Extreme Regimes of Classical and Quantum Gravity Models. Theory, Observations, and the Role of Symmetries

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (30 November 2023) | Viewed by 7656

Special Issue Editor


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Guest Editor
Department of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria
Interests: quantum gravity; general relativity; quantum field theory

Special Issue Information

Dear Colleagues,

General relativity and, more in general, extended theories of gravity provide a geometric formulation of the gravitational interaction.

Reconciling gravity with quantum mechanics is one of the most profound open problems in physics. Over the last few decades, efforts in this direction have led to a broad range of classical and quantum theoretical models which have revealed exciting connections and symmetries between different aspects of gravity and quantum physics. Observational physics also fulfills a crucial role in this field, since it is entrusted with the task of validating the wide variety of proposed models. 

Analyzing gravity and its symmetries in the most extreme regimes represents a tool to gain precious information on the classical and quantum aspects of the gravitational interaction. Therefore, this Special Issue is focused on original approaches to the theoretical and/or the observational investigation of either the low-energy or the high-energy regimes of classical and/or quantum gravity theories. We cordially and earnestly invite researchers to contribute their original and high-quality research papers which can inspire advances in observational and theoretical gravity physics. Potential topics include but are not limited to:

  • Gravitational waves;
  • Black hole and neutron star physics;
  • Compact objects;
  • Exotic compact objects (such as wormholes and boson stars);
  • Approximation methods for the description of the N-body relativistic dynamics (such as post-Newtonian technique, numerical relativity, perturbation theory, gravitational self-force formalism); 
  • N-body problem in gravity theories;
  • Effective-field theory approaches to quantum gravity;
  • Gravity induced entanglement;
  • Geometric formulations of gravity theories based on a broad use of geometric tools, such as differential geometry, geometric measure theory, and geometric algebra;
  • Investigation of the global structure of spacetimes via differential and algebraic topology methods.

Dr. Emmanuele Battista
Guest Editor

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Keywords

  • gravitation
  • general relativity
  • extended theories of gravity
  • quantum gravity
  • differential geometry
  • geometric measure theory
  • geometric algebra
  • differential and algebraic topology
  • gravitational waves
  • black hole physics
  • black hole merger
  • neutron star merger
  • neutron stars
  • compact objects
  • exotic compact objects
  • wormholes
  • boson stars
  • N-body relativistic dynamics
  • N-body problem
  • post-Newtonian method
  • numerical relativity
  • perturbation theory
  • gravitational self-force formalism
  • effective-field theory models of gravity
  • gravity-induced entanglement

Published Papers (5 papers)

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Research

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24 pages, 8755 KiB  
Article
Spherical Particle Orbits around a Rotating Black Hole in Massive Gravity
by Mohsen Fathi, José R. Villanueva and Norman Cruz
Symmetry 2023, 15(8), 1485; https://doi.org/10.3390/sym15081485 - 27 Jul 2023
Viewed by 646
Abstract
In this paper, we present a rotating de Rham–Gabadadze–Tolley black hole with a positive cosmological constant under massive gravity, achieved by applying a modified Newman–Janis algorithm. The black hole exhibited stable orbits of constant radii, prompting a numerical study of the behavior of [...] Read more.
In this paper, we present a rotating de Rham–Gabadadze–Tolley black hole with a positive cosmological constant under massive gravity, achieved by applying a modified Newman–Janis algorithm. The black hole exhibited stable orbits of constant radii, prompting a numerical study of the behavior of the solutions to a nonic equation governing the radii of planar orbits around the black hole. Additionally, we investigated the stability of orbits near the event horizon and provide a comprehensive analytical examination of the solutions to the angular equations of motion. This was followed by a simulation of some spherical particle orbits around the black hole. Full article
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10 pages, 273 KiB  
Article
Quantum Mechanics of the Extended Snyder Model
by Stjepan Meljanac and Salvatore Mignemi
Symmetry 2023, 15(7), 1373; https://doi.org/10.3390/sym15071373 - 06 Jul 2023
Cited by 2 | Viewed by 662
Abstract
We investigate a quantum mechanical harmonic oscillator based on the extended Snyder model. This realization of the Snyder model is constructed as a quantum phase space generated by D spatial coordinates and D(D1)/2 tensorial degrees of [...] Read more.
We investigate a quantum mechanical harmonic oscillator based on the extended Snyder model. This realization of the Snyder model is constructed as a quantum phase space generated by D spatial coordinates and D(D1)/2 tensorial degrees of freedom, together with their conjugated momenta. The coordinates obey nontrivial commutation relations and generate a noncommutative geometry, which admits nicer properties than the usual realization of the model, in particular giving rise to an associative star product. The spectrum of the harmonic oscillator is studied through the introduction of creation and annihilation operators. Some physical consequences of the introduction of the additional degrees of freedom are discussed. Full article
15 pages, 935 KiB  
Article
On the Nature of Bondi–Metzner–Sachs Transformations
by Zahra Mirzaiyan and Giampiero Esposito
Symmetry 2023, 15(4), 947; https://doi.org/10.3390/sym15040947 - 21 Apr 2023
Viewed by 1124
Abstract
This paper investigates, as a first step, the four branches of BMS transformations, motivated by the classification into elliptic, parabolic, hyperbolic and loxodromic proposed a few years ago in the literature. We first prove that to each normal elliptic transformation of the complex [...] Read more.
This paper investigates, as a first step, the four branches of BMS transformations, motivated by the classification into elliptic, parabolic, hyperbolic and loxodromic proposed a few years ago in the literature. We first prove that to each normal elliptic transformation of the complex variable ζ used in the metric for cuts of null infinity, there is a corresponding BMS supertranslation. We then study the conformal factor in the BMS transformation of the u variable as a function of the squared modulus of ζ. In the loxodromic and hyperbolic cases, this conformal factor is either monotonically increasing or monotonically decreasing as a function of the real variable given by the modulus of ζ. The Killing vector field of the Bondi metric is also studied in correspondence with the four admissible families of BMS transformations. Eventually, all BMS transformations are re-expressed in the homogeneous coordinates suggested by projective geometry. It is then found that BMS transformations are the restriction to a pair of unit circles of a more general set of transformations. Within this broader framework, the geometry of such transformations is studied by means of its Segre manifold. Full article
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16 pages, 715 KiB  
Article
On the Traversable Yukawa–Casimir Wormholes
by Pedro Henrique Ferreira de Oliveira, Geová Alencar, Ivan Carneiro Jardim and Ricardo Renan Landim
Symmetry 2023, 15(2), 383; https://doi.org/10.3390/sym15020383 - 01 Feb 2023
Cited by 5 | Viewed by 1524
Abstract
Wormholes require negative energy, and therefore an exotic matter source. Since Casimir’s energy is negative, it has been speculated as a good candidate to source those objects a long time ago. However, only very recently a full solution for 3+1 dimensions [...] Read more.
Wormholes require negative energy, and therefore an exotic matter source. Since Casimir’s energy is negative, it has been speculated as a good candidate to source those objects a long time ago. However, only very recently a full solution for 3+1 dimensions has been found by Garattini, thus the Casimir energy can be a source of traversable wormholes. We have recently shown that this can be generalized to higher dimensional spacetimes. Lately, Garattini sought to analyze the effects of Yukawa-type terms on shape functions and obtained promising results. However, his approach breaks down the usual relation between the energy density and the radial pressure of the Casimir field. In this work, we study the effects of the same three Yukawa-type corrective factors on the shape function of the Casimir wormhole keeping the usual way to obtain the radial pressure from the energy density. We show that, in addition to being able to construct traversable wormholes that satisfy all the necessary conditions, it is possible to obtain adequate constraints on the constants to recover the standard case with no double limit used by Garatinni. We show that, for some values of the Yukawa parameter, it is possible to generate a repulsive gravitational wormhole. Finally, we analyze the stability of the solutions and find the upper bounds for the Yukawa factor. Full article
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Review

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46 pages, 2882 KiB  
Review
The D4/D8 Model and Holographic QCD
by Si-Wen Li and Xiao-Tong Zhang
Symmetry 2023, 15(6), 1213; https://doi.org/10.3390/sym15061213 - 07 Jun 2023
Cited by 5 | Viewed by 2926
Abstract
As a top-down holographic approach, the D4/D8 model is expected to be a holographic version of QCD, since it almost includes all the elementary features of QCD based on string theory. In this manuscript, we review the fundamental properties of the D4/D8 model [...] Read more.
As a top-down holographic approach, the D4/D8 model is expected to be a holographic version of QCD, since it almost includes all the elementary features of QCD based on string theory. In this manuscript, we review the fundamental properties of the D4/D8 model with respect to the D4-brane background and the embedding of the flavor branes, holographic quark, gluon, meson, baryon and glueball with various symmetries; then, we take a look at some interesting applications and developments based on this model. Full article
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