Loop-and-allied QG bibliography

[John86]

http://arxiv.org/abs/1011.0061
The Conformal Constraint in Canonical Quantum Gravity
Authors: Gerard 't Hooft
(Submitted on 30 Oct 2010)
Abstract: Perturbative canonical quantum gravity is considered, when coupled to a renormalizable model for matter fields. It is proposed that the functional integral over the dilaton field should be disentangled from the other integrations over the metric fields. This should generate a conformally invariant theory as an intermediate result, where the conformal anomalies must be constrained to cancel out. When the residual metric is treated as a background, and if this background is taken to be flat, this leads to a novel constraint: in combination with the dilaton contributions, the matter lagrangian should have a vanishing beta function. The zeros of this beta function are isolated points in the landscape of quantum field theories, and so we arrive at a denumerable, or perhaps even finite, set of quantum theories for matter, where not only the coupling constants, but also the masses and the cosmological constant are all fixed, and computable, in terms of the Planck units.

 

[atyy]

http://arxiv.org/abs/1008.1062
Global aspects of the space of 6D N = 1 supergravities
Vijay Kumar, David R. Morrison, Washington Taylor
"If these models cannot be realized through some novel string construction, it will indicate that string theory imposes strong constraints on 6D N = 1 supergravity theories beyond the known stringent anomaly cancellation and gauge kinetic term sign constraints. If these additional constraints can be understood in terms of new quantum consistency conditions on the set of low-energy eective theories, it will provide a new window on general theories of quantum gravity; if not, it will indicate the existence of stringy constraints which may distinguish string theory from other possible UV-complete quantum gravity theories."

http://arxiv.org/abs/1011.0726
6D supergravity without tensor multiplets
Vijay Kumar, Daniel Park, Washington Taylor
We systematically investigate the finite set of possible gauge groups and matter content for N = 1 supergravity theories in six dimensions with no tensor multiplets, focusing on nonabelian gauge groups which are a product of SU(N) factors. We identify a number of models which obey all known low-energy consistency conditions, but which have no known string theory realization. Many of these models contain novel matter representations, suggesting possible new string theory constructions. Many of the most exotic matter structures arise in models which precisely saturate the gravitational anomaly bound on the number of hypermultiplets. Such models have a rigid symmetry structure, in the sense that there are no moduli which leave the full gauge group unbroken.

 

[John86]

http://arxiv.org/abs/1011.0746
Entropic Time
Authors: Ariel Caticha
(Submitted on 2 Nov 2010)
Abstract: The formulation of quantum mechanics within the framework of entropic dynamics includes several new elements. In this paper we concentrate on one of them: the implications for the theory of time. Entropic time is introduced as a book-keeping device to keep track of the accumulation of changes. One new feature is that, unlike other concepts of time appearing in the so-called fundamental laws of physics, entropic time incorporates a natural distinction between past and future.

 

[MTd2]

Pointed out by Peter Woit:

http://media.physics.harvard.edu/video/index.php?id=COLLOQ_VERLINDE_102510.flv&width=640&height=360

Emergency of Gravity Colloquium at harvard

Erik Verlinde 25 Oct 2010

 

[MTd2]

http://arxiv.org/abs/1011.1024

Path Integrals and the WKB approximation in Loop Quantum Cosmology

Abhay Ashtekar, Miguel Campiglia, Adam Henderson
(Submitted on 3 Nov 2010)
We follow the Feynman procedure to obtain a path integral formulation of loop quantum cosmology starting from the Hilbert space framework. Quantum geometry effects modify the weight associated with each path so that the effective measure on the space of paths is different from that used in the Wheeler-DeWitt theory. These differences introduce some conceptual subtleties in arriving at the WKB approximation. But the approximation is well defined and provides intuition for the differences between loop quantum cosmology and the Wheeler-DeWitt theory from a path integral perspective.

 

[MTd2]

http://arxiv.org/abs/1011.1456

Asymptotic safety: a simple example

Jens Braun, Holger Gies, Daniel D. Scherer
(Submitted on 5 Nov 2010)
We use the Gross-Neveu model in 2<d<4 as a simple fermionic example for Weinberg's asymptotic safety scenario: despite being perturbatively nonrenormalizable, the model defines an interacting quantum field theory being valid to arbitrarily high momentum scales owing to the existence of a non-Gaussian fixed point. Using the functional renormalization group, we study the UV behavior of the model in both the purely fermionic as well as a partially bosonized language. We show that asymptotic safety is realized at non-Gaussian fixed points in both formulations, the universal critical exponents of which we determine quantitatively. The partially bosonized formulation allows to make contact to the large-Nf expansion where the model is known to be renormalizable to all-orders. In this limit, the fixed-point action as well as all universal critical exponents can be computed analytically. As asymptotic safety has become an important scenario for quantizing gravity, our description of a well-understood model is meant to provide for an easily accessible and controllable example of modern nonperturbative quantum field theory.

 

[marcus]

http://arxiv.org/abs/1011.1811
Observing the Big Bounce with Tensor Modes in the Cosmic Microwave Background: Phenomenology and Fundamental LQC Parameters
Julien Grain, A. Barrau, T. Cailleteau, J. Mielczarek
12 pages, 5 figures
(Submitted on 8 Nov 2010)
"Cosmological models where the standard Big Bang is replaced by a bounce have been studied for decades. The situation has however dramatically changed in the last years for two reasons. First, because new ways to probe the early Universe have emerged, in particular thanks to the Cosmic Microwave Background (CMB). Second, because some well grounded theories -- especially Loop Quantum Cosmology -- unambiguously predict a bounce, at least for homogeneous models. In this article, we investigate into the details the phenomenological parameters that could be constrained or measured by next-generation B-mode CMB experiments. We point out that an important observational window could be opened. We then show that those constraints can be converted into very meaningful limits on the fundamental Loop Quantum Cosmology (LQC) parameters. This establishes the early universe as an invaluable quantum gravity laboratory."

brief mention:
http://arxiv.org/abs/1011.1630
Ultraviolet Divergences in Cosmological Correlations
Steven Weinberg
26 pages, 1 figure
(Submitted on 7 Nov 2010)
"A method is developed for dealing with ultraviolet divergences in calculations of cosmological correlations, which does not depend on dimensional regularization. An extended version of the WKB approximation is used to analyze the divergences in these calculations, and these divergences are controlled by the introduction of Pauli--Villars regulator fields... Explicit formulas are given for the counterterms needed to cancel all dependence on the regulator properties, and an explicit prescription is given for calculating finite regulator-independent correlation functions..."

 

[John86]

http://arxiv.org/abs/1011.1657
Physics from information
Authors: Jae-Weon Lee
(Submitted on 7 Nov 2010)
Abstract: This is an ongoing review on my conjecture that information processing at causal horizons is the key ingredient of all physics.
Assuming that information is fundamental and the information propagates with finite velocity, one can find that main physical laws such as Newton's second law and Einstein equation simply describe the energy-information relation (dE=TdS) for matter or space time crossing a causal horizon with temperature T for observers. Quantum mechanics arises from ignorance of the observers about matter crossing the horizon, which explains why superluminal communication is impossible even with quantum entanglement. This approach also explains the origin of Jacobson's thermodynamic formalism of Einstein gravity and Verlinde's entropic gravity. When applied to a cosmic causal horizon, the conjecture reproduces the observed dark energy and demands the zero cosmological constant.

http://arxiv.org/abs/1011.1604
Noncommutative (generalized) sine-Gordon/massive Thirring correspondence, integrability and solitons
Authors: H. Blas, H. L. Carrion
(Submitted on 7 Nov 2010)
Abstract: Some properties of the correspondence between the non-commutative versions of the (generalized) sine-Gordon (NCGSG$_{1,2}$) and the massive Thirring (NCGMT$_{1,2}$) models are studied. Our method relies on the master Lagrangian approach to deal with dual theories. The master Lagrangians turn out to be the NC versions of the so-called affine Toda model coupled to matter fields (NCATM$_{1,2}$), in which the Toda field $g$ belongs to certain subgroups of $ GL(3)$, and the matter fields lie in the higher grading directions of an affine Lie algebra. Depending on the form of $g$ one arrives at two different NC versions of the NCGSG$_{1,2}$/NCGMT$_{1,2}$ correspondence. In the NCGSG$_{1,2}$ sectors, through consistent reduction procedures, we find NC versions of some well-known models, such as the NC sine-Gordon (NCSG$_{1,2}$) (Lechtenfeld et al. and Grisaru-Penati proposals, respectively), NC (bosonized) Bukhvostov-Lipatov (NCbBL$_{1,2}$) and NC double sine-Gordon (NCDSG$_{1,2}$) models. The NCGMT$_{1,2}$ models correspond to Moyal product extension of the generalized massive Thirring model. The NCGMT$_{1,2}$ models posses constrained versions with relevant Lax pair formulations, and other sub-models such as the NC massive Thirring (NCMT$_{1,2}$), the NC Bukhvostov-Lipatov (NCBL$_{1,2}$) and constrained versions of the last models with Lax pair formulations. We have established that, except for the well known NCMT$_{1,2}$ zero-curvature formulations, generalizations ($n_{F} \ge 2$, $n_F=$number of flavors) of the massive Thirring model allow zero-curvature formulations only for constrained versions of the models and for each one of the various constrained sub-models defined for less than $n_F$ flavors, in the both NCGMT$_{1,2}$ and ordinary space-time descriptions (GMT), respectively. The non-commutative solitons and kinks of the $ GL(3)$ NCGSG$_{1,2}$ models are investigated.

http://arxiv.org/abs/1011.1811
Observing the Big Bounce with Tensor Modes in the Cosmic Microwave Background: Phenomenology and Fundamental LQC Parameters
Authors: Julien Grain, A. Barrau, T. Cailleteau, J. Mielczarek
(Submitted on 8 Nov 2010)
Abstract: Cosmological models where the standard Big Bang is replaced by a bounce have been studied for decades. The situation has however dramatically changed in the last years for two reasons. First, because new ways to probe the early Universe have emerged, in particular thanks to the Cosmic Microwave Background (CMB). Second, because some well grounded theories -- especially Loop Quantum Cosmology -- unambiguously predict a bounce, at least for homogeneous models. In this article, we investigate into the details the phenomenological parameters that could be constrained or measured by next-generation B-mode CMB experiments. We point out that an important observational window could be opened. We then show that those constraints can be converted into very meaningful limits on the fundamental Loop Quantum Cosmology (LQC) parameters. This establishes the early universe as an invaluable quantum gravity laboratory.

 

[atyy]

http://arxiv.org/abs/1011.2149
Generalized Spinfoams
You Ding, Muxin Han, Carlo Rovelli
(Submitted on 9 Nov 2010)
We reconsider the spinfoam dynamics that has been recently introduced, in the generalized Kaminski-Kisielowski-Lewandowski (KKL) version where the foam is not dual to a triangulation. We study the Euclidean as well as the Lorentzian case. We show that this theory can still be obtained as a constrained BF theory satisfying the simplicity constraint, now discretized on a general oriented 2-cell complex. This constraint implies that boundary states admit a (quantum) geometrical interpretation in terms of polyhedra, generalizing the tetrahedral geometry of the simplicial case. We also point out that the general solution to this constraint (imposed weakly) depends on a quantum number r_f in addition to those of loop quantum gravity. We compute the vertex amplitude and recover the KKL amplitude in the Euclidean theory when r_f=0. We comment on the eventual physical relevance of r_f, and the formal way to eliminate it.

 

[MTd2]

http://arxiv.org/abs/1011.2041

Inducing Barbero-Immirzi Connections along SU(2)-reductions of Bundles on Spacetime

L. Fatibene, M. Ferraris, M. Francaviglia
(Submitted on 9 Nov 2010)
We shall present here a general apt technique to induce connections along bundle reductions which is different from the standard restriction. The technique is a generalization of the mechanism presented in [1] to define at spacetime level the Barbero-Immirzi (BI) connection used in LQG. The general prescription to define such a reduced connection is interesting from a mathematical viewpoint and it allows a general and direct control on transformation laws of the induced object. Moreover, unlike what happens by using standard restriction, we shall show that once a bundle reduction is given, then any connection induces a reduced connection with no constraint on the original holonomy as it happens when connections are simply restricted.

 

[marcus]

http://arxiv.org/abs/1011.2463
The Hamiltonian constraint in Polymer Parametrized Field Theory
Alok Laddha, Madhavan Varadarajan
53 pages
(Submitted on 10 Nov 2010)
"Recently, a generally covariant reformulation of 2 dimensional flat spacetime free scalar field theory known as Parameterised Field Theory was quantized using Loop Quantum Gravity (LQG) type 'polymer' representations. Physical states were constructed, without intermediate regularization structures, by averaging over the group of gauge transformations generated by the constraints, the constraint algebra being a Lie algebra. We consider classically equivalent combinations of these constraints corresponding to a diffeomorphism and a Hamiltonian constraint, which, as in gravity, define a Dirac algebra. Our treatment of the quantum constraints parallels that of LQG and obtains the following results, expected to be of use in the construction of the quantum dynamics of LQG:
(i) the (triangulated) Hamiltonian constraint acts only on vertices, its construction involves some of the same ambiguities as in LQG and its action on diffeomorphism invariant states admits a continuum limit
(ii) if the regulating holonomies are in representations tailored to the edge labels of the state, all previously obtained physical states lie in the kernel of the Hamiltonian constraint,
(iii) the commutator of two (density weight 1) Hamiltonian constraints as well as the operator correspondent of their classical Poisson bracket converge to zero in the continuum limit defined by diffeomorphism invariant states, and vanish on the Lewandowski- Marolf (LM) habitat
(iv) the rescaled density 2 Hamiltonian constraints and their commutator are ill defined on the LM habitat despite the well defined-ness of the operator correspondent of their classical Poisson bracket there
(v) there is a new habitat which supports a non-trivial representation of the Poisson-Lie algebra of density 2 constraints."

http://arxiv.org/abs/1011.2726
The 1/N expansion of colored tensor models
Razvan Gurau
(Submitted on 11 Nov 2010)
"In this paper we perform the 1/N expansion of the colored three dimensional Boulatov tensor model. As in matrix models, we obtain a systematic topological expansion, with more and more complicated topologies suppressed by higher and higher powers of N. We compute the first orders of the expansion and prove that only graphs corresponding to three spheres S³ contribute to the leading order in the large N limit."

Gurau's work is relevant to GFT, and cites a lot of LQG papers

brief mention:
http://arxiv.org/abs/1011.2545
Solitonic Models Based on Quantum Groups and the Standard Model
Robert J. Finkelstein
59 pages, review of the author's way of representing particles as knots.

 

[marcus]

http://arxiv.org/abs/1011.2779
Inflationary observables in loop quantum cosmology
Martin Bojowald, Gianluca Calcagni
40 pages
(Submitted on 11 Nov 2010)
"The full set of cosmological observables coming from linear scalar and tensor perturbations of loop quantum cosmology is computed in the presence of inverse-volume corrections. Background inflationary solutions are found at linear order in the quantum corrections; depending on the values of quantization parameters, they obey an exact or perturbed power-law expansion in conformal time. The comoving curvature perturbation is shown to be conserved at large scales, just as in the classical case. Its associated Mukhanov equation is obtained and solved. Combined with the results for tensor modes, this yields the scalar and tensor indices, their running, and the tensor-to-scalar ratio, which are all first order in the quantum correction. The latter could be sizable in phenomenological scenarios. Contrary to a pure minisuperspace parametrization, the lattice refinement parametrization is in agreement with both anomaly cancellation and our results on background solutions and linear perturbations. The issue of the choice of parametrization is also discussed in relation with a possible superluminal propagation of perturbative modes, and conclusions for quantum spacetime structure are drawn."

http://arxiv.org/abs/1011.2961
Static isolated horizons: SU(2) invariant phase space, quantization, and black hole entropy
Alejandro Perez, Daniele Pranzetti
22 pages, 1 figure
(Submitted on 12 Nov 2010)
"We study the classical field theoretical formulation of static generic isolated horizons in a manifestly SU(2) invariant formulation. We show that the usual classical description requires revision in the non-static case due to the breaking of diffeomorphism invariance at the horizon leading to the non conservation of the usual pre-symplectic structure. We argue how this difficulty could be avoided by a simple enlargement of the field content at the horizon that restores diffeomorphism invariance. Restricting our attention to static isolated horizons we study the effective theories describing the boundary degrees of freedom. A quantization of the horizon degrees of freedom is proposed. By defining a statistical mechanical ensemble where only the area A of the horizon is fixed macroscopically-states with fluctuations away from spherical symmetry are allowed-we show that it is possible to obtain agreement with the Hawking's area law---S = A/4 (in Planck Units)---without fixing the Immirzi parameter to any particular value: consistency with the area law only imposes a relationship between the Immirzi parameter and the level of the Chern-Simons theory involved in the effective description of the horizon degrees of freedom."

http://arxiv.org/abs/1011.3022
High-order quantum back-reaction and quantum cosmology with a positive cosmological constant
Martin Bojowald, David Brizuela, Hector H. Hernandez, Michael J. Koop, Hugo A. Morales-Tecotl
33 pages, 9 figures
(Submitted on 12 Nov 2010)
"When quantum back-reaction by fluctuations, correlations and higher moments of a state becomes strong, semiclassical quantum mechanics resembles a dynamical system with a high-dimensional phase space. Here, systematic numerical methods to derive the dynamical equations including all quantum corrections to high order in the moments are introduced, together with a quantum cosmological example to illustrate some implications. The results show, for instance, that the initial Gaussian form of an initial state is maintained only briefly, but that the evolving state settles down to a new characteristic shape afterwards. At some point during the evolution all moments considered become of equal size and no truncation to finite order is possible. But until that time is reached, numerical evaluations provide a large amount of information about dynamical quantum states."

http://arxiv.org/abs/1011.3040
An effective approach to the problem of time: general features and examples
Martin Bojowald, Philipp A Hoehn, Artur Tsobanjan
59 pages, 9 figures
(Submitted on 12 Nov 2010)
"The effective approach to quantum dynamics allows a reformulation of the Dirac quantization procedure for constrained systems in terms of an infinite-dimensional constrained system of classical type. For semiclassical approximations, the quantum constrained system can be truncated to finite size and solved by the reduced phase space or gauge-fixing methods. In particular, the classical feasibility of local internal times is directly generalized to quantum systems, overcoming the main difficulties associated with the general problem of time in the semiclassical realm. The key features of local internal times and the procedure of patching global solutions using overlapping intervals of local internal times are described and illustrated by two quantum mechanical examples. The choice of time is tantamount to a choice of gauge at the effective level and changing the clock is, therefore, equivalent to a gauge transformation. This article complements the conceptual discussion in arXiv:1009.5953."

http://arxiv.org/abs/1011.2794
Entropy Production during Asymptotically Safe Inflation
Alfio Bonanno, Martin Reuter
17 pages, 4 figures, Invited contribution to the special issue of Entropy on "Entropy in Quantum Gravity"
(Submitted on 11 Nov 2010)
"The Asymptotic Safety scenario predicts that the deep ultraviolet of Quantum Einstein Gravity is governed by a nontrivial renormalization group fixed point. Analyzing its implications for cosmology using renormalization group improved Einstein equations we find that it can give rise to a phase of inflationary expansion in the early Universe. Inflation is a pure quantum effect here and requires no inflaton field. It is driven by the cosmological constant and ends automatically when the renormalization group evolution has reduced the vacuum energy to the level of the matter energy density. The quantum gravity effects also provide a natural mechanism for the generation of entropy. It could easily account for the entire entropy of the present Universe in the massless sector."

 

[MTd2]

http://arxiv.org/abs/1011.2794

Entropy Production during Asymptotically Safe Inflation

Alfio Bonanno, Martin Reuter
(Submitted on 11 Nov 2010)
The Asymptotic Safety scenario predicts that the deep ultraviolet of Quantum Einstein Gravity is governed by a nontrivial renormalization group fixed point. Analyzing its implications for cosmology using renormalization group improved Einstein equations we find that it can give rise to a phase of inflationary expansion in the early Universe. Inflation is a pure quantum effect here and requires no inflaton field. It is driven by the cosmological constant and ends automatically when the renormalization group evolution has reduced the vacuum energy to the level of the matter energy density. The quantum gravity effects also provide a natural mechanism for the generation of entropy. It could easily account for the entire entropy of the present Universe in the massless sector.

http://arxiv.org/abs/1011.3022

High-order quantum back-reaction and quantum cosmology with a positive cosmological constant

Martin Bojowald, David Brizuela, Hector H. Hernandez, Michael J. Koop, Hugo A. Morales-Tecotl
(Submitted on 12 Nov 2010)
When quantum back-reaction by fluctuations, correlations and higher moments of a state becomes strong, semiclassical quantum mechanics resembles a dynamical system with a high-dimensional phase space. Here, systematic numerical methods to derive the dynamical equations including all quantum corrections to high order in the moments are introduced, together with a quantum cosmological example to illustrate some implications. The results show, for instance, that the initial Gaussian form of an initial state is maintained only briefly, but that the evolving state settles down to a new characteristic shape afterwards. At some point during the evolution all moments considered become of equal size and no truncation to finite order is possible. But until that time is reached, numerical evaluations provide a large amount of information about dynamical quantum states.

http://arxiv.org/abs/1011.3040

An effective approach to the problem of time: general features and examples

Martin Bojowald, Philipp A Hoehn, Artur Tsobanjan
(Submitted on 12 Nov 2010)
The effective approach to quantum dynamics allows a reformulation of the Dirac quantization procedure for constrained systems in terms of an infinite-dimensional constrained system of classical type. For semiclassical approximations, the quantum constrained system can be truncated to finite size and solved by the reduced phase space or gauge-fixing methods. In particular, the classical feasibility of local internal times is directly generalized to quantum systems, overcoming the main difficulties associated with the general problem of time in the semiclassical realm. The key features of local internal times and the procedure of patching global solutions using overlapping intervals of local internal times are described and illustrated by two quantum mechanical examples. The choice of time is tantamount to a choice of gauge at the effective level and changing the clock is, therefore, equivalent to a gauge transformation. This article complements the conceptual discussion in arXiv:1009.5953.

http://arxiv.org/abs/1011.2961

Static isolated horizons: SU(2) invariant phase space, quantization, and black hole entropy

Alejandro Perez, Daniele Pranzetti
(Submitted on 12 Nov 2010)
We study the classical field theoretical formulation of static generic isolated horizons in a manifestly SU(2) invariant formulation. We show that the usual classical description requires revision in the non-static case due to the breaking of diffeomorphism invariance at the horizon leading to the non conservation of the usual pre-symplectic structure. We argue how this difficulty could be avoided by a simple enlargement of the field content at the horizon that restores diffeomorphism invariance. Restricting our attention to static isolated horizons we study the effective theories describing the boundary degrees of freedom. A quantization of the horizon degrees of freedom is proposed. By defining a statistical mechanical ensemble where only the area A of the horizon is fixed macroscopically-states with fluctuations away from spherical symmetry are allowed-we show that it is possible to obtain agreement with the Hawking's area law---S = A/4 (in Planck Units)---without fixing the Immirzi parameter to any particular value: consistency with the area law only imposes a relationship between the Immirzi parameter and the level of the Chern-Simons theory involved in the effective description of the horizon degrees of freedom.

 

[marcus]

http://arxiv.org/abs/1011.3335
Effective Theory in Spinfoam Cosmology: A First Order LQG-corrected FRW Cosmology and the Stiff Fluid
Christian Röken
(Submitted on 15 Nov 2010)
"We present an effective theory of a basic holomorphic spinfoam cosmology peaked on homogeneous isotropic metrics. The quantum-corrected Hamiltonian constraint of this effective theory is motivated by an operator equation H W = 0, satisfied by the LQG transition amplitude W, reduced to a classical phase space symplectic structure. The analysis of this quantity shows that this effective model gives first order corrections to the classical FRW dynamical expressions in h resembling a universe with an ultralight irrotational stiff perfect fluid as matter-energy content. Such an exotic fluid can also be regarded as a massless real scalar field."

http://arxiv.org/abs/1011.3418
Quantum of volume in de Sitter space
Jakub Mielczarek, Wlodzimierz Piechocki
12 pages, 3 figures
(Submitted on 15 Nov 2010)
"We apply the nonstandard loop quantum cosmology method to quantize a flat FRW cosmological model with a free scalar field and the cosmological constant Λ >0. Modification of the Hamiltonian in terms of loop geometry parametrized by a length λ introduces a scale dependence of the model. The spectrum of the volume operator is discrete and depends on Λ. Relating quantum of the volume with an elementary lattice cell leads to an explicit dependence of Λ on λ. Based on this assumption, we investigate the possibility of interpreting Λ as a running constant."

Copied from Arivero:
αβγδεζηθικλμνξοπρσςτυφχψω...ΓΔΘΛΞΠΣΦΨΩ...∏∑∫∂√ ...± ÷...←↓→↑↔~≈≠≡≤≥...½...∞...(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
___________

 

[marcus]

http://arxiv.org/abs/1011.3641
A Unified Theory of Non-Linear Electrodynamics and Gravity
Alexander Torres-Gomez, Kirill Krasnov, Carlos Scarinci
31 pages
(Submitted on 16 Nov 2010)
"We describe a class of unified theories of electromagnetism and gravity. The Lagrangian is of the BF type, with a potential for the B-field, the gauge group is U(2) (complexified). Given a choice of the potential function the theory is a deformation of (complex) general relativity and electromagnetism, and describes just two propagating polarisations of the graviton and two of the photon. When gravity is switched off the theory becomes the usual non-linear electrodynamics with a general structure function. The Einstein-Maxwell theory can be recovered by sending some of the parameters of the defining potential to zero, but for any generic choice of the potential the theory is indistinguishable from Einstein-Maxwell at low energies. A real theory is obtained by imposing suitable reality conditions. We also study the spherically-symmetric solution and show how the usual Reissner-Nordstrom solution is recovered."

http://arxiv.org/abs/1011.3667
Coarse graining theories with gauge symmetries
Benjamin Bahr, Bianca Dittrich, Song He
31 pages, 3 pictures
(Submitted on 16 Nov 2010)
"Discretizations of continuum theories often do not preserve the gauge symmetry content. This occurs in particular for diffeomorphism symmetry in general relativity, which leads to severe difficulties both in canonical and covariant quantization approaches. We discuss here the method of perfect actions, which attempts to restore gauge symmetries by mirroring exactly continuum physics on a lattice via a coarse graining process. Analytical results can only be obtained via a perturbative approach, for which we consider the first steps, namely the coarse graining of the linearized theory. The linearized gauge symmetries are exact also in the discretized theory, hence we develop a formalism to deal with gauge systems. Finally we provide a discretization of linearized gravity as well as a coarse graining map and show that with this choice the 3D linearized gravity action is invariant under coarse graining."

Brief mention (only indirect connection with QG):
http://arxiv.org/abs/1011.3532
The moment of truth for WIMP Dark Matter
Gianfranco Bertone
To appear in Nature (Nov 18, 2010)
(Submitted on 15 Nov 2010)
We know that dark matter constitutes 85% of all the matter in the Universe, but we do not know of what it is made. Amongst the many Dark Matter candidates proposed, WIMPs (weakly interacting massive particles) occupy a special place, as they arise naturally from well motivated extensions of the standard model of particle physics. With the advent of the Large Hadron Collider at CERN, and a new generation of astroparticle experiments, the moment of truth has come for WIMPs: either we will discover them in the next five to ten years, or we will witness the inevitable decline of WIMP paradigm.

 

[MTd2]

http://arxiv.org/abs/1011.3888

Dual DSR

Jose A. Magpantay
(Submitted on 17 Nov 2010)
We develop the physics of dual kappa Poincare algebra, which we will call dual DSR. First, we show that the dual kappa Poincare algebra is isomorphic to de Sitter algebra and its spactime is essentially de Sitter spacetime. Second, we show how to derive the coproduct rules for Beltrami and conformal coordinates of de Sitter spacetime. It follows from the current literature on de Sitter relativity that the speed of light c and the de Sitter length are the two invariant scales of the physics of dual kappa Poincare algebra. Third, we derive the Casimir invariant of the dual kappa Popincare algebra and use this to derive an expression for the speed of light, our fourth result. Fifth, the field equation for the scalar field is derived from the Casimir invariant. The results for the coordinate speed of light and the scalar field theory are the same as in de Sitter theory in the planar coordinate basis. Thus, we have shown that the physics of dual kappa Poincare algebra (in the dual bicrossproduct basis), which can be apprpriately called dual DSR, is essentially de Sitter relativity. Finally, we note that dual DSR is not a quantum theory of spacetime but a quantum theory of momenta.

 

[marcus]

http://arxiv.org/abs/1011.4249
On the measure problem in slow roll inflation and loop quantum cosmology
Alejandro Corichi, Asieh Karami
12 pages, 3 figures
(Submitted on 18 Nov 2010)
"We consider the measure problem in standard slow-roll inflationary models from the perspective of loop quantum cosmology (LQC). Following recent results by Ashtekar and Sloan, we study the probability of having enough e-foldings and focus on the transition of the theory to the 'continuum limit', where general relativity (GR) is recovered. Contrary to the standard expectation, the probability of having enough inflation, that is close to one in LQC, grows and tends to 1 as one approaches the classical limit. We study the origin of the tension between these results with those by Gibbons and Turok, and offer an explanation that brings these apparent contradictory results into a coherent picture. As we show, the conflicting results stem from different choices of initial conditions. The singularity free scenario of loop quantum cosmology offers a natural choice of initial conditions, and suggests that enough inflation is generic."

http://arxiv.org/abs/1011.4290
Two-point functions in (loop) quantum cosmology
Gianluca Calcagni, Steffen Gielen, Daniele Oriti
28 pages
(Submitted on 18 Nov 2010)
"The path-integral formulation of quantum cosmology with a massless scalar field as a sum-over-histories of volume transitions is discussed, with particular but non-exclusive reference to loop quantum cosmology. Exploiting the analogy with the relativistic particle, we give a complete overview of the possible two-point functions, pointing out the choices involved in their definitions, deriving their vertex expansions and the composition laws they satisfy. We clarify the origin and relations of different quantities previously defined in the literature, in particular the tie between definitions using a group averaging procedure and those in a deparametrized framework. Finally, we draw some conclusions about the physics of a single quantum universe (where there exist superselection rules on positive- and negative-frequency sectors and different choices of inner product are physically equivalent) and multiverse field theories where the role of these sectors and the inner product are reinterpreted."

 

[marcus]

http://arxiv.org/abs/1011.3706
Concentric circles in WMAP data may provide evidence of violent pre-Big-Bang activity
V.G.Gurzadyan, R.Penrose
8 pages, 6 figs
(Submitted on 16 Nov 2010)
"Conformal cyclic cosmology (CCC) posits the existence of an aeon preceding our Big Bang 'B', whose conformal infinity 'I' is identified, conformally, with 'B', now regarded as a spacelike 3-surface. Black-hole encounters, within bound galactic clusters in that previous aeon, would have the observable effect, in our CMB sky, of families of concentric circles over which the temperature variance is anomalously low, the centre of each such family representing the point of 'I' at which the cluster converges. These centres appear as fairly randomly distributed fixed points in our CMB sky. The analysis of Wilkinson Microwave Background Probe's (WMAP) cosmic microwave background 7-year maps does indeed reveal such concentric circles, of up to 6 sigma significance. This is confirmed when the same analysis is applied to BOOMERanG98 data, eliminating the possibility of an instrumental cause for the effects. These observational predictions of CCC would not be easily explained within standard inflationary cosmology."

 

[marcus]

http://pirsa.org/10110071/
Is temperature the speed of time? Thermal time and the Tolman effect
Matteo Smerlak
Perimeter video lecture, 16 November 2010
"Why is a vertical column of gas at thermal equilibrium slighly hotter at the bottom than a the top? My answer in this talk will be that time runs slower in a deeper gravitational potential, and temperature is nothing but the (inverse) speed of time. Specifically, I will (i) introduce Rovelli's notion of thermal time, (ii) use it to provide a 'principle' characterization of thermal equilibrium in stationary spacetimes, and (iii) effortlessly derive the Tolman-Ehrenfest relation. This approach contrasts with the 'constructive' accounts of thermal equilibrium in curved spacetimes given in the literature, and vindicates the time-temperature relationship cropping up in the Hawking-Unruh and Kubo-Martin-Schwinger relations."

Seminar talk based on this paper:
http://arxiv.org/abs/1005.2985
Thermal time and the Tolman-Ehrenfest effect: temperature as the "speed of time"
Carlo Rovelli, Matteo Smerlak

 

[MTd2]

http://arxiv.org/abs/1011.4705

Spinfoam Cosmology: quantum cosmology from the full theory

Francesca Vidotto
(Submitted on 21 Nov 2010)
Quantum cosmology is usually studied quantizing symmetry-reduced variables. Is it possible, instead, to define quantum cosmology starting from the full quantum gravity theory? In Loop Quantum Gravity (LQG), it is possible to cut the degrees of freedom in a suitable way, in order to define a cosmological model. Such a model provides a tool for describing general fluctuations of the quantum geometry at the bounce that replaces the initial singularity. I focus on its simplest version, a "dipole" formed by two tetrahedra. This has been shown to describe a universe with anisotropic and inhomogenous degrees of freedom. Its dynamics can be given using the spinfoam formalism. I briefly review the present state of this approach.

 

[MTd2]

http://arxiv.org/abs/1011.4618

Evolution of cosmological perturbations in an RG-driven inflationary scenario

Adriano Contillo
(Submitted on 20 Nov 2010)
A gauge-invariant, linear cosmological perturbation theory of an almost homogeneous and isotropic universe with dynamically evolving Newton constant G and cosmological constant $\Lambda$ is presented. The equations governing the evolution of the comoving fractional spatial gradients of the matter density, G and $\Lambda$ are thus obtained. Explicit solutions are discussed in cosmologies, featuring an accelerated expansion, where both G and $\Lambda$ vary according to renormalization group equations in the vicinity of an ultraviolet fixed point. Finally, a similar analysis is carried out in the late universe regime described by the part of the renormalization group trajectory close to the gaussian fixed point.

 

[marcus]

http://arxiv.org/abs/1011.5516
Inflation and Loop Quantum Cosmology
Aurelien Barrau
5 pages, Proceedings of the 35th International Conference on High Energy Physics, Paris, 2010 (ICHEP 2010)
(Submitted on 24 Nov 2010)
"On the one hand, inflation is an extremely convincing scenario: it solves most cosmological paradoxes and generates fluctuations that became the seeds for the growth of structures. It, however, suffers from a 'naturalness' problem: generating initial conditions for inflation is far from easy. On the other hand, loop quantum cosmology is very successful: it solves the Big Bang singularity through a non-perturbative and background-independent quantization of general relativity. It, however, suffers from a key drawback: it is extremely difficult to test. Recent results can let us hope that inflation and LQC could mutually cure those pathologies: LQC seems to naturally generate inflation and inflation could allow us to test LQC."

http://arxiv.org/abs/1011.5628
Black Hole Entropy, Loop Gravity, and Polymer Physics
Eugenio Bianchi
13 pages, 2 figures
(Submitted on 25 Nov 2010)
"Loop Gravity provides a microscopic derivation of Black Hole entropy. In this paper, I show that the microstates counted admit a semiclassical description in terms of shapes of a tessellated horizon. The counting of microstates and the computation of the entropy can be done via a mapping to an equivalent statistical mechanical problem: the counting of conformations of a closed polymer chain. This correspondence suggests a number of intriguing relations between the thermodynamics of Black Holes and the physics of polymers."

http://arxiv.org/abs/1011.5676
Coherent states for FLRW space-times
Elena Magliaro, Antonino Marciano, Claudio Perini
10 pages, 1 figure
(Submitted on 25 Nov 2010)
"We construct a class of coherent spin-network states that capture proprieties of curved space-times of the Friedmann-Lamaiître-Robertson-Walker type on which they are peaked. The data coded by a coherent state are associated to a cellular decomposition of a spatial (t=const.) section with dual graph given by the complete five-vertex graph, though the construction can be easily generalized to other graphs. The labels of coherent states are complex SL(2,C) variables, one for each link of the graph and are computed through a smearing process starting from a continuum extrinsic and intrinsic geometry of the canonical surface. The construction covers both Euclidean and Lorentzian signatures; in the Euclidean case and in the limit of flat space we reproduce the simplicial 4-simplex semiclassical states used in Spin Foams."

http://arxiv.org/abs/1011.5754
Background independent condensed matter models for quantum gravity
Alioscia Hamma, Fotini Markopoulou
Contribution submitted to the focus issue of the New Journal of Physics on "Classical and Quantum Analogues for Gravitational Phenomena and Related Effects", R. Schuetzhold, U. Leonhardt and C. Maia, Eds.
(Submitted on 26 Nov 2010)
"A number of recent proposals for a quantum theory of gravity are based on the idea that spacetime geometry and gravity are derivative concepts and only apply at an approximate level. There are two fundamental challenges to any such approach. At the conceptual level, there is a clash between the 'timelessness' of general relativity and emergence. Second, the lack of a fundamental spacetime makes difficult the straightforward application of well-known methods of statistical physics to the problem. We recently initiated a study of such problems using spin systems based on evolution of quantum networks with no a priori geometric notions as models for emergent geometry and gravity. In this article we review two such models. The first is a model of emergent (flat) space and matter and we show how to use methods from quantum information theory to derive features such as speed of light from a non-geometric quantum system. The second model exhibits interacting matter and geometry, with the geometry defined by the behavior of matter. This model has primitive notions of gravitational attraction which we illustrate with a toy black hole, and exhibits entanglement between matter and geometry and thermalization of the quantum geometry."

 

[John86]

http://arxiv.org/abs/1011.5593
Minimal conditions for the existence of a Hawking-like flux
Authors: Carlos Barcelo (IAA-CSIC, Granada), Stefano Liberati (SISSA, Trieste), Sebastiano Sonego (Universita di Udine), Matt Visser (Victoria University of Wellington)
(Submitted on 25 Nov 2010)
Abstract: We investigate the minimal conditions that an asymptotically flat general relativistic spacetime must satisfy in order for a Hawking-like Planckian flux of particles to arrive at future null infinity. We demonstrate that there is no requirement that any sort of horizon form anywhere in the spacetime. We find that the irreducible core requirement is encoded in an approximately exponential "peeling" relationship between affine coordinates on past and future null infinity. As long as a suitable adiabaticity condition holds, then a Planck-distributed Hawking-like flux will arrive at future null infinity with temperature determined by the e-folding properties of the outgoing null geodesics. The temperature of the Hawking-like flux can slowly evolve as a function of time. We also show that the notion of "peeling" of null geodesics is distinct, and in general different, from the usual notion of "inaffinity" used in Hawking's definition of surface gravity.

http://arxiv.org/abs/1011.4634
Quasi-normal frequencies: Semi-analytic results for highly damped modes
Authors: Jozef Skakala, Matt Visser
(Submitted on 21 Nov 2010)
Abstract: Black hole highly-damped quasi-normal frequencies (QNFs) are very often of the form (offset)} + i n (gap). We have investigated the genericity of this phenomenon for the Schwarzschild--deSitter (SdS) black hole by considering a model potential that is piecewise Eckart (piecewise Poeschl-Teller), and developing an analytic ``quantization condition'' for the highly-damped quasi-normal frequencies. We find that the (offset) + i n(gap) behaviour is common but not universal, with the controlling feature being whether or not the ratio of the surface gravities is a rational number. We furthermore observed that the relation between rational ratios of surface gravities and periodicity of QNFs is very generic, and also occurs within different analytic approaches applied to various types of black hole spacetimes. These observations are of direct relevance to any physical situation where highly-damped quasi-normal modes are important.

http://arxiv.org/abs/1011.4538
Entropy bounds for uncollapsed matter
Authors: Gabriel Abreu (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 19 Nov 2010)
Abstract: In any static spacetime the quasilocal Tolman mass contained within a volume can be reduced to a Gauss-like surface integral involving the flux of a suitably defined generalized surface gravity. By introducing some basic thermodynamics, and invoking the Unruh effect, one can then develop elementary bounds on the quasilocal entropy that are very similar in spirit to the holographic bound, and closely related to entanglement entropy.

http://arxiv.org/abs/1009.0080
Generic master equations for quasi-normal frequencies
Authors: Jozef Skakala (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 1 Sep 2010 (v1), last revised 23 Nov 2010 (this version, v2))
Abstract: Generic master equations governing the highly-damped quasi-normal frequencies [QNFs] of one-horizon, two-horizon, and even three-horizon spacetimes can be obtained through either semi-analytic or monodromy techniques. While many technical details differ, both between the semi-analytic and monodromy approaches, and quite often among various authors seeking to apply the monodromy technique, there is nevertheless widespread agreement regarding the the general form of the QNF master equations. Within this class of generic master equations we can establish some rather general results, relating the existence of "families" of QNFs of the form omega_{a,n} = (offset)_a + i n (gap) to the question of whether or not certain ratios of parameters are rational or irrational.

 

[marcus]

http://arxiv.org/abs/1011.6257
One-loop quantum gravity repulsion in the early Universe
Bogusław Broda
7 pages
(Submitted on 29 Nov 2010)
"Perturbative quantum gravity is used to compute the lowest order corrections to the classical, spatially flat cosmological FLRW solution (for the radiation). The presented approach is analogous to the approach used to compute quantum corrections to the Coulomb potential in electrodynamics, or rather to the approach used to compute quantum corrections to the Schwarzschild solution in gravity. In the framework of the standard perturbative quantum gravity, it is shown that the corrections to the classical deceleration, coming from the one-loop graviton vacuum polarization (self-energy), have (UV cutoff free) opposite to the classical repulsive properties which are not negligible in the very early Universe. The repulsive "quantum forces" are akin to those known from loop quantum cosmology."

 

[murray92]

http://arxiv.org/abs/1008.1046
An Estimate of Λin Resummed Quantum Gravity in the Context of Asymptotic Safety
B.F.L. Ward
(Submitted on 5 Aug 2010 (v1), last revised 18 Oct 2010 (this version, v3))
We show that, by using recently developed exact resummation techniques based on the extension of the methods of Yennie, Frautschi and Suura to Feynman's formulation of Einstein's theory, we get quantum field theoretic descriptions for the UV fixed-point behaviors of the dimensionless gravitational and cosmological constants postulated by Weinberg. Connecting our work to the attendant phenomenological asymptotic safety analysis of Planck scale cosmology by Bonanno and Reuter, we predict the value of the cosmological constant \Lambda. We find the encouraging estimate \rho_\Lambda\equiv \frac{\Lambda}{8\pi G_N} \simeq (2.400\times 10^{-3}eV)^4.

I was bit suprised this wasn't mentioned. But - if true, and his methods hold- this is one of the BIG papers, ...
(just thought I'd chip it in)
... If anybody has anything interesting to say about the paper please start a thread.

 

[marcus]

http://arxiv.org/abs/1011.6442
Surprises in the Evaporation of 2-Dimensional Black Holes
Abhay Ashtekar, Frans Pretorius, Fethi M. Ramazanoğlu
4 pages, 3 figures
(Submitted on 30 Nov 2010)
"Quantum evaporation of Callen-Giddings-Harvey-Strominger (CGHS) black holes is analyzed in the mean field approximation. The resulting semi-classical theory incorporates back reaction. Detailed analytical and numerical calculations show that, while some of the assumptions underlying the standard evaporation paradigm are borne out, several are not. Furthermore, if the black hole is initially macroscopic, the evaporation process exhibits remarkable universal properties. Although the literature on CGHS black holes is quite rich, these features had escaped previous analyses, in part because of lack of required numerical precision, and in part because certain properties and symmetries of the model were not recognized. Finally, our results provide support for the full quantum scenario recently developed by Ashtekar, Taveras and Varadarajan."
To help interpret this abstract I will add that of the earlier ATV paper, published in Physical Review Letters:
http://arxiv.org/abs/0801.1811
Information is Not Lost in the Evaporation of 2-dimensional Black Holes
Abhay Ashtekar, Victor Taveras, Madhavan Varadarajan
4 pages, 2 figures
(Submitted on 11 Jan 2008)
"We analyze Hawking evaporation of the Callen-Giddings-Harvey-Strominger (CGHS) black holes from a quantum geometry perspective and show that information is not lost, primarily because the quantum space-time is sufficiently larger than the classical. Using suitable approximations to extract physics from quantum space-times we establish that: i)future null infinity of the quantum space-time is sufficiently long for the the past vacuum to evolve to a pure state in the future; ii) this state has a finite norm in the future Fock space; and iii) all the information comes out at future infinity; there are no remnants."

A LQG blog (new) associated with the International LQG Seminar (ILQGS, teleconference with slides, some Tuesdays)
http://ilqgs.blogspot.com/

 

[John86]

http://arxiv.org/abs/1011.6466
Cosmic alignment of the aether
Authors: Isaac Carruthers, Ted Jacobson
(Submitted on 30 Nov 2010)
Abstract: In Einstein-aether theory and Horava gravity, a timelike unit vector is coupled to the spacetime metric. It has previously been shown that in an exponentially expanding homogeneous, isotropic background, small perturbations of the vector relax back to the isotropic frame. Here we investigate large deviations from isotropy, maintaining homogeneity. We find that, for generic values of the coupling constants, the aether and metric relax to the isotropic configuration if the initial aether hyperbolic boost angle and its time derivative in units of the cosmological constant are less than something of order unity. For larger angles or angle derivatives, the behavior is strongly dependent on the values of the coupling constants. Generally there is runaway behavior, in which the anisotropy increases with time, and/or singularities occur.

http://arxiv.org/abs/1005.3293
Minimal Scales from an Extended Hilbert Space
Authors: Martin Kober, Piero Nicolini
(Submitted on 18 May 2010 (v1), last revised 30 Nov 2010 (this version, v2))
Abstract: We consider an extension of the conventional quantum Heisenberg algebra, assuming that coordinates as well as momenta fulfil nontrivial commutation relations. As a consequence, a minimal length and a minimal mass scale are implemented. Our commutators do not depend on positions and momenta and we provide an extension of the coordinate coherent state approach to Noncommutative Geometry. We explore, as toy model, the corresponding quantum field theory in a (2+1)-dimensional spacetime. Then we investigate the more realistic case of a (3+1)-dimensional spacetime, foliated into noncommutative planes. As a result, we obtain propagators, which are finite in the ultraviolet as well as the infrared regime

http://arxiv.org/abs/1008.0154
Gauge Theories under Incorporation of a Generalized Uncertainty Principle
Authors: Martin Kober
(Submitted on 1 Aug 2010 (v1), last revised 23 Oct 2010 (this version, v2))
Abstract: There is considered an extension of gauge theories according to the assumption of a generalized uncertainty principle which implies a minimal length scale. A modification of the usual uncertainty principle implies an extended shape of matter field equations like the Dirac equation. If there is postulated invariance of such a generalized field equation under local gauge transformations, the usual covariant derivative containing the gauge potential has to be replaced by a generalized covariant derivative. This leads to a generalized interaction between the matter field and the gauge field as well as to an additional self interaction of the gauge field. Since the existence of a minimal length scale seems to be a necessary assumption of any consistent quantum theory of gravity, the gauge principle is a constitutive ingredient of the standard model and even gravity can be described as gauge theory of local translations or Lorentz transformations, the presented extension of gauge theories appears as a very important consideration.

 

[marcus]

http://arxiv.org/abs/1012.0053
Symmetry Reduction of Loop Quantum Gravity
Johannes Brunnemann, Tim A. Koslowski
34 pages, 2 figures
(Submitted on 30 Nov 2010)
"We reexamine the non-embedability of the configuration space of standard Loop Quantum Cosmology into the configuration space of full Loop Quantum Gravity. For this purpose we first consider a perturbation series around piecewise linear Loop Quantum Gravity into which standard Loop Quantum Cosmology is embeddable, which hints to use a Liouville Green expansion. Using the Liouville Green expansion and results from asymptotic analysis, we find that an arbitrary cylindrical function has asymptotically almost periodic dependence on the minisuperspace parameter in agreement with arXiv:1010.0449v1 . This allows us to construct an explicit extension of standard Loop Quantum Cosmology that permits embedability."

http://arxiv.org/abs/1012.0077
Evaporation of 2-Dimensional Black Holes
Abhay Ashtekar, Frans Pretorius, Fethi M. Ramazanoğlu
18 pages
(Submitted on 1 Dec 2010)
"We present a detailed analysis of results from a new study of the quantum evaporation of Callan-Giddings-Harvey-Strominger (CGHS) black holes within the mean field approximation. This semi-classical theory incorporates back reaction. Our analytical and numerical calculations show that, while some of the assumptions underlying the standard evaporation paradigm are borne out, several are not. One of the anticipated properties we confirm is that the semi-classical space-time is asymptotically flat at right future null infinity, I_R⁺, yet incomplete in the sense that null observers reach a future Cauchy horizon in finite affine time. Unexpected behavior includes that the Bondi mass traditionally used in the literature can become negative even when the area of the horizon is macroscopic; an improved Bondi mass remains positive until the end of semi-classical evaporation, yet the final value can be arbitrarily large relative to the Planck mass; and the flux of the quantum radiation at I_R⁺ is non-thermal even when the horizon area is large compared to the Planck scale. Furthermore, if the black hole is initially macroscopic, the evaporation process exhibits remarkable universal properties. Although the literature on CGHS black holes is quite rich, these features had escaped previous analyses, in part because of lack of required numerical precision, and in part due to misinterpretation of certain properties and symmetries of the model. Finally, our results provide support for the full quantum scenario recently developed by Ashtekar, Taveras and Varadarajan, and also offer a number of interesting problems to the mathematical relativity and geometric analysis communities."

 

[MTd2]

http://arxiv.org/abs/1012.0119
Entropy density of spacetime and the Navier-Stokes fluid dynamics of null surfaces

T. Padmanabhan
(Submitted on 1 Dec 2010)
It has been known for several decades that Einstein's field equations, when projected onto a null surface, exhibits a structure very similar to non-relativistic Navier-Stokes equation. I show that this result arises quite naturally when gravitational dynamics is viewed as an emergent phenomenon. Extremising the spacetime entropy density associated with the null surfaces leads to a set of equations which, when viewed in the local inertial frame, becomes identical to the Navier-Stokes (NS) equation. This is in contrast with the usual description of Damour-Navier-Stokes (DNS) equation in a general coordinate system, in which there appears a Lie derivative rather than convective derivative. I discuss this difference, its importance and why it is more appropriate to view the equation in a local inertial frame. The viscous force on fluid, arising from the gradient of the viscous stress-tensor, involves the second derivatives of the metric and does not vanish in the local inertial frame while the viscous stress-tensor itself vanishes so that inertial observers detect no dissipation. We thus provide an entropy extremisation principle that leads to the DNS equation, which makes the hydrodynamical analogy with gravity completely natural and obvious. Several implications of these results are discussed.

 

[MTd2]

http://xxx.lanl.gov/abs/1012.0013

An alternative to the gauge theoretic setting

Bert Schroer
(Submitted on 30 Nov 2010)
The standard formulation of gauge theories results from the Lagrangian (functional integral) quantization of classical gauge theories. A more intrinsic qunantum theoretical access in the spirit of Wigner's representation theory shows that there is a fundamental clash between the pointlike localization of zero mass (vector, tensor) potentials and the Hilbert space (positivity, unitarity) structure of QT. The quantization approach has no other way than to stay with pointlike localization and sacrifice the Hilbert space whereas the approach build on the intrinsic quantum concept of modular localization keeps the Hilbert space and trades the conflict creating pointlike generation with the tightest consistent localization:: semiinfinite spacelike string localization. Whereas these potentials in the presence of interactions stay quite close to associated pointlike field strength, the interacting matter fields to which they are coupled bear the brunt of the nonlocal aspect in that they are string.generated in a way which cannot be undone by any differentiation. The new stringlike approach to gauge theory also revives the idea of a Schwinger-Higgs screening mechanism as a deeper and less metaphoric description of the Higgs spontaneous symmetry breaking and its accompanying tale about "God's particle" and its mass generation for all other particles.