Symmetry and Asymmetry in Gravity Research

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

Deadline for manuscript submissions: closed (30 June 2023) | Viewed by 9509

Special Issue Editors


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Guest Editor
Birla Institute of Technology and Science, Pilani, India
Interests: theoretical dark energy; extended theories of gravity; wormhole geometry

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Guest Editor
Department of Mathematics, COMSATS University Islamabad, Lahore Campus, Lahore 54000, Pakistan
Interests: cosmology; modified gravitational theories; symmetries; wormholes; compact objects and black holes

Special Issue Information

Dear Colleagues,

Gravity, a long-ranged interaction between the objects, is one of the four fundamental forces of nature. Einstein described gravity as “the curvature of spacetime” and proposed an interesting theory of gravity known as General Relativity (GR).  In order to deal with the shortcomings of GR, numerous extensions have been proposed in the literature by incorporating some additional degrees of freedom. The Lagrangian density of GR and its extended versions consist of some unknown functions whose analytical form and viability pose a considerable challenge to researchers. The dynamical field equations of such frameworks usually lead to a system of non-linear partial differential equations and, consequently, the determination of exact solutions becomes a laborious task.  In this respect, symmetries provide a powerful tool to find exact solutions of a system by reducing its order. Physically, symmetries refer to conservation laws, while on mathematical grounds, symmetries reduce dynamics of the system due to the presence of cyclic variables and provide an effective way to analyze complicated differential equations.

The purpose of this Special Issue is to put forward new exact models in the gravitational framework of GR as well as its generalizations in regard to symmetry that can describe the latest cosmological advances and fit the observational data well. We welcome mathematicians, physicists, and other scientists to submit their research articles based on the recent advancements in the field of gravitation focusing on the role of symmetries to this Special Issue.

In this Special Issue, original research articles, reviews, communications and concept papers are welcome. We look forward to receiving your contributions.

Prof. Dr. Bivudutta Mishra
Dr. Muhammad Zubair
Guest Editors

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Keywords

  • gravity
  • modifications of Einstein’s gravity theory
  • partial differential equations
  • gravitational/cosmological models
  • analytical solutions
  • lie symmetries
  • noether and noether gauge symmetries
  • scaling/rotational symmetries
  • conservation laws

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Published Papers (6 papers)

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Research

10 pages, 288 KiB  
Article
Planck Constants in the Symmetry Breaking Quantum Gravity
by Grigory E. Volovik
Symmetry 2023, 15(5), 991; https://doi.org/10.3390/sym15050991 - 27 Apr 2023
Cited by 4 | Viewed by 1294
Abstract
We consider the theory of quantum gravity in which gravity emerges as a result of the symmetry-breaking transition in the quantum vacuum. The gravitational tetrads, which play the role of the order parameter in this transition, are represented by the bilinear combinations of [...] Read more.
We consider the theory of quantum gravity in which gravity emerges as a result of the symmetry-breaking transition in the quantum vacuum. The gravitational tetrads, which play the role of the order parameter in this transition, are represented by the bilinear combinations of the fermionic fields. In this quantum gravity scenario the interval ds in the emergent general relativity is dimensionless. Several other approaches to quantum gravity, including the model of superplastic vacuum and BF theories of gravity support this suggestion. The important consequence of such metric dimension is that all the diffeomorphism invariant quantities are dimensionless for any dimension of spacetime. These include the action S, cosmological constant Λ, scalar curvature R, scalar field Φ, wave function ψ, etc. The composite fermion approach to quantum gravity suggests that the Planck constant can be the parameter of the Minkowski metric. Here, we extend this suggestion by introducing two Planck constants, bar and slash /h, which are the parameters of the correspondingly time component and space component of the Minkowski metric, gMinkμν=diag(2,/h2,/h2,/h2). The parameters bar and slash /h are invariant only under SO(3) transformations, and, thus, they are not diffeomorphism invariant. As a result they have non-zero dimensions—the dimension of time for and dimension of length for /h. Then, according to the Weinberg criterion, these parameters are not fundamental and may vary. In particular, they may depend on the Hubble parameter in the expanding Universe. They also change sign at the topological domain walls resulting from the symmetry breaking. Full article
(This article belongs to the Special Issue Symmetry and Asymmetry in Gravity Research)
13 pages, 337 KiB  
Article
Evolution of Generalized Brans–Dicke Parameter within a Superbounce Scenario
by Sunil Kumar Tripathy, Sasmita Kumari Pradhan, Biswakalpita Barik, Zashmir Naik and B. Mishra
Symmetry 2023, 15(4), 790; https://doi.org/10.3390/sym15040790 - 24 Mar 2023
Cited by 2 | Viewed by 1171
Abstract
We studied a superbounce scenario in a set up of the Brans–Dicke (BD) theory. The BD parameter was considered to be time-dependent and was assumed to evolve with the Brans–Dicke scalar field. In the superbounce scenario, the model bounced at an epoch corresponding [...] Read more.
We studied a superbounce scenario in a set up of the Brans–Dicke (BD) theory. The BD parameter was considered to be time-dependent and was assumed to evolve with the Brans–Dicke scalar field. In the superbounce scenario, the model bounced at an epoch corresponding to a Big Crunch provided the ekpyrotic phase continued until that time. Within the given superbounce scenario, we investigated the evolution of the BD parameter for different equations of state. We chose an axially symmetric metric that has an axial symmetry along the x-axis. The metric was assumed to incorporate an anisotropic expansion effect. The effect of asymmetric expansion and the anisotropic parameter on the evolving and non-evolving parts of the BD parameter was investigated. Full article
(This article belongs to the Special Issue Symmetry and Asymmetry in Gravity Research)
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13 pages, 502 KiB  
Article
A Transition Model in f(R,T) Theory via Observational Constraints
by Rishi Kumar Tiwari, Bhupendra Kumar Shukla, Değer Sofuoğlu and Dilay Kösem
Symmetry 2023, 15(4), 788; https://doi.org/10.3390/sym15040788 - 24 Mar 2023
Cited by 3 | Viewed by 1443
Abstract
A particular form of the time-dependent deceleration parameter is used to examine the accelerated expansion of the universe and the phase transition in this expansion in the context of f(R,T) gravity theory for the flat FRW model. The [...] Read more.
A particular form of the time-dependent deceleration parameter is used to examine the accelerated expansion of the universe and the phase transition in this expansion in the context of f(R,T) gravity theory for the flat FRW model. The modified field equations are solved under the choice of f(R,T)=R+2f(T). The best fit values of the model parameters that would be consistent with the recent observational datasets that are estimated. For this estimation, 57 points from Cosmic Chronometers (CC) datasets and 1048 points from Pantheon supernovae datasets are used. Bayesian analysis and likelihood function are applied together with Markov Chain Monte Carlo (MCMC) method at 1σ and 2σ confidence levels. Then, the physical behavior of parameters such as density, pressure and cosmographic parameters corresponding to these constrained values of the model parameters are analyzed. Looking at the deceleration parameter, it is seen that the universe has passed from a decelerating expansion phase to an accelerating phase. As a result, it has been shown that the cosmological model f(R,T) that we discussed can explain the accelerating expansion of the late universe well without resorting to any dark energy component in the energy-momentum tensor. Full article
(This article belongs to the Special Issue Symmetry and Asymmetry in Gravity Research)
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23 pages, 12067 KiB  
Article
Traversable Wormhole Solutions Admitting Noether Symmetry in f(R,T2) Theory
by Muhammad Zeeshan Gul and Muhammad Sharif
Symmetry 2023, 15(3), 684; https://doi.org/10.3390/sym15030684 - 8 Mar 2023
Cited by 24 | Viewed by 1698
Abstract
This paper uses the Noether symmetry approach to examine the viable and stable traversable wormhole solutions in the framework of the f(R,T2) theory, where R is the Ricci scalar and [...] Read more.
This paper uses the Noether symmetry approach to examine the viable and stable traversable wormhole solutions in the framework of the f(R,T2) theory, where R is the Ricci scalar and T2=TμνTμν is the self-contraction of the stress–energy tensor. For this purpose, we consider a specific model of this modified theory to obtain the exact solutions of the Noether equations. Further, we formulate the generators of the Noether symmetry and first integrals of motion. We analyze the presence of viable and stable traversable wormhole solutions corresponding to different redshift functions. In order to determine whether this theory provides physically viable and stable wormhole geometry or not, we check the graphical behavior of the null energy constraint, causality condition and adiabatic index for an effective stress–energy tensor. It is found that viable and stable traversable wormhole solutions exist in this modified theory. Full article
(This article belongs to the Special Issue Symmetry and Asymmetry in Gravity Research)
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12 pages, 312 KiB  
Article
Stability Properties of Self-Similar Solutions in Symmetric Teleparallel f(Q)-Cosmology
by Andronikos Paliathanasis
Symmetry 2023, 15(2), 529; https://doi.org/10.3390/sym15020529 - 16 Feb 2023
Cited by 4 | Viewed by 1239
Abstract
Self-similar cosmological solutions correspond to spacetimes that admit a homothetic symmetry. The physical properties of self-similar solutions can describe important eras of the cosmological evolution. Recently, self-similar cosmological solutions were derived for symmetric teleparallel fQ-theory with different types of connections. In [...] Read more.
Self-similar cosmological solutions correspond to spacetimes that admit a homothetic symmetry. The physical properties of self-similar solutions can describe important eras of the cosmological evolution. Recently, self-similar cosmological solutions were derived for symmetric teleparallel fQ-theory with different types of connections. In this work, we study the stability properties of the self-similar cosmological solutions in order to investigate the effects of the different connections on the stability properties of the cosmic history. For the background geometry, we consider the isotropic Friedmann–Lemaître–Robertson–Walker space and the anisotropic and homogeneous Bianchi I space, for which we investigate the stability properties of Kasner-like universes. Full article
(This article belongs to the Special Issue Symmetry and Asymmetry in Gravity Research)
13 pages, 583 KiB  
Article
Observational Constraints on F(T,TG) Gravity with Hubble’s Parametrization
by Salim Harun Shekh, Nurgissa Myrzakulov, Anirudh Pradhan and Assem Mussatayeva
Symmetry 2023, 15(2), 321; https://doi.org/10.3390/sym15020321 - 23 Jan 2023
Cited by 6 | Viewed by 1708
Abstract
Any new gravitational theories can be built with the help of a gauge theory with local Poincare symmetry. This local Poincare symmetry can set up a space-time with torsion. In the present study, the authors working on the parametrization approach towards Hubble’s parameter [...] Read more.
Any new gravitational theories can be built with the help of a gauge theory with local Poincare symmetry. This local Poincare symmetry can set up a space-time with torsion. In the present study, the authors working on the parametrization approach towards Hubble’s parameter in the frame of modified teleparallel Gauss-Bonnet gravity which is established on the torsion invariant T and the teleparallel equivalent of the Gauss-Bonnet term TG, say F(T,TG) gravity. In particular, gravity is responsible for an integrated explanation of the cosmological history from early-time inflation to late-time acceleration expansion, by lacking the addition of a cosmological constant. The domino effect acquired is reliable with recent cosmological outcomes. A transition scenario from a decelerating phase to an accelerating phase of cosmic evolution has been detected. Using the combined datasets (SNe-Ia+BAO+CMB+H(z)), we have constrained the transition redshift zt (at which the universe transit from a decelerating phase to an accelerating) and established the best fit value of zt. Next, we paralleled the renovated results of q(z) and ω(z) and found that the outcomes are well-suited with a ΛCDM universe. Full article
(This article belongs to the Special Issue Symmetry and Asymmetry in Gravity Research)
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