Our picks for third quarter 2009 MIP (most important QG paper)

[marcus]

Of these nine candidates, please indicate the paper or papers which you think will contibute most significantly to future research in 4D quantum gravity. Multiple choice is possible in the poll, so pick several if you wish.

http://arxiv.org/abs/0909.4221 Ashtekar, Campiglia, Henderson
http://arxiv.org/cits/0909.4221 Loop Quantum Cosmology and Spin Foams

http://arxiv.org/abs/0909.3426 't Hooft
http://arxiv.org/cits/0909.3426 Quantum Gravity without Space-time Singularities or Horizons

http://arxiv.org/abs/0909.3265 Benedetti, Machado, Saueressig
http://arxiv.org/cits/0909.3265 Four-Derivative Interactions in Asymptotically Safe Gravity

http://arxiv.org/abs/0909.0939 Lewandowski, Kamiński, Kisielowski
http://arxiv.org/cits/0909.0939 Spin-Foams for All Loop Quantum Gravity

http://arxiv.org/abs/0908.4476 Christensen, Khavkine, Livine, Speziale
http://arxiv.org/cits/0908.4476 Sub-leading Asymptotic Behaviour of Area Correlations in the Barrett-Crane Model

http://arxiv.org/abs/0907.4323 Dittrich, Bahr
http://arxiv.org/cits/0907.4323 Improved and Perfect Actions in Discrete Gravity

http://arxiv.org/abs/0907.4238 Woodard
http://arxiv.org/cits/0907.4238 How Far Are We from the Quantum Theory of Gravity?

http://arxiv.org/abs/0907.4064 Krasnov
http://arxiv.org/cits/0907.4064 Gravity as BF Theory Plus Potential

http://arxiv.org/abs/0907.2440 Barrett, Dowdall, Fairbairn, Hellmann, Pereira
http://arxiv.org/cits/0907.2440 Lorentzian Spin Foam Amplitudes: Graphical Calculus and Asymptotics

I'll try to give a thumbnail for each one, and say why it might prove important. The list is most recent first so I'll review them in that order.

 

[marcus]

Brief thumbnail reviews. Most recent papers first.

http://arxiv.org/abs/0909.4221 Ashtekar, Campiglia, Henderson
http://arxiv.org/cits/0909.4221 Loop Quantum Cosmology and Spin Foams
Until now, Loop cosmo has not used the spinfoam approach, but has been based on a simplified version of canonical LQG. But in the full theory, spinfoam has become the principal way dynamics is handled, so it's time to link cosmology to spinfoam.

http://arxiv.org/abs/0909.3426 't Hooft
http://arxiv.org/cits/0909.3426 Quantum Gravity without Space-time Singularities or Horizons
't Hooft chose this for his annual Erice talk. Radical message: spacetime must be represented in the theory, conformal (scale) symmetries rule, and there's a conformal symmetry which turns black holes inside out. Total mind-blower.

http://arxiv.org/abs/0909.3265 Benedetti, Machado, Saueressig
http://arxiv.org/cits/0909.3265 Four-Derivative Interactions in Asymptotically Safe Gravity
The whole AsymSafe program depends on establishing the finite dimensionality of the hypersurface that is attracted towards the UV fixed point, in the renormalization flow. Benedetti et al. carry this program forward, with progressively less restrictive truncation.

http://arxiv.org/abs/0909.0939 Lewandowski, Kamiński, Kisielowski
http://arxiv.org/cits/0909.0939 Spin-Foams for All Loop Quantum Gravity
Rigorously confirms the fit between spin foams and the spin networks of canonical LQG.

http://arxiv.org/abs/0908.4476 Christensen, Khavkine, Livine, Speziale
http://arxiv.org/cits/0908.4476 Sub-leading Asymptotic Behaviour of Area Correlations in the Barrett-Crane Model
Computing spinfoam amplitudes. The old BC model serves as warmup to tackling the new EPRL model. Use is made of Western Ontario's "Beowulf Cluster" supercomputer.

http://arxiv.org/abs/0907.4323 Dittrich, Bahr
http://arxiv.org/cits/0907.4323 Improved and Perfect Actions in Discrete Gravity
Introduces Regge with curved blocks. Exact (not merely approximate) lattice quantum gravity.

http://arxiv.org/abs/0907.4238 Woodard
http://arxiv.org/cits/0907.4238 How Far Are We from the Quantum Theory of Gravity?
A 100-page commissioned review of the whole field. A particle physicist (Sidney Coleman was his PhD advisor) with thorough expertise in General Relativity makes a cool critical assessment of all the various approaches.

http://arxiv.org/abs/0907.4064 Krasnov
http://arxiv.org/cits/0907.4064 Gravity as BF Theory Plus Potential
Longshot. Author walks away from the Holst form of the Lagrangian that everybody else is using. Takes the Plebanski form and extends it to a larger class of actions. Gets something that might accommodate renormalization more completely than the Holst-based spinfoams now being investigated. I like his nerve and think a few outriders who get clear away from the rest of the wagon-train should be encouraged.

http://arxiv.org/abs/0907.2440 Barrett, Dowdall, Fairbairn, Hellmann, Pereira
http://arxiv.org/cits/0907.2440 Lorentzian Spin Foam Amplitudes: Graphical Calculus and Asymptotics
Graphic calculus means inventing something like Feynman diagrams to organize and conceptualize spin foam amplitude calculations. Authors prove that the set of Lorentz rep labels which EPRL chose is actually forced. It would seem to be the only right set of representations to use for labeling spin foams! Firms up the new model's formula for amplitudes.

Apologies to anyone whose favorite has been missed. I started out with a list of 14 or 15 candidates, all good interesting papers! I had to cut down the list to make a workable poll.

 

[marcus]

I had to take care of something else and didn't vote my picks on the poll until just now. In the mean time Atyy swiftly got in there and voted first Very glad to see we agree on a couple!

Five of us have registered our picks already. Thanks to everyone who responded!

 

[marcus]

Thanks to everyone who responded so far by listing their choices in the poll!
It's now almost one month into the fourth quarter. Still too early to gauge the papers' longterm impact, but we can begin to watch the citations to some of the more useful ones mount up. All but two of the 3rd quarter papers on our poll have been cited at least once in other authors' research.

We can also start to accumulate a list of 4th quarter papers that seem likely candidates for the 4th quarter MIP poll. Here are some October 2009 papers that impressed me personally as potentially important contributions to QG research.

Percacci http://arxiv.org/abs/0910.5167 (everybody seems interested in this one)
Gravity from a Particle Physicists' perspective
Krasnov http://arxiv.org/abs/0910.4028 (MTd2 called special attention to this)
Metric Lagrangians with two propagating degrees of freedom
Baratin-Wise http://arxiv.org/abs/0910.1542 (John Baez put the spotlight on this one)
2-Group Representations for Spin Foams
Ashtekar et al. http://arxiv.org/abs/0910.1278 (extends quantum cosmology to non-isotropic cases)
Loop quantum cosmology of Bianchi type II models
Padmanabhan http://arxiv.org/abs/0910.0839 (observer-dependent entropy)
A Dialogue on the Nature of Gravity

 

[ccdantas]

This is very intriguing. If I'm not mistaken:

’tHooft:
spacetime -> non-emergent
horizons -> observer dependent
rationale -> add conformal transfs. to symmetry ops.

Padmanabhan:
spacetime -> emergent
horizons -> observer dependent
rationale -> entropy observer dependent/gravity thermodyn. interpretation

I think that both these papers are extremely interesting by themselves and fundamental. Both views are intriguing. It would be interesting to see whether they can be conciliated.

 

[marcus]

More 4th quarter papers for possible inclusion in poll.

Ashtekar Sloan http://arxiv.org/abs/0912.4093
Loop quantum cosmology and slow roll inflation

Dittrich Höhn http://arxiv.org/abs/0912.1817
From covariant to canonical formulations of discrete gravity

Lewandowski Kamiński Kisielowski http://arxiv.org/abs/0912.0540
The EPRL intertwiners and corrected partition function

Shaposhnikov Wetterich http://arxiv.org/abs/0912.0208
Asymptotic safety of gravity and the Higgs boson mass

EDIT: Krasnov Torres http://arxiv.org/abs/0911.3793
Gravity-Yang-Mills-Higgs unification by enlarging the gauge group (see post #8)

{{EDIT: I would like to remove this one, as the less essential of the two Krasnov papers http://arxiv.org/pdf/0911.4903
Effective metric Lagrangians from an underlying theory with two propagating degrees of freedom}}

Freidel Livine http://arxiv.org/abs/0911.3553
The Fine Structure of SU(2) Intertwiners from U(N) Representations

Thiemann Engle Han http://arxiv.org/abs/0911.3433
Canonical path integral measures for Holst and Plebanski gravity. I. Reduced Phase Space Derivation

Weinberg http://arxiv.org/abs/0911.3165
Asymptotically Safe Inflation

Rovelli Ding http://arxiv.org/abs/0911.0543
The volume operator in covariant quantum gravity

Percacci Narain http://arxiv.org/abs/0911.0386
Renormalization Group Flow in Scalar-Tensor Theories. I

 

[Gianni2k]

I would have included the Causal Set programme by R.Sorkin.

But as a string theorist myself I'm really interested in the review by Coleman's student, thank you Marcus.

 

[atyy]

http://arxiv.org/abs/0911.3793 ?

Has newer stuff than http://arxiv.org/abs/0911.4903 , which is more expository. If you list both, I'll vote for both.

 

[marcus]

Your recommendation is good. I was wondering which of those two Krasnov's to include.

At least for now, I'd like to edit and replace my original Krasnov pick by the one you suggest.

We could generally go over to picking bundles of papers by same author on the same theme (which isn't necessarily bad, we've done that sometimes in the past, but gets cumbersome), or we could stick to listing only one hopefully representative paper.

 

[atyy]

At least for now, I'd like to edit and replace my original Krasnov by the one you suggest.

My preference too. Happy Christmas (or whatever you celebrate) BTW!

http://www.youtube.com/watch?v=j1Ea-fIPj6k&feature=related

 

[marcus]

...
http://arxiv.org/abs/0907.4238 Woodard
http://arxiv.org/cits/0907.4238 How Far Are We from the Quantum Theory of Gravity?
A 100-page commissioned review of the whole field. A particle physicist (Sidney Coleman was his PhD advisor) with thorough expertise in General Relativity makes a cool critical assessment of all the various approaches.
...

I would have included the Causal Set programme by R.Sorkin.

But as a string theorist myself I'm really interested in the review by Coleman's student, thank you Marcus.

You are very welcome, Gianni! Thanks for your comment. I'm glad you found the pointer to Woodard's paper helpful. (I gather he must be the Coleman's student you were referring to.)
Anyone who wants can still vote their choice(s) in the poll. Woodard's review of the whole scene probably deserves more notice. So far it only got one vote in our poll, but we can hardly pretend to be infallible judges .

 

[MTd2]

Hmm, what about that Robert Finkelstein paper?

 

[marcus]

Hmm, what about that Robert Finkelstein paper?

It's hard to assess the actual importance. He is over 90 years old. He has written several papers on that general topic, which fail to cite research in the same area by other people. For some reason he seems to be working in isolation. As if out of touch.
http://personnel.physics.ucla.edu/directory/faculty/index.php?f_name=finkelstein
If this were to change---and if that series of papers started being cited by other researchers---I would feel more confident about gauging its relative importance.
Here is his output since 1990, showing cites:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+A+FINKELSTEIN%2C+ROBERT++J+AND+DATE+%3E+1990&FORMAT=www&SEQUENCE=citecount%28d%29
The titles are interesting--he clearly has interesting ideas. Also the titles are somewhat repetitive, recycling the same interesting topical keywords. I have to reserve judgement. Hard to assess.

 

[MTd2]

The importance I see in this approach, as I stated a long time ago, is on finding a way that can goes around Coleman Mandula, without supersymmetry. The only way know, as far as I know, is using quantum groups. I don't know why this is the only way, but it is stated in wikipedia ( ), and sounds like beating the string theorists on their own game.