Loop-and-allied QG bibliography

[marcus]

http://arxiv.org/abs/1101.4049
Cosmological constant in spinfoam cosmology
Eugenio Bianchi, Thomas Krajewski, Carlo Rovelli, Francesca Vidotto
4 pages, 2 figures
(Submitted on 20 Jan 2011)
"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/1101.4182
The 1/N expansion of colored tensor models in arbitrary dimension
Razvan Gurau, Vincent Rivasseau
4 pages, 3 figures
(Submitted on 21 Jan 2011)
"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."

 

[marcus]

http://arxiv.org/abs/1101.4294
Radiative corrections in the Boulatov-Ooguri tensor model: The 2-point function
Joseph Ben Geloun, Valentin Bonzom
24 pages, 3 figures
(Submitted on 22 Jan 2011)
"The Boulatov-Ooguri tensor model generates a sum over spacetime topologies for the D-dimensional BF theory. We study here the quantum corrections to the propagator of the theory. In particular, we find that the radiative corrections at the second order in the coupling constant yield a mass renormalization. They also exhibit a divergence which cannot be balanced with a counter-term in the initial action, and which usually corresponds to the wave-function renormalization."

 

[Kevin_Axion]

http://www.perimeterscholars.org/303.html
Renate Loll is beginning her course at PI for the PSI program. The first lecture was posted today which will be followed by 14 more. If anyone is interested in learning Quantum Gravity (including LQG, CDT etc.) this is a very good resource, make sure you know your GR and Differential Geometry!

Move if necessary

 

[marcus]

http://arxiv.org/abs/1101.4788
Gravity as a diffeomorphism invariant gauge theory
Kirill Krasnov
24 pages
(Submitted on 25 Jan 2011)
"A general diffeomorphism invariant SU(2) gauge theory is a gravity theory with two propagating polarisations of the graviton. We develop this description of gravity, in particular for future applications to the perturbative quantisation. Thus, the linearised theory, gauge symmetries, gauge fixing are discussed in detail, and the propagator is obtained. The propagator takes a simple form of that of Yang-Mills theory with an additional projector on diffeomorphism equivalence classes of connections inserted. In our approach the gravitational perturbation theory takes a rather unusual form in that the Planck length determined from the self-coupling of the graviton is no longer fundamental but becomes a derived quantity."

http://arxiv.org/abs/1101.4775
Perfect discretization of reparametrization invariant path integrals
Benjamin Bahr, Bianca Dittrich, Sebastian Steinhaus
22+8 pages
(Submitted on 25 Jan 2011)
"To obtain a well defined path integral one often employs discretizations. In the case of gravity and reparametrization invariant systems, the latter of which we consider here as a toy example, discretizations generically break diffeomorphism and reparametrization symmetry, respectively. This has severe implications, as these symmetries determine the dynamics of the corresponding system. Indeed we will show that a discretized path integral with reparametrization invariance is necessarily also discretization independent and therefore uniquely determined by the corresponding continuum quantum mechanical propagator. We use this insight to develop an iterative method for constructing such a discretized path integral, akin to a Wilsonian RG flow. This allows us to address the problem of discretization ambiguities and of an anomaly--free path integral measure for such systems. The latter is needed to obtain a path integral, that can act as a projector onto the physical states, satisfying the quantum constraints. We will comment on implications for discrete quantum gravity models, such as spin foams."

brief mention:
http://arxiv.org/abs/1101.4916
On the Semiclassical Approach to Quantum Cosmology
Edward Anderson

 

[MTd2]

http://arxiv.org/abs/1101.4783

NC GUTs: A Status Report

C.P.Martin
(Submitted on 25 Jan 2011)
I review the main results that have been obtained so far on the construction of noncommutative GUTs

***

One of these days I asked something about this...

 

[marcus]

http://arxiv.org/abs/1101.5061
A Short and Subjective Introduction to the Spinfoam Framework for Quantum Gravity
Etera R. Livine
90 pages
(Submitted on 26 Jan 2011)
"This is my Thèse d'Habilitation (HDR) on the topic of spinfoam models for quantum gravity, which I presented in l'Ecole Normale Supérieure de Lyon on december 16 2010. The spinfoam framework is a proposal for a regularized path integral for quantum gravity, inspired from Topological Quantum Field Theory (TQFT) and state-sum models. It can also be seen as defining transition amplitudes for the quantum states of geometry for Loop Quantum Gravity (LQG)."

http://arxiv.org/abs/1101.5136
Extremal and nonextremal Kerr/CFT correspondences
S. Carlip
16 pages
(Submitted on 26 Jan 2011)
"I rederive the Kerr/CFT correspondence without first taking the near-horizon extremal Kerr limit. This method extends easily to nonextremal black holes, for which the temperature and central charge behave poorly at the horizon but the entropy remains finite. A computation yields one-half of the standard Bekenstein-Hawking entropy, with hints that the other half may be related to a conformal field theory at the inner horizon. I then present an alternative approach, based on a stretched Killing horizon, in which the full entropy is obtained and the temperature and central charge remain well-behaved even in the nonextremal case."

 

[marcus]

http://arxiv.org/abs/1101.5391
Observational constraints on loop quantum cosmology
Martin Bojowald, Gianluca Calcagni, Shinji Tsujikawa
4 pages, 3 figures
(Submitted on 27 Jan 2011)
"In the inflationary scenario of loop quantum cosmology (LQC) in the presence of inverse-volume corrections, we give analytic formulas for the power spectra of scalar and tensor perturbations convenient to confront with observations. Since inverse-volume corrections can provide strong contributions to the running spectral indices, inclusion of terms higher than the second-order runnings in the power spectra is crucially important. Using the recent data of cosmic microwave background (CMB) and other cosmological experiments, we place bounds on the quantum corrections for a quadratic inflaton potential."

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
Report number: IGC-11/1-1, AEI-2011-004
Cite as: arXiv:1101.5391v1 [astro-ph.CO]

I bolded some key language. Interesting that this was posted in the Astrophysics section of Arxiv, in astro-ph, not in hep-th or gr-qc. Tsujikawa is astrophysics-phenomenology---not a QG-ist. It's a shift towards the observational side.

 

[atyy]

http://arxiv.org/abs/1101.5185
Einstein Manifolds As Yang-Mills Instantons
John J. Oh, Hyun Seok Yang
(Submitted on 27 Jan 2011)
We show that every Einstein manifolds are Yang-Mills instantons in O(4) = SU(2)L × SU(2)R
gauge theory. It is shown that any Einstein manifold with or without a cosmological constant always arises as the sum of SU(2)L instantons and SU(2)R anti-instantons. It explains why an Einstein manifold is stable because two kinds of instantons belong to different gauge groups, one in SU(2)L and the other in SU(2)R, and so they cannot decay into a vacuum. We discuss the topological aspects of Einstein manifolds.

http://arxiv.org/abs/1101.5315
Special Geometries Emerging from Yang-Mills Type Matrix Models
Daniel N. Blaschke
(Submitted on 27 Jan 2011)
Abstract: I review some recent results which demonstrate how various geometries, such as Schwarzschild and Reissner-Nordstroem, can emerge from Yang-Mills type matrix models with branes. Furthermore, explicit embeddings of these branes as well as appropriate Poisson structures and star-products which determine the non-commutativity of space-time are provided. These structures are motivated by higher order terms in the effective matrix model action which semi-classically lead to an Einstein-Hilbert type action.

 

[MTd2]

http://arxiv.org/abs/1101.5552

Asymptotic freedom of Yang-Mills theory with gravity

Sarah Folkerts, Daniel F. Litim, Jan M. Pawlowski
(Submitted on 28 Jan 2011)
We study the high energy behaviour of Yang-Mills theory under the inclusion of gravity. In the weak-gravity limit, the running gauge coupling receives no contribution from the gravitational sector, if all symmetries are preserved. This holds true with and without cosmological constant. We also show that asymptotic freedom persists in general field-theory-based gravity scenarios including gravitational shielding as well as asymptotically safe gravity.

http://arxiv.org/abs/1101.5401

Asymptotically Safe Cosmology

Mark Hindmarsh, Daniel Litim, Christoph Rahmede
(Submitted on 27 Jan 2011)
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/1101.5585

2+1 gravity with positive cosmological constant in LQG: a proposal for the physical state

Daniele Pranzetti
(Submitted on 28 Jan 2011)
In this paper, I investigate the possible quantization, in the context of LQG, of three dimensional gravity in the case of positive cosmological constant {\Lambda} and try to make contact with alternative quantization approaches already existing in the literature. Due to the appearance of an anomaly in the constraints algebra, previously studied as a first step of the analysis, alternative techniques developed for the quantization of systems with constraints algebras not associated with a structure Lie group need to be adopted. Therefore, I introduce an ansatz for a physical state which gives some transition amplitudes in agreement with what one would expect from the Turaev-Viro model. Moreover, in order to check that this state implements the right dynamicss, I show that it annihilates the master constraint for the theory up to the first order in {\Lambda}.

http://arxiv.org/abs/1101.5592

Loop Quantum Gravity and Cosmology: A dynamical introduction

Martin Bojowald
(Submitted on 28 Jan 2011)
Loop quantum gravity and cosmology are reviewed with an emphasis on evaluating the dynamics, rather than constructing it. The three crucial parts of such an analysis are (i) deriving effective equations, (ii) controlling the theory's microscopic degrees of freedom that lead to its spatial discreteness and refinement, and (iii) ensuring consistency and anomaly-freedom. All three issues are crucial for making the theory testable by conceptual and observational means, and they remain challenging. Throughout this review, the Hamiltonian nature of the theory will play a large role for properties of space-time structure within the framework discussed.

 

[marcus]

http://arxiv.org/abs/1101.5792
Particle Creation by Loop Black Holes
Emanuele Alesci, Leonardo Modesto
14 pages, 6 figures
(Submitted on 30 Jan 2011)
"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
Induced standard model and unification
John W. Barrett
(Submitted on 31 Jan 2011)
"A proposal that the bosonic action of the standard model is induced from the fermionic action is investigated."

http://arxiv.org/abs/1101.6007
QED coupled to QEG
Ulrich Harst, Martin Reuter
25 pages, 3 figures
(Submitted on 31 Jan 2011)
"We discuss the non-perturbative renormalization group flow of Quantum Electrodynamics (QED) coupled to Quantum Einstein Gravity (QEG) and explore the possibilities for defining its continuum limit at a fixed point that would lead to a non-trivial, i.e. interacting field theory. We find two fixed points suitable for the Asymptotic Safety construction. In the first case, the fine-structure constant vanishes at the fixed point and its infrared ("renormalized") value is a free parameter not determined by the theory itself. In the second case, the fixed point value of the fine-structure constant is non-zero, and its infrared value is a computable prediction of the theory."

A notable paper included despite no direct explicit connection with QG
http://arxiv.org/abs/1101.5690
Division Algebras and Quantum Theory
John C. Baez
30 pages, 3 figures
(Submitted on 29 Jan 2011)
"Quantum theory may be formulated using Hilbert spaces over any of the three associative normed division algebras: the real numbers, the complex numbers and the quaternions. Indeed, these three choices appear naturally in a number of axiomatic approaches. However, there are internal problems with real or quaternionic quantum theory. Here we argue that these problems can be resolved if we treat real, complex and quaternionic quantum theory as part of a unified structure. Dyson called this structure the 'three-fold way'. It is perhaps easiest to see it in the study of irreducible unitary representations of groups on complex Hilbert spaces. These representations come in three kinds: those that are not isomorphic to their own dual (the truly 'complex' representations), those that are self-dual thanks to a symmetric bilinear pairing (which are 'real', in that they are the complexifications of representations on real Hilbert spaces), and those that are self-dual thanks to an antisymmetric bilinear pairing (which are 'quaternionic', in that they are the underlying complex representations of representations on quaternionic Hilbert spaces). This three-fold classification sheds light on the physics of time reversal symmetry, and it already plays an important role in particle physics. More generally, Hilbert spaces of anyone of the three kinds - real, complex and quaternionic - can be seen as Hilbert spaces of the other kinds, equipped with extra structure."

 

[atyy]

http://arxiv.org/abs/1102.0270
Topological Phases: An Expedition off Lattice
Michael H. Freedman, Lukas Gamper, Charlotte Gils, Sergei V. Isakov, Simon Trebst, Matthias Troyer
(Submitted on 1 Feb 2011)
Motivated by the goal to give the simplest possible microscopic foundation for a broad class of topological phases, we study quantum mechanical lattice models where the topology of the lattice is one of the dynamical variables. However, a fluctuating geometry can remove the separation between the system size and the range of local interactions, which is important for topological protection and ultimately the stability of a topological phase. In particular, it can open the door to a pathology, which has been studied in the context of quantum gravity and goes by the name of `baby universe', Here we discuss three distinct approaches to suppressing these pathological fluctuations. We complement this discussion by applying Cheeger's theory relating the geometry of manifolds to their vibrational modes to study the spectra of Hamiltonians. In particular, we present a detailed study of the statistical properties of loop gas and string net models on fluctuating lattices, both analytically and numerically.

 

[marcus]

http://arxiv.org/abs/1102.0954
The Holst Action by the Spectral Action Principle
Frank Pfaeffle, Christoph A. Stephan
11 pages
(Submitted on 4 Feb 2011)
"We investigate the Holst action for closed Riemannian 4-manifolds with orthogonal connections. For connections whose torsion has zero Cartan type component we show that the Holst action can be recovered from the heat asymptotics for the natural Dirac operator acting on left-handed spinor fields."

(If anyone is coming in new to this, Holst action is the action used in Spinfoam LQG and Spectral Action Principle means they are talking Connes NC geometry realization of standard model matter. The title indicates they want to put Connes-style standard model matter together with LQG. Read the paper to get more detail.)

In post #1410 I logged a paper by John Barrett, "Induced standard model and unification". In the course of revision this has been given a new title:
http://arxiv.org/abs/1101.6078
State sum models, induced gravity and the spectral action
John W. Barrett
13 pages
(Submitted on 31 Jan 2011)
"A proposal that the bosonic action of 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/1102.0789
The emergence of a universal limiting speed
Mohamed M. Anber, John F. Donoghue
13 pages, 3 figures
(Submitted on 3 Feb 2011)
"We display several examples of how fields with different limiting velocities (the "speed of light") at a high energy scale can nevertheless have a common limiting velocity at low energies due to the effects of interactions. We evaluate the interplay of the velocities through the self-energy diagrams and use the renormalization group to evolve the system to low energy. The differences normally vanish only logarithmically, so that an exponentially large energy trajectory is required in order to satisfy experimental constraints. However, we also display a model in which the running is power-law, which could be more phenomenologically useful. The largest velocity difference should be in system with the weakest interaction, which suggests that the study of the speed of gravitational waves would be the most stringent test of this phenomenon."

 

[marcus]

http://arxiv.org/abs/1102.1688
State Sums and Geometry
Frank Hellmann
PhD Thesis, 106 pages
(Submitted on 8 Feb 2011)
"In this thesis I review the definition of topological quantum field theories through state sums on triangulated manifolds. I describe the construction of state sum invariants of 3-manifolds from a graphical calculus and show how to evaluate the invariants as boundary amplitudes. I review how to define such a graphical calculus through SU(2) representation theory. I then review various geometricity results for the representation theory of SU(2), Spin(4) and SL(2,C), and define coherent boundary manifolds for state sums based on these representations. I derive the asymptotic geometry of the SU(2) based Ponzano-Regge invariant in three dimensions, and the SU(2) based Ooguri models amplitude in four dimensions. As a corollary to the latter results I derive the asymptotic behaviour of various recently proposed spin foam models motivated from the Plebanski formulation of general relativity. Finally the asymptotic geometry of the SL(2,C) based model is derived."

 

[marcus]

http://arxiv.org/abs/1102.1844
Comment on `Lost in Translation: Topological Singularities in Group Field Theory'
Matteo Smerlak
(Submitted on 9 Feb 2011)
"Gurau argued in [arXiv:1006.0714] that the gluing spaces arising as Feynman diagrams of three-dimensional group field theory are not all pseudo-manifolds. I dispute this conclusion: albeit not properly triangulated, these spaces are genuine pseudo-manifolds, viz. their singular locus is of codimension at most two."

 

[atyy]

http://arxiv.org/abs/1102.1592
Emergent of non-gravitational fields in dimensional reduction of 4d spin foam models
Somayeh Fani, Kamran Kaviani
(Submitted on 8 Feb 2011 (v1), last revised 9 Feb 2011 (this version, v2))
We consider a Kaluza-Klein like approach for a 4d spin foam model. We apply this approach to a 4d TOCY model based on group field theory; and using the Peter-Weyl expansion of the gravitational field we find a mechanism for generation of matter and new dimensions from pure gravity.

 

[MTd2]

http://arxiv.org/abs/1102.2226

Discrete and continuum third quantization of Gravity

Steffen Gielen, Daniele Oriti
(Submitted on 10 Feb 2011)
We give a brief introduction to matrix models and the group field theory (GFT) formalism as realizations of the idea of a third quantization of gravity, and present in some more detail the idea and basic features of a continuum third quantization formalism in terms of a field theory on the space of connections, building up on the results of loop quantum gravity that allow to make the idea slightly more concrete. We explore to what extent one can rigorously define such a field theory. Concrete examples are given for the simple case of Riemannian GR in 3 spacetime dimensions. We discuss the relation between GFT and this formal continuum third quantized gravity, and what it can teach us about the continuum limit of GFTs.

 

[marcus]

Not directly about QG, but Baez is "family" and it could apply to Jacobson, Verlinde gravity conceivably

http://arxiv.org/abs/1102.2098
Renyi Entropy and Free Energy
John C. Baez
(Submitted on 10 Feb 2011)
"The Renyi entropy is a generalization of the usual concept of entropy which depends on a parameter beta. Any probability distribution can be seen as the Gibbs state for some Hamiltonian at temperature 1. Starting with this Hamiltonian, we can then compute the free energy at temperature T, and up to a certain factor this turns out to be the Renyi entropy where beta = 1/T. More precisely, the free energy is (1 - T) times the Renyi entropy. This is true not only classically but also quantum-mechanically."

 

[physikdan]

http://arxiv.org/abs/1102.1592
Emergent of non-gravitational fields in dimensional reduction of 4d spin foam models
Somayeh Fani, Kamran Kaviani
(Submitted on 8 Feb 2011 (v1), last revised 9 Feb 2011 (this version, v2))
We consider a Kaluza-Klein like approach for a 4d spin foam model. We apply this approach to a 4d TOCY model based on group field theory; and using the Peter-Weyl expansion of the gravitational field we find a mechanism for generation of matter and new dimensions from pure gravity.

It is inersting that they do Kaluza-Klein strategy to a very different subject ! and ern some how similar results.

 

[marcus]

Please start a separate discussion thread about the paper. We don't discuss papers in this thread. This is a bibliography thread to help us keep track of current Loop-and-allied research. It overloads and makes it less useful to have discussion crowding in.
I would welcome a discussion thread about this paper by the two guys at Teheran (have already asked Atyy what he thinks of it.)

 

[marcus]

http://arxiv.org/abs/1102.2376
Local covariance and background independence
Klaus Fredenhagen, Katarzyna Rejzner
9 pages, submitted for the Proceedings of the conference "Quantum field theory and gravity", Regensburg (28 Sep - 1 Oct 2010)
(Submitted on 11 Feb 2011)
"One of the many conceptual difficulties in the development of quantum gravity is the role of a background geometry for the structure of quantum field theory. To some extent the problem can be solved by the principle of local covariance. The principle of local covariance was originally imposed in order to restrict the renormalization freedom for quantum field theories on generic spacetimes. It turned out that it can also be used to implement the request of background independence. Locally covariant fields then arise as background independent entities."

 

[marcus]

http://arxiv.org/abs/1102.2694
Scalar Perturbation in a Big Bounce of Loop Quantum Cosmology
Yu Li, Jian-Yang Zhu
6 pages, 5 figures
(Submitted on 14 Feb 2011)
"We study the behaviors of the scalar perturbation in the bounce phase of the effective loop quantum cosmology. Two models are discussed: one is the universe fulfilled by a messless scalar field; the other is a more realistic model which can translate to the universe dominated by radiation. We find that the behaviors of the Bardeen potential near both the bounce point and the transition point of null energy condition are good. This is different from the bounce models in pure general relativity, and we may conclude that the bounce in loop quantum cosmology is reasonable."

http://arxiv.org/abs/1102.2695
Stability analysis of an autonomous system in loop quantum cosmology
Kui Xiao, Jian-Yang Zhu
9 pages
(Submitted on 14 Feb 2011)
"We discuss the stability properties of an autonomous system in loop quantum cosmology (LQC) scenario. The system is described by a self-interacting scalar field phi with positive potential V coupled with a barotropic fluid in Universe. Considering Gamma = V V"/V'² as a function of $$\lambda=V'/V$$, the autonomous system is extended from 3-dimension to 4-dimension. We find that the dynamical behaviors of some fixed points suit for all potential, and some just suit for the concrete potential. Considering the higher-order derivatives of the potential, we get an infinite-dimensional autonomous system which can describe the dynamical behavior of scalar field with more general potential. We find that there is just a scalar-field-dominated scaling solution in LQC scenario."

http://arxiv.org/abs/1102.2720
Application of higher order holonomy corrections to perturbation theory of cosmology
Yu Li, Jian-Yang Zhu
7 pages, 1 figure
(Submitted on 14 Feb 2011)
"Applying the higher order holonomy corrections to the perturbation theory of cosmology, the lattice power law of Loop Quantum Cosmology, $$\tilde{\mu}\propto p^{\beta}$$, is analysed and the range of beta is decided to be [-1,0] which is different from the conventional range $$-0.1319>\beta\geq-5/2$$. At the same time, we find that there is a anomaly free condition in this theory, and we obtain this condition in the vector and tensor mode. We also find that the nonzero mass of gravitational wave essentially results from the quantum nature of Riemannian geometry of loop quantum gravity."

http://arxiv.org/abs/1102.2758
Interacting modified Chaplygin gas in loop quantum cosmology
Mubasher Jamil, Ujjal Debnath
7 pages, 7 figures, accepted for publication in 'Astrophysics and Space Science'
(Submitted on 14 Feb 2011)
"We investigate the background dynamics when dark energy is coupled to dark matter in the universe described by loop quantum cosmology. We consider dark energy of the form modified Chaplygin gas. The dynamical system of equations is solved numerically and a stable scaling solution is obtained. It henceforth resolves the famous cosmic coincidence problem in modern cosmology. The statefinder parameters are also calculated to classify this dark energy model."

http://arxiv.org/abs/1102.2613
Photon Gas Thermodynamics in Doubly Special Relativity
Xinyu Zhang, Lijing Shao, Bo-Qiang Ma
17 pages, 7 figures
(Submitted on 13 Feb 2011)
"Doubly special relativity (DSR), with both an invariant velocity and an invariant length scale, elegantly preserves the principle of relativity between moving observers, and appears as a promising candidate of the quantum theory of gravity. We study the modifications of photon gas thermodynamics in the framework of DSR with an invariant length |lambda|, after properly taking into account the effects of modified dispersion relation, upper bounded energy-momentum space, and deformed integration measure. We show that with a positive lambda, the grand partition function, the energy density, the specific heat, the entropy, and the pressure are smaller than those of special relativity (SR), while the velocity of photons and the ratio of pressure to energy are larger. In contrast, with a negative $\lambda$, the quantum gravity effects show up in the opposite direction. However, these effects only manifest themselves significantly when the temperature is larger than 10^-3 E_Planck. Thus, DSR can have considerable influence on the early universe in cosmological study."

http://arxiv.org/abs/1102.2784
New Limits on Planck Scale Lorentz Violation from Gamma-ray Burst Polarization
Floyd W. Stecker
3 pages, submitted to Phys. Rev. Letters
(Submitted on 14 Feb 2011)
"Constraints on possible Lorentz invariance violation to first order in E/M_Planck for photons in the framework of effective field theory are discussed. Using the detection of polarized soft gamma-ray emission from the gamma-ray burst GRB041219a that indicates the absence of vacuum birefringence, together with a method for estimating the redshift of the burst, we improve the previous constraints on the dimension 5 Lorentz violating modification to the Lagrangian of an effective local QFT for QED by 4 orders of magnitude."

http://arxiv.org/abs/1102.2855
Causality, Bell's theorem, and Ontic Definiteness
Joe Henson
40 pages (26 main text), 3 figures
(Submitted on 14 Feb 2011)
"Bell's theorem shows that the reasonable relativistic causal principle known as 'local causality' is not compatible with the predictions of quantum mechanics. It is not possible maintain a satisfying causal principle of this type while dropping any of the better-known assumptions of Bell's theorem. However, another assumption of Bell's theorem is the use of classical logic. One part of this assumption is the principle of 'ontic definiteness', that is, that it must in principle be possible to assign definite truth values to all propositions treated in the theory. Once the logical setting is clarified somewhat, it can be seen that rejecting this principle does not in any way undermine the type of causal principle used by Bell. Without ontic definiteness, the deterministic causal condition known as Einstein Locality succeeds in banning superluminal influence (including signalling) whilst allowing correlations that violate Bell's inequalities. Objections to altering logic, and the consequences for operational and realistic viewpoints, are also addressed."

 

[MTd2]

http://arxiv.org/abs/1102.3130

Physical Boundary State for the Quantum 4-Simplex

Maité Dupuis, Etera R. Livine
(Submitted on 15 Feb 2011)
In the spinfoam framework for quantum gravity, we investigate the conditions to have a physical quantum state for the Barrett-Crane model for the 4d quantum gravity path integral. More precisely, we look at the simplest case of a single 4-simplex boundary and show that the requirement of working with a physical boundary state fixes the width of the semi-classical Gaussian wave-packet for the boundary 3d geometry. This is directly relevant to the graviton propagator calculations done in this framework, since the Gaussian width enters the numerical factors in front of the graviton correlations in the large scale asymptotical limit. Finally, we discuss the application of our computations to the Barrett-Crane model beyond the first order (of a single 4-simplex in the bulk) and to the more recent EPRL-FK spinfoam model.

 

[marcus]

http://arxiv.org/abs/1102.2948
Energy equipartition and minimal radius in entropic gravity
Hanno Sahlmann
4 pages, 3 figures
(Submitted on 15 Feb 2011)
"In this article, we investigate the assumption of equipartition of energy in arguments for the entropic nature of gravity. It has already been pointed out by other authors that equipartition is not valid for low temperatures. Here we additionally point out that it is similarly not valid for systems with bounded energy. Many explanations for black hole entropy suggest that the microscopic systems responsible have a finite dimensional state space, and thus finite maximum energy. Assuming this to be the case leads to drastic corrections to Newton's law for high gravitational fields, and in particular to a singularity in acceleration at finite radius away from a point mass. This is suggestive of the physics at the Schwarzschild radius. We show, however, that the location of the singularity scales differently."

 

[marcus]

http://arxiv.org/abs/1102.3297
An action for higher spin gauge theory in four dimensions
Nima Doroud, Lee Smolin
28 pages
(Submitted on 16 Feb 2011)
"An action principle is presented for Vasiliev's Bosonic higher spin gauge theory in four spacetime dimensions. The action is of the form of a broken topological field theory, and arises by an extension of the MacDowell-Mansouri formulation of general relativity. In the latter theory the local degrees of freedom of general relativity arise by breaking the gauge invariance of a topological theory from sp(4) to the Lorentz algebra. In Vasiliev's theory the infinite number of degrees of freedom with higher spins similarly arise by the breaking of a topological theory with an infinite dimensional gauge symmetry extending sp(4) to the Lorentz algebra.
The Hamiltonian formulation of Vasilev's theory is then derived from our action, and it is shown that the Hamiltonian is a linear combination of constraints, as expected for a diffeomorphism invariant theory. The constraint algebra is computed and found to be first class."

Strictly speaking the next doesn't belong in this bibliography which focuses on non-string QG research papers: Loop-and-allied QG. But Torsten is PF Beyond forum "family", so in any event here is a new Torsten paper!

http://arxiv.org/abs/1102.3274
Quantum D-branes and exotic smooth R⁴
Torsten Asselmeyer-Maluga, Jerzy Krol
16 pages, see arXiv/1101.3169 for Part 1 This is part 2 of the work based on the talk "Small exotic smooth R⁴ and string theory'' given at the International Congress of Mathematicians, ICM2010, 19-28.08.2010, Hyderabad, India
(Submitted on 16 Feb 2011)
"In this paper, we present the idea that the formalism of string theory is connected with the dimension 4 in a new way, not covered by phenomenological or model-building approaches. The main connection is given by structures induced by small exotic smooth R⁴'s having intrinsic meaning for physics in dimension 4. We extend the notion of stable quantum D-branes in a separable noncommutative C* algebras over convolution algebras corresponding to the codimension-1 foliations of S³ which are mainly connected to small exotic R⁴. The tools of topological K-homology and K-theory as well KK-theory describe stable quantum branes in the C* algebras when naturally extended to algebras. In case of convolution algebras, small exotic smooth R⁴'s embedded in exotic R⁴ correspond to a generalized quantum branes on the algebras. These results extend the correspondence between exotic R⁴ and classical D and NS branes from our previous work."

 

[marcus]

http://arxiv.org/abs/1102.3660
Lectures on loop gravity
Carlo Rovelli
24 pages. 10 figures. I am still correcting and updating the lectures. Comments and corrections very welcome.
(Submitted on 17 Feb 2011)
"This is the 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. The approximations needed to compute physical quantities are discussed. Some applications are described, including the recent derivation of de Sitter cosmology from full quantum gravity."


http://arxiv.org/abs/1102.3474
A Hamiltonian Formulation of the BKL Conjecture
Abhay Ashtekar, Adam Henderson, David Sloan
26 pages, 3 figures
(Submitted on 17 Feb 2011)
"The Belinskii, Khalatnikov and Lifgarbagez conjecture [bkl1] posits that on approach to a space-like singularity in general relativity the dynamics are well approximated by `ignoring spatial derivatives in favor of time derivatives.' In [ahs1] we examined this idea from within a Hamiltonian framework and provided a new formulation of the conjecture in terms of variables well suited to loop quantum gravity. We now present the details of the analytical part of that investigation. While our motivation came from quantum considerations, thanks to some of its new features, our formulation should be useful also for future analytical and numerical investigations within general relativity."

 

[marcus]

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
(Submitted on 18 Feb 2011)
"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."

Brief mention (unrelated but of wider interest):
http://arxiv.org/abs/1102.3926
Habitability of the Goldilocks Planet Gliese 581g: Results from Geodynamic Models
W. von Bloh, M. Cuntz, S. Franck, C. Bounama
(Submitted on 18 Feb 2011)

 

[MTd2]

http://arxiv.org/abs/1102.4109

Various Facets of Spacetime Foam

Y. Jack Ng
(Submitted on 20 Feb 2011)
Spacetime foam manifests itself in a variety of ways. It has some attributes of a turbulent fluid. It is the source of the holographic principle. Cosmologically it may play a role in explaining why the energy density has the critical value, why dark energy/matter exists, and why the effective dynamical cosmological constant has the value as observed. Astrophysically the physics of spacetime foam helps to elucidate why the critical acceleration in modified Newtonian dynamics has the observed value; and it provides a possible connection between global physics and local galactic dynamics involving the phenomenon of flat rotation curves of galaxies and the observed Tully-Fisher relation. Spacetime foam physics also sheds light on nonlocal gravitational dynamics.

 

[marcus]

http://arxiv.org/abs/1102.4755
Path Integral and Effective Hamiltonian in Loop Quantum Cosmology
Haiyun Huang, Yongge Ma, Li Qin
9 pages
(Submitted on 23 Feb 2011)
"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/1102.4624
Renormalisation group and the Planck scale
Daniel F. Litim
14 pages, 6 figures, to appear in the Philosophical Transactions A of the Royal Society, London
(Submitted on 22 Feb 2011)
"I discuss the renormalisation group approach to gravity, its link to Steven Weinberg's asymptotic safety scenario, and give an overview of results with applications to particle physics and cosmology."

http://arxiv.org/abs/1102.4637
Speed of particles and a relativity of locality in kappa-Minkowski quantum spacetime
Giovanni Amelino-Camelia, Niccoló Loret, Giacomo Rosati
(Submitted on 22 Feb 2011)
"The last decade of research on kappa-Minkowski noncommutative spacetime has been strongly characterized by a controversy concerning the speed of propagation of massless particles. Most arguments suggested that this speed should depend on the momentum of the particle strongly enough to be of interest for some ongoing experimental studies. But the only explicit derivations of worldlines in kappa-Minkowski predicted no momentum dependence for the speed of massless particles. We return to this controversy equipped with the recent understanding (arXiv:1006.2126, arXiv:1007.0718, arXiv:1008.2962, arXiv:1101.0931) that in some quantum spacetimes coincidences of events assessed by an observer who is distant from the events can be artifactual, and particularly Smolin's thesis (arXiv:1007.0718) that kappa-Minkowski should be an example of such a spacetime. We therefore set up our investigation in such a way that we never rely on the assessment of coincidences of events by distant observers. This allows us to verify explicitly that in kappa-Minkowski simultaneously-emitted massless particles of different momentum are detected at different times, and establish a linear dependence of the detection times on momentum."

http://arxiv.org/abs/1102.4643
Analysis of the Semiclassical Solution of CDT
T. Trzesniewski
41 pages, 18 figures. Master Thesis, supervised by prof. dr hab. J. Jurkiewicz and defended in June 2010
(Submitted on 23 Feb 2011)
"Causal dynamical triangulations (CDT) constitute a background independent, nonperturbative approach to quantum gravity, in which the gravitational path integral is approximated by the weighted sum over causally well-behaving simplicial manifolds i.e. causal triangulations. This thesis is an analysis of the data from the Monte Carlo computer simulations of CDT in 3+1 dimensions. It is confirmed here that there exist the semiclassical limit of CDT for so-called (4,1) (or equivalent (1,4)) simplices, being a discrete version of the mini-superspace model. Next, the form of the corresponding discrete action is investigated. Furthermore, it is demonstrated that the effective, semiclassical solution works also after the inclusion of remaining (3,2) and (2,3) simplices, treated collectively. A specific form of the resulting extended discrete action is examined and a transition from the broader framework to the former narrower one is shown."

 

[marcus]

http://arxiv.org/abs/1102.5012
Asymptotically Safe Lorentzian Gravity
Elisa Manrique, Stefan Rechenberger, Frank Saueressig
4 pages, 2 figures
(Submitted on 24 Feb 2011)
"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."

 

[MTd2]

http://arxiv.org/abs/1102.5084

Quantum Theory at Planck Scale, Limiting Values, Deformed Gravity and Dark Energy Problem

A.E. Shalyt-Margolin
(Submitted on 24 Feb 2011)
Within a theory of the existing fundamental length on the order of Planck's a high-energy deformation of the General Relativity for the space with horizon has been constructed. On this basis, Markov's work of the early eighties of the last century has been given a new interpretation to show that the heuristic model considered by him may be placed on a fundamental footing. The obtained results have been applied to solving of the dark energy problem, making it possible to frame the following hypothesis: a dynamic cosmological term is a measure of deviation from a thermodynamic identity (the first law of thermodynamics) of the high-energy (Planck's) deformation of Einstein equations for horizon spaces in their thermodynamic interpretation.

 

[MTd2]

Garrett Lisi presents today a talk at Institute for Astronomy, University of Hawaii.

http://www.ifa.hawaii.edu/specialevents/

Upcoming Events
Friday, February 25, 2011
Maikalani Community Lecture: Garrett Lisi, "A Geometry Theory of Everything," 6:30 p.m. at the Maikalani building in Pukalani. Free. Flier
Using pure geometry, Einstein described gravity as the warping of four-dimensional spacetime, with the measurements of rulers and clocks differing based on their position and motion. Similarly, the other forces and particles of nature are described as the twisting of geometric structures over spacetime, and around each other. Examining the patterns of twists, we’ll find that gravity and every elementary particle in our Universe may be facets of the most beautiful structure known to mathematics dancing over spacetime according to the laws of quantum physics.

The slides are available here:

www.deferentialgeometry.org , february 25th

 

[marcus]

http://arxiv.org/abs/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/1102.5439
Discreteness of the volume of space from Bohr-Sommerfeld quantization
Eugenio Bianchi, Hal M. Haggard
4 pages, 4 figures
(Submitted on 26 Feb 2011)
"A major challenge for any theory of quantum gravity is to quantize general relativity while retaining some part of its geometrical character. We present new evidence for the idea that this can be achieved by directly quantizing space itself. We compute the Bohr-Sommerfeld volume spectrum of a tetrahedron and show that it reproduces the quantization of a grain of space found in loop gravity."

 

[atyy]

http://arxiv.org/abs/1102.5524
Entanglement renormalization for quantum fields
Jutho Haegeman, Tobias J. Osborne, Henri Verschelde, Frank Verstraete
(Submitted on 27 Feb 2011)
p4, concluding paragraph: Looking further afield, the cMERA constitutes a realization of the holographic principle. It is tempting to speculate, building on [19], that cMERA are a natural candidate to establish a link between entanglement renormalization and the best known realization of the holographic principle, namely the AdS/CFT correspondence.

 

[atyy]

http://arxiv.org/abs/1103.0731
Geometric Aspects of Gauge and Spacetime Symmetries
Steffen Gielen
(Submitted on 3 Mar 2011)
We investigate several problems in relativity and particle physics where symmetries play a central role; in all cases geometric properties of Lie groups and their quotients are related to physical effects. The first part is concerned with symmetries in gravity. We apply the theory of Lie group deformations to isometry groups of exact solutions in general relativity, relating the algebraic properties of these groups to physical properties of the spacetimes. We then make group deformation local, generalising deformed special relativity (DSR) by describing gravity as a gauge theory of the de Sitter group. We find that in our construction Minkowski space has a connection with torsion; physical effects of torsion seem to rule out the proposed framework as a viable theory. A third chapter discusses a formulation of gravity as a topological BF theory with added linear constraints that reduce the symmetries of the topological theory to those of general relativity. We discretise our constructions and compare to a similar construction by Plebanski which uses quadratic constraints. In the second part we study CP violation in the electroweak sector of the standard model and certain extensions of it. We quantify fine-tuning in the observed magnitude of CP violation by determining a natural measure on the space of CKM matrices, a double quotient of SU(3), introducing different possible choices and comparing their predictions for CP violation. While one generically faces a fine-tuning problem, in the standard model the problem is removed by a measure that incorporates the observed quark masses, which suggests a close relation between a mass hierarchy and suppression of CP violation. Going beyond the standard model by adding a left-right symmetry spoils the result, leaving us to conclude that such additional symmetries appear less natural.

 

[marcus]

http://arxiv.org/abs/1103.1597
On the Asymptotics of Quantum Group Spinfoam Model
You Ding, Muxin Han
25 pages, 1 figure
(Submitted on 8 Mar 2011)
"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/1103.1428
Graviton propagator asymptotics and the classical limit of ELPR/FK spin foam models
Aleksandar Mikovic, Marko Vojinovic
(Submitted on 8 Mar 2011)
"We study the classical limit of ELPR/FK spin foam models by computing the large-distance asymptotics of the spin foam graviton propagator. This is done by analyzing the large-spin asymptotics of the boundary spin-network wavefunction which corresponds to a flat space. By using the stationary phase method we determine the wavefunction asymptotics, which then determines the large-distance asymptotics of the corresponding graviton propagator. We show that the graviton propagator behaves for large distances as the inverse distance to the fourth power, which implies that general relativity is not the classical limit of the ELPR/FK spin foam models. Our result is a direct consequence of the large-spin asymptotics of the ELPR/FK spin-foam vertex amplitude and we show that the vertex amplitude can be modified such that the new amplitude has the desired asymptotics."