Loop-and-allied QG bibliography

[marcus]

http://arxiv.org/abs/1408.3050
A scenario for black hole evaporation on a quantum geometry
Rodolfo Gambini, Jorge Pullin
(Submitted on 13 Aug 2014)
We incorporate elements of the recently discovered exact solutions of the quantum constraints of loop quantum gravity for vacuum spherically symmetric space-times into the paradigm of black hole evaporation due to Ashtekar and Bojowald. The quantization of the area of the surfaces of symmetry of the solutions implies that the number of nice slices that can be fit inside the black hole is finite. The foliation eventually moves through the region where the singularity in the classical theory used to be and all the particles that fell into the black hole due to Hawking radiation emerge finally as a white hole. This yields a variant of a scenario advocated by Arkani-Hamed et al. Fluctuations in the horizon that naturally arise in the quantum space time allow radiation to emerge during the evaporation process due to stimulated emission allowing evaporation to proceed beyond Page time without reaching the maximum entanglement limit until the formation of the white hole. No firewalls nor remnants arise in this scenario.
5 pages.

http://arxiv.org/abs/1408.2959
Localization and diffusion in polymer quantum field theory
Michele Arzano, Marco Letizia
(Submitted on 13 Aug 2014)
Polymer quantization is a non-standard approach to quantizing a classical system inspired by background independent approaches to quantum gravity such as loop quantum gravity. When applied to field theory it introduces a characteristic polymer scale at the level of the fields classical configuration space. Compared with models with space-time discreteness or non-commutativity this is an alternative way in which a characteristic scale can be introduced in a field theoretic context. Motivated by this comparison we study here localization and diffusion properties associated with polymer field observables and dispersion relation in order to shed some light on the novel physical features introduced by polymer quantization. While localization processes seems to be only mildly affected by polymer effects, we find that polymer diffusion differs significantly from the "dimensional reduction" picture emerging in other Planck-scale models beyond local quantum field theory.
16 pages, 5 figures

 

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http://arxiv.org/abs/1408.3260
Lorentzian Connes Distance, Spectral Graph Distance and Loop Gravity
Carlo Rovelli
(Submitted on 14 Aug 2014)
Connes' formula defines a distance in loop quantum gravity, via the spinfoam Dirac operator. A simple notion of spectral distance on a graph can be extended do the discrete Lorentzian context, providing a physically natural example of Lorentzian spectral geometry, with a neat space of Dirac operators. The Hilbert structure of the fermion space is Lorentz covariant rather than invariant.

 

[marcus]

http://arxiv.org/abs/1408.3420
Entanglement in curved spacetimes and cosmology
Eduardo Martin-Martinez, Nicolas C. Menicucci
(Submitted on 14 Aug 2014)
We review recent results regarding entanglement in quantum fields in cosmological spacetimes and related phenomena in flat spacetime such as the Unruh effect. We being with a summary of important results about field entanglement and the mathematics of Bogoliubov transformations that is very often used to describe it. We then discuss the Unruh-DeWitt detector model, which is a useful model of a generic local particle detector. This detector model has been successfully used as a tool to obtain many important results. In this context we discuss two specific types of these detectors: a qubit and a harmonic oscillator. The latter has recently been shown to have important applications when one wants to probe nonperturbative physics of detectors interacting with quantum fields. We then detail several recent advances in the study and application of these ideas, including echoes of the early universe, entanglement harvesting, and a nascent proposal for quantum seismology.
29 pages, 7 figures. Accepted in Classical and Quantum Gravity. Currently in press. (Special Issue focused on the topic of "Entanglement and Quantum Gravity")

 

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http://arxiv.org/abs/1408.3989
Observing Shape in Spacetime
Sean Gryb
(Submitted on 18 Aug 2014)
The notion of "reference frame" is a central theoretical construct for interpreting the physical implications of spacetime diffeomorphism invariance in General Relativity. However, the alternative formulation of classical General Relativity known as Shape Dynamics suggest that a subset of spacetime diffeomorphisms - namely hypersurface deformations - are, in a certain sense, dual to spatial conformal (or Weyl) invariance. Moreover, holographic gauge/gravity dualities suggest that bulk spacetime diffeomorphism invariance can be replaced by the properties of boundary CFTs. How can these new frameworks be compatible with the traditional notion of reference frame so fundamental to our interpretation of General Relativity? In this paper, we address this question by investigating the classical case of maximally symmetric spacetimes with a positive cosmological constant. We find that it is possible to define a notion of "Shape Observer" that represents a conformal reference frame that is dual to the notion of inertial reference frame in spacetime. We then provide a precise dictionary relating the two notions. These Shape Observers are holographic in the sense that they are defined on the asymptotic conformal boundaries of spacetime but know about bulk physics. This leads to a first principles derivation of an exact classical holographic correspondence that can easily be generalized to more complicated situations and may lead to insights regarding the interpretation of the conformal invariance manifest in Shape Dynamics.
23 pages, 3 figures.

http://arxiv.org/abs/1408.4023
Black holes and Boyle's law -- the thermodynamics of the cosmological constant
Brian P. Dolan
(Submitted on 18 Aug 2014)
When the cosmological constant, Λ, is interpreted as a thermodynamic variable in the study of black hole thermodynamics a very rich structure emerges. It is natural to interpret Λ as a pressure and define the thermodynamically conjugate variable to be the thermodynamic volume of the black hole (which need not bear any relation to the geometric volume). Recent progress in this new direction for black hole thermodynamics is reviewed.
31 pages, 3 figures. Review article

 

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http://arxiv.org/abs/1408.4336
From General Relativity to Quantum Gravity
Abhay Ashtekar, Martin Reuter, Carlo Rovelli
(Submitted on 19 Aug 2014)
In general relativity (GR), spacetime geometry is no longer just a background arena but a physical and dynamical entity with its own degrees of freedom. We present an overview of approaches to quantum gravity in which this central feature of GR is at the forefront. However, the short distance dynamics in the quantum theory are quite different from those of GR and classical spacetimes and gravitons emerge only in a suitable limit. Our emphasis is on communicating the key strategies, the main results and open issues. In the spirit of this volume, we focus on a few avenues that have led to the most significant advances over the past 2-3 decades.
54 pages, 5 figures. To appear in General Relativity and Gravitation: A Centennial Survey, commissioned by the International Society for General Relativity and Gravitation and to be published by Cambridge University Press. Abhay Ashtekar served as the 'coordinating author' and combined the three contributions

http://arxiv.org/abs/1408.4127
Towards phase transitions between discrete and continuum quantum spacetime from the Renormalization Group
Astrid Eichhorn, Tim Koslowski
(Submitted on 18 Aug 2014)
We establish the functional Renormalization Group as an exploratory tool to investigate a possible phase transition between a pre-geometric discrete phase and a geometric continuum phase in quantum gravity. In this paper, based on the analysis of [1], we study three new aspects of the double-scaling limit of matrix models as Renormalization Group fixed points: Firstly, we investigate multicritical fixed points, which are associated with quantum gravity coupled to conformal matter. Secondly, we discuss an approximation that reduces the scheme dependence of our results as well as computational effort while giving good numerical results. This is a consequence of the approximation being a solution to the unitary Ward-identity associated to the U(N) symmetry of the hermitian matrix model. Thirdly, we discuss a scenario that relates the double scaling limit to fixed points of continuum quantum gravity.
14 pages, 1 figure

http://arxiv.org/abs/1408.4118
Dynamics of Gauge Field Inflation
Stephon Alexander, Dhrubo Jyoti, Arthur Kosowsky, Antonino Marciano
(Submitted on 18 Aug 2014)
We analyze the existence and stability of dynamical attractor solutions for cosmological inflation driven by the coupling between fermions and a gauge field. Assuming a spatially homogeneous and isotropic gauge field and fermion current,... We prove the existence of exactly one stable solution, and demonstrate the stability numerically. Inflation arises without fine tuning, and does not require postulating any effective potential or non-standard coupling.
7 pages, 2 figures

http://arxiv.org/abs/1408.4427
Dark matter, dark energy and the time evolution of masses in the Universe
Joan Sola
(Submitted on 19 Aug 2014)
...
12 pages, 2 tables, accepted for publication in Int. J. of Mod. Phys.
http://inspirehep.net/author/profile/J.Sola.1

 

[marcus]

http://arxiv.org/abs/1408.4635
Quantum shells in a quantum space-time
Rodolfo Gambini, Jorge Pullin
(Submitted on 20 Aug 2014)
We study the quantum motion of null shells in the quantum space-time of a black hole in loop quantum gravity. We treat the shells as test fields and use an effective dynamics for the propagation equations. The shells propagate through the region where the singularity was present in the classical black hole space-time, but is absent in the quantum space-time, eventually emerging through a white hole to a new asymptotic region of the quantum space-time. The profiles of the shells get distorted due to the quantum fluctuations in the Planckian region that replaces the singularity. The evolution of the shells is unitary throughout the whole process.
5 pages, 3 figures

brief mention, of possible interest:
http://arxiv.org/abs/1408.4770
Holographic Holes and Differential Entropy
Matthew Headrick, Robert C. Myers, Jason Wien
(Submitted on 20 Aug 2014)
61 pages

 

[marcus]

http://arxiv.org/abs/1408.4791
Geometrical variables with direct thermodynamic significance in Lanczos-Lovelock gravity
Sumanta Chakraborty, T. Padmanabhan
(Submitted on 19 Aug 2014)
It has been shown in an earlier work [arXiv:1303.1535] that there exists a pair of canonically conjugate variables (f^bc,N^a_bc) in general relativity which also act as thermodynamically conjugate variables on any horizon. In particular their variations (f^bc∂N^a_bc, N^a_bc∂f^bc), which occur in the surface term of the Einstein-Hilbert action, when integrated over a null surface, have direct correspondence with (S∂T, T∂S ) where (T,S) are the temperature and entropy. We generalize these results to Lanczos-Lovelock models in this paper. We identify two such variables in Lanczos-Lovelock models such that (a) our results reduce to that of general relativity in the appropriate limit and (b) the variation of surface term in the action, when evaluated on a null surface, has direct thermodynamic interpretation as in the case of general relativity. The variations again correspond to S∂T and T∂S where S is now the appropriate Wald entropy for the Lanczos-Lovelock model. The implications are discussed.
22 pages

 

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http://arxiv.org/abs/1408.5367
Rethinking Connes' approach to the standard model of particle physics via non-commutative geometry
Shane Farnsworth, Latham Boyle
(Submitted on 22 Aug 2014)
Connes' non-commutative geometry (NCG) is a generalization of Riemannian geometry that is particularly apt for expressing the standard model of particle physics coupled to Einstein gravity. In a previous paper, we suggested a reformulation of this framework that is: (i) simpler and more unified in its axioms, and (ii) allows the Lagrangian for the standard model of particle physics (coupled to Einstein gravity) to be specified in a way that is tighter and more explanatory than the traditional algorithm based on effective field theory. Here we explain how this same reformulation yields a new perspective on the symmetries of a given NCG. Applying this perspective to the NCG traditionally used to describe the standard model we find, instead, an extension of the standard model by an extra U(1)_B−L gauge symmetry, and a single extra complex scalar field σ, which is a singlet under SU(3)_C×SU(2)_L×U(1)_Y, but has B−L=2. This field has cosmological implications, and offers a new solution to the discrepancy between the observed Higgs mass and the NCG prediction.
5 pages

 

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http://arxiv.org/abs/1408.6646
Classical and Quantum Polyhedra
John Schliemann
(Submitted on 28 Aug 2014)
Quantum polyhedra constructed from angular momentum operators are the building blocks of space in its quantum description as advocated by Loop Quantum Gravity. Here we extend previous results on the semiclassical properties of quantum polyhedra. Regarding tetrahedra, we compare the results from a canonical quantization of the classical system with a recent wave function based approach to the large-volume sector of the quantum system. Both methods agree in the leading order of the resulting effective operator (given by an harmonic oscillator), while minor differences occur in higher corrections. Perturbative inclusion of such corrections improves the approximation to the eigenstates. Moreover, the comparison of both methods leads also to a full wave function description of the eigenstates of the (square of the) volume operator at negative eigenvalues of large modulus.
For the case of general quantum polyhedra described by discrete angular momentum quantum numbers we formulate a set of quantum operators fulfilling in the semiclassical regime the standard commutation relations between momentum and position. Differently from previous formulations, the position variable here is chosen to have dimension of (Planck) length squared which facilitates the identification of quantum corrections.

 

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http://arxiv.org/abs/1408.7112
Group Field Theory and Loop Quantum Gravity
Daniele Oriti
(Submitted on 29 Aug 2014)
We introduce the group field theory formalism for quantum gravity, mainly from the point of view of loop quantum gravity, stressing its promising aspects. We outline the foundations of the formalism, survey recent results and offer a perspective on future developments.

 

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http://arxiv.org/abs/1409.0144
Entanglement entropy production in gravitational collapse: covariant regularization and solvable models
Eugenio Bianchi, Tommaso De Lorenzo, Matteo Smerlak
(Submitted on 30 Aug 2014)
We study the dynamics of vacuum entanglement in the process of gravitational collapse and subsequent black hole evaporation. In the first part of the paper, we introduce a covariant regularization of entanglement entropy tailored to curved spacetimes; this regularization allows us to propose precise definitions for the concepts of black hole "exterior entropy" and "radiation entropy." For a Vaidya model of collapse we find results consistent with the standard thermodynamic properties of Hawking radiation. In the second part of the paper, we compute the vacuum entanglement entropy of various spherically-symmetric spacetimes of interest, including the nonsingular black hole model of Bardeen, Hayward, Frolov and Rovelli-Vidotto and the "black hole fireworks" model of Haggard-Rovelli. We discuss specifically the role of event and trapping horizons in connection with the behavior of the radiation entropy at future null infinity. We observe in particular that (i) in the presence of an event horizon the radiation entropy diverges at the end of the evaporation process, (ii) in models of nonsingular evaporation (with a trapped region but no event horizon) the generalized second law holds only at early times and is violated in the "purifying" phase, (iii) at late times the radiation entropy can become negative (i.e. the radiation can be less correlated than the vacuum) before going back to zero leading to an up-down-up behavior for the Page curve of a unitarily evaporating black hole.
35 pages, 14 figures

side interest:
http://arxiv.org/abs/1409.0469
On tidal capture of primordial black holes by neutron stars
Guillaume Defillon, Etienne Granet, Petr Tinyakov, Michel H.G. Tytgat
(Submitted on 1 Sep 2014)
7 pages

 

[marcus]

http://arxiv.org/abs/1409.0836
A note on the secondary simplicity constraints in loop quantum gravity
Fabio Anzà, Simone Speziale
(Submitted on 2 Sep 2014)
A debate has appeared in the literature on loop quantum gravity and spin foams, over whether secondary simplicity constraints should imply the shape matching conditions reducing twisted geometries to Regge geometries. We address the question using a model in which secondary simplicity constraints arise from a dynamical preservation of the primary ones, and answer it in the affirmative. The origin of the extra condition is to be found in the different graph localisations of the various constraints. Our results are consistent with previous claims by Dittrich and Ryan, and extend their validity to Lorentzian signature and a priori arbitrary cellular decompositions. Finally, we show how the (gauge-invariant version of the) twist angle ξ featuring in twisted geometries equals on-shell the Regge dihedral angle multiplied by the Immirzi parameter, thus recovering the discrete extrinsic geometry from the Ashtekar-Barbero holonomy.
15 pages

 

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http://arxiv.org/abs/1409.0917
Identification of a gravitational arrow of time
Julian Barbour, Tim Koslowski, Flavio Mercati
(Submitted on 2 Sep 2014)
It is widely believed that special initial conditions must be imposed on any time-symmetric law if its solutions are to exhibit behavior of any kind that defines an `arrow of time'. We show that this is not so. The simplest non-trivial time-symmetric law that can be used to model a dynamically closed universe is the Newtonian N-body problem with vanishing total energy and angular momentum. Because of special properties of this system (likely to be shared by any law of the Universe), its typical solutions all divide at a uniquely defined point into two halves. In each a well-defined measure of shape complexity fluctuates but grows irreversibly between rising bounds from that point. Structures that store dynamical information are created as the complexity grows and act as `records'. Each solution can be viewed as having a single past and two distinct futures emerging from it. Any internal observer must be in one half of the solution and will only be aware of the records of one branch and deduce a unique past and future direction from inspection of the available records.
6 pages. To appear in Physical Review Letters

http://arxiv.org/abs/1409.0985
The Entropy of Higher Dimensional Nonrotating Isolated Horizons from Loop Quantum Gravity
Jingbo Wang, Chao-Guang Huang
(Submitted on 3 Sep 2014)
In this paper, we extend the calculation of the entropy of the nonrotating isolated horizons in 4 dimensional spacetime to that in a higher dimensional spacetime. We show that the boundary degrees of freedom on an isolated horizon can be described effectively by a punctured SO(1,1) BF theory. Then the entropy of the nonrotating isolated horizon can be calculated out by counting the microstates. It satisfies the Bekenstein-Hawking law.
13 pages.

 

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http://arxiv.org/abs/1409.1450
The continuum limit of loop quantum gravity - a framework for solving the theory
Bianca Dittrich
(Submitted on 4 Sep 2014)
The construction of a continuum limit for the dynamics of loop quantum gravity is unavoidable to complete the theory. We explain that such a construction is equivalent to obtaining the continuum physical Hilbert space, which encodes the solutions of the theory. We present iterative coarse graining methods to construct physical states in a truncation scheme and explain in which sense this scheme represents a renormalization flow. We comment on the role of diffeomorphism symmetry as an indicator for the continuum limit.

 

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possibly of interest although not in line with usual QG assumptions:
http://arxiv.org/abs/1409.1501
The lifetime problem of evaporating black holes: Mutiny or resignation
Carlos Barceló, Raúl Carballo-Rubio, Luis J. Garay, Gil Jannes
(Submitted on 4 Sep 2014)
It is logically possible that regularly evaporating black holes exist in Nature. In fact, the prevalent theoretical view is that these are indeed the real objects behind the curtain in astrophysical scenarios. There are several proposals for regularizing the classical singularity of black holes so that their formation and evaporation do not lead to information-loss problems. One characteristic is shared by most of these proposals: these regularly evaporating black holes present long-lived trapping horizons, with absolutely enormous evaporation lifetimes in whatever measure. Guided by the discomfort with these enormous and thus inaccessible lifetimes, we elaborate here on an alternative regularization of the classical singularity, previously proposed by the authors in an emergent gravity framework, which leads to a completely different scenario. In our scheme the collapse of a stellar object would result in a genuine time-symmetric bounce, which in geometrical terms amounts to the connection of a black-hole geometry with a white-hole geometry in a regular manner. The two most differential characteristics of this proposal are: i) The complete bouncing geometry is a solution of standard classical General Relativity everywhere except in a transient region that necessarily extends beyond the gravitational radius associated with the total mass of the collapsing object. ii) The duration of the bounce as seen by external observers is very brief (fractions of milliseconds for neutron-star-like collapses). This scenario motivates the search for new forms of stellar equilibrium different from black holes. In a brief epilogue we compare our proposal with a similar geometrical setting recently proposed by Haggard and Rovelli.
20 pages, 2 figures

 

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Bill Unruh just gave a talk at Perimeter which may be of interest. video and slides PDF are online:
http://pirsa.org/14090066/
Firewalls- A GR perspective
Speaker(s): Bill Unruh
Abstract: This talk will examine the Firewall argument and a number of possible approaches to it, with a variety of simple examples to try to clarify various aspects of the arguments.
Date: 04/09/2014 - 3:00 pm

James Bardeen just gave a talk at Perimeter based on this June 2014 paper:
http://arxiv.org/abs/1406.4098
Black hole evaporation without an event horizon
James M. Bardeen
(Submitted on 16 Jun 2014)
A reformulation of the calculation of the semi-classical energy-momentum tensor on a Schwarzschild background, the Bousso covariant entropy bound, and the ER=EPR conjecture of Maldacena and Susskind taken together suggest a scenario for the evaporation of a large spherically symmetric black hole formed in gravitational collapse in which 1) the classical r = 0 singularity is replaced by an initially small non-singular core inside an inner apparent horizon, 2) the radius of the core grows with time due to the increasing entanglement between Hawking radiation quanta outside the black hole and the Hawking partner quanta in the core contributing to the quantum back-reaction, and 3) by the Page time the trapped surfaces disappear and all quantum information stored in the interior is free to escape. The scenario preserves unitarity without any need for a "firewall" in the vicinity of the outer apparent horizon. Qbits in the Hawking radiation are never mutually entangled, and their number never exceeds the Bekenstein-Hawking entropy of the black hole. The quantum back-reaction, while it must be very large in the deep interior of the black hole, can be described semi-classically in the vicinity of the outer apparent horizon up until close to the Page time. An explicit toy model for the metric in the interior of the black hole, and how its associated energy-momentum tensor can be continued to the exterior in a semi-classical approximation, is discussed.
28 pages.

The PIRSA link for the talk is:
http://pirsa.org/14090001/
Black hole evaporation without firewalls
Speaker(s): James Bardeen
Abstract: There need not be any conflict between unitarity, locality, and regularity of the horizon in black hole evaporation. I discuss a scenario in which the initial collapse that forms the black hole results in a small non-singular core inside an inner event horizon. This core grows as the result of quantum back-reaction associated with the increasing entanglement entropy of Hawking radiation quanta and their partners trapped inside the core. By the Page time the inner and outer apparent horizons either merge into a degenerate horizon, shutting off the Hawking radiation and leaving a massive remnant, or they disappear completely, allowing the trapped quantum information to escape. The scenario is justified by appeals to the Bousso covariant entropy bound and the ER=EPR conjecture. The talk is largely based on arxiv.org/1406.4098.
Date: 02/09/2014 - 11:00 am

 

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http://arxiv.org/abs/1409.1800
Geometry and Physics of Null Infinity
Abhay Ashtekar
(Submitted on 5 Sep 2014)
In asymptotically Minkowski space-times, one finds a surprisingly rich interplay between geometry and physics in both the classical and quantum regimes. On the mathematical side it involves null geometry, infinite dimensional groups, symplectic geometry on the space of gravitational connections and geometric quantization via Kähler structures. On the physical side, null infinity provides a natural home to study gravitational radiation and its structure leads to several interesting effects such as an infinite dimensional enlargement of the Poincarè group, geometrical expressions of energy and momentum carried by gravitational waves, emergence of non-trivial `vacuum configurations' and an unforeseen interplay between infrared properties of the quantum gravitational field and the enlargement of the asymptotic symmetry group. The goal of this article is to present a succinct summary of this subtle and beautiful interplay.
20 pages. Invited article for the volume "Surveys in Differential Geometry", a Jubilee Volume on General Relativity and Mathematics celebrating 100 Years of General Relativity, edited by L. Bieri and S.T. Yau

http://arxiv.org/abs/1409.1902
Fourth order deformed general relativity
Peter D. Cuttell, Mairi Sakellariadou
(Submitted on 5 Sep 2014)
Whenever the condition of anomaly freedom is imposed within the framework of effective approaches to loop quantum cosmology, one seems to conclude that a deformation of general covariance is required. Here, starting from a general deformation we regain an effective gravitational Lagrangian including terms up to fourth order in extrinsic curvature. We subsequently constrain the form of the corrections, and then investigate the conditions for the occurrence of a big bounce and the realisation of an inflationary era, in the presence of a perfect fluid or scalar field.
29 pages, 2 figures

http://arxiv.org/abs/1409.1751
Canonical Quantum Gravity on Noncommutative Spacetime
Martin Kober
(Submitted on 4 Sep 2014)
In this paper canonical quantum gravity on noncommutative space-time is considered. The corresponding generalized classical theory is formulated by using the moyal star product, which enables the representation of the field quantities depending on noncommuting coordinates by generalized quantities depending on usual coordinates. But not only the classical theory has to be generalized in analogy to other field theories. Besides, the necessity arises to replace the commutator between the gravitational field operator and its canonical conjugated quantity by a corresponding generalized expression on noncommutative space-time. Accordingly the transition to the quantum theory has also to be performed in a generalized way and leads to extended representations of the quantum theoretical operators. If the generalized representations of the operators are inserted to the generalized constraints, one obtains the corresponding generalized quantum constraints including the Hamiltonian constraint as dynamical constraint. After considering quantum geometrodynamics under incorporation of a coupling to matter fields, the theory is transferred to the Ashtekar formalism. The holonomy representation of the gravitational field as it is used in loop quantum gravity opens the possibility to calculate the corresponding generalized area operator.
17 pages

side interest:
http://arxiv.org/abs/1409.1818
The twin paradox in the presence of gravity
M. Gasperini
(Submitted on 5 Sep 2014)
Conventional wisdom, based on kinematic (flat-space) intuition, tell us that a static twin is aging faster than his traveling twin brother. However, such a situation could be exactly inverted if the two twins are embedded in an external gravitational field, and if the (dynamical) distortion of the space-time geometry, due to gravity, is strong enough to compensate the kinematic effect of the relative twin motion.
5 pages, 2 figures. Published in Mod. Phys. Lett. A 29 (2014)

huge monograph on ψ-ontic versus epistemic Q-interpretation by Perimeter guy
http://arxiv.org/abs/1409.1570
Is the quantum state real? A review of ψ-ontology theorems
M. S. Leifer
(Submitted on 4 Sep 2014)
116 pages

brief mention:
http://arxiv.org/abs/1409.1837
Back-reaction of the Hawking radiation flux on a gravitationally collapsing star II: Fireworks instead of firewalls
Laura Mersini-Houghton, Harald P. Pfeiffer
(Submitted on 5 Sep 2014)
9 pages, 6 figures.

 

[atyy]

http://arxiv.org/abs/1409.2407
Decorated tensor network renormalization for lattice gauge theories and spin foam models
Bianca Dittrich, Sebastian Mizera, Sebastian Steinhaus
(Submitted on 8 Sep 2014)
Tensor network techniques have proved to be powerful tools that can be employed to explore the large scale dynamics of lattice systems. Nonetheless, the redundancy of degrees of freedom in lattice gauge theories (and related models) poses a challenge for standard tensor network algorithms. We accommodate for such systems by introducing an additional structure decorating the tensor network. This allows to explicitly preserve the gauge symmetry of the system under coarse graining and straightforwardly interpret the fixed point tensors. Using this novel information encoded in the decoration might eventually lead to new methods incorporating both analytical and numerical techniques.

http://arxiv.org/abs/1409.2471
Quanta of Geometry
Ali H. Chamseddine, Alain Connes, Viatcheslav Mukhanov
(Submitted on 8 Sep 2014)
In the construction of spectral manifolds in noncommutative geometry, a higher degree Heisenberg commutation relation involving the Dirac operator and the Feynman slash of real scalar fields naturally appears and implies, by equality with the index formula, the quantization of the volume. We first show that this condition implies that the manifold decomposes into disconnected spheres which will represent quanta of geometry. We then refine the condition by involving the real structure and two types of geometric quanta, and show that connected manifolds with large quantized volume are then obtained as solutions. When this condition is adopted in the gravitational action it leads to the quantization of the four volume with the cosmological constant obtained as an integration constant. Restricting the condition to a three dimensional hypersurface implies quantization of the three volume and the possible appearance of mimetic dark matter. When restricting to a two dimensional hypersurface, under appropriate boundary conditions, this results in the quantization of area and has many interesting applications to black hole physics.

 

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in case there is a connection with the paper that Mukhanov coauthored with Connes and Chamseddine, mentioned in the preceding post:
http://arxiv.org/abs/1409.2335
Inflation without Selfreproduction
Viatcheslav Mukhanov
(Submitted on 8 Sep 2014)
We find a rather unique extension of inflationary scenario which avoids selfreproduction and thus resolves the problems of multiverse, predictability and initial conditions. In this theory the amplitude of the cosmological perturbations is expressed entirely in terms of the total duration of inflation.
11 pages.

 

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http://arxiv.org/abs/1409.3150
Group field theories for all loop quantum gravity
Daniele Oriti, James P. Ryan, Johannes Thürigen
(Submitted on 10 Sep 2014)
Group field theories represent a 2nd quantized reformulation of the loop quantum gravity state space and a completion of the spin foam formalism. States of the canonical theory, in the traditional continuum setting, have support on graphs of arbitrary valence. On the other hand, group field theories have usually been defined in a simplicial context, thus dealing with a restricted set of graphs. In this paper, we generalize the combinatorics of group field theories to cover all the loop quantum gravity state space. As an explicit example, we describe the GFT formulation of the KKL spin foam model, as well as a particular modified version. We show that the use of tensor model tools allows for the most effective construction. In order to clarify the mathematical basis of our construction and of the formalisms with which we deal, we also give an exhaustive description of the combinatorial structures entering spin foam models and group field theories, both at the level of the boundary states and of the quantum amplitudes.
49 pages, 24 figures.

http://arxiv.org/abs/1409.3157
Information loss, made worse by quantum gravity
Martin Bojowald
(Submitted on 10 Sep 2014)
Quantum gravity is often expected to solve both the singularity problem and the information-loss problem of black holes. This article presents an example from loop quantum gravity in which the singularity problem is solved in such a way that the information-loss problem is made worse. Quantum effects in this scenario, in contrast to previous non-singular models, do not eliminate the event horizon and introduce a new Cauchy horizon where determinism breaks down. Although infinities are avoided, for all practical purposes the core of the black hole plays the role of a naked singularity. Recent developments in loop quantum gravity indicate that this aggravated information loss problem is likely to be the generic outcome, putting strong conceptual pressure on the theory.
12 pages, 1 figure.

 

[marcus]

This appeared in open-access form today.
http://iopscience.iop.org/1742-6596/532/1/012020/
http://iopscience.iop.org/1742-6596/532/1/012020/pdf/1742-6596_532_1_012020.pdf
Categorical generalization of spinfoam models
A Mikovic and M Vojinovic
Departamento de Matematica, Universidade Lusofona de Humanidades e Tecnologias
Grupo de Fisica Matematica, Universidade de Lisboa
We give a brief review of the problem of quantum gravity. After the discussion of the nonrenormalizability of general relativity, we briefly mention the main research directions which aim to resolve this problem. Our attention then focuses on the approach of Loop Quantum Gravity, specifically spinfoam models. These models have some issues concerning the semiclassical limit and coupling of matter fields. The recent developments in category theory provide us with the necessary formalism to introduce a new action for general relativity and perform covariant quantization so that the issues of spinfoam models are successfully resolved.
10 pages.

My comment: the approach uses 2-groups. John Baez advocated applying 2-groups to spinfoam QG. We haven't heard much about that in recent years.

This paper is not available on arxiv, but a related one from 2011 is available and may help provide context:
http://arxiv.org/abs/1110.4694
Poincare 2-group and quantum gravity
Aleksandar Mikovic, Marko Vojinovic
(Submitted on 21 Oct 2011)
We show that General Relativity can be formulated as a constrained topological theory for flat 2-connections associated to the Poincaré 2-group. Matter can be consistently coupled to gravity in this formulation. We also show that the edge lengths of the spacetime manifold triangulation arise as the basic variables in the path-integral quantization, while the state-sum amplitude is an evaluation of a colored 3-complex, in agreement with the category theory results. A 3-complex amplitude for Euclidean quantum gravity is proposed.
12 pages, published in Class. Quant. Grav. 29 (2012)

 

[marcus]

http://arxiv.org/abs/1409.3526
A 2-categorical state sum model
Aristide Baratin, Laurent Freidel
(Submitted on 11 Sep 2014)
It has long been argued that higher categories provide the proper algebraic structure underlying state sum invariants of 4-manifolds. This idea has been refined recently, by proposing to use 2-groups and their representations as specific examples of 2-categories. The challenge has been to make these proposals fully explicit. Here we give a concrete realization of this program. Building upon our earlier work with Baez and Wise on the representation theory of 2-groups, we construct a four-dimensional state sum model based on a categorified version of the Euclidean group. We define and explicitly compute the simplex weights, which may be viewed a categorified analogue of Racah-Wigner 6j-symbols. These weights solve an hexagon equation that encodes the formal invariance of the state sum under the Pachner moves of the triangulation. This result unravels the combinatorial formulation of the Feynman amplitudes of quantum field theory on flat spacetime proposed in [1], which was shown to lead after gauge-fixing to Korepanov's invariant of 4-manifolds.
13 pages

http://arxiv.org/abs/1409.3751
Canonical formulation of Poincare BFCG theory and its quantization
Aleksandar Mikovic, Miguel A. Oliveira
(Submitted on 12 Sep 2014)
We find the canonical formulation of the Poincare BFCG theory in terms of the spatial 2-connection and its canonically conjugate momenta. We show that the Poincare BFCG action is dynamically equivalent to the BF action for the Poincare group and we find the canonical transformation relating the two. We study the canonical quantization of the Poincare BFCG theory by passing to the Poincare-connection basis. The quantization in the 2-connection basis can be then achieved by performing a Fourier transform. We also briefly discuss how to approach the problem of constructing a basis of spin-foam states, which are the categorical generalization of the spin-network states from Loop Quantum Gravity.
15 pages

http://arxiv.org/abs/1409.3770
An Isometric Dynamics for a Causal Set Approach to Discrete Quantum Gravity
Stan Gudder
(Submitted on 12 Sep 2014)
We consider a covariant causal set approach to discrete quantum gravity. We first review the microscopic picture of this approach. In this picture a universe grows one element at a time and its geometry is determined by a sequence of integers called the shell sequence. We next present the macroscopic picture which is described by a sequential growth process. We introduce a model in which the dynamics is governed by a quantum transition amplitude. The amplitude satisfies a stochastic and unitary condition and the resulting dynamics becomes isometric. We show that the dynamics preserves stochastic states. By "doubling down" on the dynamics we obtain a unitary group representation and a natural energy operator. These unitary operators are employed to define canonical position and momentum operators.
18 pages, 1 figure

http://arxiv.org/abs/1409.3816
Asymptotics with a positive cosmological constant: I. Basic framework
Abhay Ashtekar, Beatrice Bonga, Aruna Kesavan
(Submitted on 12 Sep 2014)
The asymptotic structure of the gravitational field of isolated systems has been analyzed in great detail in the case when the cosmological constant Λ is zero. The resulting framework lies at the foundation of research in diverse areas in gravitational science. Examples include: i) positive energy theorems in geometric analysis; ii) the coordinate invariant characterization of gravitational waves in full, non-linear general relativity; iii) computations of the energy-momentum emission in gravitational collapse and binary mergers in numerical relativity and relativistic astrophysics; and iv) constructions of asymptotic Hilbert spaces to calculate S-matrices and analyze the issue of information loss in the quantum evaporation of black holes. However, by now observations have established that Λ is positive in our universe. In this paper we show that, unfortunately, the standard framework does not extend from the Λ=0 case to the Λ>0 case in a physically useful manner. In particular, we do not have positive energy theorems, nor an invariant notion of gravitational waves in the non-linear regime, nor asymptotic Hilbert spaces in dynamical situations of semi-classical gravity. A suitable framework to address these conceptual issues of direct physical importance is developed in subsequent papers.
41 pges, 5 figures

 

[marcus]

http://arxiv.org/abs/1409.4031
Fast Radio Bursts and White Hole Signals
Aurélien Barrau, Carlo Rovelli, Francesca Vidotto
(Submitted on 14 Sep 2014)
We estimate the size of a primordial black hole exploding today via a white hole transition, and the power in the resulting explosion, using a simple model. We point out that Fast Radio Bursts, strong signals with millisecond duration, probably extragalactic and having unknown source, have wavelength not far from the expected size of the exploding hole. We also discuss the possible higher energy components of the signal.
5 pages

http://arxiv.org/abs/1409.4117
Problem of Time and Background Independence: the Individual Facets
Edward Anderson
(Submitted on 14 Sep 2014)
I lay out the problem of time facets as arising piecemeal from a number of aspects of background independence. Almost all of these already have simpler classical counterparts. This approach can be viewed as a facet by facet completion of the observation that Barbour-type relationalism is a background independent precursor to 2 of the 9 facets. That completion proceeds in an order dictated by the additional layers of mathematical structure required to support each. Moreover, the 'nonlinear nature' of the interactions between the Problem of Time facets renders a joint study of them mandatory. The current article is none the less a useful prequel via gaining a conceptual understanding of each facet, prior to embarking on rendering some combinations of facets consistent and what further obstructions arise in attempting such joint considerations. See [20, 21, 26] for up to date studies of this more complicated joint version. I also identify new facets (threading based), subfacets (of observables and of reconstructions) and further source of variety from how far down the levels of mathematical structure these facets extend.
40 pages, 13 figures

possible side-interest:
http://arxiv.org/abs/1409.4143
Comment on "Dark matter searches going bananas: the contribution of Potassium (and Chlorine) to the 3.5 keV line"
Esra Bulbul, Maxim Markevitch, Adam R. Foster, Randall K. Smith, Michael Loewenstein, Scott W. Randall
(Submitted on 15 Sep 2014)
The recent paper by Jeltema & Profumo(2014) claims that contributions from K XVIII and Cl XVII lines can explain the unidentified emission line found by Bulbul et al 2014 and also by Boyarsky et al, 2014a, 2014b. We show that their analysis relies upon incorrect atomic data and inconsistent spectroscopic modeling. We address these points and summarize in the appendix the correct values for the relevant atomic data from AtomDB.

 

[marcus]

http://arxiv.org/abs/1409.5984
Supersymmetry and noncommutative geometry Part III: The noncommutative supersymmetric Standard Model
Wim Beenakker, Walter D. van Suijlekom, Thijs van den Broek
(Submitted on 21 Sep 2014)
In a previous paper we developed a formalism to construct (potentially) supersymmetric theories in the context of noncommutative geometry. We apply this formalism to explore the existence of a noncommutative version of the minimal supersymmetric Standard Model (MSSM). We obtain the exact particle content of the MSSM and identify (in form) its interactions but conclude that their coefficients are such that the standard action functional used in noncommutative geometry is in fact not supersymmetric.
19 pages, 3 figures

http://arxiv.org/abs/1409.5823
General Relativity and Gravitation: A Centennial Perspective
Abhay Ashtekar, Beverly K. Berger, James Isenberg, Malcolm A. H. MacCallum
(Submitted on 19 Sep 2014)
To commemorate the 100th anniversary of general relativity, the International Society on General Relativity and Gravitation (ISGRG) commissioned a Centennial Volume, edited by the authors of this article. We jointly wrote introductions to the four Parts of the Volume which are collected here. Our goal is to provide a bird's eye view of the advances that have been made especially during the last 35 years, i.e., since the publication of volumes commemorating Einstein's 100th birthday. The article also serves as a brief preview of the 12 invited chapters that contain in-depth reviews of these advances. The volume will be published by Cambridge University Press and released in June 2015 at a Centennial conference sponsored by ISGRG and the Topical Group of Gravitation of the American Physical Society.
37 pages

http://arxiv.org/abs/1409.6218
Polymer inflation
Syed Moeez Hassan, Viqar Husain, Sanjeev S. Seahra
(Submitted on 22 Sep 2014)
We consider the semi-classical dynamics of a free massive scalar field in a homogeneous and isotropic cosmological spacetime. The scalar field is quantized using the polymer quantization method assuming that it is described by a gaussian coherent state. For quadratic potentials, the semi-classical equations of motion yield a universe that has an early "polymer inflation" phase which is generic and almost exactly de Sitter, followed by a epoch of slow-roll inflation. We compute polymer corrections to the slow roll formalism, and discuss the probability of inflation in this model using a physical Hamiltonian arising from time gauge fixing. These results show the extent to which a quantum gravity motivated quantization method affects early universe dynamics.
12 pages, 5 figures

 

[marcus]

http://arxiv.org/abs/1409.6311
Production of Sterile Neutrino Dark Matter and the 3.5 keV line
Alexander Merle, Aurel Schneider
(Submitted on 22 Sep 2014)
The recent observation of an X-ray line at an energy of 3.5 keV mainly from galaxy clusters has generated a buzz in the Dark Matter community. If confirmed, this signal could stem from a decaying sterile neutrino of a mass of 7.1 keV. Such a particle could make up all the Dark Matter, but it is not clear how it was produced in the early Universe. In this paper we show that it is possible to discriminate between different production mechanisms with present-day astronomical data. The most stringent constraint comes from the Lyman-α forest and seems to disfavor all but one of the main production mechanisms proposed in the literature, which is the production via decay of heavy scalar singlets. Pinning down the production mechanism will help to decide whether the X-ray signal indeed comprises an indirect detection of Dark Matter.
7 pages, 3 figures

http://arxiv.org/abs/1409.6753
Horizon complementarity in elliptic de Sitter space
Lucas Fabian Hackl, Yasha Neiman
(Submitted on 23 Sep 2014)
We study a quantum field in elliptic de Sitter space dS₄/Z₂ - the spacetime obtained from identifying antipodal points in dS₄. We find that the operator algebra and Hilbert space cannot be defined for the entire space, but only for observable causal patches. This makes the system into an explicit realization of the horizon complementarity principle. In the absence of a global quantum theory, we propose a recipe for translating operators and states between observers. This translation involves information loss, in accordance with the fact that two observers see different patches of the spacetime. As a check, we recover the thermal state at the de Sitter temperature as a state that appears the same to all observers. This thermal state arises from the same functional that, in ordinary dS₄, describes the Bunch-Davies vacuum.
23 pages + 5 pages of appendices, 6 figures

 

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http://arxiv.org/abs/arXiv:1409.7117[/PLAIN]
Symplectic and Semiclassical Aspects of the Schläfli Identity
Hal M. Haggard, Austin Hedeman, Eugene Kur, Robert G. Littlejohn
(Submitted[/PLAIN] on 24 Sep 2014)
The Schläfli identity, which is important in Regge calculus and loop quantum gravity, is examined from a symplectic and semiclassical standpoint in the special case of flat, 3-dimensional space. In this case a proof is given, based on symplectic geometry. A series of symplectic and Lagrangian manifolds related to the Schläfli identity, including several versions of a Lagrangian manifold of tetrahedra, are discussed. Semiclassical interpretations of the various steps are provided. Possible generalizations to 3-dimensional spaces of constant (nonzero) curvature, involving Poisson-Lie groups and q-deformed spin networks, are discussed.
40 pages, 8 figures

http://arxiv.org/abs/1409.7073
'The End'
Nemanja Kaloper, Antonio Padilla
(Submitted on 24 Sep 2014)
Recently we proposed a mechanism for sequestering the Standard Model vacuum energy that predicts that the universe will collapse. Here we present a simple mechanism for bringing about this collapse, employing a scalar field whose potential is linear and becomes negative, providing the negative energy density required to end the expansion. The slope of the potential is chosen to allow for the expansion to last until the current Hubble time, about 1010 years, to accommodate our universe. Crucially, this choice is technically natural due to a shift symmetry. Moreover, vacuum energy sequestering selects radiatively stable initial conditions for the collapse, which guarantee that immediately before the turnaround the universe is dominated by the linear potential which drives an epoch of accelerated expansion for at least an efold. Thus a single, technically natural choice for the slope ensures that the collapse is imminent and is preceded by the current stage of cosmic acceleration, giving a new answer to the 'Why Now?' problem.
8 pages

 

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http://arxiv.org/abs/1409.7455
Point particles in 2+1 dimensions: general relativity and loop gravity descriptions
Jonathan Ziprick
(Submitted on 26 Sep 2014)
We develop a Hamiltonian description of point particles in (2+1)-dimensions using connection and frame-field variables for general relativity. The topology of each spatial hypersurface is that of a punctured two-sphere with particles residing at the punctures. We describe this topology with a CW complex (a collection of two-cells glued together along edges), and use this to fix a gauge and reduce the Hamiltonian. The equations of motion for the fields describe a dynamical triangulation where each vertex moves according to the equation of motion for a free relativistic particle. The evolution is continuous except for when triangles collapse (i.e. the edges become parallel) causing discrete, topological changes in the underlying CW complex.
We then introduce the loop gravity phase space parameterized by holonomy-flux variables on a graph (a network of one-dimensional links). By embedding a graph within the CW complex, we find a description of this system in terms of loop variables. The resulting equations of motion describe the same dynamical triangulation as the connection and frame-field variables. In this framework, the collapse of a triangle causes a discrete change in the underlying graph, giving a concrete realization of the graph-changing moves that many expect to feature in full loop quantum gravity. The main result is a dynamical model of loop gravity which agrees with general relativity and is well-suited for quantization using existing methods.
31 pages, 14 figures

http://arxiv.org/abs/1409.7871
Was Einstein Right? A Centenary Assessment
Clifford M. Will
(Submitted on 28 Sep 2014)
This article is an overview of 100 years of testing general relativity, to be published in the book General Relativity and Gravitation: A Centennial Perspective, to commemorate the 100th anniversary of general relativity. It is effectively an abridged version of the recent update of the author's Living Review in Relativity (http://arxiv.org/abs/1403.7377)
33 pages, 8 figures, to be published in General Relativity and Gravitation: A Centennial Perspective, eds. A. Ashtekar, B. Berger, J. Isenberg and M. A. H. MacCallum (Cambridge University Press), 2015.

brief mention:
http://arxiv.org/abs/1409.7726
A Correction to the Immirzi Parameter of SU(2) Spin Networks
Muhammad Sadiq
(Submitted on 26 Sep 2014)
7 pages.

 

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http://arxiv.org/abs/1410.0026
Renormalization of lattice-regularized quantum gravity models I. General considerations
Joshua H. Cooperman
(Submitted on 30 Sep 2014)
Lattice regularization is a standard technique for the nonperturbative definition of a quantum theory of fields. Several approaches to the construction of a quantum theory of gravity adopt this technique either explicitly or implicitly. A crucial complement to lattice regularization is the process of renormalization through which a continuous description of the quantum theory arises. I provide a comprehensive conceptual discussion of the renormalization of lattice-regularized quantum gravity models. I begin with a presentation of the renormalization group from the Wilsonian perspective. I then consider the application of the renormalization group in four contexts: quantum field theory on a continuous nondynamical spacetime, quantum field theory on a lattice-regularized nondynamical spacetime, quantum field theory of continuous dynamical spacetime, and quantum field theory of lattice-regularized dynamical spacetime. The first three contexts serve to identify successively the particular issues that arise in the fourth context. These issues originate in the inescability of establishing all scales solely on the basis of the dynamics. While most of this discussion rehearses established knowledge, the attention that I pay to these issues, especially the previously underappreciated role of standard units of measure, is largely novel. I conclude by briefly reviewing past studies of renormalization of lattice-regularized quantum gravity models. In the second paper of this two-part series, I illustrate the ideas presented here by proposing a renormalization group scheme for causal dynamical triangulations.
26 pages. This is the much delayed second paper in the two-part series

http://arxiv.org/abs/1410.0203
Signatures of primordial black hole dark matter
K. M. Belotsky, A. D. Dmitriev, E. A. Esipova, V. A. Gani, A. V. Grobov, M. Yu. Khlopov, A. A. Kirillov, S. G. Rubin, I. V. Svadkovsky
(Submitted on 1 Oct 2014)
The nonbaryonic dark matter of the Universe is assumed to consist of new stable forms of matter. Their stability reflects symmetry of micro world and mechanisms of its symmetry breaking. In the early Universe heavy metastable particles can dominate, leaving primordial black holes (PBHs) after their decay, as well as the structure of particle symmetry breaking gives rise to cosmological phase transitions, from which massive black holes and/or their clusters can originate. PBHs can be formed in such transitions within a narrow interval of masses about 10¹⁷g and, avoiding severe observational constraints on PBHs, can be a candidate for the dominant form of dark matter. PBHs in this range of mass can give solution of the problem of reionization in the Universe at the redshift z∼5...10. Clusters of massive PBHs can serve as a nonlinear seeds for galaxy formation, while PBHs evaporating in such clusters can provide an interesting interpretation for the observations of point-like gamma-ray sources. Analysis of possible PBH signatures represents a universal probe for super-high energy physics in the early Universe in studies of indirect effects of the dark matter.

of possible side interest:
http://arxiv.org/abs/1410.0355
Dark matter voids in the SDSS galaxy survey
Florent Leclercq, Jens Jasche, P.M. Sutter, Nico Hamaus, Benjamin Wandelt
(Submitted on 1 Oct 2014)
12 pages, 6 figures, sub

brief mention, PhD thesis from Philosophy department of U. Sydney:
http://arxiv.org/abs/1410.0345
Appearing Out of Nowhere: The Emergence of Spacetime in Quantum Gravity
Karen Crowther
(Submitted on 1 Oct 2014)
=================added by editing to save a post==========================
http://arxiv.org/abs/1410.0632
Scale-dependent homogeneity measures for causal dynamical triangulations
Joshua H. Cooperman
(Submitted on 2 Oct 2014)
I propose two scale-dependent measures of the homogeneity of the quantum geometry determined by an ensemble of causal triangulations. The first measure is volumetric, probing the growth of volume with graph geodesic distance. The second measure is spectral, probing the return probability of a random walk with diffusion time. Both of these measures, particularly the first, are closely related to those used to assess the homogeneity of our own universe on the basis of galaxy redshift surveys. I employ these measures to quantify the quantum spacetime homogeneity as well as the temporal evolution of quantum spatial homogeneity of ensembles of causal triangulations in the well-known physical phase. According to these measures, the quantum spacetime geometry exhibits some degree of inhomogeneity on sufficiently small scales and a high degree of homogeneity on sufficiently large scales. This inhomogeneity appears unrelated to the phenomenon of dynamical dimensional reduction. I also uncover evidence for power-law scaling of both the typical scale on which inhomogeneity occurs and the magnitude of inhomogeneity on this scale with the ensemble average spatial volume of the quantum spatial geometries.
25 pages, 19 figures

http://arxiv.org/abs/1410.0670
Making the case for causal dynamical triangulations
Joshua H. Cooperman
(Submitted on 2 Oct 2014)
The aim of the causal dynamical triangulations approach is to define nonperturbatively a quantum theory of gravity as the continuum limit of a lattice-regularized model of dynamical geometry. My aim in this paper is to give a concise yet comprehensive, impartial yet personal presentation of the causal dynamical triangulations approach.
8.5 pages plus references, 5 figures

 

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http://arxiv.org/abs/1410.1058
Loop quantization of a 3D Abelian BF model with sigma-model matter
Diego C.M. Mendonça, Olivier Piguet
(Submitted on 4 Oct 2014)
The main goal of this work is to explore the symmetries and develop the dynamics associated to a 3D Abelian BF model coupled to scalar fields submitted to a sigma model like constraint, at the classical and quantum levels. We apply to the present model the techniques of Loop Quantum Gravity, construct its physical Hilbert space and its observables.
14 pages, 3 figures

http://arxiv.org/abs/1410.1486
Black Hole Thermodynamics
S. Carlip
(Submitted on 6 Oct 2014)
The discovery in the early 1970s that black holes radiate as black bodies has radically affected our understanding of general relativity, and offered us some early hints about the nature of quantum gravity. In this chapter I will review the discovery of black hole thermodynamics and summarize the many independent ways of obtaining the thermodynamic and (perhaps) statistical mechanical properties of black holes. I will then describe some of the remaining puzzles, including the nature of the quantum microstates, the problem of universality, and the information loss paradox.
Invited review article. A few parts based on an earlier review, arXiv:0807.4520.
47 pages, 7 figures. To appear in Int. J. Mod. Phys. D and in "One Hundred Years of General Relativity: Cosmology and Gravity," edited by Wei-Tou Ni (World Scientific, Singapore, 2015)

 

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http://arxiv.org/abs/1410.1714
Loop quantum gravity and observations
A. Barrau, J. Grain
(Submitted on 7 Oct 2014)
Quantum gravity has long been thought to be completely decoupled from experiments or observations. Although it is true that smoking guns are still missing, there are now serious hopes that quantum gravity phenomena might be tested. We review here some possible ways to observe loop quantum gravity effects either in the framework of cosmology or in astroparticle physics.