit of spinfoam LQG. Pretty much all are topics of current interest.
==================
For convenience I'll gather some potentially useful links:
Here is Rovelli's group at Marseille
http://www.cpt.univ-mrs.fr/~quantumgravity/
Here's the QG bunch at Perimeter
http://www.perimeterinstitute.ca/Scientific/Research/Quantum_Gravity/
Here is Thiemann's group at Erlangen
http://theorie3.physik.uni-erlangen.de/people.html
Here is Meusburger's group at Erlangen
http://www.algeo.math.uni-erlangen.de/people/meusburger-catherine/prof-dr-catherine-meusburger/research-group.html
Here is Dittrich's group at AEI
http://www.aei.mpg.de/english/research/teams/canonicalCovariantDynamics/index.html
http://www.aei.mpg.de/english/research/teams/canonicalCovariantDynamics/members/index.php
Here is Oriti's group at AEI
http://www.aei.mpg.de/english/research/teams/microscopicQuantumStructure/members/index.php
Livine's QG group at Lyon
http://www.ens-lyon.fr/PHYSIQUE/index.php?langue=anglais&page=equipe4&souspage=gravite
Pullin's QG group at LSU is part of overall gravity physics, no separate page
http://relativity.phys.lsu.edu/
Ashtekar's Institute for Gravitation and the Cosmos
http://gravity.psu.edu/
see the QG part
By now anyone who follows QG will be familiar with the strong research group at Marseille, so I won't list names there. Perimeter has a lot of well-known people, among the younger researchers: Eugenio Bianchi, Valentin Bonzom, Razvan Gurau, Tim Koslowski, Cecelia Flori, Joseph Ben Geloun. Thiemann's group currently includes Maïté Dupuis, Derek Wise, Emanuele Alesci, Enrique Borja among others. Meusburger's group includes Winston Fairbairn. Dittrich's AEI group incudes Dario Benedetti, Song He, James Ryan, Sebastian Steinhaus (giving the ILQGS presentation this semester), Wojciech Kaminski,...
Oriti's group includes Fotini Markopoulou (as visitor), Matteo Smerlak, Isabeau Premont-Schwarz, Gianluca Calcagni, Lorenzo Sindoni,...
Livine's group at Lyon includes Johannes Tambornino
QG at LSU incudes Jorge Pullin, Parampreet Singh, and Jacobo Diaz-Polo
I should also ennumerate the QG bunch at Penn State. There is a lot to keep track of. Maybe in a later post.
αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔ ~≈≠≡ ≤≥½∞⇐⇑⇒⇓⇔∴∃⋅ℝℤℕℂ
To continue the above list:
In the above I should have noted that Kristina Giesel has joined the faculty of Thiemann's group at Erlangen. Also in the above Perimeter QG bunch I should have included Steffen Gielen. This month he moved from AEI (Dittrich group) to Perimeter. http://www.aei.mpg.de/~gielen/
Barrett's QG group at Nottingham
http://www.nottingham.ac.uk/mathematics/research/groups/mathematical-physics/quantum-gravity.aspx (faculty: John Barrett, Kirill Krasnov, Jorma Louko)
More detail on QG at Penn State
http://cft.igc.psu.edu/
(besides many well-known faculty, younger members include Elena Magliaro, Claudio Perini, William Nelson, Adam Henderson, Ivan Agullo---David Sloan until recently of this group is now at Utrecht, Ed Wilson-Ewing has moved on to Marseille, Jon Engle is now faculty at Florida-Atlantic, Param Singh now faculty at LSU)
I shouldn't forget to mention two divisions of the University of Paris: Orsay (Vincent Rivasseau is there) and Paris-Diderot (Marc Geiller). Geiller is giving the February 28 ILQGS talk mentioned in the preceding post, on the Freidel Geiller Ziprick paper.
Hanno Sahlmann has started a QG group at the AsiaPacific CPT (Pohang University of Science and Technology)
Some resource links:
Loops 2011 (many videos and slides pdf of the talks)
http://www.iem.csic.es/loops11/
Undergrad LQG textbook
http://www.amazon.com/First-Course-Loop-Quantum-Gravity/dp/0199590753
A First Course in Loop Quantum Gravity
Rodolfo Gambini, Jorge Pullin
Oxford University Press.
Master's program at Nottingham
http://pgstudy.nottingham.ac.uk/postgraduate-courses/gravity-particles-and-fields-masters-msc_1163.aspx
Latest review papers
http://arxiv.org/abs/1201.4598
Introduction to Loop Quantum Gravity (Abhay Ashtekar)
and
http://arxiv.org/abs/1108.0893
Loop Quantum Cosmology: A Status Report (Abhay Ashtekar, Parampreet Singh)
Searches for Loop and String/M papers by year (results for 2011 now appear complete):
LOOP RESEARCH BY YEAR (loop quantum gravity, loop quantum cosmology, spin foam)
2006 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2006&d2d=&d2m=&d2y=2006&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (77 found)
2007 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2007&d2d=&d2m=&d2y=2007&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (120 found)
2008 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2008&d2d=&d2m=&d2y=2008&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (142 found)
2009 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2009&d2d=&d2m=&d2y=2009&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (145 found)
2010 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2010&d2d=&d2m=&d2y=2010&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (152 found)
2011 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2011&d2d=&d2m=&d2y=2011&sf=&so=a&rm=citation&rg=25&sc=0&of=hb (203 found)
2012 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=quantum+cosmology%3A+loop+space&f1=keyword&op1=o&m2=e&p2=quantum+gravity%3A+loop+space&f2=keyword&op2=o&m3=e&p3=spin%3A+foam&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2012&d2d=&d2m=&d2y=2012&sf=&so=a&rm=citation&rg=25&sc=0&of=hb
STRING,MEMBRANE,AdS/CFT RESEARCH BY YEAR
(search terms "string model", "membrane model" and "AdS/CFT correspondence")
2006 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2006&d2d=&d2m=&d2y=2006&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1029 found)
2007 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2007&d2d=&d2m=&d2y=2007&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1050 found)
2008 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2008&d2d=&d2m=&d2y=2008&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1128 found)
2009 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2009&d2d=&d2m=&d2y=2009&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1133 found)
2010 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2010&d2d=&d2m=&d2y=2010&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (1044 found)
2011 http://inspirebeta.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2011&d2d=&d2m=&d2y=2011&sf=&so=a&rm=citation&rg=10&sc=0&of=hb (928 found)
2012 http://inspirehep.net/search?ln=en&as=1&m1=e&p1=string+model&f1=keyword&op1=o&m2=e&p2=membrane+model&f2=keyword&op2=o&m3=e&p3=AdS%2FCFT+correspondence&f3=keyword&action_search=Search&dt=&d1d=&d1m=&d1y=2012&d2d=&d2m=&d2y=2012&sf=&so=a&rm=citation&rg=10&sc=0&of=hb
A great series of Perimeter video lectures going back to 2003
PIRSA QUANTUM GRAVITY SERIES
http://pirsa.org/S005
select "semester"=all and "year"=all.
Among the more recent are talks by Eugenio Bianchi, Elena Magliaro, Edward Wilson-Ewing, Aristide Baratin, Philipp Höhn, Maïté Dupuis, Muxin Han, Matteo Smerlak
This recent talk by Joseph Ben Geloun was for some reason not catalogued in the QG series
http://pirsa.org/12010132/ so it does not show up in the above search. (topic GFT, tensor field theory)
ινξςυφΓΘΛΞΠΣΦΨ⋅ℤℕ
Phenomenology issues affecting various models, which may already be ruled out, are part of the general QG phenomenology picture http://backreaction.blogspot.com/2012/02/no-evidence-for-spacetime-foam.html that we need to keep track of.
Although the observations discussed here seem not relevant to LQG specifically. In LQG space is not in a simple or naive sense "grainy". Its network states are quantum states of geometry (i.e. refer to relations among geometric measurements)---they're not imagined to be "what space is made of". Lorentz violation such as energydependent speed of light or the blurring of images one might get with a grainy substance are not predictions. One way to say it is QG is not about what space IS but rather it is about HOW IT RESPONDS to measurement. Analogous to basic quantum theory in other areas.
==quote Bee, above link==
...the authors have presented an analysis of the images of 157 high-redshift (z > 4) quasi-stellar objects. They found no blurring. With that, also the holographic foam model is ruled out. Or, to be precise, the parameter α is constrained into a range that is implausible for quantum gravitational effects.
As it is often the case in the phenomenology of quantum gravity, the plausible models are difficult, if not impossible, to constrain by data. And the implausible ones nobody misses when they are ruled out. This is a case of the latter.
==endquote==
fellupahill
Feb2-12, 09:03 PM
I read alot of Three Roads to Quantum Gravity last night. I found a free, legal, online pdf source if anyone wants to check it out too. Kinda for laymen, but it filled in the blanks for me :)
Three Roads is certainly one way to get an introduction to QG. Right now I want to focus on the TESTING issue which has surfaced fairly recently. Bee Hossenfelder is a QG phenomenologist and she has just posted a paper written with Leonardo Modesto that discusses a completely new mode of QG testing.
It sounds weird to me and dubious but I respect Bee a lot and maybe I have to get used to it.
It is based on Modesto's 2008 paper that CLAIMS that in LQG a black hole will not have a singularity but will open up out the bottom to make a new spacetime region.
Maybe this could be tested and proved wrong without it showing the whole theory to be wrong.
Maybe it is not an airtight case, maybe he made some special assumption or did not derive it correctly from the full LQG theory.
Anyway it gives an opportunity to test SOMETHING, and Bee is involved. So here is Modesto
s original 2008 paper:
==quote==
http://arxiv.org/abs/0811.2196
Space-Time Structure of Loop Quantum Black Hole
Leonardo Modesto
In this paper we have improved the semiclassical analysis of loop quantum black hole (LQBH) in the conservative approach of constant polymeric parameter. In particular we have focused our attention on the space-time structure. We have introduced a very simple modification of the spherically symmetric Hamiltonian constraint in its holonomic version...
=endquote==
NOW HERE IS THE NEW PAPER:
http://arxiv.org/abs/1202.0412
Emission spectra of self-dual black holes
Sabine Hossenfelder, Leonardo Modesto, Isabeau Prémont-Schwarz
(Submitted on 2 Feb 2012)
We calculate the particle spectra of evaporating self-dual black holes that are potential dark matter candidates. We first estimate the relevant mass and temperature range and find that the masses are below the Planck mass, and the temperature of the black holes is small compared to their mass. In this limit, we then derive the number-density of the primary emission particles, and, by studying the wave-equation of a scalar field in the background metric of the black hole, show that we can use the low energy approximation for the greybody factors. We finally arrive at the expression for the spectrum of secondary particle emission from a dark matter halo constituted of self-dual black holes.
15 pages, 6 figures
I LIKE THIS BECAUSE it is a way to DISPROVE the existence of these weird double-mouthed black holes by looking for, and not finding, their distinctive radiation. It's empirical. And if they actually found some matching radiation it might be quite surprising. So good either way.
A good introduction to the topic of LQBH (loop quantum black holes) Modesto-style is
http://arxiv.org/abs/0905.3170
Self-dual Black Holes in LQG: Theory and Phenomenology
Leonardo Modesto, Isabeau Prémont-Schwarz
(Submitted on 20 May 2009)
In this paper we have recalled the semiclassical metric obtained from a classical analysis of the loop quantum black hole (LQBH). We show that the regular Reissner-Nordstrom-like metric is self-dual in the sense of T-duality: the form of the metric obtained in Loop quantum Gravity (LQG) is invariant under the exchange "r ↔ a0/r" where "a0" is proportional to the minimum area in LQG and "r" is the standard Schwarzschild radial coordinate at asymptotic infinity. Of particular interest, the symmetry imposes that if an observer at "r" close to infinity sees a black hole of mass "m" an observer in the other asymptotic infinity beyond the horizon (at "r" close to "0") sees a dual mass "mp/m" ("mp" is the Planck mass). We then show that small LQBH are stable and could be a component of dark matter. Ultra-light LQBHs created shortly after the Big Bang would now have a mass of approximately "10-5 mp" and emit radiation with a typical energy of about 1013 - 1014 eV but they would also emit cosmic rays of much higher energies, albeit few of them. If these small LQBHs form a majority of the dark matter of the Milky Way's Halo, the production rate of ultra-high-energy-cosmic-rays (UHECR) by these ultra light black holes would be compatible with the observed rate of the Auger detector.
18 pages, 32 figures. Extra Plot, Improved Numerical Results
I think the more recent paper I'll call HMP http://arxiv.org/abs/1202.0412
Emission spectra of self-dual black holes refines and corrects some of these estimates. Here is an excerpt
==quote Hossenfelder Modesto Prémont-Schwarz (HMP)==
Integrating the inverse of dM/dt to obtain the lifetime, one finds that the time it takes for the black hole to completely evaporate exceeds the lifetime of the universe for m >~ 10−5mp. The primordially produced black holes with masses of about 10−3mp thus would still not have entirely decayed today. Moreover, they would have an average temperature of T ≈ 10−9mp ≈ 109 TeV, which is about in the energy range of the ultra high energetic cosmic rays (UHECRs) whose origin is still unclear. We thus see why the self-dual black holes can make for an interesting phenomenology. However, to arrive at observational consequences we have to make this rough estimate more precise. For this, we take ...
==endquote==
One way to see where a field is going is to check the conferences, what speakers and themes emerge as important. We've done that in the past in this thread. 2011 was a big year for Loop, in terms of research output and conferences, so 2012 is likely to be comparatively quiet. One upcoming event is this June Prague Relativity and Gravitation conference:
http://ae100prg.mff.cuni.cz/program
Here are excerpts from the invited speaker list.
...
Abhay Ashtekar (Institute for Gravitation and the Cosmos, Penn State University, University Park )
T.B.A.[my guess is Loop cosmology: inflation, initial conditions at the bounce, power spectrum]
...
Julian Barbour (Department of Physics, University of Oxford, Oxford)
Prague and the conception of general relativity: Kepler, Mach and Einstein
...
Karel Kuchař (Department of Physics, University of Utah, Salt Lake City )
Canonical quantum gravity: Einstein's posthumous anathema
Jerzy Lewandowski (Department of Physics, University of Warsaw, Warsaw)
Loop quantum gravity: The status report
...
Hermann Nicolai (Albert-Einstein-Institut Golm, Potsdam)
Quantum gravity: the view from particle physics
...
Misao Sasaki (Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto)
Inflation and birth of cosmological perturbations
...
Bernard Schutz (Albert-Einstein-Institute Golm, Potsdam)
Gravity talks: observing the Universe with gravitational waves
Alexei Starobinsky (Landau Institute for Theoretical Physics, Moscow)
f(R) gravity--the most straightforward generalization of the Einstein gravity
Robert Wald (Enrico Fermi Institute, University of Chicago, Chicago)
T.B.A.
Clifford Will (Department of Physics, Washington University, St. Louis)
Testing general relativity: Centenary highlights and future prospects
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Ashtekar has new quantum cosmology results with coauthors Agullo and Nelson, that have not been posted yet but were presented in seminar by Nelson
http://relativity.phys.lsu.edu/ilqgs/nelson101811.pdf
http://relativity.phys.lsu.edu/ilqgs/nelson101811.wav
http://relativity.phys.lsu.edu/ilqgs/nelson101811.aif
and which will be the subject of an invited presentation by Agullo at the April American Physical Society meeting.
They are important results so it seems possible that Ashtekar will feature the new paper in his Prague talk this June.
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This year's Marcel Grossmann meeting (July, in Stockholm) has these relevant parallel sessions:
http://www.icra.it/mg/mg13/parallel_sessions.htm
L. Quantum Gravity
QG1 Loop Quantum Gravity, Quantum Geometry, Spin Foams (Jerzy Lewandowski)
QG2 Quantum Gravity Phenomenology (Giovanni Amelino-Camelia)
QG3 Asymptotic Safeness and Symmetry Breaking in Quantum Gravity (Eckehard W. Mielke)
QG4 Loop quantum gravity: cosmology and black holes (Jorge Pullin, Parampreet Singh)
for more information: http://www.icra.it/mg/mg13/
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