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Symmetry
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Symmetry/Asymmetry and the Dark Universe
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Symmetry/Asymmetry and the Dark Universe

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

Deadline for manuscript submissions: 31 July 2024 | Viewed by 2325

Special Issue Editor

Prof. Dr. Anirudh Pradhan

E-Mail Website
Guest Editor
Centre for Cosmology, Astrophysics and Space Science, GLA University, Mathura 281406, Uttar Pradesh, India
Interests: classical gravity and cosmology; dark energy; modified gravity; radiation physics

Special Issue Information

Dear Colleagues,

Until the 20th century, the principles of symmetry were unconsciously applied in theoretical physics. Newton’s law of mechanics embodied the principle of symmetry, notably the principle of equivalence of inertial frames (Galilean invariance). These symmetries implied conservation laws.

The situation changed dramatically in the 20th century, beginning with Einstein. In 1905, Einstein led great advancement in the field by putting symmetry first and regarding the principle of symmetry as a primary constraint on the allowable dynamical laws. Ten years later, this point of view was supported by Einstein’s construction of general relativity. The principle of equivalence, which is a principle of local symmetry involving the invariance of the laws of nature under local changes in space-time coordinates, dictated the dynamics of gravity, and of space-time itself.

According to contemporary astrophysical observations, expansion of the present-day cosmos is accelerating due to a large negative pressure called Dark Energy (DE), along with other observations such as Cosmic Microwave Background (CMB) anisotropies, measured using a Wilkinson Microwave Anisotropy Probe (WMAP) satellite and a Large-Scale Structure (LSS). It is thought that about two-thirds of the Universe is formed of DE, while the remainder consists of relativistic Dark Matter (DM) and baryons.

Modified gravity theories (MGTs) are a new paradigm of modern physics that explain the major problems in Einstein’s theory of General Relativity (GR). MGTs became popular due to their ability to provide an alternative framework instead of searching for new material ingredients. Thus, one of the expected outcomes of MGTs is to address the phenomenology of gravity at galactic, extragalactic, and cosmological scales.

Papers on any of the following topics are welcome:

  1. Einstein’s general theory of relativity and exact solution;
  2. Modified gravity theories/alternative theories of gravity;
  3. Gravitational collapse of intermediate-mass stars;
  4. Problems based on black holes, Dark Energy, and Dark Matter.

Prof. Dr. Anirudh Pradhan
Guest Editor

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

  • general relativity
  • modified gravity theories
  • cosmology
  • dark energy
  • observational constraints
  • accelerating universe
  • energy conditions

Published Papers (3 papers)

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Research

14 pages, 445 KiB  
Article
The Schwarzschild–de Sitter Metric of Nonlocal dS Gravity
by Ivan Dimitrijevic, Branko Dragovich, Zoran Rakic and Jelena Stankovic
Symmetry 2024, 16(5), 544; https://doi.org/10.3390/sym16050544 - 1 May 2024
Viewed by 320
Abstract
It is already known that a simple nonlocal de Sitter gravity model, which we denote as dS gravity, contains an exact vacuum cosmological solution that mimics dark energy and dark matter and is in very good agreement with the standard model of [...] Read more.
It is already known that a simple nonlocal de Sitter gravity model, which we denote as dS gravity, contains an exact vacuum cosmological solution that mimics dark energy and dark matter and is in very good agreement with the standard model of cosmology. This success of dS gravity motivated us to investigate how it works at a lower-than-cosmic scale—galactic and the solar system. This paper contains our investigation of the corresponding Schwarzschild–de Sitter metric of the dS gravity model. To obtain an exact solution, it is necessary to solve the corresponding nonlinear differential equation, which is a very complicated and difficult problem. What we obtained is a solution to a linearized equation, which is related to space metrics far from the massive body, where the gravitational field is weak. The obtained approximate solution is of particular interest for examining the possible role of nonlocal de Sitter gravity dS in describing the effects in galactic dynamics that are usually attributed to dark matter. This solution was tested on the Milky Way and the spiral galaxy M33 and is in good agreement with observational measurements. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry and the Dark Universe)
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20 pages, 1061 KiB  
Article
The Algebra and Calculus of Stochastically Perturbed Spacetime with Classical and Quantum Applications
by Dragana Pilipović
Symmetry 2024, 16(1), 36; https://doi.org/10.3390/sym16010036 - 28 Dec 2023
Viewed by 760
Abstract
We consider an alternative to dark matter as a potential solution to various remaining problems in physics: the addition of stochastic perturbations to spacetime to effectively enforce a minimum length and establish a fundamental uncertainty at minimum length (ML) scale. To explore the [...] Read more.
We consider an alternative to dark matter as a potential solution to various remaining problems in physics: the addition of stochastic perturbations to spacetime to effectively enforce a minimum length and establish a fundamental uncertainty at minimum length (ML) scale. To explore the symmetry of spacetime to such perturbations both in classical and quantum theories, we develop some new tools of stochastic calculus. We derive the generators of rotations and boosts, along with the connection, for stochastically perturbed, minimum length spacetime (“ML spacetime”). We find the metric, the directional derivative, and the canonical commutator preserved. ML spacetime follows the Lie algebra of the Poincare group, now expressed in terms of the two-point functions of the stochastic fields (per Ito’s lemma). With the fundamental uncertainty at ML scale a symmetry of spacetime, we require the translational invariance of any classical theory in classical spacetime to also include the stochastic spacetime perturbations. As an application of these ideas, we consider galaxy rotation curves for massive bodies to find that—under the Robertson–Walker minimum length theory—rotational velocity becomes constant as the distance to the center of the galaxy becomes very large. The new tools of stochastic calculus also set the stage to explore new frontiers at the quantum level. We consider a massless scalar field to derive the Ward-like identity for ML currents. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry and the Dark Universe)
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19 pages, 828 KiB  
Article
Transit f(Q,T) Gravity Model: Observational Constraints with Specific Hubble Parameter
by A. P. Kale, Y. S. Solanke, S. H. Shekh and A. Pradhan
Symmetry 2023, 15(10), 1835; https://doi.org/10.3390/sym15101835 - 27 Sep 2023
Viewed by 819
Abstract
The present analysis deals with the study of the f(Q,T) theory of gravity, which was recently considered by many cosmologists. In this theory of gravity, the action is taken as an arbitrary function [...] Read more.
The present analysis deals with the study of the f(Q,T) theory of gravity, which was recently considered by many cosmologists. In this theory of gravity, the action is taken as an arbitrary function f(Q,T), where Q is non-metricity and T is the trace of the energy–momentum tensor for matter fluid. In this study, we took two different forms of the function f(Q,T) as f(Q,T)=a1Q+a2T and f(Q,T)=a3Q2+a4T, and discussed the physical properties of the models. Also, we obtained the various cosmological parameters for the Friedmann–Lemaître–Robertson–Walker (FLRW) universe by defining the transit form of a scale factor that yielded the Hubble parameter in redshift form, as H(z)=H0(λ+1)λ+(1+z)δ. We obtained the best-fit values of model parameters using the least squares method for observational constraints on available datasets, like Hubble H(z), Supernova SNe-Ia, etc., by applying the root mean squared error formula (RMSE). For the obtained approximate best-fit values of model parameters, we observed that the deceleration parameter q(z) shows a signature-flipping (transition) point within the range of 0.623≤z0≤1.668. Thus, it shows the decelerated expansion transiting into the accelerated universe expansion with ω→−1 as z→−1 in the extreme future. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry and the Dark Universe)
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