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Intuitive content of Loop GravityRovelli's programby marcus
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#1837
Nov112, 08:24 PM

Astronomy
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PF Gold
P: 23,084

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


#1838
Nov512, 12:11 AM

Astronomy
Sci Advisor
PF Gold
P: 23,084

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


#1839
Nov512, 07:18 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

http://arxiv.org/abs/1211.0823
Polymer quantization and Symmetries Ghanashyam Date, Nirmalya Kajuri (Submitted on 5 Nov 2012) Polymer quantization was discovered during the construction of Loop Quantum Cosmology. For the simplest quantum theory of one degree of freedom, the implications for dynamics were studied for the harmonic oscillator as well as some other potentials. For more degrees of freedom, the possibility of continuous, kinematic symmetries arises. While these are realised on the Hilbert space of polymer quantum mechanics, their infinitesimal versions are not supported. For an invariant Hamiltonian, these symmetry realizations imply infinite degeneracy suggesting that the symmetry should be spontaneously or explicitly broken. The estimation of symmetry violations in some cases have been analysed before. Here we explore the alternative of shifting the arena to the distributional states. We discuss both the polymer quantum mechanics case as well as polymer quantized scalar field. 18 pages http://arxiv.org/abs/1211.0825 Going beyond the Standard Model with noncommutative geometry Thijs van den Broek, Walter D. van Suijlekom (Submitted on 5 Nov 2012) The derivation of the full Standard Model from noncommutative geometry has been a promising sign for possible applications of the latter in High Energy Physics. Many believe, however, that the Standard Model cannot be the final answer. We translate several demands whose origin lie in physics to the context of noncommutative geometry and use these to put constraints on the fermionic content of models. We show that the Standard Model only satisfies these demands provided it has a righthanded neutrino in each 'generation'. We also prove that the Minimal Supersymmetric Standard Model is not among the models that satisfy our constraints, but pose a solution that is a slight extension of the MSSM. 19 pages 


#1840
Nov612, 07:12 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

http://arxiv.org/abs/1211.1354
An Extension of the Quantum Theory of Cosmological Perturbations to the Planck Era Ivan Agullo, Abhay Ashtekar, William Nelson (Submitted on 6 Nov 2012) Cosmological perturbations are generally described by quantum fields on (curved but) classical spacetimes. While this strategy has a large domain of validity, it can not be justified in the quantum gravity era where curvature and matter densities are of Planck scale. Using techniques from loop quantum gravity, the standard theory of cosmological perturbations is extended to overcome this limitation. The new framework sharpens conceptual issues by distinguishing between the true and apparent transPlanckian difficulties and provides sufficient conditions under which the true difficulties can be overcome within a quantum gravity theory. In a companion paper, this framework is applied to the standard inflationary model, with interesting implications to theory as well as observations. 50 pages. This is first of the two detailed papers on which arXiv 1209.1609 (PRL at press) is based http://arxiv.org/abs/1211.1244 SchwingerDyson Equations in Group Field Theories of Quantum Gravity Thomas Krajewski (Submitted on 6 Nov 2012) In this talk, we elaborate on the operation of graph contraction introduced by Gurau in his study of the SchwingerDyson equations. After a brief review of colored tensor models, we identify the Lie algebra appearing in the SchwingerDyson equations as a Lie algebra associated to a Hopf algebra of the ConnesKreimer type. Then, we show how this operation also leads to an analogue of the Wilsonian flow for the effective action. Finally, we sketch how this formalism may be adapted to group field theories. 6 pages. Talk given at "The XXIX International Colloquium on GroupTheoretical Methods in Physics", Chern Institute of Mathematics August 2012, submitted to the conference proceedings 


#1841
Nov612, 09:12 PM

PF Gold
P: 1,955

http://arxiv.org/abs/1211.1131
A Construct of Dynamics, Space and Gravity from Loops Madhavan Venkatesh (Submitted on 6 Nov 2012) An attempt is made to construct space and obtain dynamics from Loop Algebras and their elements. We define three new products between loops namely 'Vertical Product', 'Horizontal Product' and 'Total Product'. As for the dynamics, we obtain corresponding "velocity" and "canonical momenta" from it. Also, we build a new "Energy Variable" that is dependent on the velocity and momentum alone. Then, we apply the loop constructs to General Relativity and arrive at the Einstein Field Equations, although presented in a different form. The key feature of this formalism is that the metric is not arbitarized as prevalent on the space beforehand but is rather induced by restricting the Killing Form to the Cartan Subalgebra of the underlying Lie Algebra. Then we go on to show that "Dynamics is Structure" and that both do not depend on length or time. 


#1842
Nov1112, 07:14 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

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


#1843
Nov1212, 07:33 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

http://arxiv.org/abs/1211.2702
Dynamical evaporation of quantum horizons Daniele Pranzetti (Submitted on 12 Nov 2012) We describe the black hole evaporation process driven by the dynamical evolution of the quantum gravitational degrees of freedom resident at the horizon, as identified by the Loop Quantum Gravity kinematics. Using a parallel with the Brownian motion, we interpret the first law of quantum dynamical horizon in terms of a fluctuationdissipation relation applied to this fundamental discrete structure. In this way, the horizon evolution is described in terms of relaxation to an equilibrium state balanced by the excitation of Planck scale constituents of the horizon. We investigate the final stage of the evaporation process and show how, from this setting, the emergence of several conservative scenarios for the information paradox can be microscopically derived. Namely, the leakage of part of the horizon quantum geometry information prior to the Planckian phase and the stabilization of the hole surface shrinkage forming a massive remnant, which can eventually decay, are described. 14 pages, 2 figures http://arxiv.org/abs/1211.2731 Horizon thermodynamics and composite metrics Lorenzo Sindoni (Submitted on 12 Nov 2012) We examine the conditions under which the thermodynamic behaviour of gravity can be explained within an emergent gravity scenario, where the metric is defined as a composite operator. We show that due to the availability of a boundary of a boundary principle for the quantum effective action, Clausiuslike relations can always be constructed. Hence, any true explanation of the thermodynamic nature of the metric tensor has to be referred to an equilibration process, associated to the presence of an Htheorem, possibly driven by decoherence induced by the pregeometric degrees of freedom, and their entanglement with the geometric ones. 11 pages, 1 figure 


#1844
Nov1812, 07:19 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

not QG but possibly of interest to quantum relativists:
http://arxiv.org/abs/1211.3880 The symplectic 2form for gravity in terms of free null initial data Michael P. Reisenberger (Submitted on 16 Nov 2012) A hypersurface formed of two null sheets, or "light fronts", swept out by the future null normal geodesics emerging from a common spacelike 2disk can serve as a Cauchy surface for a region of spacetime. Already in the 1960s free (unconstrained) initial data for general relativity were found for such hypersurfaces. Here an expression is obtained for the symplectic 2form of vacuum general relativity in terms of such free data. This can be done, even though variations of the geometry do not in general preserve the nullness of the initial hypersurface, because of the diffeomorphism gauge invariance of general relativity. The present expression for the symplectic 2form has been used previously to calculate the Poisson brackets of the free data. 44 pages, 2 figures http://arxiv.org/abs/1211.3816 Is a tabletop search for Planck scale signals feasible? Jacob D. Bekenstein (Submitted on 16 Nov 2012) Quantum gravity theory is untested experimentally. Could it be tested with tabletop experiments? While the common feeling is pessimistic, a detailed inquiry shows it possible to sidestep the onerous requirement of localization of a probe on Planck length scale. I suggest a tabletop experiment which, given state of the art ultrahigh vacuum and cryogenic technology, could already be sensitive enough to detect Planck scale signals. The experiment combines a single photon's degree of freedom with one of a macroscopic probe to test Wheeler's conception of "spacetime foam", the assertion that on length scales of the order Planck's, spacetime is no longer a smooth manifold. The scheme makes few assumptions beyond energy and momentum conservations, and is not based on a specific quantum gravity scheme. 8 pages, 2 figures 


#1845
Nov1912, 07:16 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

http://arxiv.org/abs/1211.4183
Loop quantum BransDicke cosmology Xiangdong Zhang, Yongge Ma (Submitted on 18 Nov 2012) The spatially flat and isotropic cosmological model of BransDicke theory with coupling parameter ω ≠ 3/2 is quantized by the approach of loop quantum cosmology. An interesting feature of this model is that, although the BransDicke scalar field is nonminimally coupled with curvature, it can still play the role of an emergent time variable. In the quantum theory, the classical differential equation which represents cosmological evolution is replaced by a quantum difference equation. The effective Hamiltonian and modified dynamical equations of loop quantum BransDicke cosmology are also obtained, which lay a foundation for the phenomenological investigation to possible quantum gravity effects in cosmology. The effective equations indicate that the classical big bang singularity is again replaced by a quantum bounce in loop quantum BransDicke cosmology. 11pages http://arxiv.org/abs/1211.4151 Lectures on renormalization and asymptotic safety Sandor Nagy (Submitted on 17 Nov 2012) A short introduction is given on the functional renormalization group method, putting emphasis on its nonperturbative aspects. The method enables to find nontrivial fixed points in quantum field theoretic models which make them free from divergences and leads to the concept of asymptotic safety. It can be considered as a generalization of the asymptotic freedom which plays a key role in the perturbative renormalization. We summarize and give a short discussion of some important models, which are asymptotically safe such as the GrossNeveu model, the nonlinear σ model, the sineGordon model, and the model of quantum Einstein gravity. We also give a detailed analysis of infrared behavior of the models where a spontaneous symmetry breaking takes place. The deep infrared behavior of the broken phase cannot be treated within the framework of perturbative calculations. We demonstrate that there exists an infrared fixed point in the broken phase which creates a new scaling regime there, however its structure is hidden by the singularity of the renormalization group equations. The phase spaces of these models show several similar properties, namely the models has the same phase and fixed point structure. These results can only be uncovered by the functional renormalization group method. 32 pages, 20 figures. Based on the talk presented at the Theoretical Physics School on Quantum Gravity, Szeged, Hungary, 2731 August 2012 


#1846
Nov2012, 07:33 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

http://arxiv.org/abs/1211.4807
Holonomyflux spinfoam amplitude Claudio Perini (Submitted on 20 Nov 2012) We introduce a holomorphic representation for the Lorentzian EPRL spinfoam on arbitrary 2complexes. The representation is obtained via the AshtekarLewandowskiMarolfMouraoThiemann heat kernel coherent state transform. The new variables are classical holonomyflux phase space variables (h,X) ≈ T*SU(2) of Hamiltonian loop quantum gravity prescribing the holonomies of the Ashtekar connection A = Γ + γK, and their conjugate gravitational fluxes. For small heat kernel 'time' the spinfoam amplitude is peaked on classical spacetime geometries, where at most countably many curvatures are allowed for nonzero BarberoImmirzi parameter. We briefly comment on the possibility to use the alternative flipped classical limit. 33 pages not QG but possibly of interest: http://arxiv.org/abs/1211.4848 Scrutinizing the Cosmological Constant Problem and a possible resolution Denis Bernard, André LeClair (Submitted on 20 Nov 2012) We suggest a new perspective on the Cosmological Constant Problem by scrutinizing its standard formulation. In classical and quantum mechanics without gravity, there is no definition of the zero point of energy. Furthermore, the Casimir effect only measures how the vacuum energy changes as one varies a geometric modulus. This leads us to propose that the physical vacuum energy in a FriedmanLemaitreRobertsonWalker expanding universe only depends on the time variation of the scale factor a(t). Equivalently, requiring that empty Minkowski space is stable is a principle that fixes the ambiguity in the zero point energy. We describe two different choices of vacuum, one of which is consistent with the current universe consisting only of matter and vacuum energy. The resulting vacuum energy density is proportional to (k_{c}H_{0})^{2}, where k_{c} is a momentum cutoff and H_{0} is the Hubble constant; for a cutoff close to the Planck scale, values of the vacuum energy density in agreement with astrophysical measurements are obtained. Another choice of vacuum is more relevant to the early universe consisting of only radiation and vacuum energy, and we suggest it as a possible model of inflation. 22 pages, 1 figure 


#1847
Nov2112, 07:15 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

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


#1848
Nov2512, 07:10 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

http://arxiv.org/abs/1211.5180
Path Integral of Bianchi I models in Loop Quantum Cosmology Xiao Liu, Fei Huang, JianYang Zhu (Submitted on 22 Nov 2012) A path integral formulation of the Bianchi I models containing a massless scalar field in loop quantum cosmology is constructed. Following the strategy used in the homogenous and isotropic case, the calculation is extended to the simplest nonisotropic models according to the μbar and μ'bar scheme. It is proved from the path integral angle that the quantum dynamic lacks the full invariance with respect to fiducial cell scaling in the μbar scheme, but it does not in the μ'bar scheme. The investigation affirms the equivalence of the canonical approach and the path integral approach in loop quantum cosmology. 10 pages http://arxiv.org/abs/1211.5310 Power spectrum and anisotropy of super inflation in loop quantum cosmology XiaoJun Yue, JianYang Zhu (Submitted on 22 Nov 2012) We investigate the scalar mode of perturbation of super inflation in the version of loop quantum cosmology in which the gauge invariant holonomy corrections are considered. Given a background solution, we calculate the power spectrum of the perturbation in the classical and LQC conditions. Then we compute the anisotropy originated from the perturbation. It is found that in the presence of the gauge invariant holonomy corrections the power spectrum is exponentially blue and the anisotropy also grows exponentially in the epoch of super inflation. 12 pages,4 figures My note: JianYang Zhu is at Beijing Normal (BNU) same department as Prof. Yongge Ma. 


#1849
Nov2612, 07:58 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

http://arxiv.org/abs/1211.5878
Frequently asked questions about Shape Dynamics H. Gomes, T. Koslowski (Submitted on 26 Nov 2012) Barbour's interpretation of Mach's principle led him to postulate that gravity should be formulated as a dynamical theory of spatial conformal geometry, or in his terminology, "shapes." Recently, it was shown that the dynamics of General Relativity can indeed be formulated as the dynamics of shapes. This new Shape Dynamics theory, unlike earlier proposals by Barbour and his collaborators, implements local spatial conformal invariance as a gauge symmetry that replaces refoliation invariance in General Relativity. It is the purpose of this paper to answer frequent questions about (new) Shape Dynamics, such as its relation to Poincaré invariance, General Relativity, Constant Mean (extrinsic) Curvature gauge, earlier Shape Dynamics, and finally the conformal approach to the initial value problem of General Relativity. Some of these relations can be clarified by considering a simple model: free electrodynamics and its dual shift symmetric formulation. This model also serves as an example where symmetry trading is used for usual gauge theories. 19 pages http://arxiv.org/abs/1211.5939 Action principle for the connection dynamics of scalartensor theories Zhenhua Zhou, Haibiao Guo, Yu Han, Yongge Ma (Submitted on 26 Nov 2012) A firstorder action for scalartensor theories of gravity is proposed. The Hamiltonian analysis of the action gives a connection dynamical formalism, which is equivalent to the connection dynamics derived from the geometrical dynamics by canonical transformations. Therefore, the action principle underlying loop quantum scalartensor theories is recovered. 5 pages http://arxiv.org/abs/1211.5714 The quantum geometry of tensorial group field theories Daniele Oriti (Submitted on 24 Nov 2012) We remark the importance of adding suitable pregeometric content to tensor models, obtaining what has recently been called tensorial group field theories, to have a formalism that could describe the structure and dynamics of quantum spacetime. We also review briefly some recent results concerning the definition of such pregeometric content, and of models incorporating it. 6 pages; contribution to the proceedings of The XXIX International Colloquium on GroupTheoretical Methods in Physics, August 2026, 2012, Chern Institute of Mathematics, Tianjin, China 


#1850
Nov2712, 07:21 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

http://arxiv.org/abs/1211.6269
The Matter Bounce Scenario in Loop Quantum Cosmology Edward WilsonEwing (Submitted on 27 Nov 2012) In the matter bounce scenario, a dustdominated contracting spacetime generates scaleinvariant perturbations that, assuming a nonsingular bouncing cosmology, propagate to the expanding branch and set appropriate initial conditions for the radiationdominated era. Since this scenario depends on the presence of a bounce, it seems appropriate to consider it in the context of loop quantum cosmology where a bouncing universe naturally arises. It turns out that quantum gravity effects play an important role beyond simply providing the bounce. Indeed, quantum gravity corrections to the MukhanovSasaki equations significantly modify some of the results obtained in a purely classical setting: while the predicted spectra of scalar and tensor perturbations are both almost scaleinvariant with identical small red tilts in agreement with previous results, the tensor to scalar ratio is now expected to be r≈ 9 x 10^{4}, which is much smaller than the original classical prediction. Finally, for the predicted amplitude of the scalar perturbations to agree with observations, the critical density in loop quantum cosmology must be of the order ρ_{crit} ~ 10^{9} ρ_{Planck}. 8 pages [My comment: !!!] brief mention: http://arxiv.org/abs/1211.6337 The Cosmological Constant Alex Harvey (Submitted on 23 Nov 2012) Contrary to popular mythology, Einstein did not invent the cosmological constant just in order construct his model universe. He discussed it earlier in "The Foundations of General Relativity" in connection with the proper structure of the sourcefree field equations. There he dismissed it as arbitrary and unnecessary. It was later that he found its inclusion to be essential to the construction of his model. 3 pages 


#1851
Nov3012, 02:45 AM

P: 246

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


#1852
Dec212, 09:40 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

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


#1853
Dec312, 06:04 AM

P: 246

http://arxiv.org/abs/1211.7122
Patterns in the fabric of nature Steven Weinstein (Submitted on 29 Nov 2012) From classical mechanics to quantum field theory, the physical facts at one point in space are held to be independent of those at other points in space. I propose that we can usefully challenge this orthodoxy in order to explain otherwise puzzling correlations at both cosmological and microscopic scales. http://arxiv.org/abs/1211.7081 The Universe is not a Computer Ken Wharton (Submitted on 29 Nov 2012) When we want to predict the future, we compute it from what we know about the present. Specifically, we take a mathematical representation of observed reality, plug it into some dynamical equations, and then map the timeevolved result back to realworld predictions. But while this computational process can tell us what we want to know, we have taken this procedure too literally, implicitly assuming that the universe must compute itself in the same manner. Physical theories that do not follow this computational framework are deemed illogical, right from the start. But this anthropocentric assumption has steered our physical models into an impossible corner, primarily because of quantum phenomena. Meanwhile, we have not been exploring other models in which the universe is not so limited. In fact, some of these alternate models already have a wellestablished importance, but are thought to be mathematical tricks without physical significance. This essay argues that only by dropping our assumption that the universe is a computer can we fully develop such models, explain quantum phenomena, and understand the workings of our universe. http://arxiv.org/abs/1211.7337 A linear theory underlying quantum mechanics Casey Blood (Submitted on 30 Nov 2012) Linearity allows several versions of reality to simultaneously exist in the state vector. But it implies that there is no interaction between versions, and that there will never be perception of more than one version. It also implies, in conjunction with group representation theory, that the particlelike properties of mass, energy, momentum, spin and charge are attributes of the state vectors. These results can be used to show there is no evidence for the objective existence of particles. The properties of the wave function are sufficient to explain all the particlelike properties of matter. Representation theory is also extensively employed in the Standard Model, with gauge fields transforming as representations of the internal symmetry group. And when applied to the permutation group, it is essential for understanding symmetric and antisymmetric states. In fact all of quantum mechanics is set up exactly as if it were the representation of an underlying prerepresentational theory. A linear equation structure for the underlying theory is suggested, and it is shown in outline how quantum field theory emerges as a representational form of the prerepresentational theory. http://arxiv.org/abs/1211.7070 Nonviolent nonlocality Steven B. Giddings (Submitted on 29 Nov 2012) If quantum mechanics governs nature, black holes must evolve unitarily, providing a powerful constraint on the dynamics of quantum gravity. Such evolution apparently must in particular be nonlocal, when described from the usual semiclassical geometric picture, in order to transfer quantum information into the outgoing state. While such transfer from a disintegrating black hole has the dangerous potential to be violent to generic infalling observers, this paper proposes the existence of a more innocuous form of information transfer, to relatively soft modes in the black hole atmosphere. Simplified models for such nonlocal transfer are described and parameterized, within a possibly more basic framework of a Hilbert tensor network. Sufficiently sensitive measurements by infalling observers may detect departures from Hawking's predictions, and in generic models black holes decay more rapidly. Constraints of consistency  internally and with known and expected features of physics  restrict the form of information transfer, and should provide important guides to discovery of the principles and mechanisms of the more fundamental nonlocal mechanics. 


#1854
Dec312, 08:54 PM

Astronomy
Sci Advisor
PF Gold
P: 23,084

http://arxiv.org/abs/1212.0454
Gravity can be neither classical nor quantized Sabine Hossenfelder (Submitted on 3 Dec 2012) I argue that it is possible for a theory to be neither quantized nor classical. We should therefore give up the assumption that the fundamental theory which describes gravity at shortest distances must either be quantized, or quantization must emerge from a fundamentally classical theory. To illustrate my point I will discuss an example for a theory that is neither classical nor quantized, and argue that it has the potential to resolve the tensions between the quantum field theories of the standard model and general relativity. 7 pages, third prize in the 2012 FQXi essay contest "Which of our basic physical assumptions are wrong?" http://arxiv.org/abs/1212.0371 Not on but of Olaf Dreyer (Submitted on 3 Dec 2012) In physics we encounter particles in one of two ways. Either as fundamental constituents of the theory or as emergent excitations. These two ways differ by how the particle relates to the background. It either sits on the background, or it is an excitation of the background. We argue that by choosing the former to construct our fundamental theories we have made a costly mistake. Instead we should think of particles as excitations of a background. We show that this point of view sheds new light on the cosmological constant problem and even leads to observable consequences by giving a natural explanation for the appearance of MONDlike behavior. In this context it also becomes clear why there are numerical coincidences between the MOND acceleration parameter, the cosmological constant and the Hubble parameter. 9 pages. This article received a forth prize in the 2012 FQXi essay contest "Questioning the Foundations". More articles from this contest can be found on the FQXi website at fqxi.org brief mention: http://arxiv.org/abs/1212.0500 Vector fields on C*algebras, semigroups of endomorphisms and gauge groups Innocenti Maresin 


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