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Symmetry
Special Issues
Black Holes, Cosmology, Quantum Gravity, and Their Symmetries
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Black Holes, Cosmology, Quantum Gravity, and Their Symmetries

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

Deadline for manuscript submissions: closed (15 March 2023) | Viewed by 8638

Special Issue Editors

Dr. Gonzalo J. Olmo

E-Mail Website
Guest Editor
Associate Professor, Department of Theoretical Physics & IFIC, University of Valencia & CSIC, C/ Dr. Moliner 50, 46100 Burjassot, Valencia, Spain
Interests: black holes; singularities; quantum fields in curved space-time; inflation; modified gravity; Palatini formalism; stellar structure models; compact objects
Special Issues, Collections and Topics in MDPI journals
Dr. Adrián Del Río Vega

E-Mail Website
Guest Editor
Universidade de Lisboa - UL, Avenida Rovisco Pais 1, 1049-001, Portugal
Prof. Dr. Eduardo J. Sánchez Villaseñor

E-Mail Website
Guest Editor
Departamento de Matematicas, Universidad Carlos III de Madrid. Avda. de la Universidad 30, 28911 Leganes, Spain
Interests: classical and quantum aspects of general relativity; field theory; statistical mechanics and combinatorics

Special Issue Information

Dear colleagues,

A fascinating lesson that follows from our current understanding of gravitational physics and quantum theory is that the large-scale structure of the universe cannot be fully understood without a clear description of its microscopic properties and symmetries. This ultimately requires a consistent combination of gravity and quantum, a challenging endeavor that still remains one of the deepest open questions of theoretical physics.

 

The exploration of the early universe with high-precision technologies, the observation of gravitational waves generated by the coalescence of massive compact objects, the study of analog models of event horizons in the laboratory, the development of statistical techniques to address thermodynamic questions of black holes, and many other research lines and innovative approaches to longstanding questions are contributing to a growing body of knowledge that, sooner or later, will open new avenues to eventually find a successful theory that accurately describes the dynamics of gravitation in the strongest regimes.

 

In this Special Issue, we embark with the hope of bringing together novel results on classical and quantum aspects of black holes and other compact objects, gravitational waves, early- and late-time cosmology, and different approaches to quantum gravity. Review articles are also welcome, as they play a very important role for the dissemination of well-established results in emerging and recently consolidated topics. Short communications are also encouraged to facilitate the rapid diffusion of innovative and relevant results and ideas.

 

We look forward to your contribution.


Prof. Dr. Gonzalo J. Olmo
Dr. Adrián Del Río Vega
Prof. Dr. Eduardo J. Sánchez Villaseñor
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • black holes
  • quantum gravity
  • cosmology
  • gravitational waves
  • compact objects
  • inflation
  • analog models
  • metric-affine gravity
  • modified gravity
  • symmetries and symmetry breaking

 

Published Papers (5 papers)

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Research

9 pages, 265 KiB  
Article
Particle Creation and the Schwinger Model
by José Navarro-Salas and Silvia Pla
Symmetry 2022, 14(11), 2435; https://doi.org/10.3390/sym14112435 - 17 Nov 2022
Cited by 1 | Viewed by 1298
Abstract
We study the particle creation process in the Schwinger model coupled with an external classical source. One can approach the problem by taking advantage of the fact that the full quantized model is solvable and equivalent to a (massive) gauge field with a [...] Read more.
We study the particle creation process in the Schwinger model coupled with an external classical source. One can approach the problem by taking advantage of the fact that the full quantized model is solvable and equivalent to a (massive) gauge field with a non-local effective action. Alternatively, one can also face the problem by following the standard semiclassical route. This means quantizing the massless Dirac field and considering the electromagnetic field as a classical background. We evaluate the energy created by a generic, homogeneous, and time-dependent source. The results match exactly in both approaches. This proves in a very direct and economical way the validity of the semiclassical approach for the (massless) Schwinger model, in agreement with a previous analysis based on the linear response equation. Our discussion suggests that a similar analysis for the massive Schwinger model could be used as a non-trivial laboratory to confront a fully quantized solvable model with its semiclassical approximation, therefore mimicking the long-standing confrontation of quantum gravity with quantum field theory in curved spacetime. Full article
(This article belongs to the Special Issue Black Holes, Cosmology, Quantum Gravity, and Their Symmetries)
15 pages, 1459 KiB  
Article
The Shadows of Regular Black Holes with Asymptotic Minkowski Cores
by Yi Ling and Meng-He Wu
Symmetry 2022, 14(11), 2415; https://doi.org/10.3390/sym14112415 - 15 Nov 2022
Cited by 13 | Viewed by 1000
Abstract
We investigate the shadows cast by a sort of new regular black hole which are characterized by an asymptotic Minkowski core and sub-Planckian curvature. First, we extend the metric with spherical symmetry to the one of rotating Kerr-like black holes and derive the [...] Read more.
We investigate the shadows cast by a sort of new regular black hole which are characterized by an asymptotic Minkowski core and sub-Planckian curvature. First, we extend the metric with spherical symmetry to the one of rotating Kerr-like black holes and derive the null geodesics with a circular orbit near the horizon of the black hole. Then, we plot the shadows of black holes with different values for the deviation parameter. It is found that the size of the shadow shrinks with the increase in the deviation parameter, while the shape of the shadow becomes more deformed. In particular, by comparing with the shadow a Bardeen black hole and Hayward black hole with the same parameter values, we find that, in general, the shadows of black holes with Minkowski cores have larger deformations than those with de Sitter cores, which potentially provides a strategy to distinguish these two sorts of regular black holes with different cores by astronomical observation in the future. Full article
(This article belongs to the Special Issue Black Holes, Cosmology, Quantum Gravity, and Their Symmetries)
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24 pages, 1161 KiB  
Article
Singularity-Free and Cosmologically Viable Born-Infeld Gravity with Scalar Matter
by David Benisty, Gonzalo J. Olmo and Diego Rubiera-Garcia
Symmetry 2021, 13(11), 2108; https://doi.org/10.3390/sym13112108 - 06 Nov 2021
Cited by 4 | Viewed by 1871
Abstract
The early cosmology, driven by a single scalar field, both massless and massive, in the context of Eddington-inspired Born-Infeld gravity, is explored. We show the existence of nonsingular solutions of bouncing and loitering type (depending on the sign of the gravitational theory’s parameter, [...] Read more.
The early cosmology, driven by a single scalar field, both massless and massive, in the context of Eddington-inspired Born-Infeld gravity, is explored. We show the existence of nonsingular solutions of bouncing and loitering type (depending on the sign of the gravitational theory’s parameter, ϵ) replacing the Big Bang singularity, and discuss their properties. In addition, in the massive case, we find some new features of the cosmological evolution depending on the value of the mass parameter, including asymmetries in the expansion/contraction phases, or a continuous transition between a contracting phase to an expanding one via an intermediate loitering phase. We also provide a combined analysis of cosmic chronometers, standard candles, BAO, and CMB data to constrain the model, finding that for roughly |ϵ|≲5·10−8m2 the model is compatible with the latest observations while successfully removing the Big Bang singularity. This bound is several orders of magnitude stronger than the most stringent constraints currently available in the literature. Full article
(This article belongs to the Special Issue Black Holes, Cosmology, Quantum Gravity, and Their Symmetries)
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24 pages, 407 KiB  
Article
Three Roads to the Geometric Constraint Formulation of Gravitational Theories with Boundaries
by Fernando Barbero, Marc Basquens, Valle Varo and Eduardo J. S. Villaseñor
Symmetry 2021, 13(8), 1430; https://doi.org/10.3390/sym13081430 - 04 Aug 2021
Cited by 1 | Viewed by 1744
Abstract
The Hamiltonian description of mechanical or field models defined by singular Lagrangians plays a central role in physics. A number of methods are known for this purpose, the most popular of them being the one developed by Dirac. Here, we discuss other approaches [...] Read more.
The Hamiltonian description of mechanical or field models defined by singular Lagrangians plays a central role in physics. A number of methods are known for this purpose, the most popular of them being the one developed by Dirac. Here, we discuss other approaches to this problem that rely on the direct use of the equations of motion (and the tangency requirements characteristic of the Gotay, Nester and Hinds method), or are formulated in the tangent bundle of the configuration space. Owing to its interesting relation with general relativity we use a concrete example as a test bed: an extension of the Pontryagin and Husain–Kuchař actions to four dimensional manifolds with boundary. Full article
(This article belongs to the Special Issue Black Holes, Cosmology, Quantum Gravity, and Their Symmetries)
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9 pages, 298 KiB  
Article
Invariant Scalar Product and Associated Structures for Tachyonic Klein–Gordon Equation and Helmholtz Equation
by Francisco F. López-Ruiz, Julio Guerrero and Victor Aldaya
Symmetry 2021, 13(7), 1302; https://doi.org/10.3390/sym13071302 - 20 Jul 2021
Cited by 1 | Viewed by 1466
Abstract
Although describing very different physical systems, both the Klein–Gordon equation for tachyons (m2<0) and the Helmholtz equation share a remarkable property: a unitary and irreducible representation of the corresponding invariance group on a suitable subspace of solutions is [...] Read more.
Although describing very different physical systems, both the Klein–Gordon equation for tachyons (m2<0) and the Helmholtz equation share a remarkable property: a unitary and irreducible representation of the corresponding invariance group on a suitable subspace of solutions is only achieved if a non-local scalar product is defined. Then, a subset of oscillatory solutions of the Helmholtz equation supports a unirrep of the Euclidean group, and a subset of oscillatory solutions of the Klein–Gordon equation with m2<0 supports the scalar tachyonic representation of the Poincaré group. As a consequence, these systems also share similar structures, such as certain singularized solutions and projectors on the representation spaces, but they must be treated carefully in each case. We analyze differences and analogies, compare both equations with the conventional m2>0 Klein–Gordon equation, and provide a unified framework for the scalar products of the three equations. Full article
(This article belongs to the Special Issue Black Holes, Cosmology, Quantum Gravity, and Their Symmetries)
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