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Symmetry and Asymmetry in Gravity Research

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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 10014

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Special Issue Editors

Prof. Dr. Bivudutta Mishra

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Guest Editor

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

Dr. Muhammad Zubair

E-Mail Website
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

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

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

Open AccessArticle

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 1365

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.

d s

in the emergent general relativity is dimensionless. Several other approaches to quantum gravity, including the model of superplastic vacuum and

B F

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 ℏ can be the parameter of the Minkowski metric. Here, we extend this suggestion by introducing two Planck constants, bar ℏ and slash

/ h

, which are the parameters of the correspondingly time component and space component of the Minkowski metric,

g_{Mink}^{μ ν} = diag (- ℏ^{2}, / h^{2}, / h^{2}, / h^{2})

. The parameters bar ℏ and slash

/ h

are invariant only under

S O (3)

transformations, and, thus, they are not diffeomorphism invariant. As a result they have non-zero dimensions—the dimension of time for ℏ 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

Open AccessArticle

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 1249

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 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

Open AccessArticle

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 1523

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 + 2 f (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

1 σ

and

2 σ

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

Open AccessArticle

Traversable Wormhole Solutions Admitting Noether Symmetry in

f (R, T^{2})

Theory

by Muhammad Zeeshan Gul and Muhammad Sharif

Symmetry 2023, 15(3), 684; https://doi.org/10.3390/sym15030684 - 8 Mar 2023

Cited by 25 | Viewed by 1801

Abstract

This paper uses the Noether symmetry approach to examine the viable and stable traversable wormhole solutions in the framework of the

f (R, T^{2})

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, T^{2})

theory, where

R

is the Ricci scalar and

T^{2} = T_{μ ν} T^{μ ν}

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

Open AccessArticle

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 1309

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

f (Q)

-theory with different types of connections. In [...] Read more.

f (Q)

-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

Open AccessArticle

Observational Constraints on

F (T, T_{G})

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 1772

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.

T

and the teleparallel equivalent of the Gauss-Bonnet term

T_{G}

, say

F (T, T_{G})

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

z_{t}

(at which the universe transit from a decelerating phase to an accelerating) and established the best fit value of

z_{t}

. Next, we paralleled the renovated results of

q (z)

and

ω (z)

and found that the outcomes are well-suited with a

Λ

CDM universe. Full article

(This article belongs to the Special Issue Symmetry and Asymmetry in Gravity Research)

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