Loop-and-allied QG bibliography

[marcus]

http://arxiv.org/abs/1007.3368
The Definition of Mach's Principle
Julian Barbour
30 pages. To be published in Foundations of Physics as invited contribution to Peter Mittelstaedt's 80th Birthday Festschrift.
(Submitted on 20 Jul 2010)
"Two definitions of Mach's principle are proposed. Both are related to gauge theory, are universal in scope and amount to formulations of causality that take into account the relational nature of position, time, and size. One of them leads directly to general relativity and may have relevance to the problem of creating a quantum theory of gravity."

http://arxiv.org/abs/1007.3723
Vertex Expansion for the Bianchi I model
Miguel Campiglia, Adam Henderson, William Nelson
15 pages, 2 figures
(Submitted on 21 Jul 2010)
"A perturbative expansion of Loop Quantum Cosmological transitions amplitudes of Bianchi I models is performed. Following the procedure outlined in [1,2] for isotropic models, it is shown that the resulting expansion can be written in the form of a series of amplitudes each with a fixed number of transitions mimicking a spin foam expansion. This analogy is more complete than in the isotropic case, since there are now the additional anisotropic degrees of freedom which play the role of 'colouring' of the spin foams. Furthermore, the isotropic expansion is recovered by integrating out the anisotropies."

http://arxiv.org/pdf/1007.3732v1
Chiral Effects in Quantum Gravity as Consequence of Instantonic Transitions
Simone Mercuri
8 pages
(Submitted on 21 Jul 2010)
"Instantonic solutions of the Holst modified action for General Relativity indicate that gravity becomes chiral through quantum effects. The resulting violation of parity reflects in a different Newton's constant for right and left modes: a measurement of the TB correlation on CMB can reveal the existence of such an effect."
==sample excerpt from Mercuri's paper==
" In this paper, by using a WKB approximation, we demonstrate that in fact the Holst action can produce a parity violation in the quantum regime. This provides a clear theoretical support to the assumption made in [1] that left and right gravitons are characterized by a different gravitational constant.
Furthermore, this fact is particularly interesting in consideration of the fact that the Holst action is the Lagrangian counterpart of the Ashtekar–Barbero reformulation of canonical General Relativity [5, 6], which is the basis of the non-perturbative quantization of GR, i.e. Loop Quantum Gravity [7–10].
Therefore a result indicating that in fact a parity violation can be generated by the quantization of the Holst action, even in the WKB approximation, would suggest that the same effect could characterize the full LQG theory.
==endquote==
Simone Mercuri is one of Ashtekar's group at Penn State IGC.

 

[atyy]

http://arxiv.org/abs/1007.3970
The Jarzynski Identity and the AdS/CFT Duality
Djordje Minic, Michel Pleimling
We point out a remarkable analogy between the Jarzynski identity from non-equilibrium statistical physics and the AdS/CFT duality. We apply the logic that leads to the Jarzynski identity to renormalization group (RG) flows of quantum field theories and then argue for the natural connection with the AdS/CFT duality formula. This application can be in principle checked in Monte Carlo simulations of RG flows. Given the existing generalizations of the Jarzynski identity in non-equilibrium statistical physics, and the analogy between the Jarzynski identity and the AdS/CFT duality, we are led to suggest natural but novel generalizations of the AdS/CFT dictionary.

 

[marcus]

This has a lot about LQG even though the main topic is a different QG approach:

http://arxiv.org/abs/1007.4094
Modular Theory, Non-commutative Geometry and Quantum Gravity
Paolo Bertozzini, Roberto Conti, Wicharn Lewkeeratiyutkul
48 pages, contribution to SIGMA special issue "Noncommutative Spaces and Fields"
(Submitted on 23 Jul 2010)
"This paper contains the first written exposition of some ideas (announced in a previous survey) on an approach to quantum gravity based on Tomita-Takesaki modular theory and A.Connes non-commutative geometry aiming at the reconstruction of spectral geometries from an operational formalism of states and categories of observables in a covariant theory. Care has been taken to provide a coverage of the relevant background on modular theory, its applications in non-commutative geometry and physics and to the detailed discussion of the main foundational issues raised by the proposal."

 

[atyy]

http://arxiv.org/abs/1007.4234
Topological Insulators and Superconductors from String Theory
Shinsei Ryu, Tadashi Takayanagi
Relevant in a non-string bibliography because "our string theory realization includes the honeycomb lattice Kitaev model in two spatial dimensions, and its higher-dimensional extensions".

 

[atyy]

http://arxiv.org/abs/1007.4829
New Phenomena in NC Field Theory and Emergent Spacetime Geometry
Badis Ydri
(Submitted on 27 Jul 2010)
Abstract: We give a brief review of two nonperturbative phenomena typical of noncommutative field theory which are known to lead to the perturbative instability known as the UV-IR mixing. The first phenomena concerns the emergence/evaporation of spacetime geometry in matrix models which describe perturbative noncommutative gauge theory on fuzzy backgrounds. In particular we show that the transition from a geometrical background to a matrix phase makes the description of noncommutative gauge theory in terms of fields via the Weyl map only valid below a critical value g_*. The second phenomena concerns the appearance of a nonuniform ordered phase in noncommutative scalar \phi^4 field theory and the spontaneous symmetry breaking of translational/rotational invariance which happens even in two dimensions. We argue that this phenomena also originates in the underlying matrix degrees of freedom of the noncommutative field theory. Furthermore it is conjectured that in addition to the usual WF fixed point at $\theta=0$ there must exist a novel fixed point at \theta=\infty corresponding to the quartic hermitian matrix model.

http://arxiv.org/abs/1007.5049
Gauge non-invariance as tests of emergent gauge symmetry
John F. Donoghue, Mohamed Anber, Ufuk Aydemir
(Submitted on 28 Jul 2010)
Abstract: We motivate the concept of emergent gauge symmetry and discuss ways that this concept can be tested. The key idea is that if a symmetry is emergent, one should look for small violations of this symmetry because the underlying fundamental theory does not contain the symmetry. We describe our recent work implementing this idea in the gravity sector. We also describe the reasons why violations of gauge symmetry may well be linked to violations of Lorentz invariance.

 

[MTd2]

http://arxiv.org/abs/1007.5066

Finite entanglement entropy from the zero-point-area of spacetime
Authors: T. Padmanabhan
(Submitted on 28 Jul 2010)

Abstract: The calculation of entanglement entropy S of quantum fields in spacetimes with horizon shows that, quite generically, S (a) is proportional to the area A of the horizon and (b) is divergent. I argue that this divergence, which arises even in the case of Rindler horizon in flat spacetime, is yet another indication of a deep connection between horizon thermodynamics and gravitational dynamics. In an emergent perspective of gravity, which accommodates this connection, the fluctuations around the equipartition value in the area elements will lead to a minimal quantum of area, of the order of L_P^2, which will act as a regulator for this divergence. In a particular prescription for incorporating L_P^2 as zero-point-area of spacetime, this does happen and the divergence in entanglement entropy is regularized, leading to S proportional to (A/L_P^2) in Einstein gravity. In more general models of gravity, the surface density of microscopic degrees of freedom is different which leads to a modified regularisation procedure and the possibility that the entanglement entropy - when appropriately regularised - matches the Wald entropy.

 

[marcus]

http://arxiv.org/abs/1007.5066
Finite entanglement entropy from the zero-point-area of spacetime
Thanu Padmanabhan
9 pages
(Submitted on 28 Jul 2010)
"The calculation of entanglement entropy S of quantum fields in spacetimes with horizon shows that, quite generically, S (a) is proportional to the area A of the horizon and (b) is divergent. I argue that this divergence, which arises even in the case of Rindler horizon in flat spacetime, is yet another indication of a deep connection between horizon thermodynamics and gravitational dynamics. In an emergent perspective of gravity, which accommodates this connection, the fluctuations around the equipartition value in the area elements will lead to a minimal quantum of area, of the order of L_P², which will act as a regulator for this divergence. In a particular prescription for incorporating L_P² as zero-point-area of spacetime, this does happen and the divergence in entanglement entropy is regularized, leading to S proportional to (A/L_P²) in Einstein gravity. In more general models of gravity, the surface density of microscopic degrees of freedom is different which leads to a modified regularisation procedure and the possibility that the entanglement entropy - when appropriately regularised - matches the Wald entropy."

 

[marcus]

http://arxiv.org/abs/1007.5500
The propagator in polymer quantum field theory
Golam Mortuza Hossain, Viqar Husain, Sanjeev S. Seahra
4 pages, 1 figure
(Submitted on 30 Jul 2010)
"We study free scalar field theory on flat spacetime using a background independent (polymer) quantization procedure. Specifically we compute the propagator using a method that takes the energy spectrum and position matrix elements of the harmonic oscillator as inputs. We obtain closed form results in the infrared and ultraviolet regimes that give Lorentz invariance violating dispersion relations, and show suppression of propagation at sufficiently high energy."
==sample excerpt==
In this paper we explore a background independent (“polymer”) quantization method that arose in loop quantum gravity (LQG) [1] and apply it to scalar field theory. In this approach the Hilbert space used for quantization is different from the one employed in usual quantum theory. This Hilbert space is such that its inner product does not make use of a spacetime metric, even if one is available, as in QFT on a fixed background. Rather the inner product comes from an underlying group structure...
==endquote==

 

[MTd2]

http://arxiv.org/abs/1008.0354

EPRL/FK Group Field Theory

Joseph Ben Geloun, Razvan Gurau, Vincent Rivasseau
(Submitted on 2 Aug 2010)
The purpose of this short note is to clarify the Group Field Theory vertex and propagators corresponding to the EPRL/FK spin foam models and to detail the subtraction of leading divergences of the model.

 

[John86]

http://arxiv.org/abs/1008.0283
Unknown system boundaries cannot be determined within quantum Darwinism
Authors: Chris Fields
(Submitted on 2 Aug 2010)
Abstract: Observers restricted to interactions with environmental degrees of freedom that nondestructively encode pointer states of a system of interest S cannot determine from such interactions which degrees of freedom of S interact directly or indirectly with the environment E. Without a specification of the S-E boundary, such observers cannot use einselection and quantum Darwinism to calculate the pointer states of S or their environmental encodings. Quantum Darwinism requires S-E boundary specifications assumed or stipulated on the basis of classical-scale observations, and therefore cannot be regarded as providing a predictive, purely quantum-mechanical explanation of the "emergence" of classicality.

http://arxiv.org/abs/1008.0373
Little Boxes: The Simplest Demonstration of the Failure of Einstein's Attempt to Show the Incompleteness of Quantum Theory
Authors: John D. Norton
(Submitted on 2 Aug 2010)
Abstract: The failure of Einstein's co-authored "EPR" attempt to show the incompleteness of quantum theory is demonstrated directly for spatial degrees of freedom using only elementary notions. A GHZ construction is realized in the position properties of three particles whose quantum waves are distributed over three two-chambered boxes. The same system is modeled more realistically using three spatially separated, singly ionized hydrogen molecules.

http://arxiv.org/abs/1008.0033
Emergent Photons and Gravitons:The Problem of Vacuum Structure
Authors: J. D. Bjorken
(Submitted on 30 Jul 2010)
Abstract: We discuss vacuum condensates associated with emergent QED and with torsion, as well as the possible role of the Kodama wave function in quantum cosmology

http://arxiv.org/abs/1008.0154
Gauge Theories under Incorporation of a Generalized Uncertainty Principle
Authors: Martin Kober
(Submitted on 1 Aug 2010)
Abstract: It 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 it 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.

 

[John86]

http://arxiv.org/abs/1006.3480
Six-dimensional Methods for Four-dimensional Conformal Field Theories
Authors: Steven Weinberg
(Submitted on 17 Jun 2010 (v1), last revised 2 Aug 2010 (this version, v2))
Abstract: The calculation of both spinor and tensor Green's functions in four-dimensional conformally invariant field theories can be greatly simplified by six-dimensional methods. For this purpose, four-dimensional fields are constructed as projections of fields on the hypercone in six-dimensional projective space, satisfying certain transversality conditions. In this way some Green's functions in conformal field theories are shown to have structures more general than those commonly found by use of the inversion operator. These methods fit in well with the assumption of AdS/CFT duality. In particular, it is transparent that if fields on AdS$_5$ approach finite limits on the boundary of AdS$_5$, then in the conformal field theory on this boundary these limits transform with conformal dimensionality zero if they are tensors (of any rank), but with conformal dimension 1/2 if they are spinors or spinor-tensors.

 

[marcus]

Someone at Beyond forum was asking about BFL Ward's work on resummed QG. Here's a new paper.
http://arxiv.org/abs/1008.1046
An Estimate of Λ in Resummed Quantum Gravity in the Context of Asymptotic Safety
B.F.L. Ward (1) ((1) Department of Physics, Baylor University, Waco, TX, USA)
(Submitted on 5 Aug 2010)
"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 Λ. We find the encouraging estimate $$\rho_\Lambda\equiv \frac{\Lambda}{8\pi G_N} \simeq (2.379\times 10^{-3}eV)^4$$ "

I remember now! It was Murray92 who was asking about Ward's work. https://www.physicsforums.com/showthread.php?p=2813182#post2813182
Here is another Ward paper that just appeared on arxiv.

http://arxiv.org/abs/1008.1052
"Low'' Energy GUTs
B.F.L. Ward (1) ((1) Department of Physics, Baylor University, Waco, TX, USA)
9 pages
(Submitted on 5 Aug 2010)
"We introduce a new approach to the subject of grand unification which allows the GUT scale to be small, \lesssim 200 TeV, so that it is within the reach of {\em conceivable} laboratory accelerated colliding beam devices. Central to the approach is a novel abstraction of the heterotic string symmetry group physics ideas to render baryon number violating effects small enough to have escaped detection to date."

This Chamseddine Connes paper is a good explanation of their NCG+standard model for a wide audience. It communicates the basics without showing a lot of calculation.
http://arxiv.org/abs/1008.0985
Space-Time from the spectral point of view
Ali H. Chamseddine, Alain Connes
19 pages. To appear in the Proceedings of the 12th Marcel Grossmann meeting
(Submitted on 5 Aug 2010)
"We develop the spectral point of view on geometry based on the formalism of quantum physics. We start from the simple physical question of specifying our position in space and explain how the spectral geometric point of view provides a new paradigm to model space-time whose fine structure can be encoded by a finite geometry. The classification of the irreducible finite geometries of KO-dimension 6 singles out a "symplectic--unitary" candidate F, which when used as the fine texture of space-time delivers from pure gravity on M x F the Standard Model coupled to gravity and, once extrapolated to unification scale, gives testable predictions."

 

[MTd2]

http://arxiv.org/abs/1008.1045

Quantum Gravity via Manifold Positivity

Michael Freedman
(Submitted on 5 Aug 2010)
The macroscopic dimensions of space should not be input but rather output of a general model for physics. Here, dimensionality arises from a recently discovered mathematical bifurcation: positive versus indefinite manifold pairings. It is used to build an action on a formal chain of combinatorial space-times of arbitrary dimension. The context for such actions is 2-field theory where Feynman integrals are not over classical, but previously quantized configurations. A topologically enforced singularity of the action terminates the dimension at four and, in fact, the final fourth dimension is Lorentzian due to light-like vectors in the four dimensional manifold pairing. Our starting point is the action of causal dynamical triangulations but in a dimension-agnostic setting. It is encouraging that some hint of extra small dimensions emerges from our action.

 

[atyy]

http://focus.aps.org/story/v26/st6
http://arxiv.org/abs/1007.1130
Metric Signature Transitions in Optical Metamaterials
Igor I. Smolyaninov, Evgenii E. Narimanov
(Submitted on 7 Jul 2010)
We demonstrate that the extraordinary waves in indefinite metamaterials experience (- - + +) effective metric signature. During a metric signature change transition in such a metamaterial, a Minkowski space-time is "created" together with large number of particles populating this space-time. Such metamaterial models provide a table top realization of metric signature change events suggested to occur in Bose-Einstein condensates and quantum gravity theories.

 

[member 11137]

http://arxiv.org/abs/1008.0283
Unknown system boundaries cannot be determined within quantum Darwinism
Authors: Chris Fields
(Submitted on 2 Aug 2010)
Abstract: Observers restricted to interactions with environmental degrees of freedom that nondestructively encode pointer states of a system of interest S cannot determine from such interactions which degrees of freedom of S interact directly or indirectly with the environment E. Without a specification of the S-E boundary, such observers cannot use einselection and quantum Darwinism to calculate the pointer states of S or their environmental encodings. Quantum Darwinism requires S-E boundary specifications assumed or stipulated on the basis of classical-scale observations, and therefore cannot be regarded as providing a predictive, purely quantum-mechanical explanation of the "emergence" of classicality.

http://arxiv.org/abs/1008.0373
Little Boxes: The Simplest Demonstration of the Failure of Einstein's Attempt to Show the Incompleteness of Quantum Theory
Authors: John D. Norton
(Submitted on 2 Aug 2010)
Abstract: The failure of Einstein's co-authored "EPR" attempt to show the incompleteness of quantum theory is demonstrated directly for spatial degrees of freedom using only elementary notions. A GHZ construction is realized in the position properties of three particles whose quantum waves are distributed over three two-chambered boxes. The same system is modeled more realistically using three spatially separated, singly ionized hydrogen molecules.

http://arxiv.org/abs/1008.0033
Emergent Photons and Gravitons:The Problem of Vacuum Structure
Authors: J. D. Bjorken
(Submitted on 30 Jul 2010)
Abstract: We discuss vacuum condensates associated with emergent QED and with torsion, as well as the possible role of the Kodama wave function in quantum cosmology

http://arxiv.org/abs/1008.0154
Gauge Theories under Incorporation of a Generalized Uncertainty Principle
Authors: Martin Kober
(Submitted on 1 Aug 2010)
Abstract: It 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 it 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.

Thanks Marcus for all these very interesting references (I like the Bjorken's article on emergent photons and gravitons) and the introduction of considerations concerning the torsion into the theory. Respect for Martin Kober.

 

[marcus]

Blackforest,
Thanks go to John86 for spotting the papers you mentioned! However we don't usually include comment/discussion in this bibliography thread. Including more than an occasional very brief comment would risk overloading the thread. Please feel free to start a separate thread for discussion of any paper(s) you find especially interesting, or to send us PMs (private messages) related to this collection of links to articles.

 

[marcus]

http://arxiv.org/abs/1008.1196
The gravitational effect of the vacuum
George F. R. Ellis, Jeff Murugan, Henk van Elst
(Submitted on 6 Aug 2010)
"The quantum field theoretic prediction for the vacuum energy density leads to a value for the effective cosmological constant that is incorrect by between 60 to 120 orders of magnitude. We review an old proposal of replacing Einstein's Field Equations by their trace-free part (the Trace-Free Einstein Equations), together with an independent assumption of energy--momentum conservation by matter fields. We confirm that while this does not solve the fundamental issue of why the cosmological constant has the value it has, it is indeed a viable theory that resolves the problem of the discrepancy between the vacuum energy density and the observed value of the cosmological constant. We also point out that this proposal may have a valid quantum field theory basis in terms of a spin-2 field theory for the graviton interaction with matter."

Briefly noted (partly because of the authors' prominence)
http://arxiv.org/abs/1008.1066
Born in an Infinite Universe: a Cosmological Interpretation of Quantum Mechanics
Anthony Aguirre, Max Tegmark, David Layzer
17 pages, 2 figures
(Submitted on 5 Aug 2010)
"We study the quantum measurement problem in the context of an infinite, statistically uniform space, as could be generated by eternal inflation. It has recently been argued that when identical copies of a quantum measurement system exist, the standard projection operators and Born rule method for calculating probabilities must be supplemented by estimates of relative frequencies of observers. We argue that an infinite space actually renders the Born rule redundant, by physically realizing all outcomes of a quantum measurement in different regions..."

 

[marcus]

http://arxiv.org/abs/1008.1312
Comment on arXiv:1007.0718 by Lee Smolin
Sabine Hossenfelder
(Submitted on 7 Aug 2010)
"In a recent paper it was suggested a novel interpretation of deformed special relativity. In that new approach, nonlocal effects that had previously been shown to occur and be incompatible with experiment to high precision, are interpreted as coordinate artifacts that do not lead to real physical consequences. It is argued here that if one follows through the consequences of this thought, one finds that the theory one is dealing with needs to be ordinary special relativity to precision even better than the bound on nonlocal effect already requires. Consequently, the new approach cannot be understood as a version of deformed special relativity that circumvents the bound."

http://arxiv.org/abs/1008.1340
Properties of Quantum Graphity at Low Temperature
Francesco Caravelli, Fotini Markopoulou
19 pages, 4 figures
(Submitted on 7 Aug 2010)
"We present a mapping of dynamical graphs, and, in particular, the graphs used in the Quantum Graphity models for emergent geometry, into an Ising hamiltonian on the line graph of a complete graph with a fixed number of vertices. We use this method to study the properties of Quantum Graphity models at low temperature in the limit in which the valence coupling constant of the model is much greater than the coupling constants of the loop terms. Using mean field theory we find that an order parameter for the model is the average valence of the graph. We calculate the equilibrium distribution for the valence as an implicit function of the temperature. In the approximation in which the temperature is low, we find the first two Taylor coefficients of the valence in the temperature expansion. A discussion of the susceptibility function and a generalization of the model are given in the end."

 

[marcus]

http://arxiv.org/abs/1008.1759
Unimodular loop quantum gravity and the problems of time
Lee Smolin
14 pages
(Submitted on 10 Aug 2010)
"We develop the quantization of unimodular gravity in the Plebanski and Ashtekar formulations and show that the quantum effective action defined by a formal path integral is unimodular. This means that the effective quantum geometry does not couple to terms in the expectation value of the energy-momentum tensor proportional to the metric tensor. The path integral takes the same form as is used to define spin foam models, with the additional constraint that the determinant of the four metric is constrained to be a constant by a gauge fixing term. We also review the proposal of Unruh, Wald and Sorkin--that the hamiltonian quantization yields quantum evolution in a physical time variable equal to elapsed four volume--and discuss how this may be carried out in loop quantum gravity. This then extends the results of arXiv:0904.4841 to the context of loop quantum gravity."

 

[ensabah6]

Still searching for SUSY -- the discovery of SUSY is direct relevance to QG

http://arxiv.org/abs/1008.0407

High Energy Physics - Phenomenology
Title: It's On: Early Interpretations of ATLAS Results in Jets and Missing Energy Searches
Authors: Daniele S. M. Alves, Eder Izaguirre, Jay G. Wacker
(Submitted on 2 Aug 2010)

Abstract: The first search for supersymmetry from ATLAS with 70/nb of integrated luminosity sets new limits on colored particles that decay into jets plus missing transverse energy. For gluinos that decay directly or through a one step cascade into the LSP and two jets, these limits translate into a bound of m_g > 205 GeV, regardless of the mass of the LSP. In some cases the limits extend up to m_g ~= 295 GeV, already surpassing the Tevatron's reach for compressed supersymmetry spectra.

Comments: 5 pages, 3 figures, 1 table
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex)
Cite as: arXiv:1008.0407v1 [hep-ph]

 

[marcus]

Actual experimental aparatus, measurements and all that, see figure 2 on page 6
http://arxiv.org/abs/1008.1911
Measurement of stimulated Hawking emission in an analogue system
Silke Weinfurtner, Edmund W. Tedford, Matthew C. J. Penrice, William G. Unruh, Gregory A. Lawrence
(Submitted on 11 Aug 2010)
"There is a mathematical analogy between the propagation of fields in a general relativistic space-time and long (shallow water) surface waves on moving water. Hawking argued that black holes emit thermal radiation via a quantum spontaneous emission. Similar arguments predict the same effect near wave horizons in fluid flow. By placing a streamlined obstacle into an open channel flow we create a region of high velocity over the obstacle that can include wave horizons. Long waves propagating upstream towards this region are blocked and converted into short (deep water) waves. This is the analogue of the stimulated emission by a white hole (the time inverse of a black hole), and our measurements of the amplitudes of the converted waves demonstrate the thermal nature of the conversion process for this system. Given the close relationship between stimulated and spontaneous emission, our findings attest to the generality of the Hawking process."

The next is by an author who comes to Quantum Field Theory from the direction of condensed matter, which is his main specialty at ETH Zürich. Posted in case others are especially interested in that approach--I personally cannot judge the merit.

http://arxiv.org/abs/1008.1867
Dynamic coarse-graining approach to quantum field theory
Hans Christian Öttinger
4 pages
(Submitted on 11 Aug 2010)
"We build quantum field theory on the thermodynamic master equation for dissipative quantum systems. The vacuum is represented by a thermodynamic equilibrium state; even in the low-temperature limit, the population and evolution of excited states matter. All regularization is consistently provided by a friction mechanism; with decreasing friction parameter, only shorter and shorter scales are damped out of a quantum field theory. No divergent integrals need to be manipulated, no counterterms need to be invented. Relativistic covariance is recovered in the final results. We illustrate the proposed thermodynamic approach to quantum fields for the phi⁴ theory."

 

[marcus]

http://arxiv.org/abs/1008.2768
Asymptotic Safety, Singularities, and Gravitational Collapse
Roberto Casadio, Stephen D.H. Hsu, Behrouz Mirza
6 pages
(Submitted on 16 Aug 2010)
"Asymptotic safety (an ultraviolet fixed point with finite-dimensional critical surface) offers the possibility that a predictive theory of quantum gravity can be obtained from the quantization of classical general relativity. However, it is unclear what becomes of the singularities of classical general relativity, which, it is hoped, might be resolved by quantum effects. We study dust collapse with a running gravitational coupling and find that a future singularity can be avoided if the coupling becomes exactly zero at some finite energy scale. The singularity can also be avoided (pushed off to infinite proper time) if the coupling approaches zero sufficiently rapidly at high energies. However, the evolution deduced from perturbation theory still implies a singularity at finite proper time."

Noted in view of author's prominence:
http://arxiv.org/abs/1008.2764
Nonlocality as Evidence for a Multiverse Cosmology
Frank J. Tipler
(Submitted on 16 Aug 2010)
"I show that observations of quantum nonlocality can be interpreted as purely local phenomena, provided one assumes that the cosmos is a multiverse..."

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

http://arxiv.org/abs/1008.2962
Kinematics of a relativistic particle with de Sitter momentum space
Michele Arzano, Jerzy Kowalski-Glikman
12 pages
(Submitted on 17 Aug 2010)
"We discuss kinematical properties of a free relativistic particle with deformed phase space in which momentum space is given by (a submanifold of) de Sitter space. We provide a detailed derivation of the action, Hamiltonian structure and equations of motion for such free particle. We study the action of deformed relativistic symmetries on the phase space and derive explicit formulas for the action of the deformed Poincare' group. Finally we provide a discussion on parametrization of the particle worldlines stressing analogies and differences with ordinary relativistic kinematics."

 

[MTd2]

Asymptotic safety bibliography on Percacci's website.

http://www.percacci.it/roberto/physics/as/biblio.html

This is constantly updated. From the beginnings to the actual days.

 

[MTd2]

Another answer to the Smolin vs. Bee discussion about VSL:

http://arxiv.org/abs/1008.2962

Kinematics of a relativistic particle with de Sitter momentum space

Michele Arzano, Jerzy Kowalski-Glikman
(Submitted on 17 Aug 2010)
We discuss kinematical properties of a free relativistic particle with deformed phase space in which momentum space is given by (a submanifold of) de Sitter space. We provide a detailed derivation of the action, Hamiltonian structure and equations of motion for such free particle. We study the action of deformed relativistic symmetries on the phase space and derive explicit formulas for the action of the deformed Poincare' group. Finally we provide a discussion on parametrization of the particle worldlines stressing analogies and differences with ordinary relativistic kinematics.

 

[John86]

something different from Stu Kauffman

http://www.npr.org/blogs/13.7/2010/08/17/129250892/res-extensa-res-potentia-and-the-poised-realm

 

[MTd2]

http://arxiv.org/abs/1008.3345

Deformed Special Relativity from Asymptotically Safe Gravity

Xavier Calmet, Sabine Hossenfelder, Roberto Percacci
(Submitted on 19 Aug 2010)
By studying the notion of a fundamentally minimal length scale in asymptotically safe gravity we find that a specific version of deformed special relativity (DSR) naturally arises in this approach. We then consider two thought experiments to examine the interpretation of the scenario and discuss similarities and differences to other approaches to DSR.

 

[atyy]

http://arxiv.org/abs/1008.3439
Measuring Black Hole Formations by Entanglement Entropy via Coarse-Graining
Tadashi Takayanagi, Tomonori Ugajin
(Submitted on 20 Aug 2010)
We argue that the entanglement entropy offers us a useful coarse-grained entropy in time-dependent AdS/CFT. We show that the total von-Neumann entropy remains vanishing even when a black hole is created in a gravity dual, being consistent with the fact that its corresponding CFT is described by a time-dependent pure state. We analytically calculate the time evolution of entanglement entropy for a free Dirac fermion on a circle following a quantum quench. This is interpreted as a toy holographic dual of black hole creations and annihilations. It is manifestly free from the black hole information problem.

http://arxiv.org/abs/1008.3494
Measurement of Hawking Radiation with Ions in the Quantum Regime
Birger Horstmann, Ralf Schützhold, Benni Reznik, Serena Fagnocchi, J. Ignacio Cirac
(Submitted on 20 Aug 2010)
Abstract: This article discusses a recent proposal for the simulation of acoustic black holes with ions http://arxiv.org/abs/0904.4801. The ions are rotating on a ring with an inhomogeneous, but stationary velocity profile. Phonons cannot leave a region, in which the ion velocity exceeds the group velocity of the phonons, like light cannot escape from a black hole. The system is described by a discrete field theory with a nonlinear dispersion relation. Hawking radiation is emitted by the black hole, generating entanglement between its inside and its outside. We study schemes to detect the Hawking effect in this setup.

 

[marcus]

http://arxiv.org/abs/1008.3621
Asymptotic Safety, Emergence and Minimal Length
R. Percacci, G. P. Vacca
20 pages, 2 figures
(Submitted on 21 Aug 2010)
"There seems to be a common prejudice that asymptotic safety is either incompatible with, or at best unrelated to, the other topics in the title. This is not the case. In fact, we show that 1) the existence of a fixed point with suitable properties is a promising way of deriving emergent properties of gravity, and 2) there is a precise sense in which asymptotic safety implies a minimal length. In so doing we also discuss possible signatures of asymptotic safety in scattering experiments."

 

[MTd2]

http://arxiv.org/abs/1008.3886

The Photon Dispersion as an Indicator for New Physics ?

Wolfgang Bietenholz
(Submitted on 23 Aug 2010)
We first comment on the search for a deviation from the linear photon dispersion relation, in particular based on cosmic photons from Gamma Ray Bursts. Then we consider the non-commutative space as a theoretical concept that could lead to such a deviation, which would be a manifestation of Lorentz Invariance Violation. In particular we review a numerical study of pure U(1) gauge theory in a 4d non-commutative space. Starting from a finite lattice, we explore the phase diagram and the extrapolation to the continuum and infinite volume. These simultaneous limits - taken at fixed non-commutativity - lead to a phase of broken Poincare symmetry, where the photon appears to be IR stable, despite a negative IR divergence to one loop.

 

[marcus]

http://arxiv.org/abs/1008.4093
Lifting SU(2) Spin Networks to Projected Spin Networks
Maité Dupuis, Etera R. Livine
14 pages
(Submitted on 24 Aug 2010)
"Projected spin network states are the canonical basis of quantum states of geometry for the most recent EPR-FK spinfoam models for quantum gravity. They are functionals of both the Lorentz connection and the time normal field. We analyze in details the map from these projected spin networks to the standard SU(2) spin networks of loop quantum gravity. We show that this map is not one-to-one and that the corresponding ambiguity is parameterized by the Immirzi parameter. We conclude with a comparison of the scalar products between projected spin networks and SU(2) spin network states."

http://arxiv.org/abs/1008.3980
Noncommutative Geometric Spaces with Boundary: Spectral Action
Ali H. Chamseddine, Alain Connes
26 pages
(Submitted on 24 Aug 2010)
"We study spectral action for Riemannian manifolds with boundary, and then generalize this to noncommutative spaces which are products of a Riemannian manifold times a finite space. We determine the boundary conditions consistent with the hermiticity of the Dirac operator. We then define spectral triples of noncommutative spaces with boundary. In particular we evaluate the spectral action corresponding to the noncommutative space of the standard model and show that the Einstein-Hilbert action gets modified by the addition of the extrinsic curvature terms with the right sign and coefficient necessary for consistency of the Hamiltonian. We also include effects due to the addition of dilaton field."

 

[marcus]

http://arxiv.org/abs/1008.4351
Stability of the aether
William Donnelly, Ted Jacobson
4 pages
(Submitted on 25 Aug 2010)
"The requirements for stability of a Lorentz violating theory are analyzed. In particular we conclude that Einstein-aether theory can be stable when its modes have any phase velocity, rather than only the speed of light as was argued in a recent paper."

 

[MTd2]

http://arxiv.org/abs/1008.4147

Emergent Gauge Fields

Peter G.O. Freund
(Submitted on 24 Aug 2010)
Erik Verlinde's proposal of the emergence of the gravitational force as an entropic force is extended to abelian and non-abelian gauge fields and to matter fields. This suggests a picture with no fundamental forces or forms of matter whatsoever.

 

[marcus]

http://arxiv.org/abs/1008.4787
Comment on Asymptotically Safe Inflation
S.-H. Henry Tye, Jiajun Xu
4 pages
(Submitted on 27 Aug 2010)
"We comment on Weinberg's interesting analysis of asymptotically safe inflation (arXiv:0911.3165). We find that even if the gravity theory exhibits an ultraviolet fixed point, the energy scale during inflation is way too low to drive the theory close to the fixed point value. We choose the specific renormalization groupflow away from the fixed point towards the infrared region that reproduces the Newton's constant and today's cosmological constant. We follow this RG flow path to scales below the Planck scale to study the stability of the inflationary scenario. Again, we find that some fine tuning is necessary to get enough efolds of infflation in the asymptotically safe inflationary scenario."
[edit: http://arxiv.org/abs/0912.4093 ?]

 

[MTd2]

http://arxiv.org/abs/1008.4805

Space-time and special relativity from causal networksGiacomo Mauro D'Ariano, Alessandro Tosini
(Submitted on 27 Aug 2010)
We show how the Minkowskian space-time emerges from a topologically homogeneous causal network, presenting a simple analytical derivation of the Lorentz transformations, with metric as pure event-counting. The derivation holds generally for d=1 space dimension, however, it can be extended to d>1 for special causal networks.

 

[MTd2]

http://arxiv.org/abs/1008.5132

Massive Gravity: Resolving the Puzzles

Lasma Alberte, Ali H. Chamseddine, Viatcheslav Mukhanov
(Submitted on 30 Aug 2010)
We consider the massless limit of Higgs gravity, where the graviton becomes massive when the scalar fields acquire expectation values. We determine the Vainshtein scale and prove that massive gravity smoothly goes to General Relativity below this scale. We find that the Vainshtein scale depends on the particular action of scalar fields used to give mass to the graviton.