scholarly journals Spacetime and Deformations of Special Relativistic Kinematics

Symmetry ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1401 ◽  
Author(s):  
José Manuel Carmona ◽  
José Luis Cortés ◽  
José Javier Relancio
Keyword(s):  
Quantum Gravity ◽  
Classical Level ◽  
Relativistic Kinematics ◽  
Interaction Processes ◽  
Low Energies ◽  
Decomposition Principle

A deformation of special relativistic kinematics (possible signal of a theory of quantum gravity at low energies) leads to a modification of the notion of spacetime. At the classical level, this modification is required when one considers a model including single- or multi-interaction processes, for which absolute locality in terms of canonical spacetime coordinates is lost. We discuss the different alternatives for observable effects in the propagation of a particle over very large distances that emerge from the new notion of spacetime. A central ingredient in the discussion is the cluster decomposition principle, which can be used to favor some alternatives over the others.

scholarly journals Is classical flat Kasner spacetime flat in quantum gravity?

2016 ◽  
Vol 25 (08) ◽  
pp. 1642001 ◽  
Author(s):  
Parampreet Singh
Keyword(s):  
Quantum Gravity ◽  
Minkowski Spacetime ◽  
Quantum Geometry ◽  
Classical Level ◽  
Bianchi I ◽  
Spacetime Curvature ◽  
Loop Quantization ◽  
Universal Bounds ◽  
Vacuum Spacetime ◽  
Geometric Effects

Quantum nature of classical flat Kasner spacetime is studied using effective spacetime description in loop quantum cosmology (LQC). We find that even though the spacetime curvature vanishes at the classical level, nontrivial quantum gravitational effects can arise. For the standard loop quantization of Bianchi-I spacetime, which uniquely yields universal bounds on expansion and shear scalars and results in a generic resolution of strong singularities, we find that a flat Kasner metric is not a physical solution of the effective spacetime description, except in a limit. The lack of a flat Kasner metric at the quantum level results from a novel feature of the loop quantum Bianchi-I spacetime: quantum geometry induces nonvanishing spacetime curvature components, making it not Ricci flat even when no matter is present. The noncurvature singularity of the classical flat Kasner spacetime is avoided, and the effective spacetime transits from a flat Kasner spacetime in asymptotic future, to a Minkowski spacetime in asymptotic past. Interestingly, for an alternate loop quantization which does not share some of the fine features of the standard quantization, flat Kasner spacetime with expected classical features exists. In this case, even with nontrivial quantum geometric effects, the spacetime curvature vanishes. These examples show that the character of even a flat classical vacuum spacetime can alter in a fundamental way in quantum gravity and is sensitive to the quantization procedure.

Lie Theory Suffices to Resolve the Local Classical Problem of Time

2021 ◽  
Vol 22 ◽  
pp. 43-63
Author(s):  
Edward Anderson
Keyword(s):  
Quantum Gravity ◽  
Classical Problem ◽  
Lie Theory ◽  
Classical Level ◽  
Problem Of Time

The problem of time - a foundational question in quantum gravity - is due to conceptual gaps between GR and physics' other observationally-confirmed theories. Its multiple facets originated with Wheeler-DeWitt-Dirac over 50~years ago. They were subsequently classified by Kucha\v{r}-Isham, who argued that most of the problem is facet interferences and posed the question of how to order the facets. We show the local classical level facets are two copies of Lie theory with a Wheelerian two-way route therebetween. This solves facet ordering and facet interference. Closure by a Lie algorithm generalization of Dirac's algorithm is central.

scholarly journals Shape dynamical loop gravity from a conformal Immirzi parameter

2017 ◽  
Vol 26 (11) ◽  
pp. 1750131 ◽  
Author(s):  
Patrick J. Wong
Keyword(s):  
Quantum Gravity ◽  
Loop Quantum Gravity ◽  
Three Dimensional ◽  
Classical Level ◽  
Spatial Geometry ◽  
Loop Quantization ◽  
Loop Gravity ◽  
Precise Interpretation ◽  
Gauge Connection ◽  
Area And Volume

The Immirzi parameter of loop quantum gravity is a one-parameter ambiguity of the theory whose precise interpretation is not universally agreed upon. It is an inherent characteristic of the quantum theory as it appears in the spectra of geometric operators, despite being irrelevant at the classical level. The parameter’s appearance in the area and volume spectra to the same power as the Planck area suggest that it plays a role in determining the fundamental length scale of space. In fact, a consistent interpretation is that it represents a constant rescaling of the kinematical spatial geometry. An interesting realization is that promoting the Immirzi parameter to be a general conformal transformation leads to a system which can be identified as analogous to the linking theory of shape dynamics. A three-dimensional gravitational gauge connection is then constructed within the linking theory in a manner analogous to loop quantum gravity, thereby facilitating the application of the established procedure of loop quantization.

scholarly journals Some Remarks on High Derivative Quantum Gravity

1997 ◽  
Vol 12 (32) ◽  
pp. 5711-5734 ◽  
Author(s):  
M. Asorey ◽  
J. L. López ◽  
I. L. Shapiro
Keyword(s):  
Quantum Gravity ◽  
High Derivative ◽  
Einstein Gravity ◽  
Low Energy ◽  
Local Action ◽  
Quantum Corrections ◽  
Asymptotic Freedom ◽  
Low Energies ◽  
Gauge Fixing ◽  
High Derivative Gravity

We analyze the perturbative implications of the most general high derivative approach to quantum gravity based on a diffeomorphism-invariant local action. In particular, we consider the superrenormalizable case with a large number of metric derivatives in the action. The structure of ultraviolet divergences is analyzed in some detail. We show that they are independent of the gauge-fixing condition and the choice of field reparametrization. The cosmological counterterm is shown to vanish under certain parameter conditions. We elaborate on the unitarity problem of high derivative approaches and the distribution of masses of unphysical ghosts. We also discuss the properties of the low energy regime and explore the possibility of having a multiscale gravity with different scaling regimes compatible with Einstein gravity at low energies. Finally, we show that the ultraviolet scaling of matter theories is not affected by the quantum corrections of high derivative gravity. As a consequence, asymptotic freedom is stable under those quantum gravity corrections.

scholarly journals Quantum corrections in 4d N = 1 infinite distance limits and the weak gravity conjecture

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Daniel Klaewer ◽  
Seung-Joo Lee ◽  
Timo Weigand ◽  
Max Wiesner
Keyword(s):  
Quantum Gravity ◽  
Weak Coupling Limit ◽  
Quantum Corrections ◽  
Classical Level ◽  
Four Dimensions ◽  
Weakly Coupled ◽  
The Masses ◽  
Perturbative Corrections ◽  
Weak Gravity ◽  
Kaluza Klein

Abstract We study quantum corrections in four-dimensional theories with N = 1 supersymmetry in the context of Quantum Gravity Conjectures. According to the Emergent String Conjecture, infinite distance limits in quantum gravity either lead to decompactification of the theory or result in a weakly coupled string theory. We verify this conjecture in the framework of N = 1 supersymmetric F-theory compactifications to four dimensions including perturbative α′ as well as non-perturbative corrections. After proving uniqueness of the emergent critical string at the classical level, we show that quantum corrections obstruct precisely those limits in which the scale of the emergent critical string would lie parametrically below the Kaluza-Klein scale. Limits in which the tension of the asymptotically tensionless string sits at the Kaluza-Klein scale, by contrast, are not obstructed.In the second part of the paper we study the effect of quantum corrections for the Weak Gravity Conjecture away from the strict weak coupling limit. We propose that gauge threshold corrections and mass renormalisation effects modify the super-extremality bound in four dimensions. For the infinite distance limits in F-theory the classical super-extremality bound is generically satisfied by a sublattice of states in the tower of excitations of an emergent heterotic string. By matching the F-theory α′-corrections to gauge threshold corrections of the dual heterotic theory we predict how the masses of this tower must be renormalised in order for the Weak Gravity Conjecture to hold at the quantum level.

scholarly journals HERACLITEAN TIME PROPOSAL REVISITED

1995 ◽  
Vol 04 (01) ◽  
pp. 97-103 ◽  
Author(s):  
ORFEU BERTOLAMI
Keyword(s):  
General Relativity ◽  
Wave Function ◽  
Quantum Gravity ◽  
Relaxation Mechanism ◽  
Cosmological Term ◽  
Classical Level ◽  
Canonical Quantum Gravity ◽  
The Universe ◽  
Canonical Quantum

Difficulties in the interpretation of the wave function of the Universe in canonical quantum gravity suggest that the use of dynamical variables to play the role of time is not quite consistent. A formulation of canonical quantum gravity in which time is an extrinsic variable has been previously studied with the problem of being compatible, at the classical level, with General Relativity with a nonvanishing unspecified cosmological constant. We argue that this last problem can be circumvented by introducing a nondynamical scalar field which allows for a relaxation mechanism for the cosmological term.

scholarly journals WORMHOLES AND CHILD UNIVERSES

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1357-1364 ◽  
Author(s):  
E. I. GUENDELMAN
Keyword(s):  
Quantum Gravity ◽  
High Energy ◽  
High Energy Density ◽  
Field Theories ◽  
Minimum Length ◽  
Quantum Field Theories ◽  
Quantum Field ◽  
Classical Level ◽  
Gravitational Effects ◽  
Kaluza Klein

Evidence to the case that classical gravitation provides the clue to make sense out of quantum gravity is presented. The key observation is the existence in classical gravitation of child universe solutions or "almost" solutions, "almost" because of some singularity problems. The difficulties of these child universe solutions that are due to their generic singularity problems will be very likely be cured by quantum effects, just like for example "almost" instanton solutions are made relevant in gauge theories with the breaking of conformal invariance. Some well-motivated modifcations of general relativity where these singularity problems are absent even at the classical level are discussed. High energy density excitations, responsible for UV divergences in quantum field theories, including quantum gravity, are likely to be the source of child universes which carry them out of the original space–time. This decoupling could prevent these high UV excitations from having any influence on physical amplitudes. Child universe production could therefore be responsible for UV regularization in quantum field theories which take into account semiclassically gravitational effects. Child universe production in the last stages of black hole evaporation, the prediction of absence of trans-Planckian primordial perturbations, connection to the minimum length hypothesis, and in particular the connection to the maximal curvature hypothesis are discussed. Some discussion of superexcited states in the case these states such as Kaluza–Klein excitations are carried out. Finally, the possibility of obtaining "string like" effects from the wormholes associated with the child universes is discussed.

scholarly journals Position-dependent mass in strong quantum gravitational background fields

2021 ◽  
Author(s):  
Latévi Mohamed Lawson
Keyword(s):  
Quantum Gravity ◽  
Energy Levels ◽  
Generalized Uncertainty Principle ◽  
Planck Scale ◽  
Gravitational Effect ◽  
Noncommutative Space ◽  
Low Energies ◽  
Background Fields ◽  
Dependent Mass ◽  
Position Dependent Mass

Abstract More recently, we have proposed a set of noncommutative space that describes the quantum gravity at the Planck scale [J. Phys. A: Math. Theor. 53, 115303 (2020)]. The interesting significant result, we found is that, the generalized uncertainty principle induces a maximal measurable length of quantum gravity. This measurement revealed strong quantum gravitational effects at this scale and predicted a detection of gravity particles with low energies. In the present paper, to make evidence this prediction, we study in this space, the dynamics of a particle with position-dependent mass (PDM) trapped in an infinite square well. We show that by increasing the quantum gravitational effect, the PDM of the particle increases and induces deformations of the quantum energy levels. These deformations are more pronounced as one increases the quantum levels allowing, the particle to jump from one state to another with low energies and with high probability densities.

scholarly journals QUANTUM STATE OF WORMHOLES AND TOPOLOGICAL ARROW OF TIME

1994 ◽  
Vol 03 (03) ◽  
pp. 549-568 ◽  
Author(s):  
PEDRO F. GONZÁLEZ-DĺAZ
Keyword(s):  
Quantum Gravity ◽  
Quantum State ◽  
Semiclassical Approximation ◽  
Asymptotic Region ◽  
Analytic Extension ◽  
Arrow Of Time ◽  
Quantum Uncertainty ◽  
Time Symmetry ◽  
Low Energies ◽  
Symmetry Problem

This paper studies the time-symmetry problem in quantum gravity. The issue depends critically on the choice of the quantum state and has been considered in this paper by restricting it to the case of quantum wormholes. It is seen that pure states represented by a wave functional are time symmetric. However, a maximal analytic extension of the wormhole manifold is found that corresponds to a mixed state describable by a nondegenerate density-matrix functional that involves an extra quantum uncertainty for the three-metric, and is free from the divergences encountered so far in statistical states formulated in quantum gravity. It is then argued that, relative to one asymptotic region, the statistical quantum state of single Euclidean wormholes in semiclassical approximation is time-asymmetric and gives rise to a topological arrow of time which will reflect in the set of all quantum fields at low energies of the asymptotically flat region.

scholarly journals Decoherence and discrete symmetries in deformed relativistic kinematics

2018 ◽  
Vol 166 ◽  
pp. 00008
Author(s):  
Michele Arzano
Keyword(s):  
Black Hole ◽  
Quantum Gravity ◽  
Time Evolution ◽  
Discrete Symmetries ◽  
Quantum Systems ◽  
Precision Measurements ◽  
Relativistic Kinematics ◽  
Quantum Time ◽  
Neutral Kaons ◽  
Gravity Effects

Models of deformed Poincaré symmetries based on group valued momenta have long been studied as effective modifications of relativistic kinematics possibly capturing quantum gravity effects. In this contribution we show how they naturally lead to a generalized quantum time evolution of the type proposed to model fundamental decoherence for quantum systems in the presence of an evaporating black hole. The same structures which determine such generalized evolution also lead to a modification of the action of discrete symmetries and of the CPT operator. These features can in principle be used to put phenomenological constraints on models of deformed relativistic symmetries using precision measurements of neutral kaons.

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