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Intuitive content of Loop Gravity-Rovelli's program

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marcus
#1873
Jan9-13, 12:05 AM
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http://arxiv.org/abs/1301.1535
The 1/N expansion of multi-orientable random tensor models
S. Dartois, V. Rivasseau, A. Tanasa
(Submitted on 8 Jan 2013)
Multi-orientable group field theory (GFT) has been introduced in A. Tanasa, J. Phys. A 45 (2012) 165401, arXiv:1109.0694, as a quantum field theoretical simplification of GFT, which retains a larger class of tensor graphs than the colored one. In this paper we define the associated multi-orientable identically independent distributed multi-orientable tensor model and we derive its 1/N expansion. In order to obtain this result, a partial classification of general tensor graphs is performed and the combinatorial notion of jacket is extended to the multi-orientable graphs. We prove that the leading sector is given, as in the case of colored models, by the so-called melon graphs.
18 pages, 17 figures
marcus
#1874
Jan9-13, 07:11 PM
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http://arxiv.org/abs/1301.1949
Hamiltonian dynamics of a quantum of space: hidden symmetries and spectrum of the volume operator, and discrete orthogonal polynomials
Vincenzo Aquilanti, Dimitri Marinelli, Annalisa Marzuoli
(Submitted on 9 Jan 2013)
The action of the quantum mechanical volume operator, introduced in connection with a symmetric representation of the three-body problem and recently recognized to play a fundamental role in discretized quantum gravity models, can be given as a second order difference equation which, by a complex phase change, we turn into a discrete Schrödinger-like equation. The introduction of discrete potential-like functions reveals the surprising crucial role here of hidden symmetries, first discovered by Regge for the quantum mechanical 6j symbols; insight is provided into the underlying geometric features. The spectrum and wavefunctions of the volume operator are discussed from the viewpoint of the Hamiltonian evolution of an elementary "quantum of space", and a transparent asymptotic picture emerges of the semiclassical and classical regimes. The definition of coordinates adapted to Regge symmetry is exploited for the construction of a novel set of discrete orthogonal polynomials, characterizing the oscillatory components of torsion-like modes.
13 pages, 5 figures

http://arxiv.org/abs/1301.1933
Shape Dynamics
Tim Koslowski
(Submitted on 9 Jan 2013)
Barbour's formulation of Mach's principle requires a theory of gravity to implement local relativity of clocks, local relativity of rods and spatial covariance. It turns out that relativity of clocks and rods are mutually exclusive. General Relativity implements local relativity of clocks and spatial covariance, but not local relativity of rods. It is the purpose of this contribution to show how Shape Dynamics, a theory that is locally equivalent to General Relativity, implements local relativity of rods and spatial covariance and how a BRST formulation, which I call Doubly General Relativity, implements all of Barbour's principles.
8 pages, based on a talk given at Relativity and Gravitation 100 years after Einstein in Prague, June 2012

http://arxiv.org/abs/1301.1692
Contracted Lorentz Invariance for Gravity with a Preferred Foliation
Steffen Gielen
(Submitted on 8 Jan 2013)
In canonical gravity, the choice of a local time direction is not obviously compatible with local Lorentz invariance. One way to address this issue is to view gravity as a gauge theory on observer space, rather than spacetime. In a Lorentz covariant theory observer space is the space of unit future-directed timelike vectors; picking such a vector locally breaks the symmetry to a subgroup SO(D) of SO(D,1), so that on observer space the local symmetry group is SO(D).
Observer space geometries naturally describe any gravitational theory that only assumes local invariance under SO(D). Here we construct non-relativistic observer spaces for gravity with a fixed foliation, applicable to preferred foliation theories such as Horava-Lifgarbagez gravity. Different Horava-Lifgarbagez observers at a point are related by a change in the shift vector, leaving the preferred foliation invariant. Gravity is formulated on a non-relativistic frame bundle with structure group ISO(D); the shift vector acts as a symmetry breaking field breaking ISO(D) symmetry spontaneously to SO(D). A natural torsion-free connection is constructed, including the usual SO(D,1) connection of relativistic gravity plus terms depending on derivatives of the shift vector. This observer space geometry provides a novel geometric framework for the study of preferred foliation theories.
15 pages

brief mention (possibly useful reference/review):
http://arxiv.org/abs/1301.1836
Tomita-Takesaki Modular Theory vs. Quantum Information Theory
Lin Zhang, Junde Wu
(Submitted on 9 Jan 2013)
marcus
#1875
Jan10-13, 07:15 PM
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http://arxiv.org/abs/1301.2214
Corrigendum: The Plebanski sectors of the EPRL vertex
Jonathan Engle
(Submitted on 10 Jan 2013)
We correct what amounts to a sign error in the proof of part (i.) of theorem 3 in Class.Quant.Grav.28 225003 (arXiv:1107.0709). The Plebanski sectors isolated by the linear simplicity constraints do not change --- they are still the three sectors (deg), (II+), and (II-). What changes is the characterization of the continuum Plebanski two-form corresponding to the first two terms in the asymptotics of the EPRL vertex amplitude for Regge-like boundary data. These two terms do not correspond to Plebanski sectors (II+) and (II-), but rather to the two possible signs of the product of the sign of the sector --- +1 for (II+) and -1 for (II-) --- and the sign of the orientation εIJKLBIJ ∧ BKL determined by BIJ. This is consistent with what one would expect, as this is exactly the sign which classically relates the BF action, in Plebanski sectors (II+) and (II-), to the Einstein-Hilbert action, whose discretization is the Regge action appearing in the asymptotics.
4 pages. Corrigendum to http://arxiv.org/abs/1107.0709
John86
#1876
Jan11-13, 04:24 AM
P: 247
http://arxiv.org/abs/1301.2245
Quantum-Reduced Loop Gravity: Cosmology
Emanuele Alesci, Francesco Cianfrani
(Submitted on 10 Jan 2013)
We introduce a new framework for loop quantum gravity: mimicking the spinfoam quantization procedure we propose to study the symmetric sectors of the theory imposing the reduction weakly on the full kinematical Hilbert space of the canonical theory. As a first application of Quantum-Reduced Loop Gravity we study the inhomogeneous Bianchi I model. 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 elucidate the relationship between Loop Quantum Cosmology and the full theory.
marcus
#1877
Jan13-13, 07:16 PM
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brief mention:
http://arxiv.org/abs/1301.2515
Quantum information and randomness
Johannes Kofler, Anton Zeilinger
(Submitted on 11 Jan 2013)
This is an article for a special edition of "European Review" with a focus on the topic "Causality".
Comments: 8 pages, 3 figures

http://arxiv.org/abs/1301.2586
On the Consistency of the Consistent Histories Approach to Quantum Mechanics
Elias Okon, Daniel Sudarsky
(Submitted on 11 Jan 2013)
The Consistent Histories (CH) formalism aims at a quantum mechanical framework for the universe as a whole. CH stresses the importance of histories for quantum mechanics, as opposed to measurements, and maintains that a satisfactory formulation of quantum mechanics allows one to assign probabilities to alternative histories of the universe. It further proposes that each realm, that is, each set of histories to which probabilities can be assigned, provides a valid quantum-mechanical account, but that different realms can be mutually incompatible. Finally, some of its proponents offer an "evolutionary" explanation of our existence in the universe and of our preference for quasiclassical descriptions of nature. The present work questions the validity of claims offered by CH proponents asserting that it solves many interpretational problems in quantum mechanics. In particular, we point out that the interpretation of the framework leaves vague two crucial points, namely, whether realms are fixed or chosen and the link between measurements and histories. Our claim is that by doing so, CH overlooks the main interpretational problems of quantum mechanics. Furthermore, we challenge the evolutionary explanation offered and we critically examine the proposed notion of a realm-dependent reality.
17 pages

http://arxiv.org/abs/1301.2563
Noncommutative spectral geometry and the deformed Hopf algebra structure of quantum field theory
Mairi Sakellariadou, Antonio Stabile, Giuseppe Vitiello
(Submitted on 11 Jan 2013)
We report the results obtained in the study of Alain Connes noncommutative spectral geometry construction focusing on its essential ingredient of the algebra doubling. We show that such a two-sheeted structure is related with the gauge structure of the theory, its dissipative character and carries in itself the seeds of quantization. From the algebraic point of view, the algebra doubling process has the same structure of the deformed Hops algebra structure which characterizes quantum field theory.
11 pages. Invited talk in the Sixth International Workshop DICE2012, Castello Pasquini/Castiglioncello (Tuscany), September 17-21, 2012
John86
#1878
Jan14-13, 06:53 AM
P: 247
http://arxiv.org/abs/1301.2334
Is there vacuum when there is mass? Vacuum and non-vacuum solutions for massive gravity
Prado Martin-Moruno (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 10 Jan 2013)
Massive gravity is a theory which has a tremendous amount of freedom to describe different cosmologies; but at the same time the various solutions one encounters must fulfill some rather nontrivial constraints. Most of the freedom comes not from the Lagrangian, which contains only a small number of free parameters (typically 3 depending on counting conventions), but on the fact that one is in principle free to choose the background reference metric almost arbitrarily --- which effectively introduces a non-denumerable infinity of free parameters. In the current paper we stress that although changing the reference metric would lead to a different cosmological model, this does not mean that the dynamics of our own universe can be entirely divorced from its matter content. That is, while the choice of reference metric certainly influences the evolution of the physically observable foreground metric, the effect of matter cannot be neglected. Nevertheless, the relation between matter and geometry can be significantly changed in some specific models; effectively since the graviton would be able to curve the spacetime by itself, without the need of matter. Thus, even the set of vacuum solutions for massive gravity can have significant structure. On the other hand, in some cases the effect of the reference metric could be so strong that no conceivable material content would be able to drastically affect the cosmological evolution.
marcus
#1879
Jan15-13, 07:47 PM
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http://arxiv.org/abs/1301.3171
Black hole entropy and the renormalization group
Alejandro Satz, Ted Jacobson
(Submitted on 14 Jan 2013)
Four decades after its first postulation by Bekenstein, black hole entropy remains mysterious. It has long been suggested that the entanglement entropy of quantum fields on the black hole gravitational background should represent at least an important contribution to the total Bekenstein-Hawking entropy, and that the divergences in the entanglement entropy should be absorbed in the renormalization of the gravitational couplings. In this talk, we describe how an improved understanding of black hole entropy is obtained by combining these notions with the renormalization group. By introducing an RG flow scale, we investigate whether the total entropy of the black hole can be partitioned in a "gravitational" part related to the flowing gravitational action, and a "quantum" part related to the unintegrated degrees of freedom. We describe the realization of this idea for free fields, and the complications and qualifications arising for interacting fields.
3 pages. Conference proceedings article from talk given by A. Satz at the Thirteenth Marcel Grossmann Meeting, Stockholm, 2012
marcus
#1880
Jan15-13, 07:53 PM
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http://arxiv.org/abs/1301.3480
Gauge networks in noncommutative geometry
Matilde Marcolli, Walter D. van Suijlekom
(Submitted on 15 Jan 2013)
We introduce gauge networks as generalizations of spin networks and lattice gauge fields to almost-commutative manifolds. The configuration space of quiver representations (modulo equivalence) in the category of finite spectral triples is studied; gauge networks appear as an orthonormal basis in a corresponding Hilbert space. We give many examples of gauge networks, also beyond the well-known spin network examples. We find a Hamiltonian operator on this Hilbert space, inducing a time evolution on the C*-algebra of gauge network correspondences.
Given a representation in the category of spectral triples of a quiver embedded in a spin manifold, we define a discretized Dirac operator on the quiver. We compute the spectral action of this Dirac operator on a four-dimensional lattice, and find that it reduces to the Wilson action for lattice gauge theories and a Higgs field lattice system. As such, in the continuum limit it reduces to the Yang-Mills-Higgs system. For the three-dimensional case, we relate the spectral action functional to the Kogut-Susskind Hamiltonian.
30 pages

http://arxiv.org/abs/1301.3113
New coherent states and modified heat equations
Antonio Pittelli, Lorenzo Sindoni
(Submitted on 14 Jan 2013)
We clarify the relations between certain new coherent states for loop quantum gravity and the analytically continued heat kernel coherent states, highlighting the underlying general construction, the presence of a modified heat equation as well as the way in which the properties of the heat kernels are automatically inherited by these new states.
7 pages
marcus
#1882
Jan16-13, 11:23 AM
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If you wish, you could start a discussion thread, or two, about some of these.

==============================

EDIT to reply to the next post in sequence, post #1883: Thanks for the reminders or suggestions, Tom!

Since I can still edit, I will add the new paper of Torsten that just appeared today:

http://arxiv.org/abs/1301.3628
On the origin of inflation by using exotic smoothness
T. Asselmeyer-Maluga, J. Krol
(Submitted on 16 Jan 2013)
In this paper we discuss a spacetime having the topology of S3x R but with a different smoothness structure leading to a geometric model for inflation, called geometric inflation. In particular this spacetime is not globally hyperbolic and we obtain a time line with a spatial topology change from the 3-sphere to a homology 3-sphere and back. The topology of the spacetime remains invariant. Among the infinite possible smoothness structures of this spacetime, we choose a homology 3-sphere constructed from the knot 810 with hyperbolic geometry, i.e. admitting a homogenous metric of negative scalar curvature. We discuss the accelerated expansion for FLRW cosmology caused by the topology change. In contrast to other inflation models, this process stops after a finite time. Alternatively, the topology change can be also described by a SU(2)-valued scalar field. Then we calculate the expansion rate (having more than 60 e-folds) and the energy time scale. The coupling to matter is also interpreted geometrically and the reheating process (as well the supercooled expansion during inflation) is naturally obtained. The model depends only on a single parameter, a topological invariant of the homology 3-sphere, and assumes a Planck size universe of S3-topology. The dependence of the model on the initial state and the a geometric interpretation of quantum fluctuations are also discussed.
28 pages, 9 figures
tom.stoer
#1883
Jan16-13, 05:44 PM
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Quote Quote by marcus View Post
If you wish, you could start a discussion thread, or two, about some of these.
no discussion, simply a hint in you thread;-)
marcus
#1884
Jan17-13, 08:09 PM
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http://arxiv.org/abs/1301.4191
A bootstrap towards asymptotic safety
K. Falls, D. F. Litim, K. Nikolakopoulos, C. Rahmede
(Submitted on 17 Jan 2013)
A search strategy for asymptotic safety is put forward and tested for a simplified version of gravity in four dimensions using the renormalization group. Taking the action to be a high-order polynomial of the Ricci scalar, a self-consistent ultraviolet fixed point is found where curvature invariants become increasingly irrelevant with increasing mass dimension. Intriguingly, universal scaling exponents take near-Gaussian values despite the presence of residual interactions. Asymptotic safety of metric gravity would seem in reach if this pattern carries over to the full theory.
4 pages, 1 figure
MTd2
#1885
Jan18-13, 06:15 AM
PF Gold
P: 1,961
http://arxiv.org/abs/1301.4148

Renormalization Group approach to Gravity: the running of G and L inside galaxies and additional details on the elliptical NGC 4494

Davi C. Rodrigues, Oliver F. Piattella, Júlio C. Fabris, Ilya L. Shapiro
(Submitted on 17 Jan 2013)
We explore the phenomenology of nontrivial quantum effects on low-energy gravity. These effects come from the running of the gravitational coupling parameter L and the cosmological constant L in the Einstein-Hilbert action, as induced by the Renormalization Group (RG). The Renormalization Group corrected General Relativity (RGGR model) is used to parametrize these quantum effects, and it is assumed that the dominant dark matter-like effects inside galaxies is due to these nontrivial RG effects. Here we present additional details on the RGGR model application, in particular on the Poisson equation extension that defines the effective potential, also we re-analyse the ordinary elliptical galaxy NGC 4494 using a slightly different model for its baryonic contribution, and explicit solutions are presented for the running of G and L. The values of the NGC 4494 parameters as shown here have a better agreement with the general RGGR picture for galaxies, and suggest a larger radial anisotropy than the previously published result.
marcus
#1886
Jan20-13, 08:15 PM
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http://arxiv.org/abs/1301.4422
On the number of relevant operators in asymptotically safe gravity
Dario Benedetti
(Submitted on 18 Jan 2013)
In this short note we answer a long standing question about the asymptotic safety scenario for quantum gravity. The term asymptotic safety refers to the conjecture that (i) the quantum field theory of gravity admits a non-trivial ultraviolet fixed point, and that (ii) this has only a finite number of relevant perturbations, i.e. a finite number of UV-stable directions (or in other words, a finite number of free parameters to be fixed experimentally). Within the f(R) approximation of the functional renormalization group equation of gravity, we show that assuming the first half of the conjecture to be true, the remaining half follows from general arguments, that is, we show that assuming the existence of a non-trivial fixed point, the fact that the number of relevant directions is finite is a general consequence of the structure of the equations.
5 pages

http://arxiv.org/abs/1301.4322
Can quantum gravity be exposed in the laboratory?: A tabletop experiment to reveal the quantum foam
Jacob D. Bekenstein
(Submitted on 18 Jan 2013)
I propose an experiment that may be performed, with present low temperature and cryogenic technology, to reveal Wheeler's quantum foam. It involves coupling an optical photon's momentum to the center of mass motion of a macroscopic transparent block with parameters such that the latter is displaced in space by approximately a Planck length. I argue that such displacement is sensitive to quantum foam and will react back on the photon's probability of transiting the block. This might allow determination of the precise scale at which quantum fluctuations of space-time become large, and so differentiate between the brane-world and the traditional scenarios of spacetime.
10 pages, one figure: Keynote lecture at the international workshop "Horizon of quantum physics: from foundations to quantum enabled technologies", Taipei, October 16, 2012. To appear in the proceedings in Foundations of Physics
marcus
#1887
Jan21-13, 07:53 PM
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http://arxiv.org/abs/1301.4687
Noncommutative Spectral Geometry: A Short Review
Mairi Sakellariadou
(Submitted on 20 Jan 2013)
We review the noncommutative spectral geometry, a gravitational model that combines noncommutative geometry with the spectral action principle, in an attempt to unify General Relativity and the Standard Model of electroweak and strong interactions. Despite the phenomenological successes of the model, the discrepancy between the predicted Higgs mass and the current experimental data indicate that one may have to go beyond the simple model considered at first. We review the current status of the phenomenological consequences and their implications. Since this model lives by construction at high energy scales, namely at the Grand Unified Theories scale, it provides a natural framework to investigate early universe cosmology. We briefly review some of its cosmological consequences.
11 pages. Invited talk in the Sixth International Workshop DICE2012, Castello Pasquini/Castiglioncello (Tuscany), September 17-21, 2012

http://arxiv.org/abs/1301.4920
Massless scalar field in de Sitter spacetime: unitary quantum time evolution
Jeronimo Cortez, Daniel Martin-de Blas, Guillermo A. Mena Marugan, Jose M. Velhinho
(Submitted on 21 Jan 2013)
We prove that, under the standard conformal scaling, a massless field in de Sitter spacetime admits an O(4)-invariant Fock quantization such that time evolution is unitarily implemented. This result disproves previous claims in the literature. We discuss the relationship between this quantization with unitary dynamics and the family of O(4)-invariant Hadamard states given by Allen and Folacci, as well as with the Bunch-Davies vacuum.
Comments: 23 pages

http://arxiv.org/abs/1301.4553
Quantum Hairs and Isolated Horizon Entropy from Chern-Simons Theory
Abhishek Majhi, Parthasarathi Majumdar
(Submitted on 19 Jan 2013)
We articulate the fact that the loop quantum gravity description of the quantum states of black hole horizons, modeled as Quantum Isolated Horizons (QIHs), is completely characterized in terms of two independent integer-valued quantum 'hairs', viz,. the coupling constant of the quantum SU(2) Chern Simons theory describing QIH dynamics, and the number of punctures produced by the bulk spin network edges piercing the isolated horizon (which act as pointlike sources for the Chern Simons fields). We demonstrate that the microcanonical entropy of macroscopic (both parameters assuming very large values) QIHs can be obtained directly from the microstates of this Chern-Simons theory, using standard statistical mechanical methods, without having to additionally postulate the horizon as an ideal gas of punctures, or incorporate any additional classical or semi-classical input from general relativity vis-a-vis the functional dependence of the IH mass on its area, or indeed, without having to restrict to any special class of spins. Requiring the validity of the Bekenstein-Hawking area law relates these two parameters (as an equilibrium `equation of state') and consequently imposes restrictions on the allowed values of the Barbero-Immirzi parameter. The logarithmic correction to the area law obtained a decade ago by R. Kaul and one of us (P.M.), ensues straightforwardly, with precisely the coefficient -3/2, making it a signature of the loop quantum gravity approach to black hole entropy.
marcus
#1888
Jan22-13, 12:30 PM
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http://arxiv.org/abs/1301.5135
Einstein-Cartan gravity, Asymptotic Safety, and the running Immirzi parameter
Jan-Eric Daum, Martin Reuter
(Submitted on 22 Jan 2013)
In this paper we analyze the functional renormalization group flow of quantum gravity on the Einstein-Cartan theory space. The latter consists of all action functionals depending on the spin connection and the vielbein field (co-frame) which are invariant under both spacetime diffeomorphisms and local frame rotations. In the first part of the paper we develop a general methodology and corresponding calculational tools which can be used to analyze the flow equation for the pertinent effective average action for any truncation of this theory space. In the second part we apply it to a specific three-dimensional truncated theory space which is parametrized by Newton's constant, the cosmological constant, and the Immirzi parameter. A comprehensive analysis of their scale dependences is performed, and the possibility of defining an asymptotically safe theory on this hitherto unexplored theory space is investigated. In principle Asymptotic Safety of metric gravity (at least at the level of the effective average action) is neither necessary nor sufficient for Asymptotic Safety on the Einstein-Cartan theory space which might accommodate different "universality classes" of microscopic quantum gravity theories. Nevertheless, we do find evidence for the existence of at least one non-Gaussian renormalization group fixed point which seems suitable for the Asymptotic Safety construction in a setting where the spin connection and the vielbein are the fundamental field variables.
121 pages, 8 figures

http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=140
Proceedings of the 3rd Quantum Gravity and Quantum Geometry School, held at Zakopane in 2011, are now online. Included are lecture series providing students with an introduction to several related QG areas, and single lectures on specialized topics. Incidentally the main person responsible for editing the proceedings was Frank Hellmann, a PF member since February 2006. http://physicsforums.com/showthread....74#post4162474 The paper with Eugenio Bianchi mentioned in this post is http://arxiv.org/abs/1207.4596

http://arxiv.org/abs/1301.5110
On the Concept of Law in Physics
Claus Kiefer
(Submitted on 22 Jan 2013)
I discuss the main features of the concept of law in physics. Fundamental laws from Newtonian mechanics to general relativity are reviewed. I end with an outlook on the new form of laws in the emerging theory of quantum gravity.
10 pages, to appear in the Proceedings of the conference "The concept of law in science", Heidelberg, 4-5 June 2012

http://arxiv.org/abs/1301.5130
No Conformal Anomaly in Unimodular Gravity
Enrique Álvarez, Mario Herrero-Valea
(Submitted on 22 Jan 2013)
The conformal invariance of unimodular gravity survives quantum corrections, even in the presence of conformal matter. Unimodular gravity can actually be understood as a certain truncation of the full Einstein-Hilbert theory, where in the Einstein frame the metric tensor enjoys unit determinant. Our result is compatible with the idea that the corresponding restriction in the functional integral is consistent as well.
20 pages

recent cosmology parameters:
http://arxiv.org/abs/1212.5226
Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results
G. Hinshaw, D. Larson, E. Komatsu, D. N. Spergel, C. L. Bennett, J. Dunkley, M. R. Nolta, M. Halpern, R. S. Hill, N. Odegard, L. Page, K. M. Smith, J. L. Weiland, B. Gold, N. Jarosik, A. Kogut, M. Limon, S. S. Meyer, G. S. Tucker, E. Wollack, E. L. Wright
(see table 9, page 19---from WMAP+eCMB+BAO+H0)
Ωk = −0.0027+0.0039−0.0038
Ωtot = 1.0027+0.0038−0.0039

http://arxiv.org/abs/1210.7231
A Measurement of the Cosmic Microwave Background Damping Tail from the 2500-square-degree SPT-SZ survey
K. T. Story et al.
(see equation 21, page 14)
'' The tightest constraint on the mean curvature that we consider comes from combining the CMB, H0 , and BAO datasets:
Ωk = −0.0059±0.0040. "
marcus
#1889
Jan23-13, 07:17 PM
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http://arxiv.org/abs/1301.5362
Polymer Bose--Einstein Condensates
E. Castellanos, G. Chacon-Acosta
(Submitted on 22 Jan 2013)
In this work we analyze a non--interacting one dimensional polymer Bose--Einstein condensate in an harmonic trap within the semiclassical approximation. We use an effective Hamiltonian coming from the polymer quantization that arises in loop quantum gravity. We calculate the number of particles in order to obtain the critical temperature. The Bose--Einstein functions are replaced by series, whose high order terms are related to powers of the polymer length. It is shown that the condensation temperature presents a shift respect to the standard case, for small values of the polymer scale. In typical experimental conditions, it is possible to establish a bound for λ2 up to ≤ 10-16 m2. To improve this bound we should decrease the frequency of the trap and also decrease the number of particles.
6 pages.

http://arxiv.org/abs/1301.5481
Quantum Gravity: the view from particle physics
Hermann Nicolai
(Submitted on 23 Jan 2013)
This lecture reviews aspects of and prospects for progress towards a theory of quantum gravity from a particle physics perspective, also paying attention to recent findings of the LHC experiments at CERN.
20 pages. Invited Lecture at the conference "Relativity and Gravitation: 100 Years after Einstein in Prague", June 25 - 29, 2012, Prague, Czech Republic

http://arxiv.org/abs/1301.5495
The asymptotic safety scenario and scalar field inflation
Christoph Rahmede
(Submitted on 23 Jan 2013)
We study quantum gravity corrections to early universe cosmology as resulting within the asymptotic safety scenario. We analyse if it is possible to obtain accelerated expansion in the regime of the renormalisation group fixed point in a theory with Einstein-Hilbert gravity and a scalar field. We show how this phase impacts cosmological perturbations observed in the cosmic microwave background.
3 pages. Contribution to the proceedings of the Thirteenth Marcel Grossmann Meeting, Stockholm, 2012

http://arxiv.org/abs/1301.5496
Duality-invariant bimetric formulation of linearized gravity
Claudio Bunster, Marc Henneaux, Sergio Hörtner
(Submitted on 23 Jan 2013)
A formulation of linearized gravity which is manifestly invariant under electric-magnetic duality rotations in the internal space of the metric and its dual, and which contains both metrics as basic variables (rather than the corresponding prepotentials), is derived. In this bimetric formulation, the variables have a more immediate geometrical significance, but the action is non-local in space, contrary to what occurs in the prepotential formulation. More specifically, one finds that: (i) the kinetic term is non-local in space (but local in time); (ii) the Hamiltonian is local in space and in time; (iii) the variables are subject to two Hamiltonian constraints, one for each metric.
7 pages. Based in part on the talk "Gravitational electric-magnetic duality" given by one of us (MH) at the 8-th Workshop "Quantum Field Theory and Hamiltonian Systems" (QFTHS), 19-22 September 2012, Craiova, Romania

http://arxiv.org/abs/1301.5471
New theories of gravity
Christian G. Boehmer, Nicola Tamanini
(Submitted on 23 Jan 2013)
We propose a new point of view for interpreting Newton's and Einstein's theories of gravity. By taking inspiration from Continuum Mechanics and its treatment of anisotropies, we formulate new theories of gravity. These models are simple and natural generalisations with many interesting properties. Above all, their precise form can, in principle, be determined experimentally.
8 pages
marcus
#1890
Jan24-13, 07:17 PM
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http://arxiv.org/abs/1301.5859
Hamiltonian spinfoam gravity
Wolfgang M. Wieland
(Submitted on 24 Jan 2013)
This paper presents a Hamiltonian formulation of spinfoam-gravity, which leads to a straight-forward canonical quantisation. To begin with, we derive a continuum action adapted to the simplicial decomposition. The equations of motion admit a Hamiltonian formulation, allowing us to perform the constraint analysis. We do not find any secondary constraints, but only get restrictions on the Lagrange multipliers enforcing the reality conditions. This comes as a surprise. In the continuum theory, the reality conditions are preserved in time, only if the torsionless condition (a secondary constraint) holds true. Studying an additional conservation law for each spinfoam vertex, we discuss the issue of torsion and argue that spinfoam gravity may indeed miss an additional constraint. Next, we canonically quantise. Transition amplitudes match the EPRL (Engle--Pereira--Rovelli--Livine) model, the only difference being the additional torsional constraint affecting the vertex amplitude.
28 pages, 2 figures

http://arxiv.org/abs/1301.5704
The coevent formulation of quantum theory
Petros Wallden
(Submitted on 24 Jan 2013)
Understanding quantum theory has been a subject of debate from its birth. Many different formulations and interpretations have been proposed. Here we examine a recent novel formulation, namely the coevents formulation. It is a histories formulation and has as starting point the Feynman path integral and the decoherence functional. The new ontology turns out to be that of a coarse-grained history. We start with a quantum measure defined on the space of histories, and the existence of zero covers rules out single-history as potential reality (the Kochen Specker theorem casted in histories form is a special case of a zero cover). We see that allowing coarse-grained histories as potential realities avoids the previous paradoxes, maintains deductive non-contextual logic (alas non-Boolean) and gives rise to a unique classical domain. Moreover, we can recover the probabilistic predictions of quantum theory with the use of the Cournot's principle. This formulation, being both a realist formulation and based on histories, is well suited conceptually for the purposes of quantum gravity and cosmology.
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