Introduction To Loop Quantum Gravity

  • #151


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
 
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  • #152
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.
 
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  • #153
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:)
 
  • #154
ccdantas said:
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.
 
  • #155
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
 
  • #156
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.
 
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  • #157
marcus said:
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
 
  • #158
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:
https://www.physicsforums.com/showpost.php?p=2145438&postcount=10
 
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  • #159
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.
 
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  • #160
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.com/dp/0521860458/?tag=pfamazon01-20
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.
 
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  • #161
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
 
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  • #162
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.
 
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  • #163
marcus said:
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/
 
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  • #164
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
 
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  • #165
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/~rovelli/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
 
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  • #166
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.
 
  • #167
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/~rovelli/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!
 
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  • #168
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′) |ΨboundaryHboundary
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.
 
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  • #169
Marcus, the links did not appear.
 
  • #170
Thanks for catching that! I fixed the trouble.
 
  • #171
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?"
 
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  • #172
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/~rovelli/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 into 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)
 
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  • #173
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.)
 
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  • #174
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.
 
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  • #175
marcus said:
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?
 
  • #176
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
 
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  • #177
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+SPACE+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:
https://www.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
 
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  • #178
Leonard Susskind, Lee Smolin, Roger Penrose and Herman Nicolain in the same conference. What do you think Marcus?
 
  • #179
MTd2 said:
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:
https://www.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.
 
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  • #180
marcus said:
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 won't go.
 
  • #181
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.
 
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  • #182
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.
 
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  • #183
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.pdfThe 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.htmThe 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.
 
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  • #184
The timetable of talks at Loop 09 is up:

http://www.mighty-security.com/loop/timetable1.htm
 
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  • #185
MTd2 said:
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.
 
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  • #186
This is the schedule of George Ellis conference:

http://www.mth.uct.ac.za/~jeff/Quantum_Gravity/Schedule.html
 
  • #187
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 Azores Talk.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:
https://www.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
 
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  • #188
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+SPACE+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/~rovelli/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.
 
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  • #189
  • #190
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
 
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  • #191
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
 
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  • #192
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==
 
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  • #193
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.
 
  • #194
MTd2 said:
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.
 
  • #195
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+SPACE+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/~rovelli/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
 
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  • #196
http://www.perimeterinstitute.ca/en/Events/Gravity_at_a_Lifgarbagez_Point/Gravity_at_a_Lifgarbagez_Point/

Gravity at a Lifgarbagez 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 Lifgarbagez 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!
 
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  • #197
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.
 
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  • #198
Resources for conformal symmetry:
https://www.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
 
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  • #199
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.
 
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  • #200
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 Lifgarbagez 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 Lifgarbagez 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/in...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
 
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