Loop-and-allied QG bibliography

[marcus]

http://arxiv.org/abs/1002.0138
Ultraviolet behavior in background independent quantum field theory
Viqar Husain, Andreas Kreienbuehl
8 pages, 5 figures
(Submitted on 31 Jan 2010)
"We describe a background independent quantization of the scalar field that provides an explicit realization of Fock-like states and associated operators in a polymer Hilbert space. The vacuum expectation values of the commutator and anti-commutator of the creation and annihilation operators become energy dependent, and exhibit a surprising transition to fermionic behavior at high energy. Furthermore the approach yields a modified dispersion relation with a leading correction proportional to the momentum cubed. These results suggests a fundamental change in the ultraviolet properties of quantum fields."

Here's an odd one. Chamseddine has been a frequent co-author with Alain Connes on past NGG papers:

http://arxiv.org/abs/1002.0541
Gravity with de Sitter and Unitary Tangent Groups
Ali H. Chamseddine, Viatcheslav Mukhanov
23 pages
(Submitted on 2 Feb 2010)
"Einstein Gravity can be formulated as a gauge theory with the tangent space respecting the Lorentz symmetry. In this paper we show that the dimension of the tangent space can be larger than the dimension of the manifold and by requiring the invariance of the theory with respect to 5d Lorentz group (de Sitter group) Einstein theory is reproduced unambiguously. The other possibility is to have unitary symmetry on a complex tangent space of the same dimension as the manifold. In this case the resultant theory is Einstein-Strauss Hermitian gravity. The tangent group is important for matter couplings. We show that in the de Sitter case the 4 dimensional space time vector and scalar are naturally unified by a hidden symmetry being components of a 5d vector in the tangent space. With a de Sitter tangent group spinors can exist only when they are made complex or taken in doublets in a way similar to N=2 supersymmetry."

 

[MTd2]

http://arxiv.org/abs/1002.0488

Hidden symmetries for thermodynamics and emergence of relativity

Liu Zhao
(Submitted on 2 Feb 2010)
Verlinde recently proposed an idea about the thermodynamic origin of gravity. Though this is a beautiful idea which may resolve many long standing problems in the theories of gravity, it also raises many other problems. In this article I will comment on some of the problems of Verlinde's proposal with special emphasis on the thermodynamical origin of the principle of relativity. It is found that there is a large group of hidden symmetries of thermodynamics which contains the Poincare group of the spacetime for which space is emergent. This explains the thermodynamic origin of the principle of relativity.

http://arxiv.org/abs/1002.0500

Spin Foam State Sums and Chern-Simons Theory

Aleksandar Mikovic, Joao Faria Martins
(Submitted on 2 Feb 2010)
We review the spin foam state-sum invariants of 3-manifolds, and explain their relationship to manifold invariants coming from the Chern-Simons theory. We also explain the relationship between the known invariants of spin networks by using the Chain-Mail formalism of J. Roberts. This formalism can be understood as a quantum-group regularization of the BF theory path integrals.

 

[MTd2]

http://arxiv.org/abs/1002.0813

Ultraviolet Divergences and Scale-Dependent Gravitational Couplings

Herbert W. Hamber
(Submitted on 3 Feb 2010)
I review the field-theoretic renomalization group approach to quantum gravity, built around the existence of a non-trivial ultraviolet fixed point in four dimensions. I discuss the implications of such a fixed point, found in three largely unrelated non-perturbative approaches, and how it relates to the vacuum state of quantum gravity, and specifically to the running of $G$. One distinctive feature of the new fixed point is the emergence of a second genuinely non-perturbative scale, analogous to the scaling violation parameter in non-abelian gauge theories. I argue that it is natural to identify such a scale with the small observed cosmological constant, which in quantum gravity can arise as a non-perturbative vacuum condensate.

http://arxiv.org/abs/1002.0669

Some Aspects of Holst and Nieh-Yan Terms in General Relativity with Torsion

Kinjal Banerjee
(Submitted on 3 Feb 2010)
We explore the relation of the Holst term with the Nieh-Yan term in terms of metric variables. We show that the Holst term indeed affects the classical equations of motion in the presence of matter with spin. Therefore the correct term to add to the Einstein-Hilbert action such that the equations of motion are not affected is the Nieh-Yan term. We then calculate the torsion charge due to this term in the context of a perfect fluid sphere with torsion and show that it vanishes once a horizon is formed but not otherwise. We also show that adding on torsion to General Relativity the Einstein's equations are no longer holographic in torsion although they continue to be so for the metric.

 

[marcus]

http://arxiv.org/abs/1002.0589
Hilbert Spaces from Path Integrals
Fay Dowker, Steven Johnston, Rafael D. Sorkin
(Submitted on 2 Feb 2010)
"It is shown that a Hilbert space can be constructed for a quantum system starting from a framework in which histories are fundamental. The Decoherence Functional provides the inner product on this 'History Hilbert space'. It is also shown that the History Hilbert space is the standard Hilbert space in the case of non-relativistic quantum mechanics."

 

[atyy]

http://physics.aps.org/articles/v3/7
Liberating anyons from two dimensions
Ady Stern, Michael Levin
The combination of trivial and topological band insulators with a superconductor is bringing anyons—particles that behave neither according to purely Bose nor Fermi statistics—into the three-dimensional world.

http://arxiv.org/abs/0909.4741
Majorana Fermions and Non-Abelian Statistics in Three Dimensions
Jeffrey C.Y. Teo, C.L. Kane
(Submitted on 25 Sep 2009 (v1), last revised 28 Jan 2010 (this version, v2))
We show that three dimensional superconductors, described within a Bogoliubov de Gennes framework can have zero energy bound states associated with pointlike topological defects. The Majorana fermions associated with these modes have non-Abelian exchange statistics, despite the fact that the braid group is trivial in three dimensions. This can occur because the defects are associated with an orientation that can undergo topologically nontrivial rotations. A new feature of three dimensional systems is that there are "braidless" operations in which it is possible to manipulate the groundstate associated with a set of defects without moving or measuring them. To illustrate these effects we analyze specific architectures involving topological insulators and superconductors.

 

[MTd2]

http://arxiv.org/abs/1002.1062

Temperature and Energy of 4-dimensional Black Holes from Entropic Force

Yu-Xiao Liu, Yong-Qiang Wang, Shao-Wen Wei
(Submitted on 4 Feb 2010)
We investigate the temperature and energy on holographic screens for 4-dimensional black holes with the entropic force idea proposed by Verlinde. We find that the "Unruh-Verlinde temperature" is equal to the Hawking temperature on the event horizon of these black holes. While they are opposite to each other on the Cauchy horizon. The energy on the holographic screen at infinity is $E=M$ for all of those black holes.

http://arxiv.org/abs/1002.0871

Entropic force in the presence of black hole

Yun Soo Myung
(Submitted on 4 Feb 2010)
We derive the entropic force in the presence of the Schwarzschild black hole by using the local equipartition rule and holographic principle. On the other hand, when using the Tolman temperature, one does not arrive at the Newtonian force law.

http://arxiv.org/abs/1002.1035

A note on gravity, entropy, and BF topological field theory

Jerzy Kowalski-Glikman
(Submitted on 4 Feb 2010)
In this note I argue that the expression for entropic force, used as a starting point in Verlinde's derivation of Newton's law, can be deduced from first principles if one assumes that that the microscopic theory behind his construction is the topological $\SO(4,1)$ BF theory coupled to particles.http://arxiv.org/abs/1002.1027

Beyond Special and General Relativity. Neutrinos and Cosmology

Javier Indurain
(Submitted on 4 Feb 2010)
The widely accepted description of the present cosmic acceleration and the neutrino oscillations in terms of a cosmological constant and neutrino masses, respectively, seems conceptually not very satisfactory. From a phenomenological perspective, the possibility that those phenomena are instead the first windows to new physics at very low energies is explored.

 

[MTd2]

http://arxiv.org/abs/1002.1136

Gravity from the entropy of light

Alessandro Pesci
(Submitted on 5 Feb 2010)
The holographic principle, considered in a semiclassical setting, is shown to have direct consequences on physics at a fundamental level. In particular, a certain relation is pointed out to be the expression of holography in basic thermodynamics. It is argued moreover that through this relation holography is recognized to induce gravity if quantum mechanics is given, and an expression for the gravitational lensing is obtained in terms of the entropy per unit wavelength of black-body radiation, or, at a deeper level, in terms of the maximum entropy per unit of associated space to the elementary bit of information.

http://arxiv.org/abs/1002.1136

Notes on Entropy Force in General Spherically Symmetric Spacetimes

Rong-Gen Cai, Li-Ming Cao, Nobuyoshi Ohta
(Submitted on 5 Feb 2010 (v1), last revised 6 Feb 2010 (this version, v2))
In a recent paper [arXiv:1001.0785], Verlinde has shown that the Newton gravity appears as an entropy force. In this paper we show how gravity appears as entropy force in Einstein's equation of gravitational field in a general spherically symmetric spacetime. We mainly focus on the trapping horizon of the spacetime. We find that when matter fields are absent, the change of entropy associated with the trapping horizon indeed can be identified with an entropy force. When matter fields are present, we see that heat flux of matter fields also leads to the change of entropy. Applying arguments made by Verlinde and Smolin, respectively, to the trapping horizon, we find that the entropy force is given by the surface gravity of the horizon. The cases in the untrapped region of the spacetime are also discussed.


This one cites papers of Padmanabhan:

http://arxiv.org/abs/1002.1132

Quantum gravitational corrections to the propagator in spacetimes with constant curvature

Dawood Kothawala, S. Shankaranarayanan, L. Sriramkumar
(Submitted on 5 Feb 2010)
The existence of a minimal and fundamental length scale, say, the Planck length, is a characteristic feature of almost all the models of quantum gravity. The presence of the fundamental length is expected to lead to an improved ultra-violet behavior of the semi-classical propagators. The hypothesis of path integral duality provides a prescription to evaluate the modified propagator of a free, quantum scalar field in a given spacetime, taking into account the existence of the fundamental length in a locally Lorentz invariant manner. We use this prescription to compute the quantum gravitational modifications to the propagators in spacetimes with constant curvature, and show that: (i) the modified propagators are ultra-violet finite, and (ii) the modifications are non-perturbative in the Planck length. We discuss the implications of our results.

 

[MTd2]

http://arxiv.org/abs/1002.1462

Embedding the Bilson-Thompson model in an LQG-like framework

Deepak Vaid
(Submitted on 8 Feb 2010)
We argue that the Quadratic Spinor Lagrangian approach allows us to approach the problem of forming a geometrical condensate of spinorial tetrads in a natural manner. This, along with considerations involving the discrete symmetries of lattice triangulations, lead us to discover that the quasiparticles of such a condensate are tetrahedra with braids attached to its faces and that these braid attachments correspond to the preons in Bilson-Thompson's model of elementary particles. These "spatoms" can then be put together in a tiling to form more complex structures which encode both geometry and matter in a natural manner. We conclude with some speculations on the relation between this picture and the computational universe hypothesis.http://arxiv.org/abs/1002.1434

Interacting holographic dark energy with entropy corrections

Mubasher Jamil, M. Umar Farooq
(Submitted on 7 Feb 2010)
The holographic dark energy (HDE) is considered to be the most promising candidate of dark energy. Its definition is originally motivated from the entropy-area relation which depends on the theory of gravity under consideration. Recently a new definition of HDE is proposed with the help of quantum corrections to the entropy-area relation in the setup of loop quantum cosmology. Using this new definition, we investigate the model of interacting dark energy and derive its effective equation of state. Finally we establish a correspondence between generalized Chaplygin gas and entropy-corrected holographic dark energy.

 

[marcus]

http://arxiv.org/abs/1002.1844
On Quantum Correlations across the Black Hole Horizon
Ralf Schützhold, William G. Unruh
5 pages, 1 figure
(Submitted on 9 Feb 2010)
"Inspired by the condensed-matter analogues of black holes, we study the quantum correlations across the event horizon reflecting the entanglement between the outgoing particles of the Hawking radiation and their in-falling partners. For a perfectly covariant theory, the total correlation is conserved in time and piles up arbitrary close to the horizon in the past, where it merges into the singularity of the vacuum two-point function at the light cone. After modifying the dispersion relation (i.e., breaking Lorentz invariance) for large k, on the other hand, the light cone is smeared out and the entanglement is not conserved but actually created in a given rate per unit time."http://arxiv.org/abs/1002.1959
A spin foam model for general Lorentzian 4-geometries
Florian Conrady (Perimeter Inst. Theor. Phys.), Jeff Hnybida (Perimeter Inst. Theor. Phys. and Waterloo U.)
26 pages, 1 figure
(Submitted on 9 Feb 2010)
"We derive simplicity constraints for the quantization of general Lorentzian 4-geometries. Our method is based on the correspondence between coherent states and classical bivectors and the minimization of associated uncertainties. For spacelike geometries, this scheme agrees with the master constraint method of the model by Engle, Pereira, Rovelli and Livine (EPRL). When it is applied to general Lorentzian geometries, we obtain new constraints that include the EPRL constraints as a special case. They imply a discrete area spectrum for both spacelike and timelike surfaces. We use these constraints to define a spin foam model for general Lorentzian 4-geometries."

 

[marcus]

http://arxiv.org/abs/1002.2035
Cosmological inflation driven by holonomy corrections of loop quantum cosmology
Dah-Wei Chiou, Kai Liu
7 pages, 2 figures, 1 table
(Submitted on 10 Feb 2010)
"At the level of heuristic effective dynamics, we investigate the cosmological inflation with holonomy corrections of loop quantum cosmology (LQC) in the k=0 Friedmann-Robertson-Walker model with a single inflaton field subject to a simple potential. In the symmetric bouncing scenario of LQC, the condition for occurrence of the quantum bounce naturally and uniquely fixes the initial conditions at the bouncing epoch. Around the quantum bounce, the universe undergoes a short super-inflationary phase, which drives the inflaton field to its potential hill and thus sets the proper initial conditions for the standard slow-roll inflation. Between the super-inflation and the standard inflation, there is a non-inflationary phase, which violates the slow-roll condition. The violation of slow roll is expected to give some suppression on the low angular power spectrum of the cosmic microwave background and different orders of holonomy corrections shall yield different suppressions."

 

[MTd2]

http://arxiv.org/abs/1002.2029

Condensed Geometry

Koustubh Kabe
(Submitted on 10 Feb 2010)
A spin (dependent) system treatment of gravity is adopted akin to the Sen-Ashtekar treatment. Time is reinserted into the space ``fluid'' at the quantum Level. This time - the Lorentzian one- is shown to be a vorticity of a ``fluid particle'' of the space and the effect is integrated over all the fluid particles to incorporate time in quantum gravity. This spacetime is viewed as a fluid of future light cones called the SU(2) dipoles of causality here in the paper.The future light cone structure is soldered internally to the new variables derived in this paper to accommodate a background free physics of quantum strings. The emergence of spacetime is shown to be a first order phase transition and that of separation of gravity from the unified field to be a second order phase transition. For the former case the cosmic time is chosen as the order parameter and for the latter case the angular momentum is chosen as the order parameter. A quantum black hole thus nucleates at transition temperature which is the Planck temperature, $\tau_{pl}$. Then the SU(2) dipoles enable interpretation of this black hole as a gravity gauge SL(2,$\mathbb{C}$) dual of the U(1) gauge ferromagnetic phase. The usual QFT interpretation of this effect is the existence of locally Lorentzian spacetimes.

 

[MTd2]

http://arxiv.org/abs/1002.2618

Quantum gravity effects on space-time
Martin Bojowald
Comments: 24 pages, 4 figures, plenary talk at The Nineteenth Workshop on General Relativity and Gravitation in Japan (JGRG19) at Rikkyo University, Dec 2009
Subjects: General Relativity and Quantum Cosmology (gr-qc)
General relativity promotes space-time to a physical, dynamical object subject to equations of motion. Quantum gravity, accordingly, must provide a quantum framework for space-time, applicable on the smallest distance scales. Just like generic states in quantum mechanics, quantum space-time structures may be highly counter-intuitive. But if low-energy effects can be extracted, they shed considerable light on the implications to be expected for a dynamical quantum space-time. Loop quantum gravity has provided several such effects, but even in the symmetry-reduced setting of loop quantum cosmology no complete picture of effective space-time geometries describing especially the regime near the big bang has been obtained. The overall situation regarding space-time structures and cosmology is reviewed here, with an emphasis on the role of dynamical states, effective equations, and general covariance.

http://arxiv.org/abs/1002.2454

Entropic Force Law, Emergent Gravity and the Uncertainty Principle

I. V. Vancea, M. A. Santos
(Submitted on 12 Feb 2010)
The entropic formulation of the inertia and the gravity relies on quantum, geometrical and informational arguments. The fact that the results are completely classical is missleading. In this paper we argue that the entropic formulation is a powerfull tool which provides new insights into the quantum nature of the inertia and the gravity. We use the entropic postulate to determine the quantum uncertainty in the law of inertia and in the gravity law in both Newtonian Mechanics and General Relativity. These results are obtained by considering the most general quantum property of the matter represented by the Uncertainty Principle and by postulating an expression for the uncertainty of the entropy such that: i) it is the simplest quantum generalization of the postulate of the variation of the entropy and ii) it reduces to the variation of the entropy in the absence of the uncertainty.

 

[John86]

http://arxiv.org/abs/0907.4335

From Entropic Dynamics to Quantum Theory
Authors: Ariel Caticha
(Submitted on 24 Jul 2009 (v1), last revised 12 Feb 2010 (this version, v3))
Abstract: Non-relativistic quantum theory is derived from information codified into an appropriate statistical model. The basic assumption is that there is an irreducible uncertainty in the location of particles: positions constitute a configuration space and the corresponding probability distributions constitute a statistical manifold. The dynamics follows from a principle of inference, the method of Maximum Entropy. The concept of time is introduced as a convenient way to keep track of change. A welcome feature is that the entropic dynamics notion of time incorporates a natural distinction between past and future. The statistical manifold is assumed to be a dynamical entity: its curved and evolving geometry determines the evolution of the particles which, in their turn, react back and determine the evolution of the geometry. Imposing that the dynamics conserve energy leads to the Schroedinger equation and to a natural explanation of its linearity, its unitarity,
and of the role of complex numbers. The phase of the wave function is explained as a feature of purely statistical origin. There is a quantum analogue to the gravitational equivalence principle.

http://arxiv.org/abs/1002.2593

Probabilistic time
Authors: C. Wetterich
(Submitted on 12 Feb 2010)
Abstract: The concept of time emerges as an ordering structure in a classical statistical ensemble. Local probability distributions $p_\tau(t)$ obtain by integrating out the past and future. A unitary time evolution is described by rotations of the wave function $q_\tau(t)=\pm \sqrt{p_\tau(t)}$. We establish a map to quantum physics and the Schr\"odinger equation. Our discussion of classical statistics is based on two-level observables that take the values one or zero in the states of the statistical ensemble. Then the wave functions can be mapped to elements of Grassmann algebra. Quantum field theories for fermions arise naturally from our formulation of probabilistic time.

 

[MTd2]

http://arxiv.org/abs/1002.2640
One Loop Beta Functions in Topologically Massive Gravity

R. Percacci, E. Sezgin
(Submitted on 15 Feb 2010)
We calculate the running of the three coupling constants in cosmological, topologically massive 3d gravity. We find that \nu, the dimensionless coefficient of the Chern-Simons term, has vanishing beta function. The flow of the cosmological constant and Newton's constant depends on \nu, and for any positive \nu there exist both a trivial and a nontrivial fixed point.http://arxiv.org/abs/1002.2668

Comment on "On the Origin of Gravity and the Laws of Newton" by Erik P. Verlinde

Sheldon Gao
(Submitted on 13 Feb 2010)
We show that Verlinde's idea of gravity as an entropic force is untenable. The main reason is that Verlinde made a mistake in identifying the causal relationship between physical variables when applying the first law of thermodynamics to the interacting process between a holographic screen and a particle. Moreover, it is shown that Verlinde's argument also has some other flaws.

 

[MTd2]

http://arxiv.org/abs/1002.3041

A relation between the Barbero-Immirzi parameter and the standard model

Bogusław Broda, Michał Szanecki
(Submitted on 16 Feb 2010)
It has been shown that Sakharov's induced, from the fields entering the standard model, Barbero-Immirzi parameter assumes, in the framework of euclidean formalism, the UV cutoff-independent value, 1/9. The calculus uses the Schwinger's proper-time formalism, the Seeley-DeWitt heat-kernel expansion, and it is akin to the derivation of the ABJ chiral anomaly in space-time with torsion

 

[marcus]

Strong presentation by Livine (video)
http://pirsa.org/10020027/
The U(N) structure of Loop Quantum Gravity
Etera Livine
Abstract: It has recently uncovered that the intertwiner space for LQG carries a natural representation of the U(N) unitary group. I will describe this U(N) action in details and show how it can be used to compute the LQG black hole entropy, to define coherent intertwiner states and to reformulate the LQG dynamics in new terms.
Date: 16/02/2010

The seminar talk is based on work with Laurent Freidel and others. There seem to be some landmark results. The talk makes the papers easier to understand and I'm finding it well worth watching.

In case of interest, here for reference is a 2009 paper with Freidel related to this talk:
http://arxiv.org/abs/0911.3553
The Fine Structure of SU(2) Intertwiners from U(N) Representations
Laurent Freidel, Etera R. Livine
21 pages
(Submitted on 18 Nov 2009)
"In this work we study the Hilbert space space of N-valent SU(2) intertwiners with fixed total spin, which can be identified, at the classical level, with a space of convex polyhedra with N face and fixed total boundary area. We show that this Hilbert space provides, quite remarkably, an irreducible representation of the U(N) group. This gives us therefore a precise identification of U(N) as a group of area preserving diffeomorphism of polyhedral spheres. We use this results to get new closed formulae for the black hole entropy in loop quantum gravity."

 

[marcus]

Livine gives good seminar talks. He's fast, clear, well-organized. He motivates the stuff he's talking about. So I'm including this review of spinfoams video just as if it were an arxiv paper.

http://pirsa.org/10020079/
A review of Spinfoams and Group Field Theory
Etera Livine
Abstract: We will review the definitions of spin foam models for quantum gravity and the recent advances in this field, such as the "graviton propagator", the definition of coherent states of geometry and the derivation of non-commutative field theories as describing the effective dynamics of matter coupled to quantum gravity. I will insist on the role of group field theories as providing a non-perturbative definition of spinfoams and their intricate relation with non-commutative geometry and matrix models.
Date: 17/02/2010 - 2:00 pm

http://arxiv.org/abs/1002.3298
CDT meets Horava-Lifgarbagez gravity
J. Ambjorn, A. Gorlich, S. Jordan, J. Jurkiewicz, R. Loll
14 pages, 3 figures
(Submitted on 17 Feb 2010)
"The theory of causal dynamical triangulations (CDT) attempts to define a non-perturbative theory of quantum gravity as a sum over space-time geometries. One of the assumptions in the CDT framework is the existence of a global time foliation. The same assumption is central in the quantum gravity theory recently formulated by Horava. We show that the phase diagram of CDT is surprising similar to the generic Lifgarbagez phase diagram appealed to by Horava. We argue that CDT might provide a unifying non-perturbative framework for anisotropic as well as isotropic theories of quantum gravity."

If anyone wants to look up an interesting paper that formed part of the basis of Livine's pirsa talk, here's one:

http://arxiv.org/abs/0903.3475
4d Deformed Special Relativity from Group Field Theories
Florian Girelli, Etera R. Livine, Daniele Oriti
23 pages; Physical Review D 81:024015, 2010
(Submitted on 20 Mar 2009)
"We derive a scalar field theory of the deformed special relativity type, living on non-commutative kappa-Minkowski spacetime and with a kappa-deformed Poincare symmetry, from the SO(4,1) group field theory defining the transition amplitudes for topological BF-theory in 4 space-time dimensions. This is done at a non-perturbative level of the spin foam formalism working directly with the group field theory (GFT). We show that matter fields emerge from the fundamental model as perturbations around a specific phase of the GFT, corresponding to a solution of the fundamental equations of motion, and that the non-commutative field theory governs their effective dynamics."

Another window on what Girelli Livine Oriti are doing is this talk by Girelli at the July 2009 Planck Scale conference:
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php?plik=http://panoramix.ift.uni.wroc.pl/~planckscale/video/Day4/4-2.flv&tytul=4.2%20Girelli
The talk was written up in this paper:
http://arxiv.org/abs/0910.3107
Field theories with homogenous momentum space
Florian Girelli, Etera R. Livine
9 pages, To appear in the Proceedings of the XXV Max Born Symposium, "The Planck Scale", Wroclaw, Poland, July 2009
(Submitted on 16 Oct 2009)
"We discuss the construction of a scalar field theory with momentum space given by a coset. By introducing a generalized Fourier transform, we show how the dual scalar field theory actually lives in Snyder's space-time. As a side-product we identify a star product realization of Snyder's non-commutative space, but also the deformation of the Poincare symmetries necessary to have these symmetries realized in Snyder's space-time. A key feature of the construction is that the star product is non-associative."

There was also this recent followup paper. again by Girelli Livine:
http://arxiv.org/abs/1001.2919
A Deformed Poincare Invariance for Group Field Theories
Florian Girelli, Etera R. Livine
11 pages
(Submitted on 17 Jan 2010)
"In the context of quantum gravity, group field theories are field theories that generate spinfoam amplitudes as Feynman diagrams. They can be understood as generalizations of the matrix models used for 2d quantum gravity. In particular Boulatov's theory reproduces the amplitudes of the Ponzano-Regge spinfoam model for 3d quantum gravity. Motivated by recent works on field theories on non-commutative flat spaces, we show that Boulatov's theory (and its colored version) is actually invariant under a global deformed Poincare symmetry. This allows to define a notion of flat/excited geometry states when considering scalar perturbations around classical solutions of the group field equations of motion. As a side-result, our analysis seems to point out that the notion of braiding of group field theories should be a key feature to study further in this context."

The way I see it, the 17 February PIRSA video talk by Livine is the main window on an area of research that is especially interesting and proceeding rapidly. I have listed a few of the papers describing what went into the 17 February talk. Also there is the Planck Scale video talk by Girelli---I just watched this 25 minute talk and the lively question period following it.

 

[MTd2]

http://arxiv.org/abs/1002.3298

CDT meets Horava-Lifgarbagez gravity

J. Ambjorn, A. Gorlich, S. Jordan, J. Jurkiewicz, R. Loll
(Submitted on 17 Feb 2010)
The theory of causal dynamical triangulations (CDT) attempts to define a non-perturbative theory of quantum gravity as a sum over space-time geometries. One of the assumptions in the CDT framework is the existence of a global time foliation. The same assumption is central in the quantum gravity theory recently formulated by Ho\v{r}ava. We show that the phase diagram of CDT is surprising similar to the generic Lifgarbagez phase diagram appealed to by Ho\v rava. We argue that CDT might provide a unifying non-perturbative framework for anisotropic as well as isotropic theories of quantum gravity.

 

[marcus]

http://arxiv.org/abs/1002.3488
The Cosmological Parameters 2010
Ofer Lahav, Andrew R Liddle
25 pages. Article for The Review of Particle Physics 2010 (aka the Particle Data Book), on-line version at http://pdg.lbl.gov/. This article supersedes arXiv:astro-ph/0601168 and arXiv:astro-ph/0406681
(Submitted on 18 Feb 2010)

"This is a review article for The Review of Particle Physics 2010 (aka the Particle Data Book). It forms a compact review of knowledge of the cosmological parameters at the beginning of 2010. Topics included are Parametrizing the Universe; Extensions to the standard model; Probes; Bringing observations together; Outlook for the future."

 

[MTd2]

http://arxiv.org/abs/1002.3592

Linearized Group Field Theory and Power Counting Theorems

Joseph Ben Geloun, Thomas Krajewski, Jacques Magnen, Vincent Rivasseau
(Submitted on 18 Feb 2010)
We introduce a linearized version of group field theory. It can be viewed either as a group field theory over the additive group of a vector space or as an asymptotic expansion of any group field theory around the unit group element. We prove exact power counting theorems for any graph of such models. For linearized colored models the power counting of any amplitude is further computed in term of the homology of the graph. An exact power counting theorem is also established for a particular class of graphs of the nonlinearized models, which satisfy a planarity condition. Examples and connections with previous results are discussed.

 

[marcus]

http://arxiv.org/abs/1002.4278
Entropic Accelerating Universe
Damien A. Easson, Paul H. Frampton, George F. Smoot
10 pages, 1 figure
(Submitted on 23 Feb 2010)
"To accommodate the observed accelerated expansion of the universe, one popular idea is to invoke a driving term in the Friedmann-Lemaître equation of dark energy which must then comprise 70% of the present cosmological energy density. We propose an alternative interpretation which takes into account the temperature intrinsic to the information holographically stored on the screen which is the surface of the universe. Dark energy is thereby obviated and the acceleration is due to an entropic force naturally arising from the information storage on a surface screen. We consider an additional quantitative approach based upon the entropy and surface terms usually neglected in General Relativity and show that this leads to the entropic accelerating universe."

http://arxiv.org/abs/1002.4209
Complete quantum mechanics: an axiomatic formulation of the Montevideo interpretation
Rodolfo Gambini, Luis Pedro Garcia-Pintos, Jorge Pullin
21 pages
(Submitted on 22 Feb 2010)
"We make a first attempt to axiomatically formulate the Montevideo interpretation of quantum mechanics. In this interpretation environmental decoherence is supplemented with loss of coherence due to the use of realistic clocks to measure time to solve the measurement problem. The resulting formulation is framed entirely in terms of quantum objects without having to invoke the existence of measurable classical quantities like the time in ordinary quantum mechanics. The formulation eliminates any privileged role to the measurement process giving an objective definition of when an event occurs in a system."

The next paper is part of Fotini's program. Prémont-Schwarz is a collaborator of hers.
http://arxiv.org/abs/1002.4190
Lieb-Robinson bounds with dependence on interaction strengths
Isabeau Prémont-Schwarz, Jeff Hnybida
19 pages, 1 figure
(Submitted on 22 Feb 2010)
We propose new Lieb-Robinson bounds (bounds on the speed of propagation of information in quantum systems) with an explicit dependence on the interaction strengths of the Hamiltonian. For systems with more than two interactions it is found that the Lieb-Robinson speed is not always algebraic in the interaction strengths. We consider Hamiltonians with any finite number of bounded operators and also a certain class of unbounded operators. We obtain bounds and propagation speeds for quantum systems on lattices and also general graphs possessing a kind of homogeneity and isotropy. One area for which this formalism could be useful is the study of quantum phase transitions which occur when interactions strengths are varied."brief mention:
http://arxiv.org/abs/1002.3877
Higgs for Graviton: Simple and Elegant Solution
Ali H. Chamseddine, Viatcheslav Mukhanov
7 pages

http://arxiv.org/abs/1002.3836
BF gravity with Immirzi parameter and cosmological constant
Merced Montesinos, Mercedes Velazquez
4 pages

 

[MTd2]

http://arxiv.org/abs/1002.4568

Gravity as Quantum Entanglement Force

Jae-Weon Lee, Hyeong-Chan Kim, Jungjai Lee
(Submitted on 24 Feb 2010)
We conjecture that quantum entanglement of matter and vacuum in the universe tend to increase with time, like entropy, and there is an effective force called quantum entanglement force associated with this tendency. It is also suggested that gravity and dark energy are types of the quantum entanglement force, similar to Verlinde's entropic force. If the entanglement entropy of the universe saturates the Bekenstein bound, this gives holographic dark energy with the equation of state consistent with current observational data. This connection between quantum information and gravity gives some new insights on the origin of gravity, dark energy, the holographic principle and arrow of time.

 

[MTd2]

http://arxiv.org/abs/1002.4723

Group field theory in non-commutative metric variables

Aristide Baratin, Daniele Oriti
(Submitted on 25 Feb 2010)
We introduce a dual formulation of group field theories, making them a type of non-commutative field theories. In this formulation, the variables of the field are Lie algebra variables with a clear interpretation in terms of simplicial geometry. For Ooguri-type models, the Feynman amplitudes are simplicial path integrals for BF theories. This formulation suggests ways to impose the simplicity constraints involved in BF formulations of 4d gravity directly at the level of the group field theory action. We illustrate this by giving a new GFT definition of the Barrett-Crane model.

 

[marcus]

http://arxiv.org/abs/1002.4618
Coupling Point-Like Masses to Quantum Gravity with Causal Dynamical Triangulations
Igor Khavkine, Renate Loll, Paul Reska
24 pages, 11 figures
(Submitted on 24 Feb 2010)
"We analyze the possibility of coupling a point-like mass to four-dimensional quantum gravity in the nonperturbative setting of Causal Dynamical Triangulations (CDT). The spatial volume profile of Euclidean Schwarzschild de Sitter space in proper-time form glued to an interior matter solution is derived in the continuum and for small masses, to provide a point of comparison for the classical limit of the matter-coupled CDT model. The volume profile we compute deviates in a characteristic manner from that of the pure-gravity model. As part of the construction, we introduce a particularly simple set of proper-time coordinates on the resulting Euclidean manifold, matching the global time slicing present in CDT. To avoid having to deal with caustics which appear near the source, we excise a tubular neighbourhood around it from the spacetime. We also discuss some of the implementation details for measuring numerically the expectation value of the volume profiles in the framework of CDT when coupled appropriately to the matter source."

 

[marcus]

http://arxiv.org/abs/1002.5001
Coupling Non-Gravitational Fields with Simplicial Spacetimes
Jonathan R. McDonald, Warner A. Miller
10 pages, Accepted for publication in Classical and Quantum Gravity
(Submitted on 26 Feb 2010)
"The inclusion of source terms in discrete gravity is a long-standing problem. Providing a consistent coupling of source to the lattice in Regge Calculus (RC) yields a robust unstructured spacetime mesh applicable to both numerical relativity and quantum gravity. RC provides a particularly insightful approach to this problem with its purely geometric representation of spacetime. The simplicial building blocks of RC enable us to represent all matter and fields in a coordinate-free manner. We provide an interpretation of RC as a discrete exterior calculus framework into which non-gravitational fields naturally couple with the simplicial lattice. Using this approach we obtain a consistent mapping of the continuum action for non-gravitational fields to the Regge lattice. In this paper we apply this framework to scalar, vector and tensor fields. In particular we reconstruct the lattice action for (1) the scalar field, (2) Maxwell field tensor and (3) Dirac particles. The straightforward application of our discretization techniques to these three fields demonstrates a universal implementation of coupling source to the lattice in Regge calculus."

I don't know Warner Miller's earlier work but I see that he has co-authored with some prominent people: eg. James Hartle and Ruth Williams.

 

[MTd2]

http://arxiv.org/abs/1002.4880

Interferometers as Holographic Clocks

Craig J. Hogan
(Submitted on 25 Feb 2010)
A new fundamental limit is postulated on measurement of time in holographic theories where light sheets carry degrees of freedom that saturate the entropy limit of black hole event horizons. Holographic clock operators are associated with null displacements and spatial orientations. Null fields preserve clock phase along their propagation direction, and clock phase is invariant on null sheets, but time measurements in different directions do not commute. This hypothesis is shown to lead to spatially coherent holographic noise in relative phases of null fields propagating in different directions. Current technology allows Michelson interferometers to achieve the Planck-scale holographic noise limit in differential phase measurements. Cross-correlations of holographic phase noise between interferometers are calculated, depending on their separation and alignment.

 

[marcus]

http://arxiv.org/abs/1003.0352
Towards inhomogeneous loop quantum cosmology: triangulating Bianchi IX with perturbations
Antonino Marciano
4 pages. To appear in the proceedings of 12th Marcel Grossmann Meeting on General Relativity (MG 12), Paris, France, 12-18 Jul 2009
(Submitted on 1 Mar 2010)
"This brief article sums up results obtained in arXiv:0911.2653, which develops a constrained SU(2) lattice gauge theory in the 'dipole' approximation. This is a further step toward the issue of a (inhomogeneous) loop quantum cosmology and its merging into loop quantum gravity."

http://arxiv.org/abs/1003.0395
A brief overview of quantum field theory with deformed symmetries and their relation with quantum gravity
Antonino Marciano
4 pages. To appear in the proceedings of 12th Marcel Grossmann Meeting on General Relativity (MG 12), Paris, France, 12-18 Jul 2009
(Submitted on 1 Mar 2010)
"In this letter we outline some reasons for considering a quantum field theory symmetric under quantum groups and we sketch some results obtained with collaborators in the k-Poincare framework. We deal with this latter as a toy model towards an effective and low-energy theory of quantum gravity, the new physically relevant effects of which are Planck-scale suppressed."

http://arxiv.org/abs/1003.0285
Planck Scale Effect in the Entropic Force Law
Subir Ghosh (Indian Statistical Institute)
8 pages
(Submitted on 1 Mar 2010)
"In this note we generalize the quantum uncertainty relation proposed by Vancea and Santos [7] in the entropic force law, by introducing Planck scale modifications. The latter is induced by the Generalized Uncertainty Principle. We show that the proposed uncertainty relation of [7], involving the entropic force and the square of particle position, is in fact bounded from above from considering Planck length as the minimum measurable length."

 

[MTd2]

http://arxiv.org/abs/1003.0009

Emergent Gravity at a Lifgarbagez Point from a Bose Liquid on the Lattice

Cenke Xu, Petr Horava
(Submitted on 1 Mar 2010)
We propose a model with quantum bosons on the fcc lattice, which has a stable algebraic Bose liquid phase at low energy. We show that this phase is described by emergent quantum gravity at the Gaussian z = 3 Lifgarbagez fixed point in 3+1 dimensions. The stability of this algebraic Bose liquid phase is guaranteed by the gauge symmetry of gravitons and self-duality of the low energy field theory. By tuning one parameter in the lattice boson model we can drive a phase transition between the z = 3 Lifgarbagez gravity and another algebraic Bose liquid phase, described by gravity at the z = 2 Lifgarbagez point.

 

[marcus]

Sabine Hossenfelder's notes commenting on Verlinde's paper.
http://prime-spot.de/Physics/notes6.pdf
Her blog entry summarizing what she said in the notes:
http://backreaction.blogspot.com/2010/03/gravity-is-entropy-is-gravity-is.html

http://arxiv.org/abs/1003.0668
Entropic dark energy and sourced Friedmann equations
Ulf H. Danielsson
7 pages
(Submitted on 2 Mar 2010)
"In this paper we show that a recent attempt to derive dark energy as an entropic force suffers from the same problems as earlier attempts motivated by holography. The remedy is again the introduction of source terms."

 

[MTd2]

http://arxiv.org/abs/1003.0876

The generalized second law of thermodynamics in Horava-Lifgarbagez cosmology

Mubasher Jamil, Emmanuel N. Saridakis, M. R. Setare
(Submitted on 3 Mar 2010)
We investigate the validity of the generalized second law of thermodynamics in a universe governed by Horava-Lifgarbagez gravity. We calculate separately the entropy time-variation for the matter fluid and, using the modified entropy relation, that of the apparent horizon itself. We find that under detailed balance the generalized second law is generally valid for flat and closed geometry and it is conditionally valid for an open universe, while beyond detailed balance it is only conditionally valid for all curvatures. Furthermore, we also follow the effective approach showing that it can lead to misleading results. The non-complete validity of the generalized second law could either provide a suggestion for its different application, or act as an additional problematic feature of Horava-Lifgarbagez gravity.

 

[marcus]

http://arxiv.org/abs/1003.1015
Comments on and Comments on Comments on Verlinde's paper "On the Origin of Gravity and the Laws of Newton"
Sabine Hossenfelder
(Submitted on 4 Mar 2010)
"We offer some, hopefully clarifying, comments on Verlinde's recent claim that gravity is an entropic force. A suitable identification of quantities shows that both formulations of Newtonian gravity, the classical and the thermodynamical one, are actually equivalent. It turns out that some additional assumptions made by Verlinde are unnecessary. However, when it comes to General Relativity there remain some gaps in the argument. We comment on whether this identification can be done also for electrostatics. Finally, some thoughts on the use of this reinterpretation are offered."

 

[MTd2]

http://arxiv.org/abs/1003.1262

Is Holographic Entropy and Gravity the result of Quantum Mechanics?

Joakim Munkhammar
(Submitted on 5 Mar 2010)
In this paper we suggest a connection between quantum mechanics and Verlinde's recently proposed entropic force theory of Newtons laws. We propose an entropy based on the quantum mechanical probability density distribution. With the assumption that the holographic principle holds we propose that our suggested quantum entropy generalizes the Bekenstein entropy used by Verlinde in his approach. Based on this assumption we suggest that Verlinde's entropic theory of gravity has a quantum mechanical origin. We establish a reformulation of the Newtonian potential for gravity based on this quantum mechanical entropy. We also discuss the notion of observation and the correspondence to classical physics. Finally we give a discussion, a number of open problems and some concluding remarks.

 

[MTd2]

http://arxiv.org/abs/1003.1625

Black Holes and Photons with Entropic Force

Xiao-Gang He, Bo-Qiang Ma
(Submitted on 8 Mar 2010)
We study entropic force effects on black holes and photons. We find that application of an entropic analysis restricts the radial change $\Delta R$ of a black hole of radius $R_{\mathrm{H}}$, due to a test particle of a Schwartzchild radius $R_{h}$ moving towards the black hole by $\Delta x$ near black body surface, is given by a relation $R_{\mathrm{H}} \Delta R= R_h \Delta x/2$, or ${\Delta R}/{\lambdabar_M} = {\Delta x}/{2 \lambdabar_m}$. This relation unifies Verlinde's conjecture and the black hole entropy formula. We propose to extend the entropic force idea to massless particles such as a photon. We also find that there is an entropic force on a photon of energy $E_\gamma$, with $F=G M m_{\gamma}/R^2$, and therefore the photon has an effective gravitational mass $m_\gamma = E_\gamma/c^2$.

http://arxiv.org/abs/1003.1619

Extended Loop Quantum Gravity

L.Fatibene, M.Ferraris, M.Francaviglia
(Submitted on 8 Mar 2010)
We discuss constraint structure of extended theories of gravitation (also known as f(R) theories) in the vacuum selfdual formulation introduced in ref. [1].

http://arxiv.org/abs/1003.1528

Entropic Inflation

Damien A. Easson, Paul H. Frampton, George F. Smoot
(Submitted on 7 Mar 2010)
One of the major pillars of modern cosmology is a period of accelerating expansion in the early universe. This accelerating expansion, or inflation, must be sustained for at least 30 e--foldings. One mechanism, used to drive the acceleration, is the addition of a new energy field, called the Inflaton; often this is a scalar field. We propose an alternative mechanism which, like our approach to explain the late-time accelerating universe, uses the entropy and temperature intrinsic to information holographically stored on a screen enclosing the observed space. The acceleration is due in both cases to an emergent entropic force, naturally arising from the information storage on the horizon.

 

[atyy]

http://arxiv.org/abs/1003.1366
Fundamentals of the Exact Renormalization Group
Oliver J. Rosten
(Submitted on 6 Mar 2010)
Various aspects of the Exact Renormalization Group (ERG) are explored, starting with a review of the concepts underpinning the framework and the circumstances under which it is expected to be useful. A particular emphasis is placed on the intuitive picture provided for both renormalization in quantum field theory and universality associated with second order phase transitions. A qualitative discussion of triviality, asymptotic freedom and asymptotic safety is presented. Focusing on scalar field theory, the construction of assorted flow equations is considered using a general approach, whereby different ERGs follow from field redefinitions. It is recalled that Polchinski's equation can be cast as a heat equation, which provides intuition and computational techniques for what follows. The analysis of properties of exact solutions to flow equations includes a proof that the spectrum of the anomalous dimension at critical fixed-points is quantized. Two alternative methods for computing the beta-function in lambda phi^4 theory are considered. For one of these it is found that all explicit dependence on the non-universal differences between a family of ERGs cancels out, exactly. The Wilson-Fisher fixed-point is rediscovered a rather novel way. The discussion of nonperturbative approximation schemes focuses on the derivative expansion, and includes a refinement of the arguments that, at the lowest order in this approximation, a function can be constructed which decreases monotonically along the flow. Following a sketch of how to adapt the ERG to gauge theories in a manifestly gauge invariant fashion, a new perspective is provided on the relationship between the renormalizability of the Wilsonian effective action and of correlation functions. This suggests a new approach to quantum field theory.

 

[MTd2]

http://arxiv.org/abs/1003.1886

Asymptotics of 4d spin foam models

John W. Barrett, Richard J. Dowdall, Winston J. Fairbairn, Henrique Gomes, Frank Hellmann, Roberto Pereira
(Submitted on 9 Mar 2010)
We study the asymptotic properties of four-simplex amplitudes for various four-dimensional spin foam models. We investigate the semi-classical limit of the Ooguri, Euclidean and Lorentzian EPRL models using coherent states for the boundary data. For some classes of geometrical boundary data, the asymptotic formulae are given, in all three cases, by simple functions of the Regge action for the four-simplex geometry.http://arxiv.org/abs/1003.1847

Observables in 3d spinfoam quantum gravity with fermions

Richard J. Dowdall, Winston J. Fairbairn
(Submitted on 9 Mar 2010)
We study expectation values of observables in three-dimensional spinfoam quantum gravity coupled to Dirac fermions. We revisit the model introduced by one of the authors and extend it to the case of massless fermionic fields. We introduce observables, analyse their symmetries and the corresponding proper gauge fixing. The Berezin integral over the fermionic fields is performed and the fermionic observables are expanded in open paths and closed loops associated to pure quantum gravity observables. We obtain the vertex amplitudes for gauge-invariant observables, while the expectation values of gauge-variant observables, such as the fermion propagator, are given by the evaluation of particular spin networks.

http://arxiv.org/abs/1003.1878

Zero Cosmological Constant and Nonzero Dark Energy from Holographic Principle

Jae-Weon Lee
(Submitted on 9 Mar 2010)
It is shown that the holographic principle applied to a cosmic causal horizon demands that the cosmological constant is zero. This theory also predicts dynamical dark energy in the form of the holographic dark energy with a parameter $d=1$ and an equation of state $w_0\simeq -0.903$ comparable to current observational data.