Symmetry and Cosmology

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

Deadline for manuscript submissions: 31 December 2025 | Viewed by 1417

Special Issue Editors


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Guest Editor
Departamento de Fisica Teorica, Universidade do Estado do Rio de Janeiro, Rio de Janeiro 20550-013, Brazil
Interests: cosmic inflation; field dynamics; finite temperature quantum field theory; cosmological phase transitions; early universe physics
Special Issues, Collections and Topics in MDPI journals

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Guest Editor
Instituto de Física, Universidade Federal Fluminense, Niteroi 24210-240, Brazil
Interests: early universe; quantum gravity; stochastic gravitational waves; cosmological tensions; dark energy

Special Issue Information

Dear Colleagues,

This Special Issue, titled “Symmetry and Cosmology”, aims to provide an overview of the latest developments concerning aspects of symmetry in the field of cosmology. Symmetry plays an important role in most approaches to cosmology, ranging from the early- to late-time Universe. They are essential ingredients in the analysis of the large-scale structure of the current universe, in the scalar field description of cosmological components, in gauge symmetries, in the effective field theory for cosmological perturbations, in quantum gravity proposals, in gravitational wave predictions from the interface between cosmology and astrophysics, cosmological phase transitions, among many other topics. Altogether, this Special Issue aims to provide an overview of the current developments in such areas, discussing new concepts which could guide and stimulate efforts in understanding important aspects of symmetries in cosmology.

Prof. Dr. Rudnei O. Ramos
Prof. Dr. Leila Lobato Graef
Guest Editors

Manuscript Submission Information

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Keywords

  • symmetry
  • cosmology
  • early universe
  • large-scale structure
  • quantum gravity
  • effective field theory
  • cosmological phase transitions
  • cosmic microwave background
  • cosmological perturbations

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Published Papers (2 papers)

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Research

18 pages, 601 KB  
Article
Back-Reaction of Super-Hubble Fluctuations, Late Time Tracking, and Recent Observational Results
by Marco A. Alvarez, Leila L. Graef and Robert Brandenberger
Symmetry 2025, 17(9), 1507; https://doi.org/10.3390/sym17091507 - 10 Sep 2025
Viewed by 315
Abstract
Previous studies have suggested that the back-reaction of super-Hubble cosmological fluctuations on a symmetric background space-time, with respect to being homogeneous and isotropic, could behave like a dynamical relaxation of the cosmological constant. Moreover, this mechanism appears to be self-regulatory, potentially leading to [...] Read more.
Previous studies have suggested that the back-reaction of super-Hubble cosmological fluctuations on a symmetric background space-time, with respect to being homogeneous and isotropic, could behave like a dynamical relaxation of the cosmological constant. Moreover, this mechanism appears to be self-regulatory, potentially leading to oscillatory behavior in the effective DE. Such an effect would occur in any cosmological model with super-Hubble matter fluctuations, including the standard ΛCDM model. Apart from that, recent DESI data, which indicate that DE may be dynamical, have renewed interest in exploring scenarios leading to such an oscillatory behavior. In this study, we propose a parameterization to account for the impact of super-Hubble fluctuations on the background energy density of the Universe. We model the total effective cosmological constant as the sum of a constant and an oscillating contribution. We performed a preliminary comparison of the background dynamics of this model with recent radial BAO data from DESI. We also discuss the status of the H0 tension problem in this model. Full article
(This article belongs to the Special Issue Symmetry and Cosmology)
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12 pages, 330 KB  
Article
On the Stability of Non-Singular Solutions in Effective Theory from Kaluza–Klein Unimodular Gravity
by Júlio C. Fabris and Richard Kerner
Symmetry 2025, 17(3), 419; https://doi.org/10.3390/sym17030419 - 11 Mar 2025
Viewed by 596
Abstract
Unimodular theory incorporating the Kaluza–Klein construction in five dimensions leads, after reduction to four dimensions, to a new class of scalar–tensor theory. The vacuum cosmological solutions display a bounce with non-singular behavior the effective lower dimension model: from the four-dimensional point of view, [...] Read more.
Unimodular theory incorporating the Kaluza–Klein construction in five dimensions leads, after reduction to four dimensions, to a new class of scalar–tensor theory. The vacuum cosmological solutions display a bounce with non-singular behavior the effective lower dimension model: from the four-dimensional point of view, the solutions are completely regular. However, the propagation of gravitational waves in this geometry displays the presence of instabilities which reflect singular features of the original five-dimensional structure connected to a degenerate metric at the bounce. A four-dimensional quantum model with cosmological constant, which has a similar background behavior, is discussed and revealed to be stable. Full article
(This article belongs to the Special Issue Symmetry and Cosmology)
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