Our picks for first quarter 2011 MIP (most important QG paper)

[marcus]

Multiple choices are possible in the poll, so please select several papers if you wish. Of these twenty candidates, choose the paper or papers which you think will contribute most significantly to future quantum gravity research. Abstract summaries follow in the next post.

Diffeomorphisms in group field theories
Aristide Baratin, Florian Girelli, Daniele Oriti
http://arxiv.org/abs/1101.0590
http://arxiv.org/cits/1101.0590

The principle of relative locality
Giovanni Amelino-Camelia, Laurent Freidel, Jerzy Kowalski-Glikman, Lee Smolin
http://arxiv.org/abs/1101.0931
http://arxiv.org/cits/1101.0931

Spinfoam Fermions: PCT Symmetry, Dirac Determinant, and Correlation Functions
Muxin Han, Carlo Rovelli
http://arxiv.org/abs/1101.3264
http://arxiv.org/cits/1101.3264

Cosmological constant in spinfoam cosmology
Eugenio Bianchi, Thomas Krajewski, Carlo Rovelli, Francesca Vidotto
http://arxiv.org/abs/1101.4049
http://arxiv.org/cits/1101.4049

Asymptotically Safe Cosmology
Mark Hindmarsh, Daniel Litim, Christoph Rahmede
http://arxiv.org/abs/1101.5401
http://arxiv.org/cits/1101.5401

Particle Creation by Loop Black Holes
Emanuele Alesci, Leonardo Modesto
http://arxiv.org/abs/1101.5792
http://arxiv.org/cits/1101.5792

State sum models, induced gravity and the spectral action
John W. Barrett
http://arxiv.org/abs/1101.6078
http://arxiv.org/cits/1101.6078

Zakopane lectures on loop gravity
Carlo Rovelli
http://arxiv.org/abs/1102.3660
http://arxiv.org/cits/1102.3660

The Semiclassical Limit of Causal Dynamical Triangulations
J. Ambjorn, A. Gorlich, J. Jurkiewicz, R. Loll, J. Gizbert-Studnicki, T. Trzesniewski
http://arxiv.org/abs/1102.3929
http://arxiv.org/cits/1102.3929

Path Integral and Effective Hamiltonian in Loop Quantum Cosmology
Haiyun Huang, Yongge Ma, Li Qin
http://arxiv.org/abs/1102.4755
http://arxiv.org/cits/1102.4755

Asymptotically Safe Lorentzian Gravity
Elisa Manrique, Stefan Rechenberger, Frank Saueressig
http://arxiv.org/abs/1102.5012
http://arxiv.org/cits/1102.5012

On the Asymptotics of Quantum Group Spinfoam Model
You Ding, Muxin Han
http://arxiv.org/abs/1103.1597
http://arxiv.org/cits/1103.1597

Hamiltonian analysis of SO(4,1) constrained BF theory
R. Durka, J. Kowalski-Glikman
http://arxiv.org/abs/1003.2412
http://arxiv.org/cits/1003.2412

Probability of Inflation in Loop Quantum Cosmology
Abhay Ashtekar, David Sloan
http://arxiv.org/abs/1103.2475
http://arxiv.org/cits/1103.2475

The SU(2) Black Hole entropy revisited
Jonathan Engle, Karim Noui, Alejandro Perez, Daniele Pranzetti
http://arxiv.org/abs/1103.2723
http://arxiv.org/cits/1103.2723

Gravity as a constrained BF theory: Noether charges and Immirzi parameter
R. Durka, J. Kowalski-Glikman
http://arxiv.org/abs/1103.2971
http://arxiv.org/cits/1103.2971

Bubble divergences: sorting out topology from cell structure
Valentin Bonzom, Matteo Smerlak
http://arxiv.org/abs/1103.3961
http://arxiv.org/cits/1103.3961

The 1/N expansion of colored tensor models in arbitrary dimension
Razvan Gurau, Vincent Rivasseau
http://arxiv.org/abs/1101.4182
http://arxiv.org/cits/1101.4182

Curvature in spinfoams
Elena Magliaro, Claudio Perini
http://arxiv.org/abs/1103.4602
http://arxiv.org/cits/1103.4602

Gamma ray burst delay times probe the geometry of momentum space
Laurent Freidel, Lee Smolin
http://arxiv.org/abs/1103.5626
http://arxiv.org/cits/1103.5626

 

[marcus]

Here are the abstracts:

http://arxiv.org/abs/1101.0590
Diffeomorphisms in group field theories
Aristide Baratin, Florian Girelli, Daniele Oriti
31 pages, many figures
We study the issue of diffeomorphism symmetry in group field theories (GFT), using the recently introduced noncommutative metric representation. In the colored Boulatov model for 3d gravity, we identify a field (quantum) symmetry which ties together the vertex translation invariance of discrete gravity, the flatness constraint of canonical quantum gravity, and the topological (coarse-graining) identities for the 6j-symbols. We also show how, for the GFT graphs dual to manifolds, the invariance of the Feynman amplitudes encodes the discrete residual action of diffeomorphisms in simplicial gravity path integrals. We extend the results to GFT models for higher dimensional BF theories and discuss various insights that they provide on the GFT formalism itself.

http://arxiv.org/abs/1101.0931
The principle of relative locality
Giovanni Amelino-Camelia, Laurent Freidel, Jerzy Kowalski-Glikman, Lee Smolin
12 pages, 3 figures
We propose a deepening of the relativity principle according to which the invariant arena for non-quantum physics is a phase space rather than spacetime. Descriptions of particles propagating and interacting in spacetimes are constructed by observers, but different observers, separated from each other by translations, construct different spacetime projections from the invariant phase space. Nonetheless, all observers agree that interactions are local in the spacetime coordinates constructed by observers local to them.
This framework, in which absolute locality is replaced by relative locality, results from deforming momentum space, just as the passage from absolute to relative simultaneity results from deforming the linear addition of velocities. Different aspects of momentum space geometry, such as its curvature, torsion and non-metricity, are reflected in different kinds of deformations of the energy-momentum conservation laws. These are in principle all measurable by appropriate experiments. We also discuss a natural set of physical hypotheses which singles out the cases of momentum space with a metric compatible connection and constant curvature.

http://arxiv.org/abs/1101.3264
Spinfoam Fermions: PCT Symmetry, Dirac Determinant, and Correlation Functions
Muxin Han, Carlo Rovelli
26 pages, 9 figures
We discuss fermion coupling in the framework of spinfoam quantum gravity. We analyze the gravity-fermion spinfoam model and its fermion correlation functions. We show that there is a spinfoam analog of PCT symmetry for the fermion fields on spinfoam model, where a PCT theorem is proved for spinfoam fermion correlation functions. We compute the determinant of the Dirac operator for the fermions, where two presentations of the Dirac determinant are given in terms of diagram expansions. We compute the fermion correlation functions and show that they can be given by Feynman diagrams on the spinfoams, where the Feynman propagators can be represented by a discretized path integral of a world-line action along the edges of the underlying 2-complex.

http://arxiv.org/abs/1101.4049
Cosmological constant in spinfoam cosmology
Eugenio Bianchi, Thomas Krajewski, Carlo Rovelli, Francesca Vidotto
4 pages, 2 figures
We consider a simple modification of the amplitude defining the dynamics of loop quantum gravity, corresponding to the introduction of the cosmological constant, and possibly related to the SL(2,C)_q extension of the theory recently considered by Fairbairn-Meusburger and Han. We show that in the context of spinfoam cosmology, this modification yields the de Sitter cosmological solution.

http://arxiv.org/abs/1101.5401
Asymptotically Safe Cosmology
Mark Hindmarsh, Daniel Litim, Christoph Rahmede
8 pages
We study quantum modifications to cosmology in a Friedmann-Robertson-Walker universe with and without scalar fields by taking the renormalisation group running of gravitational and matter couplings into account. We exploit the Bianchi identity to relate the renormalisation group scale with scale factor and derive the improved cosmological evolution equations. We find two types of cosmological fixed points where the renormalisation group scale either freezes in, or continues to evolve with scale factor. We discuss the implications of each of these, and classify the different cosmological fixed points with and without gravity displaying an asymptotically safe renormalisation group fixed point. We state conditions of existence for an inflating ultraviolet cosmological fixed point for Einstein gravity coupled to a scalar field. We also discuss other fixed point solutions such as "scaling" solutions, or fixed points with equipartition between kinetic and potential energies.

http://arxiv.org/abs/1101.5792
Particle Creation by Loop Black Holes
Emanuele Alesci, Leonardo Modesto
14 pages, 6 figures
We study the black hole particle production in a regular spacetime metric obtained in a minisuperspace approach to loop quantum gravity. In different previous papers the static solution was obtained and shown to be singularity-free and self-dual. In this paper expanding a previous study of the black hole dynamics we repeat the Hawking analysis which leads to a thermal flux of particles at the future infinity. The evaporation time is infinite and the unitarity is recovered due to the regularity of the spacetime and to the characteristic behavior of the surface gravity.

http://arxiv.org/abs/1101.6078
State sum models, induced gravity and the spectral action
John W. Barrett
13 pages, 1 figure
A proposal that the bosonic action of gravity and the standard model is induced from the fermionic action is investigated. It is suggested that this might occur naturally in state sum models.

http://arxiv.org/abs/1102.3660
Zakopane lectures on loop gravity
Carlo Rovelli
24 pages, 10 figures, homeworks
This is a first version of the introductory lectures on loop quantum gravity that I will give at the quantum gravity school in Zakopane. The theory is presented in self-contained form, without emphasis on its derivation from classical general relativity. Dynamics is given in the covariant form. Some applications are described, including the recent derivation of de Sitter cosmology from full quantum gravity.

http://arxiv.org/abs/1102.3929
The Semiclassical Limit of Causal Dynamical Triangulations
J. Ambjorn, A. Gorlich, J. Jurkiewicz, R. Loll, J. Gizbert-Studnicki, T. Trzesniewski
30 pages, 10 figures
Previous work has shown that the macroscopic structure of the theory of quantum gravity defined by causal dynamical triangulations (CDT) is compatible with that of a de Sitter universe. After emphasizing the strictly nonperturbative nature of this semiclassical limit we present a detailed study of the three-volume data, which allows us to re-confirm the de Sitter structure, exhibit short-distance discretization effects, and make a first detailed investigation of the presence of higher-order curvature terms in the effective action for the scale factor. Technically, we make use of a novel way of fixing the total four-volume in the simulations.

http://arxiv.org/abs/1102.4755
Path Integral and Effective Hamiltonian in Loop Quantum Cosmology
Haiyun Huang, Yongge Ma, Li Qin
9 pages
We study the path integral formulation of Friedmann universe filled with a massless scalar field in loop quantum cosmology. All the isotropic models of k=0,+1,-1 are considered. Since the transition amplitude in the deparameterized framework can be expressed in terms of group averaging, the path integrals can be formulated for both deparameterized and timeless frameworks. It turns out that the effective Hamiltonian derived from the path integral in deparameterized framework is equivalent to the effective Hamiltonian constraint derived from the path integral in timeless framework, since they lead to same equations of motion. Moreover, the effective Hamiltonian constraints of above models derived in canonical theory are confirmed by the path integral formulation.

http://arxiv.org/abs/1102.5012
Asymptotically Safe Lorentzian Gravity
Elisa Manrique, Stefan Rechenberger, Frank Saueressig
4 pages, 2 figures
The gravitational asymptotic safety program strives for a consistent and predictive quantum theory of gravity based on a non-trivial ultraviolet fixed point of the renormalization group (RG) flow. We investigate this scenario by employing a novel functional renormalization group equation which takes the causal structure of space-time into account and connects the RG flows for Euclidean and Lorentzian signature by a Wick-rotation. Within the Einstein-Hilbert approximation, the $\beta$-functions of both signatures exhibit ultraviolet fixed points in agreement with asymptotic safety. Surprisingly, the two fixed points have strikingly similar characteristics, suggesting that Euclidean and Lorentzian quantum gravity belong to the same universality class at high energies.

http://arxiv.org/abs/1103.1597
On the Asymptotics of Quantum Group Spinfoam Model
You Ding, Muxin Han
25 pages, 1 figure
Recently a quantum group deformation of EPRL spinfoam model was proposed in arXiv:1012.4216 by one of the authors, and in arXiv:1012.4784 by Fairbairn and Meusburger. It is interesting to study the high spin asymptotics of the quantum group spinfoam model, to see if it gives the discrete Einstein gravity with cosmological constant as its semiclassical limit. In this article we propose a new technique, which can simplify the analysis of the high spin asymptotics for quantum group spinfoam vertex amplitude. This technique can generalize the spinfoam asymptotic analysis developed by Barrett, et al to quantum group spinfoam. As a preparation of asymptotic analysis, we define and analyze the coherent states and coherent intertwiners for quantum group, which has certain "factorization properties". We show that in the high spin limit of quantum group spinfoam, many q-deformed noncommutative ingredients become classical and commutative. In particular, the squared norm of coherent intertwiner and the (Euclidean) vertex amplitude become integrals on classical group, while there are some additional terms (written in terms of classical group variables) make quantum group corrections to the usual (classical group) coherent intertwiner and vertex amplitude. These quantum group correction terms turn out to be proportional to the deformation parameter, which hopefully gives the cosmological term as its semiclassical limit.

http://arxiv.org/abs/1003.2412
Hamiltonian analysis of SO(4,1) constrained BF theory
R. Durka, J. Kowalski-Glikman
9 pages
In this paper we discuss canonical analysis of SO(4,1) constrained BF theory. The action of this theory contains topological terms appended by a term that breaks the gauge symmetry down to the Lorentz subgroup SO(3,1). The equations of motion of this theory turn out to be the vacuum Einstein equations. By solving the B field equations one finds that the action of this theory contains not only the standard Einstein-Cartan term, but also the Holst term proportional to the inverse of the Immirzi parameter, as well as a combination of topological invariants. We show that the structure of the constraints of a SO(4,1) constrained BF theory is exactly that of gravity in Holst formulation. We also briefly discuss quantization of the theory.

http://arxiv.org/abs/1103.2475
Probability of Inflation in Loop Quantum Cosmology
Abhay Ashtekar, David Sloan
34 pages, 3 figures
Inflationary models of the early universe provide a natural mechanism for the formation of large scale structure. This success brings to forefront the question of naturalness: Does a sufficiently long slow roll inflation occur generically or does it require a careful fine tuning of initial parameters? In recent years there has been considerable controversy on this issue. In particular, for a quadratic potential, Kofman, Linde and Mukhanov have argued that the probability of inflation with at least 65 e-foldings is close to one, while Gibbons and Turok have argued that this probability is suppressed by a factor of ~ 10^-85. We first clarify that such dramatically different predictions can arise because the required measure on the space of solutions is intrinsically ambiguous in general relativity. We then show that this ambiguity can be naturally resolved in loop quantum cosmology (LQC) because the big bang is replaced by a big bounce and the bounce surface can be used to introduce the structure necessary to specify a satisfactory measure.
The second goal of the paper is to present a detailed analysis of the inflationary dynamics of LQC using analytical and numerical methods. By combining this information with the measure on the space of solutions, we address a sharper question than those investigated in the literature: What is the probability of a sufficiently long slow roll inflation WHICH IS COMPATIBLE WITH THE SEVEN YEAR WMAP DATA? We show that the probability is very close to 1.
The material is so organized that cosmologists who may be more interested in the inflationary dynamics in LQC than in the subtleties associated with measures can skip that material without loss of continuity.

http://arxiv.org/abs/1103.2723
The SU(2) Black Hole entropy revisited
Jonathan Engle, Karim Noui, Alejandro Perez, Daniele Pranzetti
31 pages, 8 figures
We study the state-counting problem that arises in the SU(2) black hole entropy calculation in loop quantum gravity. More precisely, we compute the leading term and the logarithmic correction of both the spherically symmetric and the distorted SU(2) black holes. Contrary to what has been done in previous works, we have to take into account "quantum corrections" in our framework in the sense that the level k of the Chern-Simons theory which describes the black hole is finite and not sent to infinity. Therefore, the new results presented here allow for the computation of the entropy in models where the quantum group corrections are important.

http://arxiv.org/abs/1103.2971
Gravity as a constrained BF theory: Noether charges and Immirzi parameter
R. Durka, J. Kowalski-Glikman
5 pages
We derive and analyze Noether charges associated with the diffeomorphism invariance for the constrained SO(2,3) BF theory. This result generalizes the Wald approach to the case of the first order gravity with a negative cosmological constant, the Holst modification and topological terms (Nieh-Yan, Euler, and Pontryagin). We show that differentiability of the action is automatically implemented by the the structure of the constrained BF model. Finally, we calculate the AdS--Schwarzschild black hole entropy from the Noether charge and we find that, unexpectedly, it does not depend on the Immirzi parameter.

http://arxiv.org/abs/1103.3961
Bubble divergences: sorting out topology from cell structure
Valentin Bonzom, Matteo Smerlak
19 pages
We conclude our analysis of bubble divergences in the flat spinfoam model. In [arXiv:1008.1476] we showed that the divergence degree of an arbitrary two-complex Gamma can be evaluated exactly by means of twisted cohomology. Here, we specialize this result to the case where Gamma is the two-skeleton of the cell decomposition of a pseudomanifold, and sharpen it with a careful analysis of the cellular and topological structures involved. Moreover, we explain in detail how this approach reproduces all the previous powercounting results for the Boulatov-Ooguri (colored) tensor models, and sheds light on algebraic-topological aspects of Gurau's 1/N expansion.

http://arxiv.org/abs/1101.4182
The 1/N expansion of colored tensor models in arbitrary dimension
Razvan Gurau, Vincent Rivasseau
4 pages, 3 figures
In this paper we extend the 1/N expansion introduced in [1] to group field theories in arbitrary dimension and prove that only graphs corresponding to spheres S^D contribute to the leading order in the large N limit.

http://arxiv.org/abs/1103.4602
Curvature in spinfoams
Elena Magliaro, Claudio Perini
6 pages, 3 figures
We consider spinfoam quantum gravity. We show in a simple case that the amplitude projects over a nontrivial (curved) classical geometry. This suggests that, at least for spinfoams without bubbles and for large values of the boundary spins, the amplitude takes the form of a path integral over Regge metrics, thus enforcing discrete Einstein equations in the classical limit.

http://arxiv.org/abs/1103.5626
Gamma ray burst delay times probe the geometry of momentum space
Laurent Freidel, Lee Smolin
21 pages, 13 figures
We study the application of the recently proposed framework of relative locality to the problem of energy dependent delays of arrival times of photons that are produced simultaneously in distant events such as gamma ray bursts. Within this framework, possible modifications of special relativity are coded in the geometry of momentum space. The metric of momentum space codes modifications in the energy momentum relation, while the connection on momentum space describes possible non-linear modifications in the laws of conservation of energy and momentum. In this paper, we study effects of first order in the inverse Planck scale, which are coded in the torsion and non-metricity of momentum space. We find that time delays of order Distance * Energies/m_p are coded in the non-metricity of momentum space. Current experimental bounds on such time delays hence bound the components of this tensor of order 1/m_p. We also find a new effect, whereby photons from distant sources can appear to arrive from angles slightly off the direction to the sources, which we call gravitational lensing. This is found to be coded into the torsion of momentum space.

 

[marcus]

A number of valuable research papers came out Jan-March and I guess I got overloaded and neglected to include two important ones in the poll. So I'll list them as afterthoughts here and anyone who wants to can register a vote just by posting on this thread and saying "vote for Gurau" or "vote for Rivasseau" ---or anything like that. I will try to keep count.

Personally I am voting for both of these, I think they are great, so they already have 1 vote apiece.

Sorry about the omission.

http://arxiv.org/abs/1102.5759
http://arxiv.org/cits/1102.5759
The complete 1/N expansion of colored tensor models in arbitrary dimension
Razvan Gurau
(Submitted on 28 Feb 2011)
"In this paper we generalize the results of [1,2] and derive the full 1/N expansion of colored tensor models in arbitrary dimensions. We detail the expansion for the independent identically distributed model and the topological Boulatov Ooguri model."

http://arxiv.org/abs/1103.1900
http://arxiv.org/cits/1103.1900
Towards Renormalizing Group Field Theory
Vincent Rivasseau
22 pages, 5 figures
(Submitted on 9 Mar 2011)
"We review some aspects of non commutative quantum field theory and group field theory, in particular recent progress on the systematic study of the scaling and renormalization properties of group field theory. We thank G. Zoupanos and the organizers of the Corfu 2010 Workshop on Noncommutative Field Theory and Gravity for encouraging us to write this review."