Loop-and-allied QG bibliography

[marcus]

http://arxiv.org/abs/1209.3403
Quantum Cosmology: Effective Theory
Martin Bojowald
(Submitted on 15 Sep 2012)
Quantum cosmology has traditionally been studied at the level of symmetry-reduced minisuperspace models, analyzing the behavior of wave functions. However, in the absence of a complete full setting of quantum gravity and detailed knowledge of specific properties of quantum states, it remained difficult to make testable predictions. For quantum cosmology to be part of empirical science, it must allow for a systematic framework in which corrections to well-tested classical equations can be derived, with any ambiguities and ignorance sufficiently parameterized. As in particle and condensed-matter physics, a successful viewpoint is one of effective theories, adapted to specific issues one encounters in quantum cosmology. This review presents such an effective framework of quantum cosmology, taking into account, among other things, space-time structures, covariance, the problem of time and the anomaly issue.
75 pages, 3 figures, Invited Topical Review for Class. Quantum Grav. 29 (2012) 213001

http://arxiv.org/abs/1209.3623
An Approach to Loop Quantum Cosmology Through Integrable Discrete Heisenberg Spin Chains
Christine C. Dantas
(Submitted on 17 Sep 2012)
The quantum evolution equation of Loop Quantum Cosmology (LQC) -- the quantum Hamiltonian constraint -- is a difference equation. We relate the LQC constraint equation in vacuum Bianchi I separable (locally rotationally symmetric) models with an integrable differential-difference nonlinear Schrödinger type equation, which in turn is known to be associated with integrable, discrete Heisenberg spin chain models in condensed matter physics. We illustrate the similarity between both systems with a simple constraint in the linear regime.
6 pages, submitted to Foundations of Physics

http://arxiv.org/abs/1209.3649
Functional renormalization with fermions and tetrads
Pietro Donà, Roberto Percacci
(Submitted on 17 Sep 2012)
We investigate some aspects of the renormalization group flow of gravity in the presence of fermions, which have remained somewhat puzzling so far. The first is the sign of the fermionic contribution to the running of Newton's constant, which depends on details of the cutoff. We argue that only one of the previously used schemes correctly implements the cutoff on eigenvalues of the Dirac operator, and it acts in the sense of screening Newton's constant. We also show that Kähler fermions give the same contribution to the running of the cosmological and Newton constant as four Dirac spinors. We then calculate the graviton contributions to the beta functions by imposing the cutoffs on the irreducible spin components of the tetrad. In this way we can probe the gauge dependence of the off-shell flow. The results resemble closely those of the metric formalism, except for an increased scheme-- and (off shell) gauge--dependence.
28 pages, 4 figures

brief mention:
http://arxiv.org/abs/1209.3511
The effective field theory treatment of quantum gravity
John F. Donoghue
(Submitted on 16 Sep 2012)
This is a pedagogical introduction to the treatment of quantum general relativity as an effective field theory...
22 pages, 3 figures. Presented at the Sixth International School on Field Theory and Gravitation, Petropolis, Brazil, April 2012, to be published in the proceedings.

http://arxiv.org/abs/1209.3339
Annual Modulation of Dark Matter: A Review
Katherine Freese, Mariangela Lisanti, Christopher Savage
(Submitted on 14 Sep 2012)
Direct detection experiments, which are designed to detect the scattering of dark matter off nuclei in detectors, are a critical component in the search for the Universe's missing matter. The count rate in these experiments should experience an annual modulation due to the relative motion of the Earth around the Sun...
37 pages, 7 figures. To appear in Review of Modern Physics

 

[marcus]

http://arxiv.org/abs/1209.4038
Fixed points and infrared completion of quantum gravity
Nicolai Christiansen, Daniel F. Litim, Jan M. Pawlowski, Andreas Rodigast
(Submitted on 18 Sep 2012)
The phase diagram of four-dimensional Einstein-Hilbert gravity is studied using Wilson's renormalization group. Smooth trajectories connecting the ultraviolet fixed point at short distances with attractive infrared fixed points at long distances are derived from the non-perturbative graviton propagator. Implications for the asymptotic safety conjecture and further results are discussed.
4 pages, 4 figures

 

[marcus]

http://arxiv.org/abs/1209.4295
A review of the large N limit of tensor models
Razvan Gurau
(Submitted on 19 Sep 2012)
Random matrix models encode a theory of random two dimensional surfaces with applications to string theory, conformal field theory, statistical physics in random geometry and quantum gravity in two dimensions. The key to their success lies in the 1/N expansion introduced by 't Hooft. Random tensor models generalize random matrices to theories of random higher dimensional spaces. For a long time, no viable 1/N expansion for tensors was known and their success was limited.
A series of recent results has changed this situation and the extension of the 1/N expansion to tensors has been achieved. We review these results in this paper.
12 pages. Proceedings of The XXIX International Colloquium on Group-Theoretical Methods in Physics, August 20-26 2012, Chern Institute of Mathematics, Nankai University, Tianjin, China

 

[marcus]

http://arxiv.org/abs/1209.4374
On the Uniqueness of Kinematics of Loop Quantum Cosmology
Abhay Ashtekar, Miguel Campiglia
(Submitted on 19 Sep 2012)
The holonomy-flux algebra A of loop quantum gravity is known to admit a natural representation that is uniquely singled out by the requirement of covariance under spatial diffeomorphisms. In the cosmological context, the requirement of spatial homogeneity naturally reduces A to a much smaller algebra, A_Red, used in loop quantum cosmology. In Bianchi I models, it is shown that the requirement of covariance under residual diffeomorphism symmetries again uniquely selects the representation of A_Red that has been commonly used. We discuss the close parallel between the two uniqueness results and also point out a difference.
9 pages

http://arxiv.org/abs/1209.4539
Holonomy Spin Foam Models: Boundary Hilbert spaces and Time Evolution Operators
Bianca Dittrich, Frank Hellmann, Wojciech Kaminski
(Submitted on 20 Sep 2012)
In this and the companion paper a novel holonomy formulation of so called Spin Foam models of lattice gauge gravity are explored. After giving a natural basis for the space of simplicity constraints we define a universal boundary Hilbert space, on which the imposition of different forms of the simplicity constraints can be studied. We detail under which conditions this Hilbert space can be mapped to a Hilbert space of projected spin networks or an ordinary spin network space.
These considerations allow to derive the general form of the transfer operators which generates discrete time evolution. We will describe the transfer operators for some current models on the different boundary Hilbert spaces and highlight the role of the simplicity constraints determining the concrete form of the time evolution operators.
51 pages, 18 figures

http://arxiv.org/abs/1209.4376
Multi-fractional spacetimes, asymptotic safety and Hořava-Lifgarbagez gravity
Gianluca Calcagni
(Submitted on 19 Sep 2012)
We compare the recently formulated multi-fractional spacetimes with field theories of quantum gravity based on the renormalization group (RG), such as asymptotic safety and Horava-Lifgarbagez gravity. The change of spacetime dimensionality with the probed scale is realized in both cases by an adaptation of the measurement tools (`rods') to the scale, but in different ways. In the multi-fractional case, by an adaptation of the position-space measure, roughly corresponding to a scale dependence of the coordinates. In the case of RG-based theories, by an adaptation of the momenta. The two pictures are mapped into each other, thus presenting the fractal structure of spacetime in RG-based theories under an alternative perspective.
17 pages, 1 table

http://arxiv.org/abs/1209.4606
Addendum to "A Renormalizable 4-Dimensional Tensor Field Theory"
Joseph Ben Geloun, Vincent Rivasseau
(Submitted on 20 Sep 2012)
This note fills a gap in the article with title above [1]. We provide the proof of Equation (82) of Lemma 5 in [1] and thereby complete its power counting analysis with a more precise next-to-leading-order estimate.
10 pages, 4 figures

 

[marcus]

http://arxiv.org/abs/1209.4892
On the role of the Barbero-Immirzi parameter in discrete quantum gravity
Bianca Dittrich, James P. Ryan
(Submitted on 21 Sep 2012)
The 1-parameter family of transformations identified by Barbero and Immirzi plays a significant role in non-perturbative approaches to quantum gravity, among them Loop Quantum Gravity and Spin Foams. It facilitates the loop quantization programme and subsequently the Barbero-Immirzi parameter (gamma) arises in both the spectra of geometrical operators and in the dynamics provided by Spin Foams. However, the debate continues as to whether quantum physics should be Barbero-Immirzi parameter dependent. Starting from a discrete SO(4)-BF theory phase space, we find two possible reductions with respect to a discrete form of the simplicity constraints. The first reduces to a phase space with gamma-dependent symplectic structure and more generally in agreement with the phase space underlying Loop Quantum Gravity restricted to a single graph - a.k.a. Twisted Geometries. The second, fuller reduction leads to a gamma-independent symplectic structure on the phase space of piecewise-flat-linear geometries - a.k.a. Regge geometries. Thus, the gamma-dependence of physical predictions is related to the choice of phase space underlying the quantization.
16 + 12 pages

brief mention:
http://arxiv.org/abs/1209.4786
Spectral dimension flow on continuum random multigraph
Georgios Giasemidis, John F. Wheater, Stefan Zohren
(Submitted on 21 Sep 2012)
We review a recently introduced effective graph approximation of causal dynamical triangulations (CDT), the multigraph ensemble. We argue that it is well suited for analytical computations and that it captures the physical degrees of freedom which are important for the reduction of the spectral dimension as observed in numerical simulations of CDT. ...
6 pages, 1 figure, to appear in the Proceedings of Sixth International School on Field Theory and Gravitation 2012 (Petropolis, Brazil)

http://arxiv.org/abs/1209.4798
Aspects of dynamical dimensional reduction in multigraph ensembles of CDT
Georgios Giasemidis, John F. Wheater, Stefan Zohren
(Submitted on 21 Sep 2012)
We study the continuum limit of a "radially reduced" approximation of Causal Dynamical Triangulations (CDT), so-called multigraph ensembles, and explain why they serve as realistic toy models to study the dimensional reduction observed in numerical simulations of four-dimensional CDT...
4 pages, 1 figure, Presented at "Gravity, Quantum, and Black Holes" session of IC-MSQUARE 2012, Budapest

 

[John86]

http://arxiv.org/abs/1209.5284
The Tensor Track: an Update
Vincent Rivasseau
(Submitted on 24 Sep 2012)
The tensor track approach to quantum gravity is based on a new class of quantum field theories, called tensor group field theories (TGFTs). We provide a brief review of recent progress and list some desirable properties of TGFTs. In order to narrow the search for interesting models, we also propose a set of guidelines for TGFT's loosely inspired by the Osterwalder-Schrader axioms of ordinary Euclidean QFT.

http://arxiv.org/abs/1209.5060
C*-algebras of Holonomy-Diffeomorphisms & Quantum Gravity I
Johannes Aastrup, Jesper M. Grimstrup
(Submitted on 23 Sep 2012)
A new approach to a unified theory of quantum gravity based on noncommutative geometry and canonical quantum gravity is presented. The approach is built around a *-algebra generated by local holonomy-diffeomorphisms on a 3-manifold and a quantized Dirac type operator; the two capturing the kinematics of quantum gravity formulated in terms of Ashtekar variables. We prove that the separable part of the spectrum of the algebra is contained in the space of measurable connections modulo gauge transformations and we give limitations to the non-separable part. The construction of the Dirac type operator -- and thus the application of noncommutative geometry -- is motivated by the requirement of diffeomorphism invariance. We conjecture that a semi-finite spectral triple, which is invariant under volume-preserving diffeomorphisms, arise from a GNS construction of a semi-classical state. Key elements of quantum field theory emerge from the construction in a semi-classical limit, as does an almost commutative algebra. Finally, we note that the spectrum of loop quantum gravity emerges from a discretization of our construction. Certain convergence issues are left unresolved. This paper is the first of two where the second paper is concerned with mathematical details and proofs concerning the spectrum of the holonomy-diffeomorphism algebra.

http://arxiv.org/abs/1209.5057
C*-algebras of Holonomy-Diffeomorphisms & Quantum Gravity II
Johannes Aastrup, Jesper M. Grimstrup
(Submitted on 23 Sep 2012)
We introduce the holonomy-diffeomorphism algebra, a C*-algebra generated by flows of vectorfields and the compactly supported smooth functions on a manifold. We show that the separable representations of the holonomy-diffeomorphism algebra are given by measurable connections, and that the unitary equivalence of the representations corresponds to measured gauge equivalence of the measurable connections. We compare the setup to Loop Quantum Gravity and show that the generalized connections found there are not contained in the spectrum of the holonomy-diffeomorphism algebra in dimensions higher than one. This is the second paper of two, where the prequel gives an exposition of a framework of quantum gravity based on the holonomy-diffeomorphism algebra.

http://arxiv.org/abs/1209.4948
Processing quantum information with relativistic motion of atoms
Eduardo Martin-Martinez, David Aasen, Achim Kempf
(Submitted on 22 Sep 2012)
We show that particle detectors, such as 2-level atoms, in non-inertial motion (or in gravitational fields) could be used to build quantum gates for the processing of quantum information. Concretely, we show that through suitably chosen non-inertial trajectories of the detectors the interaction Hamiltonian's time dependence can be modulated to yield arbitrary rotations in the Bloch sphere due to relativistic quantum effects.

http://arxiv.org/abs/1209.5196
Evidence for Bohmian velocities from conditional Schrodinger equation
H. Nikolic
(Submitted on 24 Sep 2012)
It is often argued that measurable predictions of Bohmian mechanics cannot be distinguished from those of a theory with arbitrarily modified particle velocities satisfying the same equivariance equation. By considering the wave function of a closed system in a state with definite total energy, we argue that a distinction in measurable predictions is possible. Even though such a wave function is time-independent, the conditional wave function for a subsystem depends on time through the time-dependent particle trajectories not belonging to the subsystem. If these trajectories can be approximated by classical trajectories, then the conditional wave function can be approximated by a wave function which satisfies Schrodinger equation in a classical time-dependent potential, which is in good agreement with observations. However, such an approximation cannot be justified for particle velocities significantly deviating from the Bohmian ones, implying that Bohmian velocities are observationally preferred.

http://arxiv.org/abs/1209.5271
Using Newton's Law for Dark Energy
Paul Frampton
(Submitted on 24 Sep 2012)
A model is introduced in which Newton's law is modified between matter and dark energy corpuscles (DECs). The model predicts that the DEC component is presently decelerating in its expansion at 14% of the magnitude of the matter expansion acceleration. In the future, expansion of the DEC universe will continue to decelerate.

 

[marcus]

This paper is very beautiful. Clear writing makes it broadly understandable (partly John Baez influence on Derek I imagine):
http://arxiv.org/abs/1210.0019
Lifting General Relativity to Observer Space
Steffen Gielen, Derek K. Wise
(Submitted on 28 Sep 2012)
The 'observer space' of a Lorentzian spacetime is the space of future-timelike unit tangent vectors. Using Cartan geometry, we first study the structure a given spacetime induces on its observer space, then use this to define abstract observer space geometries for which no underlying spacetime is assumed. We propose taking observer space as fundamental in general relativity, and prove integrability conditions under which spacetime can be reconstructed as a quotient of observer space. Additional field equations on observer space then descend to Einstein's equations on the reconstructed spacetime. We also consider the case where no such reconstruction is possible, and spacetime becomes an observer-dependent, relative concept. Finally, we discuss applications of observer space, including a geometric link between covariant and canonical approaches to gravity.
34 pages

http://arxiv.org/abs/1210.0418
Interpretation of the triad orientations in loop quantum cosmology
Claus Kiefer, Christian Schell
(Submitted on 1 Oct 2012)
Loop quantum cosmology allows for arbitrary superpositions of the triad variable. We show here how these superpositions can become indistinguishable from a classical mixture by the interaction with fermions. We calculate the reduced density matrix for a locally rotationally symmetric Bianchi I model and show that the purity factor for the triads decreases by decoherence. In this way, the Universe assumes a definite orientation.
12 pages, 1 figure

Late addition, somehow overlooked in July when it came out:
http://arxiv.org/abs/1207.6734
Renormalization of Tensorial Group Field Theories: Abelian U(1) Models in Four Dimensions
Sylvain Carrozza, Daniele Oriti, Vincent Rivasseau
(Submitted on 28 Jul 2012)
We tackle the issue of renormalizability for Tensorial Group Field Theories (TGFT) including gauge invariance conditions, with the rigorous tool of multi-scale analysis, to prepare the ground for applications to quantum gravity models. In the process, we define the appropriate generalization of some key QFT notions, including: connectedness, locality and contraction of (high) subgraphs. We also define a new notion of Wick ordering, corresponding to the subtraction of (maximal) melonic tadpoles. We then consider the simplest examples of dynamical 4-dimensional TGFT with gauge invariance conditions for the Abelian U(1) case. We prove that they are super-renormalizable for any polynomial interaction.
33 pages, 8 figures
EDIT: I now see that this was added to the bibliography when it came out, in post #1781,
https://www.physicsforums.com/showthread.php?p=4016291#post4016291
but I overlooked it when sifting thru the quarter's papers to assemble a list for the poll.

EDIT: Tom, interesting comment about Kiefer! I had a vague notion of him as an independent, able to do research in LQG and make a significant contribution, but apt equally well three months later to post an article in some other branch of QG. I will look more carefully now.

 

[tom.stoer]

Claus Kiefer is joining the LQC community ...

 

[marcus]

http://arxiv.org/abs/1210.0849
The polymer quantization in LQG: massless scalar field
Marcin Domagala, Michal Dziendzikowski, Jerzy Lewandowski
(Submitted on 2 Oct 2012)
The polymer quantization of matter fields is a diffeomorphism invariant framework compatible with Loop Quantum Gravity. Whereas studied by itself, it is not explicitly used in the known completely quantizable models of matter coupled to LQG. In the current paper we apply the polymer quantization to the model of massless scalar field coupled to LQG. We show that the polymer Hilbert space of the field degrees of freedom times the LQG Hilbert space of the geometry degrees of freedom admit the quantum constraints of GR and accommodate their explicit solutions. In this way the quantization can be completed. That explicit way of solving the quantum constraints suggests interesting new ideas.
19 pages, no figures, Contribution to the Proceedings of the 3rd Quantum Geometry and Quantum Gravity School in Zakopane (2011)

briefly noted, possibly of general interest:
http://arxiv.org/abs/1210.0544
Dark matter and cosmic structure
Carlos S. Frenk, Simon D. M. White
(Submitted on 1 Oct 2012)
We review the current standard model for the evolution of cosmic structure, tracing its development over the last forty years and focusing specifically on the role played by numerical simulations and on aspects related to the nature of dark matter.
27 pages. Invited review in Annalen der Physik - www.ann-phys.org

 

[marcus]

briefly noted:
http://arxiv.org/abs/1210.0944
Reverse Engineering Quantum Field Theory
Robert Oeckl (CCM-UNAM)
(Submitted on 2 Oct 2012)
An approach to the foundations of quantum theory is advertised that proceeds by "reverse engineering" quantum field theory. As a concrete instance of this approach, the general boundary formulation of quantum theory is outlined.
5 pages,

 

[marcus]

http://arxiv.org/abs/1210.1485
Loop Quantum Gravity Phenomenology: Linking Loops to Physics
Florian Girelli, Franz Hinterleitner, Seth Major
(Submitted on 4 Oct 2012)
Research during the last decade demonstrates that effects originating on the Planck scale are currently being tested in multiple observational contexts. In this review we discuss quantum gravity phenomenological models and their possible links to loop quantum gravity. Particle frameworks, including kinematic models, broken and deformed Poincaré symmetry, non-commutative geometry, relative locality and generalized uncertainty principle, and field theory frameworks, including Lorentz violating operators in effective field theory and non-commutative field theory, are discussed. The arguments relating loop quantum gravity to models with modified dispersion relations are reviewed, as well as, arguments supporting the preservation of local Lorentz invariance. The phenomenology related to loop quantum cosmology is briefly reviewed, with a focus on possible effects that might be tested in the near future. As the discussion makes clear, there remains much interesting work to do in establishing the connection, or lack thereof, between the fundamental theory of loop quantum gravity and these specific phenomenological models, in determining observational consequences of the characteristic aspects of loop quantum gravity, and in further refining current observations. Open problems related to these developments are highlighted.
75 pages. 2 figures. Invited review for SIGMA Special Issue "Loop Quantum Gravity and Cosmology"

http://arxiv.org/abs/1210.1528
Experimentally testing asymptotically safe quantum gravity with photon-photon scattering
Astrid Eichhorn
(Submitted on 4 Oct 2012)
Matter-quantum gravity interactions can be used for direct and also indirect experimental tests of quantum gravity. We focus on photon-photon scattering in asymptotically safe gravity as a direct test of the small-scale structure of spacetime, and discuss how near-future experiments can probe asymptotic safety in a setting with large extra dimensions.
3 pages. Prepared for the proceedings of the 13th Marcel Grossmann meeting

 

[marcus]

http://arxiv.org/abs/1210.1787
Spontaneous breaking of Lorentz symmetry for canonical gravity
Steffen Gielen
(Submitted on 5 Oct 2012)
In the Ashtekar-Barbero formulation of canonical general relativity based on an SU(2) connection, Lorentz covariance is a subtle issue which has been the focus of some debate. Here we present a Lorentz covariant formulation generalising the notion of a foliation of spacetime to a field of local observers which specify a time direction only locally. This field spontaneously breaks the local SO(3,1) symmetry down to a subgroup SO(3); we show that the apparent symmetry breaking to SO(3) is not in conflict with Lorentz covariance. We give a geometric picture of our construction as Cartan geometrodynamics and outline further applications of the formalism of local observers, motivating the idea that observer space, instead of spacetime, should serve as the fundamental arena for gravitational physics.
8 pages, contribution to the proceedings of the conference "Relativity and Gravitation - 100 years after Einstein in Prague"

 

[MTd2]

We missed this one ... I found here:

http://www.technologyreview.com/view/429528/topology-the-secret-ingredient-in-the-latest/?ref=rss

http://arxiv.org/abs/1210.1281

Topological order: from long-range entangled quantum matter to an unification of light and electrons

Xiao-Gang Wen
(Submitted on 4 Oct 2012)
In primary school, we were told that there are four states of matter: solid, liquid, gas, and plasma. In college, we learned that there are much more then four states of matter. For example, the phenomenon of magnetization reveals the existence of ferromagnetic phases and the phenomenon of zero-viscosity reveals the existence of superfluid phases. There many more phases in our rich world, and it is amazing that those phases can be understood systematically by the symmetry breaking theory of Landau. In this paper, we will review the progress in last 20 -- 30 years, during which we discovered that there are many new phases that cannot be described Landau symmetry breaking theory. We discuss new "topological" phenomena, such as topological degeneracy, that reveal the existence of those new phases -- topologically ordered phases. Just like zero-viscosity define the superfluid order, the new "topological" phenomena define the topological order at macroscopic level. More recently, we find that, at microscopical level, topological order is due to long-range quantum entanglements, just like fermion superfluid is due to fermion-pair condensation. Long-range quantum entanglements lead to many amazing emergent phenomena, such as fractional quantum numbers, fractional/non-Abelian statistics, and protected gapless boundary excitations. We find that long-range quantum entanglements (or topological order) provide a unified origin of light and electrons: light waves are fluctuations of long-range entanglements, and fermions are defects of long-range entanglements. Long-range quantum entanglements (and the related topological order) represent a new chapter and a future direction of condensed matter physics, or even physics in general.

 

[marcus]

http://arxiv.org/abs/1210.2252
The scaling of black hole entropy in loop quantum gravity
Amit Ghosh, Alejandro Perez
(Submitted on 8 Oct 2012)
We discuss some general properties of black hole entropy in loop quantum gravity from the perspective of local stationary observers at distance l from the horizon. The present status of the theory indicates that black hole entropy differs from the low energy (IR) expected value A/(4G) (in natural units) in the deep Planckian regime (UV). The partition function is well defined if the number of non-geometric degrees of freedom g_M(encoding the degeneracy of the area a_p eigenvalue at a puncture p) satisfy the holographic bound g_M < exp(a_p/(4G)). Our framework provides a natural renormalization mechanism such that S_UV ---> S_IR=A/(4G_Newton) as the scale l flows.
7 pages.

[my comment: notice that G is running with energy in this paper, as I read it only in the IR limit do we have G=G_Newton ]

 

[John86]

http://arxiv.org/abs/1210.2589
Everpresent Lambda - II
Maqbool Ahmed, Rafael Sorkin
(Submitted on 9 Oct 2012)
Ideas from causal set theory lead to a fluctuating, time dependent cosmological-constant of the right order of magnitude to match currently quoted "dark energy" values. Although such a term was predicted some time ago, a more detailed analysis of the resulting class of phenomenological models was begun only recently (based on numerical simulation of the cosmological equations with such a fluctuating term). In this paper we continue the investigation by studying the sensitivity of the scheme to some of the ad hoc choices made in setting it up.

 

[tom.stoer]

Updated:

http://arxiv.org/abs/1004.2260
The new vertices and canonical quantization
Authors: Sergei Alexandrov
(Submitted on 13 Apr 2010 (v1), last revised 25 Jun 2010 (this version, v3))
Abstract: We present two results on the recently proposed new spin foam models. First, we show how a (slightly modified) restriction on representations in the EPRL model leads to the appearance of the Ashtekar-Barbero connection, thus bringing this model even closer to LQG. Second, we however argue that the quantization procedure used to derive the new models is inconsistent since it relies on the symplectic structure of the unconstraint BF theory.

 

[marcus]

http://arxiv.org/abs/1210.3372
Statistical mechanics of graph models and their implications for emergent manifolds
Si Chen, Steven S. Plotkin
(Submitted on 11 Oct 2012)
Inspired by "quantum graphity" models for spacetime, a statistical model of graphs is proposed to explore possible realizations of emergent manifolds. Graphs with given numbers of vertices and edges are considered, governed by a very general Hamiltonian that merely favors graphs with near-constant valency and local rotational symmetry. The ratio of vertices to edges controls the dimensionality of the emergent manifold. The model is simulated numerically in the canonical ensemble for a given vertex to edge ratio, where it is found that the low energy states are almost triangulations of two dimensional manifolds. The resulting manifold shows topological "handles" and surface intersections in a higher embedding space as well as non-trivial fractal dimension. The transition is first order, underlying the difficulty of graph models in describing criticality that is independent of the details of the underlying graph. Another interesting phenomenon is that the entropy of the graphs are super-extensive, a fact known since Erdös, which results in a transition temperature of zero in the limit of infinite system size: infinite manifolds are always disordered. Aside from a finite universe or diverging coupling constraints as possible solutions to this problem, long-range interactions between vertex defects also resolve the problem and restore a non-zero transition temperature, in a manner similar to that in low-dimensional condensed-matter systems.
19 pages, 19 figures, 1 table

 

[marcus]

http://arxiv.org/abs/1210.3960
Constraint algebra in LQG reloaded : Toy model of an Abelian gauge theory - II Spatial Diffeomorphisms
Adam Henderson, Alok Laddha, Casey Tomlin
(Submitted on 15 Oct 2012)
In [1] we initiated an approach towards quantizing the Hamiltonian constraint in Loop Quantum Gravity (LQG) by requiring that it generates an anomaly-free representation of constraint algebra off-shell. We investigated this issue in the case of a toy model of a 2+1-dimensional U(1)³ gauge theory, which can be thought of as a weak coupling limit of Euclidean three dimensional gravity. However in [1] we only focused on the most non-trivial part of the constraint algebra that involves commutator of two Hamiltonian constraints. In this paper we continue with our analysis and obtain a representation of full constraint algebra in loop quantized framework. We show that there is a representation of the Diffeomorphism group with respect to which the Hamiltonian constraint quantized in [1] is diffeomorphism covariant. Our work can be thought of as a potential first step towards resolving some long standing issues with the Hamiltonian constraint in canonical LQG.
30 pages, 1 figure
My comment: previous paper = http://arxiv.org/abs/1204.0211

Brief mention (possible general interest):
http://arxiv.org/abs/1210.3624
A Correlation Between the Higgs Mass and Dark Matter
Mark P. Hertzberg (MIT)
(Submitted on 12 Oct 2012)
Depending on the value of the Higgs mass, the Standard Model acquires an unstable region at large Higgs field values due to RG running of couplings, which we evaluate at 2-loop. For currently favored values of the Higgs mass, this renders the electroweak vacuum only meta-stable with a long lifetime. We argue on statistical grounds that the Higgs field would be highly unlikely to begin in the small field meta-stable region in the early universe, and thus some new physics should enter in the energy range of order, or lower than, the instability scale to remove the large field unstable region. We assume that Peccei-Quinn (PQ) dynamics enters to solve the strong CP problem and, for a PQ-scale in this energy range, may also remove the unstable region. We allow the PQ-scale to scan and argue, again on statistical grounds, that its value in our universe should be of order the instability scale, rather than (significantly) lower. Since the Higgs mass determines the instability scale, which is argued to set the PQ-scale, and since the PQ-scale determines the axion properties, including its dark matter abundance, we are led to a correlation between the Higgs mass and the abundance of dark matter. We find the correlation to be in good agreement with current data.
9 pages, 3 figures

http://arxiv.org/abs/1210.4026
Covariant multi-galileons and their generalisation
Antonio Padilla, Vishagan Sivanesan
(Submitted on 15 Oct 2012)
We find a covariant completion of the flat-space multi-galileon theory, preserving second-order field equations. We then generalise this to arrive at an enlarged class of second order theories describing multiple scalars and a single tensor, and conjecture that these are a multi-scalar version of Horndeski's most general scalar-tensor theory.
11 pages
My comment: Padilla's way to distinguish vacuum curvature (Cosmo Const.) from vacuum energy.

http://arxiv.org/abs/1210.4128
Comment on "Quantum Time Crystals": a new paradigm or just another proposal of perpetuum mobile?
Patrick Bruno
(Submitted on 15 Oct 2012)
A Comment on Frank Wilczek's paper "Quantum Time Crystals" (Phys. Rev. Lett. 109, 160401 (2012); arXiv:1202.2539).
1 page

 

[marcus]

http://arxiv.org/abs/1210.4504
A new perspective on cosmology in Loop Quantum Gravity
Emanuele Alesci, Francesco Cianfrani
(Submitted on 16 Oct 2012)
We present a new cosmological model derived from Loop Quantum Gravity. The formulation is based on a projection of the kinematical Hilbert space of the full theory down to a subspace representing the proper arena for an inhomogeneous Bianchi I model. This procedure gives a direct link between the full theory and its cosmological sector. The emerging quantum cosmological model represents a simplified arena on which the complete canonical quantization program can be tested. The achievements of this analysis could also shed light on Loop Quantum Cosmology and its relation with the full theory.
5 pages

Brief mention:
http://arxiv.org/abs/1210.4174
The Physical Principle that determines the Value of the Cosmological Constant
T. Padmanabhan
(Submitted on 15 Oct 2012)
Observations indicate that the evolution of our universe can be divided into three epochs consisting of early time inflation, radiation (and matter) domination and the late time acceleration. One can associate with each of these epochs a number N which is the phase space volume of the modes which cross the Hubble radius during the corresponding epoch. This number turns out to be (approximately) the same for the cosmologically relevant ranges of the three epochs. When the initial de Sitter space is characterized by the Planck length, the natural value for N is 4π. This allows us to determine the cosmological constant which drives the late time acceleration, to be Λ L²_P = 3exp(-24π²μ) where μ is a number of order unity. This expression leads to the observed value of cosmological constant for μ ~ 1.19. The implications are discussed.
9 pages; 1 figure

 

[John86]

Interesting !..http://arxiv.org/abs/1206.4949
Fundamental quantum optics experiments conceivable with satellites -- reaching relativistic distances and velocities
David Rideout, Thomas Jennewein, Giovanni Amelino-Camelia, Tommaso F. Demarie, Brendon L. Higgins, Achim Kempf, Adrian Kent, Raymond Laflamme, Xian Ma, Robert B. Mann, Eduardo Martin-Martinez, Nicolas C. Menicucci, John Moffat, Christoph Simon, Rafael Sorkin, Lee Smolin, Daniel R. Terno
(Submitted on 21 Jun 2012 (v1), last revised 5 Oct 2012 (this version, v2))
Physical theories are developed to describe phenomena in particular regimes, and generally are valid only within a limited range of scales. For example, general relativity provides an effective description of the Universe at large length scales, and has been tested from the cosmic scale down to distances as small as 10 meters. In contrast, quantum theory provides an effective description of physics at small length scales. Direct tests of quantum theory have been performed at the smallest probeable scales at the Large Hadron Collider, ${\sim} 10^{-20}$ meters, up to that of hundreds of kilometers. Yet, such tests fall short of the scales required to investigate potentially significant physics that arises at the intersection of quantum and relativistic regimes. We propose to push direct tests of quantum theory to larger and larger length scales, approaching that of the radius of curvature of spacetime, where we begin to probe the interaction between gravity and quantum phenomena. In particular, we review a wide variety of potential tests of fundamental physics that are conceivable with artificial satellites in Earth orbit and elsewhere in the solar system, and attempt to sketch the magnitudes of potentially observable effects. The tests have the potential to determine the applicability of quantum theory at larger length scales, eliminate various alternative physical theories, and place bounds on phenomenological models motivated by ideas about spacetime microstructure from quantum gravity. From a more pragmatic perspective, as quantum communication technologies such as quantum key distribution advance into Space towards large distances, some of the fundamental physical effects discussed here may need to be taken into account to make such schemes viable.

 

[marcus]

http://arxiv.org/abs/1210.5223
Experimental search for a Lorentz invariant spacetime granularity: Possibilities and bounds
Pedro Aguilar, Yuri Bonder, Daniel Sudarsky
(Submitted on 18 Oct 2012)
We consider a search for phenomenological signatures from an hypothetical space-time granularity that respects Lorentz invariance. The model is based on the idea that the metric description of Einstein's gravity corresponds to a hydrodynamic characterization of some deeper underlying structure, and that Einstein's gravity is thus to be seen as emergent. We present the specific phenomenological model in detail and analyze the bounds on its free parameters established by a experiment specifically designed to test this model.
25 pages

Brief mention:
http://arxiv.org/abs/1210.4940
Thermodynamics of universal horizons in Einstein-aether theory
Per Berglund, Jishnu Bhattacharyya, David Mattingly
(Submitted on 17 Oct 2012)
... This suggests that the class of holographic theories may be much broader than currently assumed.
5 pages.

 

[marcus]

http://arxiv.org/abs/1210.5276
Geometric asymptotics for spin foam lattice gauge gravity on arbitrary triangulations
Frank Hellmann, Wojciech Kaminski
(Submitted on 18 Oct 2012)
We study the behavior of holonomy spin foam partition functions, a form of lattice gauge gravity, on generic 4d-triangulations using micro local analysis. To do so we adapt tools from the renormalization theory of quantum field theory on curved space times. This allows us, for the first time, to study the partition function without taking any limits on the interior of the triangulation.
We establish that for many of the most widely used models the geometricity constraints, which reduce the gauge theory to a geometric one, introduce strong accidental curvature constraints. These limit the curvature around each triangle of the triangulation to a finite set of values. We demonstrate how to modify the partition function to avoid this problem. Finally the new methods introduced provide a starting point for studying the regularization ambiguities and renormalization of the partition function.
4+6 pages, 1 figure

Brief mention:
http://arxiv.org/abs/1210.5490
Asymptotic Freedom of Rank 4 Tensor Group Field Theory
Joseph Ben Geloun
(Submitted on 19 Oct 2012)
Recently, a rank four tensor group field theory has been proved renormalizable. We provide here the key points on the renormalizability of this model and its UV asymptotic freedom.
7 pages, 3 Figures; Contribution to the XXIXth International Colloquium on Group-Theoretical Methods in Physics, Nankai, China, August 20-26, 2012

http://arxiv.org/abs/1210.5317
Comment on the black hole firewall
Sabine Hossenfelder
(Submitted on 19 Oct 2012)
Recently, it has been argued that black hole complementarity is inconsistent by showing that, for an infalling observer, it would lead to the existence of a firewall near the black hole horizon, thereby violating the equivalence principle. If true, this would necessitate to give up on at least one of the postulates of black hole complementarity. In this comment I want to address an additional assumption that went into the conclusion, that the early outgoing Hawking radiation is entangled with the late radiation.

 

[marcus]

http://arxiv.org/abs/1210.6257
Group field theories
Thomas Krajewski
(Submitted on 23 Oct 2012)
Group field theories are particular quantum field theories defined on D copies of a group which reproduce spin foam amplitudes on a space-time of dimension D. In these lecture notes, we present the general construction of group field theories, merging ideas from tensor models and loop quantum gravity. This lecture is organized as follows. In the first section, we present basic aspects of quantum field theory and matrix models. The second section is devoted to general aspects of tensor models and group field theory and in the last section we examine properties of the group field formulation of BF theory and the EPRL model. We conclude with a few possible research topics, like the construction of a continuum limit based on the double scaling limit or the relation to loop quantum gravity through Schwinger-Dyson equations
58 pages. Lectures given at the "3rd Quantum Gravity and Quantum Geometry School", March 2011, Zakopane

http://arxiv.org/abs/1210.6215
Pure connection formalism for gravity: Feynman rules and the graviton-graviton scattering
Gianluca Delfino, Kirill Krasnov, Carlos Scarinci
(Submitted on 23 Oct 2012)
We continue to develop the pure connection formalism for gravity. We derive the Feynman rules for computing the connection correlation functions, as well as the prescription for obtaining the Minkowski space graviton scattering amplitudes from the latter. The present formalism turns out to be significantly simpler than the one based on the metric in many aspects. The most drastic difference with the usual approach is that the conformal factor of the metric, which is a source of difficulties in the metric treatment, does not propagate in the connection formulation even off-shell. This simplifies both the linearized theory and the interactions. For comparison, in our approach the complete off-shell cubic GR interaction contains just 3 terms, with only a single term relevant at tree level. This should be compared to at least a dozen terms in the metric formalism. We put the technology developed to use and compute the simplest graviton-graviton scattering amplitudes...
... This serves as a good illustration of the type of parity violation present in these theories. We find that the parity-violating amplitudes are important at high energies, and that a general parity-violating member of our class of theories "likes" one helicity (negative in our conventions) more than the other in the sense that at high energies it tends to convert all present gravitons into those of negative helicity.
46 pages.

my comment: For context here is a quote from page 1.

In paper [1] one of us showed how Λ≠ 0 General Relativity (GR) can be described in the ”pure connection” formalism, in which the only field present in the Lagrangian formulation of the theory is a (complexified) SO(3) connection rather than the metric. Paper [2] made the first steps towards setting up the perturbation theory in this formalism, analyzing the free theory and obtaining the propagator...​

For additional context.

[1] K. Krasnov, “Pure Connection Action Principle for General Relativity,” Phys. Rev. Lett. 106, 251103 (2011) [arXiv:1103.4498 [gr-qc]].
[2] K. Krasnov, “Gravity as a diffeomorphism invariant gauge theory,” Phys. Rev. D 84, 024034 (2011) [arXiv:1101.4788 [hep-th]].
[3] R. Capovilla, T. Jacobson and J. Dell, “General Relativity Without the Metric,” Phys. Rev. Lett. 63, 2325 (1989).
[4] R. Capovilla, T. Jacobson and J. Dell, “A Pure spin connection formulation of gravity,” Class. Quant. Grav. 8, 59 (1991).​

http://arxiv.org/abs/1210.5621
Towards solving generic cosmological singularity problem
Wlodzimierz Piechocki
(Submitted on 20 Oct 2012)
The big bounce transition of the quantum FRW model in the setting of loop quantum cosmology is presented. We determine the physical self-adjoint Hamiltonian generating the dynamics. It is used to define, via the Stone theorem, an evolution operator. We examine properties of expectation values of physical observables in the process of the quantum big bounce transition. The dispersion of observables are studied in the context of the Heisenberg uncertainty principle. We suggest that the real nature of the bounce may become known only after we quantize the Belinskii-Khalatnikov-Lifgarbagez scenario, which concerns the generic cosmological singularity.
4 pages, no figures; talk presented at the Multiverse and Fundamental Cosmology Conference, 10-14 September, 2012, Szczecin, Poland; to be published in the AIP Conference Proceedings Series

 

[MTd2]

http://arxiv.org/abs/1210.6736

Noether current of the surface term of Einstein-Hilbert action, Virasoro algebra and entropy

Bibhas Ranjan Majhi
(Submitted on 25 Oct 2012)
A derivation of Noether current from the surface term of Einstein-Hilbert action is given. We show that the corresponding charge, calculated on the horizon, is related to the Bekenstein-Hawking entropy. Also using the charge, the same entropy is found based on the Virasoro algebra and Cardy formula approach. In this approach, the relevant diffeomorphisms are found by imposing a very simple physical argument: diffeomorphisms keep the horizon structure invariant. Finally we discuss the technical simplicities and improvements over the earlier attempts and also various important physical implications.

 

[marcus]

http://arxiv.org/abs/1210.7222
Solvable model for quantum gravity
Jack Gegenberg, Viqar Husain
We study a type of geometric theory with a non-dynamical one-form field. For a manifold that is R⁴, this is equivalent to a theory formulated on a symplectic manifold. Its dynamical variables are an su(2) gauge field and a triad of su(2) valued one-forms. Hamiltonian decomposition reveals that the theory has a true Hamiltonian, together with spatial diffeomorphism and Gauss law constraints, which generate the only local symmetries. Although perturbatively non-renormalizable, the model provides a test bed for the non-perturbative quantization techniques of loop quantum gravity.

http://arxiv.org/abs/1210.6869
Towards an Anomaly-Free Quantum Dynamics for a Weak Coupling Limit of Euclidean Gravity
Casey Tomlin, Madhavan Varadarajan
The G -->0 limit of Euclidean gravity introduced by Smolin is described by a generally covariant U(1)xU(1)xU(1) gauge theory. The Poisson bracket algebra of its Hamiltonian and diffeomorphism constraints is isomorphic to that of gravity. Motivated by recent results in Parameterized Field Theory and by the search for an anomaly-free quantum dynamics for Loop Quantum Gravity (LQG), the quantum Hamiltonian constraint of density weight 4/3 for this U(1)xU(1)xU(1) theory is constructed so as to produce a non-trivial LQG-type representation of its Poisson brackets through the following steps. First, the constraint at finite triangulation, as well as the commutator between a pair of such constraints, are constructed as operators on the 'charge' network basis. Next, the continuum limit of the commutator is evaluated with respect to an operator topology defined by a certain space of `vertex smooth' distributions. Finally, the operator corresponding to the Poisson bracket between a pair of Hamiltonian constraints is constructed at finite triangulation in such a way as to generate a `generalised' diffeomorphism and its continuum limit is shown to agree with that of the commutator between a pair of finite triangulation Hamiltonian constraints. Our results in conjunction with the recent work of Henderson, Laddha and Tomlin in a 2+1-dimensional context, constitute the necessary first steps toward a satisfactory treatment of the quantum dynamics of this model
57 pages 9 figures.

http://arxiv.org/abs/1210.6877
Towards an Anomaly-Free Quantum Dynamics for a Weak Coupling Limit of Euclidean Gravity: Diffeomorphism Covariance
Madhavan Varadarajan
The G-->0 limit of Euclidean gravity introduced by Smolin is described by a generally covariant U(1)xU(1)xU(1) gauge theory. In an earlier paper, Tomlin and Varadarajan constructed the quantum Hamiltonian constraint of density weight 4/3 for this U(1)xU(1)xU(1) theory so as to produce a non-trivial anomaly free LQG-type representation of the Poisson bracket between a pair of Hamiltonian constraints. These constructions involved a choice of regulating coordinate patches. The use of these coordinate patches is in apparent conflict with spatial diffeomorphism covariance. In this work we show how an appropriate choice of coordinate patches together with suitable modifications of these constructions results in the diffeomorphism covariance of the continuum limit action of the Hamiltonian constraint operator, while preserving the anomaly free property of the continuum limit action of its commutator.
56 pages.

 

[marcus]

http://arxiv.org/abs/1210.7248
Loop Quantum Cosmology: Anisotropy and singularity resolution
Alejandro Corichi, Asieh Karami, Edison Montoya
(Submitted on 26 Oct 2012)
In this contribution we consider the issue of singularity resolution within loop quantum cosmology (LQC) for different homogeneous models. We present results of numerical evolutions of effective equations for both isotropic as well as anisotropic cosmologies, with and without spatial curvature. To address the issue of singularity resolution we examine the time evolution of geometrical and curvature invariants that yield information about the semiclassical spacetime geometry. We discuss generic behavior found for a variety of initial conditions. Finally, we show that the modifications which come from Loop Quantum Cosmology imply a non-chaotic effective behavior in the vacuum Bianchi IX model.
12 pages, 4 figures, To appear in the Proceedings of the Relativity and Gravitation 100 Years after Einstein in Prague

http://arxiv.org/abs/1210.7596
The trouble with asymptotically safe inflation
Chao Fang, Qing-Guo Huang
(Submitted on 29 Oct 2012)
In this paper we investigate the perturbation theory of the asymptotically safe inflation and we find that all modes of gravitational waves perturbation become ghosts in order to achieve a large enough number of e-folds. Formally we can calculate the power spectrum of gravitational waves perturbation, but we find that it is negative. It indicates that there is serious trouble with the asymptotically safe inflation.
13 pages, 1 figure

 

[marcus]

http://arxiv.org/abs/1210.8138
Non-linear (loop) quantum cosmology
Martin Bojowald, Alexander L. Chinchilli, Christine C. Dantas, Matthew Jaffe, David Simpson
(Submitted on 30 Oct 2012)
Inhomogeneous quantum cosmology is modeled as a dynamical system of discrete patches, whose interacting many-body equations can be mapped to a non-linear minisuperspace equation by methods analogous to Bose-Einstein condensation. Complicated gravitational dynamics can therefore be described by more-manageable equations for finitely many degrees of freedom, for which powerful solution procedures are available, including effective equations. The specific form of non-linear and non-local equations suggests new questions for mathematical and computational investigations, and general properties of non-linear wave equations lead to several new options for physical effects and tests of the consistency of loop quantum gravity. In particular, our quantum cosmological methods show how sizeable quantum corrections in a low-curvature universe can arise from tiny local contributions adding up coherently in large regions.
20 pages

brief mention:
http://arxiv.org/abs/1210.3545
Models of Topology Change
Alfred D. Shapere, Frank Wilczek, Zhaoxi Xiong
(Submitted on 12 Oct 2012)
We show how changes in unitarity-preserving boundary conditions allow continuous interpolation among the Hilbert spaces of quantum mechanics on topologically distinct manifolds. We present several examples, including a computation of entanglement entropy production. We discuss approximate realization of boundary conditions through appropriate interactions, thus suggesting a route to possible experimental realization. We give a theoretical application to quantization of singular Hamiltonians, and give tangible form to the "many worlds" interpretation of wave functions.
7 pages, 3 figures

http://arxiv.org/abs/1210.7834
The DSR-deformed relativistic symmetries and the relative locality of 3D quantum gravity
Giovanni Amelino-Camelia, Michele Arzano, Stefano Bianco, Riccardo J. Buonocore
(Submitted on 29 Oct 2012)
...
12 pages, 3 figures

 

[marcus]

http://arxiv.org/abs/1211.0161
Emergent Isotropy-Breaking in Quantum Cosmology
Andrea Dapor, Jerzy Lewandowski
(Submitted on 1 Nov 2012)
We consider a massive quantum test Klein-Gordon field probing an isotropic quantum cosmological space-time in the background. The result obtained is surprising. It turns out, that despite the isotropy of the quantum gravitational field, the semi-classical metric experienced by a mode of the K-G field is non-isotropic. The anisotropy depends on the direction of the momentum of the mode. Specifically, what we do is to derive a semi-classical space-time which emerges to a mode of the field. The method amounts to a comparison between QFT on a quantum background and QFT on a classical curved space-time, giving rise to an emergent metric tensor. The components of the semi-classical metric tensor are calculated from the equation of propagation of the quantum K-G field in the test field approximation. The anisotropies are of a quantum nature: they are proportional to Planck constant and "dress" the isotropic classical space-time obtained in the classical limit.
6 pages

 

[marcus]

http://arxiv.org/abs/1211.0522
Horizon entanglement entropy and universality of the graviton coupling
Eugenio Bianchi
(Submitted on 2 Nov 2012)
We compute the low-energy variation of the horizon entanglement entropy for matter fields and gravitons in Minkowski space. While the entropy is divergent, the variation under a perturbation of the vacuum state is finite and proportional to the energy flux through the Rindler horizon. Due to the universal coupling of gravitons to the energy-momentum tensor, the variation of the entanglement entropy is universal and equal to the change in area of the event horizon divided by 4 times Newton's constant - independently from the number and type of matter fields. The physical mechanism presented provides an explanation of the microscopic origin of the Bekenstein-Hawking entropy in terms of entanglement entropy.
7 pages

 

[marcus]

http://arxiv.org/abs/1211.0823
Polymer quantization and Symmetries
Ghanashyam Date, Nirmalya Kajuri
(Submitted on 5 Nov 2012)
Polymer quantization was discovered during the construction of Loop Quantum Cosmology. For the simplest quantum theory of one degree of freedom, the implications for dynamics were studied for the harmonic oscillator as well as some other potentials. For more degrees of freedom, the possibility of continuous, kinematic symmetries arises. While these are realized on the Hilbert space of polymer quantum mechanics, their infinitesimal versions are not supported. For an invariant Hamiltonian, these symmetry realizations imply infinite degeneracy suggesting that the symmetry should be spontaneously or explicitly broken. The estimation of symmetry violations in some cases have been analysed before. Here we explore the alternative of shifting the arena to the distributional states. We discuss both the polymer quantum mechanics case as well as polymer quantized scalar field.
18 pages

http://arxiv.org/abs/1211.0825
Going beyond the Standard Model with noncommutative geometry
Thijs van den Broek, Walter D. van Suijlekom
(Submitted on 5 Nov 2012)
The derivation of the full Standard Model from noncommutative geometry has been a promising sign for possible applications of the latter in High Energy Physics. Many believe, however, that the Standard Model cannot be the final answer. We translate several demands whose origin lie in physics to the context of noncommutative geometry and use these to put constraints on the fermionic content of models. We show that the Standard Model only satisfies these demands provided it has a right-handed neutrino in each 'generation'. We also prove that the Minimal Supersymmetric Standard Model is not among the models that satisfy our constraints, but pose a solution that is a slight extension of the MSSM.
19 pages

 

[marcus]

http://arxiv.org/abs/1211.1354
An Extension of the Quantum Theory of Cosmological Perturbations to the Planck Era
Ivan Agullo, Abhay Ashtekar, William Nelson
(Submitted on 6 Nov 2012)
Cosmological perturbations are generally described by quantum fields on (curved but) classical space-times. While this strategy has a large domain of validity, it can not be justified in the quantum gravity era where curvature and matter densities are of Planck scale. Using techniques from loop quantum gravity, the standard theory of cosmological perturbations is extended to overcome this limitation. The new framework sharpens conceptual issues by distinguishing between the true and apparent trans-Planckian difficulties and provides sufficient conditions under which the true difficulties can be overcome within a quantum gravity theory. In a companion paper, this framework is applied to the standard inflationary model, with interesting implications to theory as well as observations.
50 pages. This is first of the two detailed papers on which arXiv 1209.1609 (PRL at press) is based

http://arxiv.org/abs/1211.1244
Schwinger-Dyson Equations in Group Field Theories of Quantum Gravity
Thomas Krajewski
(Submitted on 6 Nov 2012)
In this talk, we elaborate on the operation of graph contraction introduced by Gurau in his study of the Schwinger-Dyson equations. After a brief review of colored tensor models, we identify the Lie algebra appearing in the Schwinger-Dyson equations as a Lie algebra associated to a Hopf algebra of the Connes-Kreimer type. Then, we show how this operation also leads to an analogue of the Wilsonian flow for the effective action. Finally, we sketch how this formalism may be adapted to group field theories.
6 pages. Talk given at "The XXIX International Colloquium on Group-Theoretical Methods in Physics", Chern Institute of Mathematics August 2012, submitted to the conference proceedings

 

[MTd2]

http://arxiv.org/abs/1211.1131

A Construct of Dynamics, Space and Gravity from Loops

Madhavan Venkatesh
(Submitted on 6 Nov 2012)
An attempt is made to construct space and obtain dynamics from Loop Algebras and their elements. We define three new products between loops namely 'Vertical Product', 'Horizontal Product' and 'Total Product'. As for the dynamics, we obtain corresponding "velocity" and "canonical momenta" from it. Also, we build a new "Energy Variable" that is dependent on the velocity and momentum alone. Then, we apply the loop constructs to General Relativity and arrive at the Einstein Field Equations, although presented in a different form. The key feature of this formalism is that the metric is not arbitarized as prevalent on the space beforehand but is rather induced by restricting the Killing Form to the Cartan Sub-algebra of the underlying Lie Algebra. Then we go on to show that "Dynamics is Structure" and that both do not depend on length or time.

 

[marcus]

http://arxiv.org/abs/1211.2166
The spin connection of twisted geometry
Hal M. Haggard, Carlo Rovelli, Francesca Vidotto, Wolfgang Wieland
(Submitted on 9 Nov 2012)
Twisted geometry is a piecewise-flat geometry less rigid than Regge geometry. In Loop Gravity, it provides the classical limit for each step of the truncation utilized in the definition of the quantum theory. We define the torsionless spin-connection of a twisted geometry. The difficulty given by the discontinuity of the triad is addressed by interpolating between triads. The curvature of the resulting spin connection reduces to the Regge curvature in the case of a Regge geometry.
5 pages, 2 figures

 

[marcus]

http://arxiv.org/abs/1211.2702
Dynamical evaporation of quantum horizons
Daniele Pranzetti
(Submitted on 12 Nov 2012)
We describe the black hole evaporation process driven by the dynamical evolution of the quantum gravitational degrees of freedom resident at the horizon, as identified by the Loop Quantum Gravity kinematics. Using a parallel with the Brownian motion, we interpret the first law of quantum dynamical horizon in terms of a fluctuation-dissipation relation applied to this fundamental discrete structure. In this way, the horizon evolution is described in terms of relaxation to an equilibrium state balanced by the excitation of Planck scale constituents of the horizon. We investigate the final stage of the evaporation process and show how, from this setting, the emergence of several conservative scenarios for the information paradox can be microscopically derived. Namely, the leakage of part of the horizon quantum geometry information prior to the Planckian phase and the stabilization of the hole surface shrinkage forming a massive remnant, which can eventually decay, are described.
14 pages, 2 figures

http://arxiv.org/abs/1211.2731
Horizon thermodynamics and composite metrics
Lorenzo Sindoni
(Submitted on 12 Nov 2012)
We examine the conditions under which the thermodynamic behaviour of gravity can be explained within an emergent gravity scenario, where the metric is defined as a composite operator. We show that due to the availability of a boundary of a boundary principle for the quantum effective action, Clausius-like relations can always be constructed. Hence, any true explanation of the thermodynamic nature of the metric tensor has to be referred to an equilibration process, associated to the presence of an H-theorem, possibly driven by decoherence induced by the pregeometric degrees of freedom, and their entanglement with the geometric ones.
11 pages, 1 figure

 

[marcus]

not QG but possibly of interest to quantum relativists:
http://arxiv.org/abs/1211.3880
The symplectic 2-form for gravity in terms of free null initial data
Michael P. Reisenberger
(Submitted on 16 Nov 2012)
A hypersurface formed of two null sheets, or "light fronts", swept out by the future null normal geodesics emerging from a common spacelike 2-disk can serve as a Cauchy surface for a region of spacetime. Already in the 1960s free (unconstrained) initial data for general relativity were found for such hypersurfaces. Here an expression is obtained for the symplectic 2-form of vacuum general relativity in terms of such free data. This can be done, even though variations of the geometry do not in general preserve the nullness of the initial hypersurface, because of the diffeomorphism gauge invariance of general relativity. The present expression for the symplectic 2-form has been used previously to calculate the Poisson brackets of the free data.
44 pages, 2 figures

http://arxiv.org/abs/1211.3816
Is a tabletop search for Planck scale signals feasible?
Jacob D. Bekenstein
(Submitted on 16 Nov 2012)
Quantum gravity theory is untested experimentally. Could it be tested with tabletop experiments? While the common feeling is pessimistic, a detailed inquiry shows it possible to sidestep the onerous requirement of localization of a probe on Planck length scale. I suggest a tabletop experiment which, given state of the art ultrahigh vacuum and cryogenic technology, could already be sensitive enough to detect Planck scale signals. The experiment combines a single photon's degree of freedom with one of a macroscopic probe to test Wheeler's conception of "spacetime foam", the assertion that on length scales of the order Planck's, spacetime is no longer a smooth manifold. The scheme makes few assumptions beyond energy and momentum conservations, and is not based on a specific quantum gravity scheme.
8 pages, 2 figures

 

[marcus]

http://arxiv.org/abs/1211.4183
Loop quantum Brans-Dicke cosmology
Xiangdong Zhang, Yongge Ma
(Submitted on 18 Nov 2012)
The spatially flat and isotropic cosmological model of Brans-Dicke theory with coupling parameter ω ≠ -3/2 is quantized by the approach of loop quantum cosmology. An interesting feature of this model is that, although the Brans-Dicke scalar field is non-minimally coupled with curvature, it can still play the role of an emergent time variable. In the quantum theory, the classical differential equation which represents cosmological evolution is replaced by a quantum difference equation. The effective Hamiltonian and modified dynamical equations of loop quantum Brans-Dicke cosmology are also obtained, which lay a foundation for the phenomenological investigation to possible quantum gravity effects in cosmology. The effective equations indicate that the classical big bang singularity is again replaced by a quantum bounce in loop quantum Brans-Dicke cosmology.
11pages

http://arxiv.org/abs/1211.4151
Lectures on renormalization and asymptotic safety
Sandor Nagy
(Submitted on 17 Nov 2012)
A short introduction is given on the functional renormalization group method, putting emphasis on its nonperturbative aspects. The method enables to find nontrivial fixed points in quantum field theoretic models which make them free from divergences and leads to the concept of asymptotic safety. It can be considered as a generalization of the asymptotic freedom which plays a key role in the perturbative renormalization. We summarize and give a short discussion of some important models, which are asymptotically safe such as the Gross-Neveu model, the nonlinear σ model, the sine-Gordon model, and the model of quantum Einstein gravity. We also give a detailed analysis of infrared behavior of the models where a spontaneous symmetry breaking takes place. The deep infrared behavior of the broken phase cannot be treated within the framework of perturbative calculations. We demonstrate that there exists an infrared fixed point in the broken phase which creates a new scaling regime there, however its structure is hidden by the singularity of the renormalization group equations. The phase spaces of these models show several similar properties, namely the models has the same phase and fixed point structure. These results can only be uncovered by the functional renormalization group method.
32 pages, 20 figures. Based on the talk presented at the Theoretical Physics School on Quantum Gravity, Szeged, Hungary, 27-31 August 2012

 

[marcus]

http://arxiv.org/abs/1211.4807
Holonomy-flux spinfoam amplitude
Claudio Perini
(Submitted on 20 Nov 2012)
We introduce a holomorphic representation for the Lorentzian EPRL spinfoam on arbitrary 2-complexes. The representation is obtained via the Ashtekar-Lewandowski-Marolf-Mourao-Thiemann heat kernel coherent state transform. The new variables are classical holonomy-flux phase space variables (h,X) ≈ T*SU(2) of Hamiltonian loop quantum gravity prescribing the holonomies of the Ashtekar connection A = Γ + γK, and their conjugate gravitational fluxes. For small heat kernel 'time' the spinfoam amplitude is peaked on classical space-time geometries, where at most countably many curvatures are allowed for non-zero Barbero-Immirzi parameter. We briefly comment on the possibility to use the alternative flipped classical limit.
33 pages

not QG but possibly of interest:
http://arxiv.org/abs/1211.4848
Scrutinizing the Cosmological Constant Problem and a possible resolution
Denis Bernard, André LeClair
(Submitted on 20 Nov 2012)
We suggest a new perspective on the Cosmological Constant Problem by scrutinizing its standard formulation. In classical and quantum mechanics without gravity, there is no definition of the zero point of energy. Furthermore, the Casimir effect only measures how the vacuum energy changes as one varies a geometric modulus. This leads us to propose that the physical vacuum energy in a Friedman-Lemaitre-Robertson-Walker expanding universe only depends on the time variation of the scale factor a(t). Equivalently, requiring that empty Minkowski space is stable is a principle that fixes the ambiguity in the zero point energy. We describe two different choices of vacuum, one of which is consistent with the current universe consisting only of matter and vacuum energy. The resulting vacuum energy density is proportional to (k_cH₀)², where k_c is a momentum cut-off and H₀ is the Hubble constant; for a cut-off close to the Planck scale, values of the vacuum energy density in agreement with astrophysical measurements are obtained. Another choice of vacuum is more relevant to the early universe consisting of only radiation and vacuum energy, and we suggest it as a possible model of inflation.
22 pages, 1 figure

 

[marcus]

http://arxiv.org/abs/1211.5024
Loop quantum modified gravity and its cosmological application
Xiangdong Zhang, Yongge Ma
(Submitted on 21 Nov 2012)
A general nonperturbative loop quantization procedure for metric modified gravity is reviewed. As an example, this procedure is applied to scalar-tensor theories of gravity. The quantum kinematical framework of these theories is rigorously constructed. Both the Hamiltonian and master constraint operators are well defined and proposed to represent quantum dynamics of scalar-tensor theories. As an application to models, we set up the basic structure of loop quantum Brans-Dicke cosmology. The effective dynamical equations of loop quantum Brans-Dicke cosmology are also obtained, which lay a foundation for the phenomenological investigation to possible quantum gravity effects in cosmology.
18pages.

 

[marcus]

http://arxiv.org/abs/1211.5180
Path Integral of Bianchi I models in Loop Quantum Cosmology
Xiao Liu, Fei Huang, Jian-Yang Zhu
(Submitted on 22 Nov 2012)
A path integral formulation of the Bianchi I models containing a massless scalar field in loop quantum cosmology is constructed. Following the strategy used in the homogenous and isotropic case, the calculation is extended to the simplest non-isotropic models according to the μ-bar and μ'-bar scheme. It is proved from the path integral angle that the quantum dynamic lacks the full invariance with respect to fiducial cell scaling in the μ-bar scheme, but it does not in the μ'-bar scheme. The investigation affirms the equivalence of the canonical approach and the path integral approach in loop quantum cosmology.
10 pages

http://arxiv.org/abs/1211.5310
Power spectrum and anisotropy of super inflation in loop quantum cosmology
Xiao-Jun Yue, Jian-Yang Zhu
(Submitted on 22 Nov 2012)
We investigate the scalar mode of perturbation of super inflation in the version of loop quantum cosmology in which the gauge invariant holonomy corrections are considered. Given a background solution, we calculate the power spectrum of the perturbation in the classical and LQC conditions. Then we compute the anisotropy originated from the perturbation. It is found that in the presence of the gauge invariant holonomy corrections the power spectrum is exponentially blue and the anisotropy also grows exponentially in the epoch of super inflation.
12 pages,4 figures

My note: Jian-Yang Zhu is at Beijing Normal (BNU) same department as Prof. Yongge Ma.

 

[marcus]

http://arxiv.org/abs/1211.5878
Frequently asked questions about Shape Dynamics
H. Gomes, T. Koslowski
(Submitted on 26 Nov 2012)
Barbour's interpretation of Mach's principle led him to postulate that gravity should be formulated as a dynamical theory of spatial conformal geometry, or in his terminology, "shapes." Recently, it was shown that the dynamics of General Relativity can indeed be formulated as the dynamics of shapes. This new Shape Dynamics theory, unlike earlier proposals by Barbour and his collaborators, implements local spatial conformal invariance as a gauge symmetry that replaces refoliation invariance in General Relativity. It is the purpose of this paper to answer frequent questions about (new) Shape Dynamics, such as its relation to Poincaré invariance, General Relativity, Constant Mean (extrinsic) Curvature gauge, earlier Shape Dynamics, and finally the conformal approach to the initial value problem of General Relativity. Some of these relations can be clarified by considering a simple model: free electrodynamics and its dual shift symmetric formulation. This model also serves as an example where symmetry trading is used for usual gauge theories.
19 pages

http://arxiv.org/abs/1211.5939
Action principle for the connection dynamics of scalar-tensor theories
Zhenhua Zhou, Haibiao Guo, Yu Han, Yongge Ma
(Submitted on 26 Nov 2012)
A first-order action for scalar-tensor theories of gravity is proposed. The Hamiltonian analysis of the action gives a connection dynamical formalism, which is equivalent to the connection dynamics derived from the geometrical dynamics by canonical transformations. Therefore, the action principle underlying loop quantum scalar-tensor theories is recovered.
5 pages

http://arxiv.org/abs/1211.5714
The quantum geometry of tensorial group field theories
Daniele Oriti
(Submitted on 24 Nov 2012)
We remark the importance of adding suitable pre-geometric content to tensor models, obtaining what has recently been called tensorial group field theories, to have a formalism that could describe the structure and dynamics of quantum spacetime. We also review briefly some recent results concerning the definition of such pre-geometric content, and of models incorporating it.
6 pages; contribution to the proceedings of The XXIX International Colloquium on Group-Theoretical Methods in Physics, August 20-26, 2012, Chern Institute of Mathematics, Tianjin, China

 

[marcus]

http://arxiv.org/abs/1211.6269
The Matter Bounce Scenario in Loop Quantum Cosmology
Edward Wilson-Ewing
(Submitted on 27 Nov 2012)
In the matter bounce scenario, a dust-dominated contracting space-time generates scale-invariant perturbations that, assuming a nonsingular bouncing cosmology, propagate to the expanding branch and set appropriate initial conditions for the radiation-dominated era. Since this scenario depends on the presence of a bounce, it seems appropriate to consider it in the context of loop quantum cosmology where a bouncing universe naturally arises. It turns out that quantum gravity effects play an important role beyond simply providing the bounce. Indeed, quantum gravity corrections to the Mukhanov-Sasaki equations significantly modify some of the results obtained in a purely classical setting: while the predicted spectra of scalar and tensor perturbations are both almost scale-invariant with identical small red tilts in agreement with previous results, the tensor to scalar ratio is now expected to be r≈ 9 x 10^-4, which is much smaller than the original classical prediction. Finally, for the predicted amplitude of the scalar perturbations to agree with observations, the critical density in loop quantum cosmology must be of the order ρ_crit ~ 10^-9 ρ_Planck.
8 pages

[My comment: !]

brief mention:
http://arxiv.org/abs/1211.6337
The Cosmological Constant
Alex Harvey
(Submitted on 23 Nov 2012)
Contrary to popular mythology, Einstein did not invent the cosmological constant just in order construct his model universe. He discussed it earlier in "The Foundations of General Relativity" in connection with the proper structure of the source-free field equations. There he dismissed it as arbitrary and unnecessary. It was later that he found its inclusion to be essential to the construction of his model.
3 pages

 

[John86]

http://arxiv.org/abs/1211.6913
Black Hole Entanglement and Quantum Error Correction
Erik Verlinde, Herman Verlinde
(Submitted on 29 Nov 2012)
It was recently argued by Almheiri et al that black hole complementarity strains the basic rules of quantum information theory, such as monogamy of entanglement. Motivated by this argument, we develop a practical framework for describing black hole evaporation via unitary time evolution, based on a holographic perspective in which all black hole degrees of freedom live on the stretched horizon. We model the horizon as a unitary quantum system with finite entropy, and do not postulate that the horizon geometry is smooth. We then show that, with mild assumptions, one can reconstruct local effective field theory observables that probe the black hole interior, and relative to which the state near the horizon looks like a local Minkowski vacuum. The reconstruction makes use of the formalism of quantum error correcting codes, and works for black hole states whose entanglement entropy does not yet saturate the Bekenstein-Hawking bound. Our general framework clarifies the black hole final state proposal, and allows a quantitative study of the transition into the "firewall" regime of maximally mixed black hole states.

 

[marcus]

http://arxiv.org/abs/1211.7311
Pentahedral volume, chaos, and quantum gravity
Hal M. Haggard
(Submitted on 30 Nov 2012)
We show that chaotic classical dynamics associated to the volume of discrete grains of space leads to quantal spectra that are gapped between zero and nonzero volume. This strengthens the connection between spectral discreteness in the quantum geometry of gravity and tame ultraviolet behavior. We complete a detailed analysis of the geometry of a pentahedron, providing new insights into the volume operator and evidence of classical chaos in the dynamics it generates. These results reveal an unexplored realm of application for chaos in quantum gravity.
5 pages, 4 figures

 

[John86]

http://arxiv.org/abs/1211.7122
Patterns in the fabric of nature
Steven Weinstein
(Submitted on 29 Nov 2012)
From classical mechanics to quantum field theory, the physical facts at one point in space are held to be independent of those at other points in space. I propose that we can usefully challenge this orthodoxy in order to explain otherwise puzzling correlations at both cosmological and microscopic scales.


http://arxiv.org/abs/1211.7081
The Universe is not a Computer
Ken Wharton
(Submitted on 29 Nov 2012)
When we want to predict the future, we compute it from what we know about the present. Specifically, we take a mathematical representation of observed reality, plug it into some dynamical equations, and then map the time-evolved result back to real-world predictions. But while this computational process can tell us what we want to know, we have taken this procedure too literally, implicitly assuming that the universe must compute itself in the same manner. Physical theories that do not follow this computational framework are deemed illogical, right from the start. But this anthropocentric assumption has steered our physical models into an impossible corner, primarily because of quantum phenomena. Meanwhile, we have not been exploring other models in which the universe is not so limited. In fact, some of these alternate models already have a well-established importance, but are thought to be mathematical tricks without physical significance. This essay argues that only by dropping our assumption that the universe is a computer can we fully develop such models, explain quantum phenomena, and understand the workings of our universe.

http://arxiv.org/abs/1211.7337
A linear theory underlying quantum mechanics
Casey Blood
(Submitted on 30 Nov 2012)
Linearity allows several versions of reality to simultaneously exist in the state vector. But it implies that there is no interaction between versions, and that there will never be perception of more than one version. It also implies, in conjunction with group representation theory, that the particle-like properties of mass, energy, momentum, spin and charge are attributes of the state vectors. These results can be used to show there is no evidence for the objective existence of particles. The properties of the wave function are sufficient to explain all the particle-like properties of matter. Representation theory is also extensively employed in the Standard Model, with gauge fields transforming as representations of the internal symmetry group. And when applied to the permutation group, it is essential for understanding symmetric and antisymmetric states. In fact all of quantum mechanics is set up exactly as if it were the representation of an underlying pre-representational theory. A linear equation structure for the underlying theory is suggested, and it is shown in outline how quantum field theory emerges as a representational form of the pre-representational theory.

http://arxiv.org/abs/1211.7070
Nonviolent nonlocality
Steven B. Giddings
(Submitted on 29 Nov 2012)
If quantum mechanics governs nature, black holes must evolve unitarily, providing a powerful constraint on the dynamics of quantum gravity. Such evolution apparently must in particular be nonlocal, when described from the usual semiclassical geometric picture, in order to transfer quantum information into the outgoing state. While such transfer from a disintegrating black hole has the dangerous potential to be violent to generic infalling observers, this paper proposes the existence of a more innocuous form of information transfer, to relatively soft modes in the black hole atmosphere. Simplified models for such nonlocal transfer are described and parameterized, within a possibly more basic framework of a Hilbert tensor network. Sufficiently sensitive measurements by infalling observers may detect departures from Hawking's predictions, and in generic models black holes decay more rapidly. Constraints of consistency -- internally and with known and expected features of physics -- restrict the form of information transfer, and should provide important guides to discovery of the principles and mechanisms of the more fundamental nonlocal mechanics.

 

[marcus]

http://arxiv.org/abs/1212.0454
Gravity can be neither classical nor quantized
Sabine Hossenfelder
(Submitted on 3 Dec 2012)
I argue that it is possible for a theory to be neither quantized nor classical. We should therefore give up the assumption that the fundamental theory which describes gravity at shortest distances must either be quantized, or quantization must emerge from a fundamentally classical theory. To illustrate my point I will discuss an example for a theory that is neither classical nor quantized, and argue that it has the potential to resolve the tensions between the quantum field theories of the standard model and general relativity.
7 pages, third prize in the 2012 FQXi essay contest "Which of our basic physical assumptions are wrong?"

http://arxiv.org/abs/1212.0371
Not on but of
Olaf Dreyer
(Submitted on 3 Dec 2012)
In physics we encounter particles in one of two ways. Either as fundamental constituents of the theory or as emergent excitations. These two ways differ by how the particle relates to the background. It either sits on the background, or it is an excitation of the background. We argue that by choosing the former to construct our fundamental theories we have made a costly mistake. Instead we should think of particles as excitations of a background. We show that this point of view sheds new light on the cosmological constant problem and even leads to observable consequences by giving a natural explanation for the appearance of MOND-like behavior. In this context it also becomes clear why there are numerical coincidences between the MOND acceleration parameter, the cosmological constant and the Hubble parameter.
9 pages. This article received a forth prize in the 2012 FQXi essay contest "Questioning the Foundations". More articles from this contest can be found on the FQXi website at fqxi.org

brief mention:
http://arxiv.org/abs/1212.0500
Vector fields on C*-algebras, semigroups of endomorphisms and gauge groups
Innocenti Maresin

 

[John86]

Not really related!. But interesting.

http://arxiv.org/abs/1212.0107
On the Foundations of the Theory of Evolution
Diederik Aerts, Stan Bundervoet, Marek Czachor, Bart D'Hooghe, Liane Gabora, Philip Polk, Sandro Sozzo
(Submitted on 1 Dec 2012)
Darwinism conceives evolution as a consequence of random variation and natural selection, hence it is based on a materialistic, i.e. matter-based, view of science inspired by classical physics. But matter in itself is considered a very complex notion in modern physics. More specifically, at a microscopic level, matter and energy are no longer retained within their simple form, and quantum mechanical models are proposed wherein potential form is considered in addition to actual form. In this paper we propose an alternative to standard Neodarwinian evolution theory. We suggest that the starting point of evolution theory cannot be limited to actual variation whereupon is selected, but to variation in the potential of entities according to the context. We therefore develop a formalism, referred to as Context driven Actualization of Potential (CAP), which handles potentiality and describes the evolution of entities as an actualization of potential through a reiterated interaction with the context. As in quantum mechanics, lack of knowledge of the entity, its context, or the interaction between context and entity leads to different forms of indeterminism in relation to the state of the entity. This indeterminism generates a non-Kolmogorovian distribution of probabilities that is different from the classical distribution of chance described by Darwinian evolution theory, which stems from a 'actuality focused', i.e. materialistic, view of nature. We also present a quantum evolution game that highlights the main differences arising from our new perspective and shows that it is more fundamental to consider evolution in general, and biological evolution in specific, as a process of actualization of potential induced by context, for which its material reduction is only a special case.

 

[marcus]

not QG but possibly of interest:
http://arxiv.org/abs/1212.0585
Cosmology with a spin
Joao Magueijo, T.G. Zlosnik, T.W.B. Kibble
(Submitted on 3 Dec 2012)
Using the chiral representation for spinors we present a particularly transparent way to generate the most general spinor dynamics in a theory where gravity is ruled by the Einstein-Cartan-Holst action. In such theories torsion need not vanish, but it can be re-interpreted as a 4-fermion self-interaction within a torsion-free theory. The self-interaction may or may not break parity invariance, and may contribute positively or negatively to the energy density, depending on the couplings considered. We then examine cosmological models ruled by a spinorial field within this theory. We find that while there are cases for which no significant cosmological novelties emerge, the self-interaction can also turn a mass potential into an upside-down Mexican hat potential. Then, as a general rule, the model leads to cosmologies with a bounce, for which there is a maximal energy density, and where the cosmic singularity has been removed. These solutions are stable, and range from the very simple to the very complex.
19 pages.

http://arxiv.org/abs/1212.0601
Lorentzian Manifolds and Causal Sets as Partially Ordered Measure Spaces
Luca Bombelli, Johan Noldus, Julio Tafoya
(Submitted on 4 Dec 2012)
We consider Lorentzian manifolds as examples of partially ordered measure spaces, sets endowed with compatible partial order relations and measures, in this case given by the causal structure and the volume element defined by each Lorentzian metric. This places the structure normally used to describe spacetime in geometrical theories of gravity in a more general context, which includes the locally finite partially ordered sets of the causal set approach to quantum gravity. We then introduce a function characterizing the closeness between any two partially ordered measure spaces and show that, when restricted to compact spaces satisfying a simple separability condition, it is a distance. In particular, this provides a quantitative, covariant way of describing how close two manifolds with Lorentzian metrics are, or how manifoldlike a causal set is.
13 pages, 5 Figures

 

[marcus]

http://arxiv.org/abs/1212.2204
Electric Time in Quantum Cosmology
Stephon Alexander, Martin Bojowald, Antonino Marciano, David Simpson
(Submitted on 10 Dec 2012)
Effective quantum cosmology is formulated with a realistic global internal time given by the electric vector potential. New possibilities for the quantum behavior of space-time are found, and the high-density regime is shown to be very sensitive to the specific form of state realized.
19 pages, 5 figures.

http://arxiv.org/abs/1212.1821
Black hole thermodynamics under the microscope
Kevin Falls, Daniel F. Litim
(Submitted on 8 Dec 2012)
A coarse-grained version of the effective action is used to study the thermodynamics of black holes, interpolating from largest to smallest masses. The physical parameter of the black hole are linked to the running couplings by thermodynamics, and the corresponding equation of state includes quantum corrections for temperature, specific heat, and entropy. If quantum gravity becomes asymptotically safe, the state function predicts conformal scaling in the limit of small horizon area, and bounds on black hole mass and temperature. A metric-based derivation for the equation of state, and quantum corrections to the thermodynamical, statistical, and phenomenological definition of entropy are also given. Further implications and limitations of our study are discussed.
24 pages, 3 figures

http://arxiv.org/abs/1212.1755
Poincaré invariance and asymptotic flatness in Shape Dynamics
Henrique Gomes
(Submitted on 8 Dec 2012)
Shape Dynamics is a theory of gravity that sheds refoliation invariance in favor of spatial Weyl invariance. It is a canonical theory, constructed from a Hamiltonian, 3+1 perspective. One of the main deficits of Shape Dynamics is that its Hamiltonian is only implicitly constructed as a functional of the phase space variables. In this paper we aim to achieve a new perspective on tackling this problem. For this, we write down the equations of motion for Shape Dynamics. Although there is still an implicit function in these equations of motion, we can make it explicit for particular solutions. In particular, we construct Shape Dynamics over a curve in phase space representing a Minkowski spacetime, and use this to show that in this case Shape Dynamics possesses Poincar\'e symmetry for appropriate boundary conditions. The proper treatment of such boundary conditions leads us to completely formulate Shape Dynamics for open manifolds in the asymptotically flat case. We study the charges arising for Shape Dynamics in flat asymptotic boundary conditions and find a new component for the energy charge. This new charge, when added to the usual ADM energy to make up the total energy for Shape Dynamics, is completely Weyl invariant. We then use the equations of motion once again to find a non-trivial solution of Shape Dynamics, consisting of a flat static Universe with a point-like mass at the center. We calculate its energy and rederive the usual Schwarzschild mass.
22 pages

 

[marcus]

http://lanl.arxiv.org/abs/1212.1930
A "Helium Atom" of Space: Dynamical Instability of the Isochoric Pentahedron
C. E. Coleman-Smith, B. Muller
(Submitted on 9 Dec 2012)
We present an analysis of the dynamics of the equifacial pentahedron on the Kapovich-Millson phase space under a volume preserving Hamiltonian. The classical dynamics of polyhedra under such a Hamiltonian may arise from the classical limit of the node volume operators in loop quantum gravity. The pentahedron is the simplest nontrivial polyhedron for which the dynamics may be chaotic. We consider the distribution of polyhedral configurations throughout the space and find indications that the borders between certain configurations act as separatrices. We examine the local stability of trajectories within this phase space and find that locally unstable regions dominate although extended stable regions are present. Canonical and microcanonical estimates of the Kolmogorov-Sinai entropy suggest that the pentahedron is a strongly chaotic system. The presence of chaos is further suggested by calculations of intermediate time Lyapunov exponents which saturate to non zero values.
20 Pages, 19 Figures

Berndt Müller of the physics department at Duke has around 10,000 cites to his several hundred published papers of which, interestingly, all but one or two have been outside gr-qc, mostly theoretical nuclear physics and high-energy phenomenology. I think this must certainly be his first LQG-related. The paper cites another one (strongly related thematically) by Haggard, that was already reported in post #1852 of this thread:

http://arxiv.org/abs/1211.7311
Pentahedral volume, chaos, and quantum gravity
Hal M. Haggard
(Submitted on 30 Nov 2012)
We show that chaotic classical dynamics associated to the volume of discrete grains of space leads to quantal spectra that are gapped between zero and nonzero volume. This strengthens the connection between spectral discreteness in the quantum geometry of gravity and tame ultraviolet behavior. We complete a detailed analysis of the geometry of a pentahedron, providing new insights into the volume operator and evidence of classical chaos in the dynamics it generates. These results reveal an unexplored realm of application for chaos in quantum gravity.
5 pages, 4 figures

It's interesting that a volume gap appears in several types of analysis. I see Müller came to Duke around 1990, prior to that was at Frankfurt.
http://inspirehep.net/author/B.Muller.1/

 

[John86]

http://arxiv.org/abs/1212.2332
Inferences about Interactions: Fermions and the Dirac Equation
Kevin H. Knuth
(Submitted on 11 Dec 2012)
At a fundamental level every measurement process relies on an interaction where one entity influences another. The boundary of an interaction is given by a pair of events, which can be ordered by virtue of the interaction. This results in a partially ordered set (poset) of events often referred to as a causal set. In this framework, an observer can be represented by a chain of events. Quantification of events and pairs of events, referred to as intervals, can be performed by projecting them onto an observer chain, or even a pair of observer chains, which in specific situations leads to a Minkowski metric replete with Lorentz transformations. We illustrate how this framework of interaction events gives rise to some of the well-known properties of the Fermions, such as Zitterbewegung. We then take this further by making inferences about events, which is performed by employing the process calculus, which coincides with the Feynman path integral formulation of quantum mechanics. We show that in the 1+1 dimensional case this results in the Feynman checkerboard model of the Dirac equation describing a Fermion at rest.