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 1867

Special Issue Editor


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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

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Keywords

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

Published Papers (2 papers)

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Research

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 717
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 762
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 0.623z01.668. Thus, it shows the decelerated expansion transiting into the accelerated universe expansion with ω1 as z1 in the extreme future. Full article
(This article belongs to the Special Issue Symmetry/Asymmetry and the Dark Universe)
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