Loop-and-allied QG bibliography

[marcus]

A new paper by Amelino-Camelia
http://arxiv.org/gr-qc/0405084

A new one by Livine and Oriti
http://arxiv.org/gr-qc/0405085

any comments are welcome. I have to go out for part of the evening, so
may not get around to discussing these for a while. I would guess the
Livine/Oriti paper is interesting.

L/O:
----quote---
Does a quantum gravity theory with an invariant length and a discrete spectrum for geometric observables necessarily break Lorentz symmetry or necessarily require some sort of modification/deformation of it? The answer, as we will see, is simply “no”.
---end quote---

 

[Olias]

I believe they are Two Gems!

 

[marcus]

this thread is serving as a surrogate sticky "reference library" for useful LQG links. Thanks to all who have contributed so far!
the last time I updated the main list of references was post #163 about thirty posts back, so it's about time to update the list again

I will break it down into some categories, with textbooks and introductory survey lectures and such coming first

------- texts--------
Rovelli posted the 30 December 2003 draft of his book "Quantum Gravity", to be published this year by Cambridge University Press.
The PDF file is at his homepage
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html
The book is around 350 pages long and takes a few (like ten?) minutes to download and convert.
To download the 30 December 2003 draft of the book directly:
http://www.cpt.univ-mrs.fr/~rovelli/book.pdf

Here are Thiemann's Lecture Notes (they have been published in Berlin by Springer Verlag)
"Lectures on Loop Quantum Gravity".
A draft is online at
http://arxiv.org/gr-qc/0210094

-----a recent review article----
http://arxiv.org./abs/gr-qc/0404018

Ashtekar and Lewandowski
"Background Independent Quantum Gravity: a Status Report"
125 pages
many references

another recent survey:
Enrique Alvarez
http://arxiv.org/gr-qc/0405107
"Quantum Gravity"
( Lectures given at Karpacz. 40 pages)

this next is older and interesting partly for historical and broader perspective.
it is a Rovelli survey at a 1997 GR conference (plenary at GR15)
and you get not just LQG and string but some other approaches that
were tried in the 1990s:
http://arxiv.org/gr-qc/9803024
Carlo Rovelli
"Strings, loops and others: a critical survey of the present approaches to quantum gravity"
" 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..."

---------a newsletter: "Matters of Gravity"----
Jorge Pullin's newsletter "Matters of Gravity"
http://arxiv.org./abs/gr-qc/0403051
this is the Spring 2004 issue

-------Quantum Gravity Phenomenology and DSR---------

some recent phenomenology and DSR papers:

A new paper by Amelino-Camelia
http://arxiv.org/gr-qc/0405084


http://arxiv.org./gr-qc/0404113
"On alternative approaches to Lorentz violation invariance in loop quantum gravity inspired models
Jorge Alfaro, Marat Reyes, Hugo A. Morales-Tecotl and L.F. Urrutia


Ted Jacobson, Stefano Liberati, David Mattingly
"Quantum Gravity Phenomenology and Lorentz Violation"
http://arxiv.org./abs/gr-qc/0404067
15 April 2004

Giovanni Amelino-Camelia
"A perspective on quantum gravity phenomenology"
http://www.arxiv.org/abs/gr-qc/0402009
dated 2 February 2004

Giovanni Amelino-Camelia, Jerzy Kowalski-Glikman, Gianlucca Mandanici, and Andrea Procaccini
"Phenomenology of Doubly Special Relativity"
http://arxiv.org/gr-qc/0312124
dated 30 December 2003

Jerzy Kowalski-Glikman
"Doubly Special Relativity and quantum gravity phenomenology"
http://arxiv.org/hep-th/0312140
dated 12 December 2003

Jerzy Lukierski
"Relation between quantum ?-Poincare framework and doubly special relativity"
http://arxiv.org./hep-th/0402117
dated 18 February 2004

other less recent ones:

Jerzy Kowalski-Glikman and Sebastian Nowak
"Doubly Special Relativity and de Sitter space"
http://arxiv.org/hep-th/0304101
dated 11 October 2003

M. Daszkiewicz, K. Imilkowska, J. Kowalski-Glikman
"Velocity of particles in Doubly Special Relativity"
http://arxiv.org/hep-th/0304027
dated 3 April 2003


---------Loop Quantum Cosmology-------

Martin Bojowald
"Loop Quantum Cosmology: Recent Progress"
http://arxiv.org/gr-qc/0402053
One of the invited plenary talks at the January 2004 ICGC
conference (see list of recent conferences)

The Bianchi IX model in Loop Quantum Cosmology
Martin Bojowald, Ghanashyam Date, Golam Mortuza Hossain
41 pages
http://arxiv.org/abs/gr-qc/0404039

"Inflationary Cosmology and Quantization Ambiguities in Semi-Classical Loop Quantum Gravity"
Martin Bojowald, James E. Lidsey, David J. Mulryne, Parampreet Singh, Reza Tavakol
15 pages, 8 figures
http://arxiv.org./abs/gr-qc/0403106

Martin Bojowald and Kevin Vandersloot
"Loop Quantum Cosmology and Boundary Proposals"
http://arxiv.org/gr-qc/0312103
dated 23 December 2003

Martin Bojowald
"Quantum Gravity and the Big Bang"
http://arxiv.org./astro-ph/0309478
dated 17 September 2003, briefly summarizes how
LQG can serve to cure the big bang singularity and
motivate inflationary expansion. Short and less technical
than the other two papers.

Martin Bojowald and Kevin Vandersloot
"Loop Quantum Cosmology, Boundary Proposals, and Inflation"
http://arxiv.org/gr-qc/0303072
dated 19 March 2003

Shinji Tsujikawa, Parampreet Singh, Roy Maartens
"Loop quantum gravity effects on inflation and the CMB"
http://arxiv.org/astro-ph/0311015
from the Tsujikawa/Singh/Maartens abstract:
"In loop quantum cosmology, the universe avoids a big bang singularity and undergoes an early kinetic-dominated super-inflation phase, with a quantum-corrected Friedmann equation. As a result, an inflaton field is driven up its potential hill, thus setting the initial conditions for standard inflation. We show that this effect can raise the inflaton high enough to achieve sufficient e-foldings in the standard inflation era. We analyze the cosmological perturbations and show that loop quantum effects can leave a signature on the largest scales in the CMB, with some loss of power and running of the spectral index."

Viqar Husain and Oliver Winkler "On singularity resolution in quantum gravity"
http://arxiv.org/gr-qc/0312094
this is especially interesting because they duplicate LQC results (for example by Bojowald) using the older version of quantum gravity, ADM variables, quantized metric. Shows that the removal of the big bang singularity is "robust"---doesnt depend on using a particular formalism.

as a background reference for classical (non-quantum) cosmology:
Charles Lineweaver
"Inflation and the Cosmic Microwave Background"
http://arxiv.org/astro-ph/0305179
dated 12 May 2003

-----in case of category theory----

http://www.folli.uva.nl/CD/1999/library/pdf/barrwells.pdf
Barr is at McGill and Wells is at U Virginia
its >100 pages of lecture notes

http://www.dcs.ed.ac.uk/home/dt/CT/categories.pdf
these notes are by Daniele Turi at U. Edinburgh
they are based on Saunders Mac Lane book
"Categories for the working mathematician"[/QUOTE]

 

[marcus]

here are some recent conferences and other stuff (I still need to edit and bringh some of it up to date)
------recent conferences------

Strings meet Loops (Albert Einstein Institute, MPI-Potsdam) October 2003
http://www.aei-potsdam.mpg.de/events/stringloop.html

Loop Gravity Workshop (Mexico City) January 2004
http://www.nuclecu.unam.mx/~corichi/lqg.htm

International Conference on Gravity and Cosmology (India) January 2004
http://www.cusat.ac.in/icgc04/

Quantum Gravity Phenomenology, (40th annual Polish Winterschool in Theoretical Physics) February 2004
http://www.ws2004.ift.uni.wroc.pl/html.html


Loop/SpinFoam Conference (Marseille) May 2004
http://w3.lpm.univ-montp2.fr/~philippe/quantumgravitywebsite/
Baez report on it
http://math.ucr.edu/home/baez/week206.html


--------upcoming conferences------

General Relativity Conference (GR17) at Dublin 3 July 2004

http://www.dcu.ie/~nolanb/gr17.htm

more annoucements at
http://www.maths.qmul.ac.uk/wbin/GRnewsfind/conference?conference

Chris Isham's 60th Birthday conference
Imperial College London, around September 6-7th
for info go to the Imperial College site and click on
"Isham 60 Conference"
http://theory.ic.ac.uk/




------links to an unselective assortment of current work------

Ambjorn Jurkeiwicz Loll
http://arxiv.org./hep-th/0404156
"Emergence of a 4D World from Causal Quantum Gravity"


Carlo Rovelli and Winston Fairbairn
"Separable Hilbert space in loop quantum gravity"
http://arxiv.org/abs/gr-qc/0403047

John Baez
"Quantum Quandaries: A Category-Theoretic Perspective"
http://arxiv.org/quant-ph/0404040

Hendryk Pfeiffer has a new preprint on arxiv
called
"Quantum Gravity and the Classification of
Smooth Manifolds"
http://arxiv.org./gr-qc/0404088


Livine's thesis
http://arxiv.org/gr-qc/0309028

Girelli and Livine
"Quantizing speeds with the cosmological constant"
http://arxiv.org/gr-qc/0311032

Oriti's thesis
http://arxiv.org/gr-qc/0311066
"Spin Foam Models of Quantum Spacetime"

Karim Noui and Philippe Roche
"Cosmological Deformation of Lorentzian Spin Foam Models"
http://arxiv.org/gr-qc/0211109
The cosmological constant occurs in a number of recent quantum gravity papers, for instance the one by Girelli/Livine.

Velhinho "On the structure of the space of generalized connections"
http://arxiv.org/math-ph/0402060

Noui and Perez "Three dimensional loop quantum gravity: physical scalar product and spin foam models"
http://arxiv.org/gr-qc/0402110

Noui and Perez "Three dimensional loop quantum gravity: coupling to point particles"
http://arxiv.org/gr-qc/0402111

Noui and Perez "Dynamics of Loop Quantum Gravity and Spin Foam Models in Three Dimensions"
http://arxiv.org/gr-qc/0402112

Noui and Perez "Observability and Geometry in Three Dimensional Quantum Gravity"
http://arxiv.org/gr-qc/0402113

Freidel and Louapre "Ponzano-Regge model revisited, I."
http://arxiv.org/hep-th/0401076

Gambini and Pullin "Canonical Quantum Gravity..."
http://arxiv.org/gr-qc/0402062

Buffenoir, Henneaux, Noui, Roche
Hamiltonian Analysis of Plebanski Theory
http://arxiv.org./gr-qc/0404041
(spin foam, BF)

http://arxiv.org/abs/hep-th/0405036
Remarks on the black hole entropy and Hawking spectrum in Loop Quantum Gravity
Authors: A. Alekseev, A.P. Polychronakos, M. Smedback
Report-no: CCNY-HEP-04/3, UUITP-13/04

In this note we reply to the criticism by Corichi concerning our proposal for an equidistant area spectrum in loop quantum gravity. We further comment on the emission properties of black holes and on the statistics of links.

A new one by Livine and Oriti
http://arxiv.org/gr-qc/0405085


----------fundamental constants, Planck units, time-keeping-------

Historical source for Planck units, the 1899 paper (thanks arivero!)
http://www.bbaw.de/bibliothek/digital/struktur/10-sitz/1899-1/jpg-0600/00000494.htm

In December 2003, the National Institute of Standards and Technology (NIST) posted new CODATA recommended values for the basic Planck units

http://physics.nist.gov/cuu/Constants/

choose "universal" from the menu to find (among other things) the recommended values of
planck mass
planck length
planck time
planck temperature

A 1997 article on timekeeping, discussing GR effects allowed-for in the GPS
http://www.allanstime.com/Publications/DWA/Science_Timekeeping/TheScienceOfTimekeeping.pdf

------prospects for testing quantum gravity observationally------

Floyd Stecker
"Cosmic Physics: the High Energy Frontier
http://arxiv.org/astro-ph/0309027
dated September 2003

Stecker discusses the various earth-based and orbital instruments, currently operating, or under construction, or planned, or proposed, and the kind of data becoming available. Among many other things he discusses GLAST, planned to start operating 2007, which, if there are tiny energy-dependent differences in speed among gamma-ray-burst photons, may be able to detect same. Also discusses neutrino observation.

-------science journalism----
"The Duel: Strings versus loops"
http://arxiv.org/abs/physics/0403112

A translation of Rudy Vaas' article in the German
science magazine "Bild der Wissenschaft" roughly
comparable to the "Scientific American"

========
simply to have this link on LaTex handy:
https://www.physicsforums.com/misc/howtolatex.pdf
quotes about physics:
http://www.angelo.edu/faculty/kboudrea/cheap/cheap2_physics.htm
Michael Flohr's great set of notes on group theory in physics:
http://www.itp.uni-hannover.de/~flohr/lectures
(scroll down to "Physical Applications of Group Theory")

 

[marcus]

A Secret Tunnel Through The Horizon

http://arxiv.org/hep-th/0405160
Maulik K. Parikh
A Secret Tunnel Through The Horizon
(First prize in the Gravity Research Foundation Essay Competition)
7 pages

 

[marcus]

A poster on SPR named Chris Weed has noted Parikh's paper and recommended it, together with another that has recently appeared
http://arxiv.org/gr-qc/0405111

some more new ones:

http://arxiv.org/hep-th/0405183
"No black hole information puzzle in a relational universe"
Rodolfo Gambini, Rafael Porto, Jorge Pullin
4 pages

http://arxiv.org/gr-qc/0405119
"Automorphism covariant representations of the holonomy-flux *-algebra"
Andrzej Okolow, Jerzy Lewandowski
32 pages


Lewandowski/Okolow abstract: "We continue an analysis of representations of cylindrical functions and fluxes which are commonly used as elementary variables of Loop Quantum Gravity. We consider an arbitrary principal bundle of a compact connected structure group and following Sahlmann's ideas define a holonomy-flux *-algebra whose elements correspond to the elementary variables. There exists a natural action of automorphisms of the bundle on the algebra; the action generalizes the action of analytic diffeomorphisms and gauge transformations on the algebra considered in earlier works. We define the automorphism covariance of a *-representation of the algebra on a Hilbert space and prove that the only Hilbert space admitting such a representation is a direct sum of spaces L^2 given by a unique measure on the space of generalized connections. This result is a generalization of our previous work (Class. Quantum. Grav. 20 (2003) 3543-3567, gr-qc/0302059) where we assumed that the principal bundle is trivial, and its base manifold is R^d."

 

[marcus]

the topcite 50+ feature at Spires

there is a handy utility at Spires that I just learned about today
namely a feature of their search engine that is especially
designed to find highly cited papers. It is at:

http://www.slac.stanford.edu/spires/hep/

to illustrate, suppose you want to find influential or highly cited papers by Jan Ambjorn.
Ambjorn is the "dynamical triangulations" researcher at Niels Bohr inst. and at Utrecht, who has published recently with Renate Loll. ("Emergence of a 4D World from Causal Quantum Gravity")

In the main search field if you type
find a ambjorn and topcite 50+

then it will list those of Jan Ambjorn's papers which have received 50 or more citations to date

It turns out he has authored 34 papers which topped 50 citations.

Or you can say "topcite 100+" to restrict the search still further,
and find several of Ambjorn's papers which have topped 100.

The search engine takes several different formats and for one of them instead of saying "find a thiemann" you have to say
"find author thiemann". but the default seems to be use the letter A to stand for author.

 

[jeff]

there is a handy utility at Spires that I just learned about today
namely a feature of their search engine that is especially
designed to find highly cited papers. It is at:

http://www.slac.stanford.edu/spires/hep/

In the main search field if you type
find author ambjorn and topcite 50+

then it will list Jan Ambjorn's papers which have received 50 or more
citations to date

or you can say "topcite 100+" to restrict the search still further.

Ambjorn is the "dynamical triangulations" researcher at Niels Bohr inst. and at Utrecht, who has published recently with Renate Loll. ("Emergence of a 4D world...")

It turns out Ambjorn has published several "100+" citations papers.

This is an lqg thread. Of course maybe your posting this because you now believe lqg is wrong and you've decided to change religions.

 

[marcus]

A new PF poster named setAI pointed out a good 6-page essay by Lee Smolin today, so I will add it to this collection of links:

Sample from page 5:
"The debate between proponents of background-dependent and background independent theories is in fact just the modern version of an ancient debate. Since the Greeks, the argument has raged between those who believed that space and time have an eternally fixed, absolute character and those who thought space and time are no more than relations between events that themselves evolve in time. Plato, Aristotle, and Newton were absolutists. Heraclites, Democritus, Leibniz, Mach, and Einstein were relationalists. When we demand that the quantum theory of gravity be background-independent, we are saying we believe that the triumph that general relativity represented for the relational point of view is final and will not be reversed.


Much of the argument between string and loop theorists is a continuation of this debate. Most string theorists were trained as elementary-particle physicists and worked their whole lives in a single fixed spacetime. Many of them have never even heard of the relational/absolute debate, which is the basic historical and philosophical context for Einstein's work. Most people who work in loop quantum gravity do so because at some point in their education they understood the relational, dynamical character of spacetime as described in general relativity, and they believe in it. They don't work on string theory because they cannot take seriously any candidate for a quantum theory of gravity that is background-dependent and hence loses (or at best hides) the relational, dynamical character of space and time."
http://www.edge.org/3rd_culture/smolin03/smolin03_p5.html

It is a good essay because it combines a clearsighted overview with a personal insider's take, and also tells the history of this approach to quantum gravity from a participant's perspective.


Sample from page 3:
"Loop quantum gravity started in the early 1980s with some discoveries about classical general relativity by Amitaba Sen, then a postdoc at the University of Maryland. These were made into a beautiful reformulation of Einstein's theory by Abhay Ashtekar, then at Syracuse University and now director of the Center for Gravitational Physics at Penn State—a reformulation that brought the mathematical and conceptual language we use to describe space and time closer to the language used in particle physics and quantum physics."
http://www.edge.org/3rd_culture/smolin03/smolin03_p3.html

Another quote from page 5:
"Another reason that string theory cannot be the final word is that in string theory one studies strings moving in a fixed classical spacetime. Thus, string theory is what we call a background-dependent approach. It means that one defines the strings as moving in a fixed space and time. This may be a useful approximation, but it cannot be the fundamental theory. One of the fundamental discoveries of Einstein is that there is no fixed background. The very geometry of space and time is a dynamical system that evolves in time. The experimental observations that energy leaks from binary pulsars in the form of gravitational waves—at the rate predicted by general relativity to the unprecedented accuracy of eleven decimal places—tells us that there is no more a fixed background of spacetime geometry than there are fixed crystal spheres holding the planets up. The fundamental theory must unify quantum theory with a completely dynamical description of space and time. It must be what we call a background-independent theory. Loop quantum gravity is such a one; string theory is not."
http://www.edge.org/3rd_culture/smolin03/smolin03_p5.html

From page 6:
"So while I disagree with the leading string theorists about methodology, this hasn't kept me from working on string theory. After all, they don't own it; its open problems are there for anyone to try to solve. So I decided a few years ago to ignore their advice and try to construct the background independent form of M theory. In the process of inventing loop quantum gravity, we gained a lot of knowledge about how to make quantum theories of space and time that are background-independent."
http://www.edge.org/3rd_culture/smolin03/smolin03_p6.html

the essay seems to have been written in latter half of 2003, so is fairly recent.
thanks to setAI for flagging this one

 

[selfAdjoint]

Thinking about all this LQG vs. string business, I wonder if the "beauitiful reformulation" of Ashtekar isn't like the "beautiful reformulation of string theory" of Schwartz and Witten that has motivated so much string research. I am wondering whether in the final analysis, beauty is all it's cracked up to be as a search strategy.

The two great historical exemplars of beauty first were Einstein and Dirac. In each case their approach achieved a great success early but then led them into unproductive wastelands. And it is at least arguable that both string physics and LQG research in the Ashtekar tradition are right now spinning their wheels. Maybe it's time for a younger generation, playing Feynman and Dyson to the Witten - Ashtekar version of Einstein-Dirac to have their say. Which is why I am very interseted in the AJL paper, a possibly rough hewed (remember Feyman's early rep?) but undoubtedly novel approach to the problem of background independent quantum mechanics (and THAT, not just quantum gravity is the big kahuna).

This post is possibly not in line with your intent to have this as a colllection of documents, but I just couldn't resist, seeing the same old same old out of Smolin being posted once again.

 

[marcus]

Thinking about all this LQG vs. string business,...

...Which is why I am very interseted in the AJL paper, a possibly rough hewed (remember Feyman's early rep?) but undoubtedly novel approach to the problem of background independent quantum mechanics (and THAT, not just quantum gravity is the big kahuna)...

Amen to that.
Background independent quantum mechanics is the big kahuna.

this turns up the lights on something that was creeping around the edges of my mind also

I'm very interested in the AJL dynamical triangulations approach too. We could continue in the Marseille thread that Baez started (it is largely about AJL but Marseille was billed as a Loop+Foam conference---a lot of family resemblances: loop to foam and foam to simplicial QG---making too sharp distinctions could be a mistake.
Anyway, if we leave this thread as a catchbasket for LQG-and-related links we could followup on AJL etc at the Marseille thread if that suits you, or start a new one on the Big Kahuna!

 

[marcus]

Doubly Special Relativity, new paper by Kowalski-Glikman

http://arxiv.org/abs/hep-th/0405273

the title is "Introduction to DSR"
there was a Quantum Gravity symposium in poland
this February and Jerzy Kowalski-Glikman (the organizer) lectured on
DSR and its relation to QG

this paper was developed from his lectures at the Winterschool, and
submitted to Springer for publication in its "lecture notes in physics" series.

anything calling itself an Introduction could potentially
be useful.

the idea of DSR is that the usual minkowski space and lorentz group symmetries
of special relativity are what results from forcing c to be the same
for all observers
what if you force TWO physical quantities, not just the speed of light but also the Planck length or the Planck mass, to be the same for all observers.

----------------
more DSR news, this time from Alejandro's city of Zaragoza

just out:
http://arxiv.org/hep-th/0405285

Quantum Uncertainty in Doubly Special Relativity
Authors: Jose Luis Cortes, J. Gamboa
4 pages, no figures

The modification of the quantum mechanical commutators in a relativistic theory with an invariant length scale (DSR) is identified...

---------QG phenomenology-----
a new paper:

http://arxiv.org/quant-ph/0406007

"Could Energy Decoherence due to Quantum Gravity be observed?"
Christoph Simon, Dieter Jaksch
7 pages, no figures

Sample from abstract:
"It has recently been proposed that quantum gravity might lead to the decoherence of superpositions in energy, corresponding to a discretization of time at the Planck scale...
... We also show how local energy decoherence, which acts separately on system and phase reference, could be detected with remarkable sensitivity and over a wide range of length scales by long-distance Ramsey interferometry with metastable atomic states. The sensitivity of the experiments can be further enhanced using multi-atom entanglement."

 

[marcus]

the Spires database is an amazing resource for keeping track of activity in various research lines and seeing what topics are attracting interest

several links within that site have proven useful (for me) recently

Here is the 2003 edition of the topcites for all categories, gr-qc as well as hep-th and the rest
http://www.slac.stanford.edu/library/topcites/2003/eprints/index.shtml

Here is the general index for topcites for all the years 1992-2003:
http://www.slac.stanford.edu/library/topcites/

I posted earlier another special Spires feature which let's you find the most-cited papers by a particular author. To use it you need to know that in their code the letter A stands for author, so you say "a ambjorn" to find papers authored by ambjorn.

there is a handy utility at Spires that I just learned about today
namely a feature of their search engine that is especially
designed to find highly cited papers. It is at:

http://www.slac.stanford.edu/spires/hep/

to illustrate, suppose you want to find influential or highly cited papers by Jan Ambjorn.
Ambjorn is the "dynamical triangulations" researcher at Niels Bohr inst. and at Utrecht, who has published recently with Renate Loll. ("Emergence of a 4D World from Causal Quantum Gravity")

In the main search field if you type
find a ambjorn and topcite 50+

then it will list those of Jan Ambjorn's papers which have received 50 or more citations to date

It turns out he has authored 34 papers which topped 50 citations.

Or you can say "topcite 100+" to restrict the search still further,
and find several of Ambjorn's papers which have topped 100.

The search engine takes several different formats and for one of them instead of saying "find a thiemann" you have to say
"find author thiemann". but the default seems to be use the letter A to stand for author.

lot of good information to get out of Spires, bravo to Stanford and SLAC for hosting it, I feel I've just scratched the surface

 

[marcus]

PAM Dirac was (one of) the first to try
to construct a quantum version of
General Relativity------to quantize gravity.
So this thread being for LQG links we should have a Dirac link
and Pelastration just supplied one with two photos of Dirac and
a newspaper interview

http://faculty.rmwc.edu/tmichalik/dirac.htm

 

[marcus]

cant recommend but thought it interesting enough to keep tabs on


"Toward a Background Independent Quantum Theory of Gravity"
Authors: Vishnu Jejjala, Djordje Minic, Chia-Hsiung Tze
Comments: Awarded Honorable Mention, 2004 Gravity Research Foundation Essay Competition; 8 pages

http://arxiv.org/gr-qc/0406037

 

[marcus]

This just appeared on arXiv today.
It looks like a keeper:

http://arxiv.org/gr-qc/0406042

"Oscillatory Universes in Loop Quantum Cosmology and Initial Conditions for Inflation"
James E. Lidsey, David J. Mulryne, N. J. Nunes, Reza Tavakol
6 pages, 4 figures

Several of them wrote a paper with Martin Bojowald that posted a couple of months back. Otherwise I don't recall seeing their names before

 

[marcus]

Rovelli has redone his homepage.

The book is planned to hit the bookstores in October

there is a picture of the book and a link to the Cambridge U. P.
catalog entry for it
planned price is 45 pounds sterling
the draft is still available free at his site, by agreement with C.U.P.

He mentions another piece of writing---popular----
called "What is space? What is time?"
so far just in Italian. I would guess there will be an English version

If you want to look for it in Italian (which I understand some people can read) the title is
Che cos' e lo spazio? Che cos' e il tempo?

Rovelli homepage:
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html

 

[Olias]

Rovelli has redone his homepage.

The book is planned to hit the bookstores in October

there is a picture of the book and a link to the Cambridge U. P.
catalog entry for it
planned price is 45 pounds sterling
the draft is still available free at his site, by agreement with C.U.P.

He mentions another piece of writing---popular----
called "What is space? What is time?"
so far just in Italian. I would guess there will be an English version

If you want to look for it in Italian (which I understand some people can read) the title is
Che cos' e lo spazio? Che cos' e il tempo?

Rovelli homepage:
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html

Thanks Marcus, its a must buy!

I like the cover of the book, the use of Geometry is very evident.

The cover outline is framed with precise measurment at its edge, with the Backgound uniform colour.

As one moves inward the Author and Title are framed by a 'casimir-effect'..and a sea of points 'Quantum-Background' are pretty hazy?

Cool1

 

[sol2]

http://assets.cambridge.org/0521837332/cover/0521837332.jpg

Quantum gravity is perhaps the most important open problem in fundamental physics. It is the problem of merging quantum mechanics and general relativity, the two great conceptual revolutions in the physics of the twentieth century. The loop and spinfoam approach, presented in this book, is one of the leading research programs in the field. The first part of the book discusses the reformulation of the basis of classical and quantum Hamiltonian physics required by general relativity. The second part covers the basic technical research directions. Appendices include a detailed history of the subject of quantum gravity, hard-to-find mathematical material, and a discussion of some philosophical issues raised by the subject. This fascinating text is ideal for graduate students entering the field, as well as researchers already working in quantum gravity. It will also appeal to philosophers and other scholars interested in the nature of space and time.

http://titles.cambridge.org/catalogue.asp?isbn=0521837332

It will be a must buy for myself as well.

But I wonder about the issue of quantum geometry. How will this be formulated into the LQG perspective, as it has in strings?

The Elegant Universe, by Brian Greene, pg 231 and Pg 232

"But now, almost a century after Einstein's tour-de-force, string theory gives us a quantum-mechanical discription of gravity that, by necessity, modifies general relativity when distances involved become as short as the Planck length. Since Reinmannian geometry is the mathetical core of general relativity, this means that it too must be modified in order to reflect faithfully the new short distance physics of string theory. Whereas general relativity asserts that the curved properties of the universe are described by Reinmannian geometry, string theory asserts this is true only if we examine the fabric of the universe on large enough scales. On scales as small as Planck length a new kind of geometry must emerge, one that aligns with the new physics of string theory. This new geometry is called, quantum geometry."

I am seeing similarities arising not only from this perspective but from the current link Marcus supplied on the cosmological association (LQC ).

 

[marcus]

Olias and Sol2, I too am glad to see "Quantum Gravity" well on its
way to being available, and I will certainly buy a copy although
45 pounds sterling is a fair-size chunk of cash.

It was thoughtful of Carlo to work out an agreement with Cambridge where
the publisher will allow him to keep a draft version available free online at his website. that way if someone can't afford the book they can at least get the draft and print it out at home, or just keep it on the computer---which is already pretty useful.

speculation is always risky but I am speculating that because it's a fast-moving field there will be several editions of this book
what is coming out this year (planned for October) will be the first edition
but----with ongoing developments in quantum cosmology and the simplicial or "dynamical triangulations" approach, and whatever else (so hard to predict)----there may be a second edition, and possibly others as years go along.
and then the draft on rovelli's website will be a kind of "zero-th edition".

my favorite page in the draft version of the book is page 7---the part about the whale. I also like some things around page 52
I also really like the philosophical essays at the end
and the historical accounts

although it has a lot for the general reader, the book is primarily for graduate students looking for PhD thesis work to do and for established researchers wanting to move into the field of QG.
That is to say, it has generally accessible portions (which are admirable and enlightening, in my opinion) but also (in case other people besides Olias and Sol2 are reading this thread I want to stress) plenty that is not so accessible.

 

[marcus]

...

But I wonder about the issue of quantum geometry. How will this be formulated into the LQG perspective, as it has in strings?

The Elegant Universe, by Brian Greene, pg 231 and Pg 232

"But now, almost a century after Einstein's tour-de-force, string theory gives us a quantum-mechanical discription of gravity that, by necessity, modifies general relativity when distances involved become as short as the Planck length. Since Reinmannian geometry is the mathetical core of general relativity, this means that it too must be modified in order to reflect faithfully the new short distance physics of string theory. Whereas general relativity asserts that the curved properties of the universe are described by Reinmannian geometry, string theory asserts this is true only if we examine the fabric of the universe on large enough scales. On scales as small as Planck length a new kind of geometry must emerge, one that aligns with the new physics of string theory. This new geometry is called, quantum geometry."
...

this quote is very interesting and raises an important issue. maybe we will eventually have a thread devoted to it. for starters
how about going to arXiv and putting "quantum geometry"
into the abstract box
and doing a search for articles that say "quantum geometry" in their
abstract summary
It would give an idea of what the experts mean by it, in a technical sense.

Also in the title box, for the arXiv search engine. To find whatever
books and articles have been written about quantum geometry have that in the title. (I know some, but most likely not all.)

I am not promising that a good thread would come of this, or a clear resolution of how the term is used, even. but it is something to think about

 

[selfAdjoint]

Putting "quantum geometry" in the latest year search at hep-th brought up four papers, all of which used Quantum Geometry as a synonym for the Ashtekar program, aka LQG.

 

[marcus]

Putting "quantum geometry" in the latest year search at hep-th brought up four papers, all of which used Quantum Geometry as a synonym for the Ashtekar program, aka LQG.

go back to earlier papers
there is completely different stuff called quantum geometry
I seem to recall Majid using the term
and maybe Connes
most likely others

no clear connection with string tho
I think maybe Brian Greene was fantasizing a little
or looking ahead to a desirable future, but could be wrong

the development of a quantum geometry has to come but
may have no clear connection with string IMHO

 

[sol2]

this quote is very interesting and raises an important issue. maybe we will eventually have a thread devoted to it. for starters
how about going to arXiv and putting "quantum geometry"
into the abstract box
and doing a search for articles that say "quantum geometry" in their
abstract summary
It would give an idea of what the experts mean by it, in a technical sense.

Also in the title box, for the arXiv search engine. To find whatever
books and articles have been written about quantum geometry have that in the title. (I know some, but most likely not all.)

I am not promising that a good thread would come of this, or a clear resolution of how the term is used, even. but it is something to think about

The dimensional significance of this topic is really a difficult issue for myself as well, and the statistics really surpirsed me that you have offerred.

If such a geometry was to emerge what exactly are we describing? Jeff's comments in regard to supersymmetry are valid statements because of the complexity of the issue in regards to the metric. The complexity of points really seem to flow when you come to that level, yet it has encapsulated the ideas of dimension. So geometry has its work cut out for it no doubt.

What exactly is the hierarchy problem?The gist of it is that the universe seems to have two entirely different mass scales, and we don't understand why they are so different. There's what's called the Planck scale, which is associated with gravitational interactions. It's a huge mass scale, but because gravitational forces are proportional to one over the mass squared, that means gravity is a very weak interaction. In units of GeV [billions of electron volts], which is how we measure masses, the Planck scale is 10 to the 19th GeV. Then there's the electroweak scale, which sets the masses for the W and Z bosons. These are particles that are similar to the photons of electromagnetism and which we have observed and studied well. They have a mass of about 100 GeV. So the hierarchy problem, in its simplest manifestation, is how can you have these particles be so light when the other scale is so big.


I had mentioned in the topic of the new math thread, that such attempts at a discription woud have to be formulated in much the same way Smolin did? Klein's Ordering of geometries is really quite interesting in terms of Quantum Evolution?

Because we understand this dynamical movement in plasmatic features as supersymmetical conisderation one would have to understand how gravity moves to supergravity. If we understand the gravity field can have its differences( dimensional relationship?) then how we look at the Q<--->Q measure becomes a interesting relation in terms of understanding the metric in a different way.

ds2 = (cdt)2 - dl2

On a cosmological level this directs my attention, yet I recognize the complexity of the movement in the quantum world. Why classically does this not fit at that quantum level and what do we have to reconsider here?


Do you understand how this subject might evolve in this context?

 

[marcus]

...But I wonder about the issue of quantum geometry. How will this be formulated into the LQG perspective, as it has in strings?

The Elegant Universe, by Brian Greene, pg 231 and Pg 232

"But now, almost a century after Einstein's tour-de-force, string theory gives us a quantum-mechanical discription of gravity that, by necessity, modifies general relativity when distances involved become as short as the Planck length. Since Reinmannian geometry is the mathetical core of general relativity, this means that it too must be modified in order to reflect faithfully the new short distance physics of string theory. Whereas general relativity asserts that the curved properties of the universe are described by Reinmannian geometry, string theory asserts this is true only if we examine the fabric of the universe on large enough scales. On scales as small as Planck length a new kind of geometry must emerge, one that aligns with the new physics of string theory. This new geometry is called, quantum geometry."
...

hi Sol2, you copied in this Brian Greene quote which could be the start of a new thread so I started one, and hope we can continue the discussion there (in a harmonious fashion! I might add.)

 

[marcus]

links for loop/foam/simplicial QG preprint numbers

there is no collective name for the group of background independent QG approaches aimed at quantizing GR
Ashtekar says Quantum Geometry, but means Loop
Thiemann says Canonical Quantum General Relativity, but means Loop
Gambini says Canonical Quantum Gravity, meaning his type of Loop
the most widely used term is Loop---LQG for short
Ashtekar and Lewandowski recently used Background Independent Q.G.
in a review article, meaning Loop

then there are closely allied approaches called Spin Foam
and Simplicial Quantum Gravity (dynamical triangulations in particular)
and one of the Simplicial people has used the term Quantum Geometry
but it does not mean exactly the same as what Ashtekar means

these approaches got together at the May 2004 "loop/foam conference"
but there is no agreed on collective noun

So I have tried to construct a keyword search in arXiv that would turn up these things and this seems to work. Here are numbers of preprints
by year 1992-present.


Year 1992:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/1992/0/1

Year 1993:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/1993/0/1

Year 1994:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/1994/0/1

Year 1995:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/1995/0/1

Year 1996:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/1996/0/1

Year 1997:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/1997/0/1

Year 1998:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/1998/0/1

Year 1999:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/1999/0/1

Year 2000:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/2000/0/1

Year 2001:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/2001/0/1

Year 2002:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/2002/0/1

Year 2003:
http://arXiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/2003/0/1

Last twelve months (e.g. 14 June 2003 to 14 June 2004):
http://lanl.arXiv.org/find/nucl-ex,...am+AND+dynamical+triangulation/0/1/0/past/0/1

this is designed to catch:

loop quantum gravity
loop quantum cosmology
canonical quantum gravity
simplicial quantum gravity
nonperturbative quantum gravity
spin foam
dynamical triangulation

[EDIT afterthought]
BTW Rovelli has a new paper out on arXiv, together with Oriti and Speziale.
predictably, the last link in the above search list turned it up
http://arxiv.org/gr-qc/0406063
"...The model sheds light also on several other features of spinfoam quantum gravity: the reality of the partition function; the geometrical interpretation of the Newton constant; and the fact that the partition function of general relativity is finite in spite of the divergence of the BF one."

Here is a more inclusive version of the above search:


2001:
http://lanl.arxiv.org/find/nucl-ex,...D+spin+foam+AND+doubly+special/0/1/0/2001/0/1

2002:
http://arXiv.org/find/nucl-ex,astro...D+spin+foam+AND+doubly+special/0/1/0/2002/0/1

2003:
http://arXiv.org/find/nucl-ex,astro...D+spin+foam+AND+doubly+special/0/1/0/2003/0/1


Last Twelve Months:
http://arXiv.org/find/nucl-ex,astro...D+spin+foam+AND+doubly+special/0/1/0/past/0/1
------------------

http://arxiv.org/find/nucl-ex,astro...am+AND+dynamical+triangulation/0/1/0/past/0/1

another Loop quantum cosmology paper at arxiv today. the page of links needs to be brought up to date:
Qualitative Approach to Semi-Classical Loop Quantum Cosmology
G.V. Vereshchagin
http://arxiv.org/abs/gr-qc/0406108

 

[marcus]

refreshing the link-basket

this thread is serving as a surrogate sticky for useful loop-and-related quantum gravity links
I update it periodically.

to get a picture of QG developments in the first half of 2004 it is helpful to quote Baez post after the May 2004 marseille conference:

I just got back from the Marseille conference on loop quantum gravity and spin foams:

http://w3.lpm.univ-montp2.fr/~philippe/quantumgravitywebsite/

It was really great, so I devoted "week206" of my column This Week's Finds entirely to this conference:

http://math.ucr.edu/home/baez/week206.html

In particular, I spend a lot of time giving a very simple nontechnical introduction to the recent work of Ambjorn, Jurkiewicz and Loll in which they seem to get a 4d spacetime to emerge from a discrete quantum model - something that nobody had succeeded in doing before!

http://www.arXiv.org/abs/hep-th/0404156

I hope this lays to rest certain rumors here that I'd burnt out on quantum gravity.

a key paper mentioned here
Ambjorn Jurkiewicz Loll
"Emergence of a 4D World from Causal Quantum Gravity"
http://www.arXiv.org/abs/hep-th/0404156

other key papers, connecting quantum gravity with outgrowths of DSR namely "DDSR" or "TSR" (smolin's name: triply special relativity) and moffat's NGT an outgrowth of MOND

Kowalski-Glikman, Smolin
"Triply Special Relativity"
http://arxiv.org/abs/hep-th/0406276

Girelli Livine Oriti
"Deformed Special Relativity as an effective flat limit of quantum gravity"
http://arxiv.org/gr-qc/0406100

Moffat
Modified Gravitational Theory as an Alternative to Dark Energy and Dark Matter
http://arxiv.org/astro-ph/0403266

another interesting development, resolution of the "Black Hole Information Paradox" using relational time----a quantum mechanical clock rather than absolute ideal time

Gambini Porto Pullin
"Realistic clocks, universal decoherence and the black hole information paradox"
http://arxiv.org/abs/hep-th/0406260

also their earlier paper
“No black hole information puzzle in a relational universe,”
http://arxiv.org/hep-th/0405183 .

it is interesting that this information-loss paradox has been worked on rather hard by some wellknown stringy people like Susskind and, it seems, Maldacena--but in stringy context it is still a challenging outstanding problem which people are working on. So it is a bit of a coup to resolve it as GPP do, to resolve it at all would be respectable and they do it, as well, with apparent ease and not a lot of mess.

 

[marcus]

Since this thread is a linkbasket for links to recent LQG stuff that might be useful I will put these recent things here:


Penrose book is about LQG to some degree. "The Road to Reality"
It came out in July.

Carlo Rovelli book "Quantum Gravity" is coming out in Fall 2004 from Cambridge Uni Press. this is the first comprehensive LQG graduate-level textbook.
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html

Lee Smolin has posted "An Invitation to Loop Quantum Gravity" a 50-page survey and intro with FAQ for physicists in other fields who want to switch fields and do QG research. http://arxiv.org/hep-th/0408048
"Invitation" is intended for Reviews of Modern Physics.

John Baez gave an introduction and survey at the Dublin GR17 conference, which is available online at Baez site.
"Loop Quantum Gravity, Quantum Geometry and Spin Foams"
http://math.ucr.edu/home/baez/lectures.html#lqg

"Quantum Gravity Phenomenology" was the topic of the Winterschool-2004 (WS-2004) symposium this year, 4-14February, a 10-day conference on the initial and planned efforts to test QG by empirical observation.
http://ws2004.ift.uni.wroc.pl/html.html
click on lectures if you want slides from the various talks given at WS-2004

Observational tests of QG have already had a considerable impact as discussed by Smolin in the "Invitation" survey article starting page 27.
LQG is rapidly reaching a point where it can guide experiment---if one counts certain kinds of astronomical observation as experiment.

Cambridge Uni Press is also publishing "Universe or Multiverse" which will contain a chapter by Smolin called "Scientific Alternatives to the Anthropic Principle" where he offers an evolutionary Multiverse hypothesis that generates testable (numerical) predictions and therefore has meaning as a part of science.
http://arxiv.org/hep-th/0407213
Smolin's Multi is falsifiable, using today's tools.

------------------
In his recent paper Smolin cites "personal communication" from Martin Bojowald regarding work on eliminating the Black Hole singularity (by the appropriate quantization of gravity). So far Bojowald has only published his preliminary work on this, not the final result:

Martin Bojowald
Spherically Symmetric Quantum Geometry: States and Basic Operators
http://arxiv.org/abs/gr-qc/0407017
26 pages

"The kinematical setting of spherically symmetric quantum geometry, derived from the full theory of loop quantum gravity, is developed. This extends previous studies of homogeneous models to inhomogeneous ones where interesting field theory aspects arise. A comparison between a reduced quantization and a derivation of the model from the full theory is presented in detail, with an emphasis on the resulting quantum representation. Similar concepts for Einstein-Rosen waves are discussed briefly."

Martin Bojowald and Rafal Swiderski
The Volume Operator in Spherically Symmetric Quantum Geometry
http://arxiv.org/abs/gr-qc/0407018
25 pages

"The spherically symmetric volume operator is discussed and all its eigenstates and eigenvalues are computed. Even though the operator is more complicated than its homogeneous analog, the spectra are related in the sense that the larger spherically symmetric volume spectrum adds fine structure to the homogeneous spectrum. The formulas of this paper complete the derivation of an explicit calculus for spherically symmetric models which is needed for future physical investigations."


http://arxiv.org/hep-th/0407115
Loop Quantum Gravity and the Cyclic Universe
Martin Bojowald, Roy Maartens, Parampreet Singh
6 pages

"Loop quantum gravity introduces strong non-perturbative modifications to the dynamical equations in the semi-classical regime, which are responsible for various novel effects, including resolution of the classical singularity in a Friedman universe. Here we investigate the modifications for the case of a cyclic universe potential, assuming that we can apply the four-dimensional loop quantum formalism within the effective four-dimensional theory of the cyclic scenario. We find that loop quantum effects can dramatically alter the near-collision dynamics of the cyclic scenario. In the kinetic-dominated collapse era, the scalar field is effectively frozen by loop quantum friction, so that the branes approach collision and bounce back without actual collision."

--------------------

Representations of the Weyl Algebra in Quantum Geometry
Christian Fleischhack
63 pages
http://arxiv.org/abs/math-ph/0407006

substantial progress beyond where this was taken by Hanno Sahlmann, Thiemann, Lewandowski, Okolow. It may be that Fleishhack has reached to goals set by this earlier work

----------------------

In the next post, Meteor calls attention to the work of Date and Hossain
who showed that both Inflation and the Big Bounce were generic in isotropic LQC. I think Meteor mentioned two of their three recent papers and I will add the other one for completeness:
"Genericity of Big Bounce in isotropic loop quantum cosmology"
http://arxiv.org/gr-qc/0407074

 

[meteor]

http://arxiv.org/abs/gr-qc/0407073
Effective Hamiltonian for Isotropic Loop Quantum Cosmology

http://arxiv.org/abs/gr-qc/0407069
Genericity of inflation in isotropic loop quantum cosmology

http://arxiv.org/abs/hep-th/0407072
Corrections to the Planck's radiation law from loop quantum gravity



I've been looking quickly the third article, and apart of a proposed modification of Planck's law, there's also a proposed modification for Wien's displacement law

 

[marcus]

this thread is serving as a surrogate sticky for useful loop-and-related quantum gravity links
I update it periodically.

for a concise and up-to-date survey of LQG and allied approaches see
John Baez talk at Dublin, given Tuesday 20July2004:

Loop Quantum Gravity, Quantum Geometry and Spin Foams

It is online at his website
http://math.ucr.edu/home/baez/lectures.html#lqg

For more QG developments in the first half of 2004 here is Baez post after the May 2004 marseille conference:

I just got back from the Marseille conference on loop quantum gravity and spin foams:

http://w3.lpm.univ-montp2.fr/~philippe/quantumgravitywebsite/

It was really great, so I devoted "week206" of my column This Week's Finds entirely to this conference:

http://math.ucr.edu/home/baez/week206.html

In particular, I spend a lot of time giving a very simple nontechnical introduction to the recent work of Ambjorn, Jurkiewicz and Loll in which they seem to get a 4d spacetime to emerge from a discrete quantum model ---something that nobody had succeeded in doing before!

http://www.arXiv.org/abs/hep-th/0404156

I hope this lays to rest certain rumors here that I'd burnt out on quantum gravity.

a key paper mentioned here
Ambjorn Jurkiewicz Loll
"Emergence of a 4D World from Causal Quantum Gravity"
http://www.arXiv.org/abs/hep-th/0404156

-----------------
for me, one of the most enlightening things that has come online recently is the slides from a talk Lee Smolin gave in Poland in February at the Winterschool WS-2004. This was a 10-day symposium and the topic this year was Quantum Gravity Phenomenology
there were talks by a dozen or so experts and they are online at the WS-2004 site. Smolin gave 3 lectures and it is the third I found especially interesting.
http://ws2004.ift.uni.wroc.pl/html.html
click on lectures and scroll down to Smolin's three.

-------------------
Roger Penrose's new book "The Road to Reality" just appeared at the bookstores. It is 1000 pages. Key ideas were presented at his public lecture "Fashion, Faith, Fantasy in Modern Physics" at Dublin last week. Also last October Penrose gave 3 evening lectures on these three themes at Princeton, they are online to listen, with sketchy video.

http://www.princeton.edu/WebMedia/lectures/
scroll down to October 2003 and find the three lectures by Penrose
-----------------------------

A number of papers have appeared recently connecting quantum gravity with extensions of Special Relativity. Examples are outgrowths of DSR such as "DDSR" or "TSR" (smolin's name: triply special relativity). Another aspect involves moffat's NGT an outgrowth of MOND

Kowalski-Glikman, Smolin
"Triply Special Relativity"
http://arxiv.org/abs/hep-th/0406276

Girelli Livine Oriti
"Deformed Special Relativity as an effective flat limit of quantum gravity"
http://arxiv.org/gr-qc/0406100

Moffat
Modified Gravitational Theory as an Alternative to Dark Energy and Dark Matter
http://arxiv.org/astro-ph/0403266

another interesting development, resolution of the "Black Hole Information Paradox" using relational time----a quantum mechanical clock rather than absolute ideal time

Gambini Porto Pullin
"Realistic clocks, universal decoherence and the black hole information paradox"
http://arxiv.org/abs/hep-th/0406260

also their earlier paper
“No black hole information puzzle in a relational universe,”
http://arxiv.org/hep-th/0405183 .

this is a very incomplete listing of what has recently become available online, by way of Loop-and-related QG sources.

I really should mention Leonardo Modesto removing the Black Hole singularity before posting this.
http://arxiv.org/gr-qc/0407097
Disappearance of the Black Hole Singularity in Quantum Gravity

Also the popular series of 3 articles on LQG by Rudy Vaas (translated from German by Amitabha Sen and Martin Bojowald)


Beyond Space And Time
Ruediger Vaas
7 pages, English translation of "Jenseits von Raum und Zeit"
http://arxiv.org/physics/0401128

The Duel: Strings versus Loops
Ruediger Vaas
10 pages, English translation of "Das Duell: Strings gegen Schleifen"
http://arxiv.org/physics/0403112

The Inverted Big-Bang
Ruediger Vaas
8 pages, English translation of "Der umgestuelpte Urknall"
http://arxiv.org/physics/0407071

a more accurate translation of the title would be
"the turned-inside-out Big Bang" or "the everted Big Bang"
in Loop Quantum Cosmology the volume element gets
turned inside out at the moment of the quantum bounce
where there used to be a singularity

Should also include the recalculation of the Immirzi parameter by
Domagala, Lewandowski, and Meissner
"Black Hole Entropy from Quantum Geometry"
http://arxiv.org/gr-qc/0407051
"Black Hole Entropy in Loop Quantum Gravity"
http://arxiv.org/gr-qc/0407052