Special Issue "Modified Gravity Theories and Applications to Astrophysics and Cosmology"

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

Deadline for manuscript submissions: 20 November 2022 | Viewed by 3013

Special Issue Editors

Prof. Dr. Michael M. Tung
E-Mail Website
Guest Editor
Instituto de Matemática Multidisciplinar, Edificio 8-G, 2º piso, Camino de Vera, s/n, 46022 Valencia, Spain
Interests: applied mathematics; theoretical physics
Dr. Golden Gadzirayi Nyambuya
E-Mail Website
Guest Editor
National University of Science & Technology (NUST), Faculty of Applied Sciences – Department of Applied Physics, Fundamental Theoretical and Astrophysics Group, P. O. Box 939 Ascot, Bulawayo, Republic of Zimbabwe
Interests: fundamental theoretical physics

Special Issue Information

Dear Colleagues,

The general theory of relativity is considered today as being highly successful because of its verification in many experiments and its applications to cosmology and astrophysics. Since its initial formulation more than a century ago, a plethora of extended and modified theories have appeared.

This trend has not diminished with time, but, on the other hand, it seems to be increasing with additional difficulties in astronomical observations.

More prominently, we have the lingering problem of the anomalous rotation curves of galaxies and the extra lensing effects, not accounted for luminous matter. This problem is, apparently, solved in the context of standard cosmology by the so-called dark matter but it could equally be understood by modified gravity hypothesis such as MOND, scalar-vector-tensor theories and other.

In the solar system we have some unsolved problems, as follows: We have the lingering problem of the anomalous increase of the eccentricity of the moon’s orbit, as determined by lunar laser ranging techniques. The dissipative processes of a tidal origin have, to date, been unable to explain this anomaly. The flyby anomaly, that is, the anomalous orbital energy changes of spacecraft in planetary flybys, have also been discussed since the early 1990s. More recently, a breakdown of Kepler’s laws, similar to that found in the rotation curves of galaxies, has also been disclosed for wide binary stars.

The purpose of this Special Issue is to publish conventional and unconventional, but well-founded, approaches to the solution of these or any other new phenomena related to gravity. In particular, we are seeking papers in which new and original perspectives to these issues are provided as a way to stimulate the discussion in the astronomy and physics communities, in order to search for the solution of the riddle posed by many of these anomalies.

Topics of interest include (not exhaustively) the following:

Flyby anomalies

The secular increase of the eccentricity of the orbit of the moon

The faint young Sun paradox

Application of geopotential models for the Earth and other planets

Lunar laser ranging and radar ranging in the solar system

Conventional radiation effects in spacecraft navigation

Wide binaries as tests of classical gravity

Modified gravity models

Dark energy and cosmological accelerated expansion

Applications of gravity models to the anomalous rotation curves of galaxies

Bullet cluster and gravitational lensing

Modified Newtonian dynamics and applications in the solar system

Gravitational waves and tests of general relativity in strong gravity

Dr. Luis Acedo
Prof. Dr. Michael M. Tung
Dr. Golden Gadzirayi Nyambuya
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 1800 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

  • Flyby anomalies
  • The secular increase of the eccentricity of the orbit of the moon
  • The faint young
  • Sun paradox Application of geopotential models for the Earth and other planets Lunar laser ranging and radar ranging in the solar system
  • Conventional radiation effects in spacecraft navigation
  • Wide binaries as tests of classical gravity Modified gravity models
  • Dark energy and cosmological accelerated expansion
  • Applications of gravity models to the anomalous rotation curves of galaxies
  • Bullet cluster and gravitational lensing
  • Modified Newtonian dynamics and applications in the solar system
  • Gravitational waves and tests of general relativity in strong gravity

Published Papers (4 papers)

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Research

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Article
Stable Exponential Cosmological Type Solutions with Three Factor Spaces in EGB Model with a Λ-Term
Symmetry 2022, 14(7), 1296; https://doi.org/10.3390/sym14071296 - 22 Jun 2022
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Abstract
We study a D-dimensional Einstein–Gauss–Bonnet model which includes the Gauss–Bonnet term, the cosmological term Λ and two non-zero constants: α1 and α2. Under imposing the metric to be diagonal one, we find cosmological type solutions with exponential dependence of [...] Read more.
We study a D-dimensional Einstein–Gauss–Bonnet model which includes the Gauss–Bonnet term, the cosmological term Λ and two non-zero constants: α1 and α2. Under imposing the metric to be diagonal one, we find cosmological type solutions with exponential dependence of three scale factors in a variable u, governed by three non-coinciding Hubble-like parameters: H0, h1 and h2, obeying mH+k1h1+k2h20, corresponding to factor spaces of dimensions m>1, k1>1 and k2>1, respectively, and depending upon sign parameter ε=±1, where ε=1 corresponds to cosmological case and ε=1—to static one). We deal with two cases: (i) m<k1<k2 and (ii) 1<k1=k2=k, km. We show that in both cases the solutions exist if εα=εα2/α1>0 and αΛ>0 satisfy certain (upper and lower) bounds. The solutions are defined up to solutions of a certain polynomial master equation of order four (or less), which may be solved in radicals. In case (ii), explicit solutions are presented. In both cases we single out stable and non-stable solutions as u±. The case H=0 is also considered. Full article
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Article
Exact Solution for Relativistic Trajectories Using Modal Transseries
Symmetry 2020, 12(9), 1505; https://doi.org/10.3390/sym12091505 - 13 Sep 2020
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Abstract
In this article, we design a novel method for finding the exact solution of the geodesic equation in Schwarzschild spacetime, which represents the trajectories of the particles. This is a fundamental problem in astrophysics and astrodynamics if we want to incorporate relativistic effects [...] Read more.
In this article, we design a novel method for finding the exact solution of the geodesic equation in Schwarzschild spacetime, which represents the trajectories of the particles. This is a fundamental problem in astrophysics and astrodynamics if we want to incorporate relativistic effects in high precision calculations. Here, we show that exact analytical expressions can be given, in terms of modal transseries for the spiral orbits as they approach the limit cycles given by the two circular orbits that appear for each angular momentum value. The solution is expressed in terms of transseries generated by transmonomials of the form enθ, n=1, 2, , where θ is the angle measured in the orbital plane. Examples are presented that verify the effect of the solutions. Full article
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Article
Excluded Volume for Flat Galaxy Rotation Curves in Newtonian Gravity and General Relativity
Symmetry 2020, 12(3), 398; https://doi.org/10.3390/sym12030398 - 04 Mar 2020
Cited by 2 | Viewed by 953
Abstract
Using the classical vacuum solutions of Newtonian gravity that do not explicitly involve matter, dark matter, or the gravitational constant, subject to an averaging process, a form of gravity relevant to the flattening of galaxy rotation curves results. The latter resembles the solution [...] Read more.
Using the classical vacuum solutions of Newtonian gravity that do not explicitly involve matter, dark matter, or the gravitational constant, subject to an averaging process, a form of gravity relevant to the flattening of galaxy rotation curves results. The latter resembles the solution found if the vacuum is simply assigned a gravitational field density, and a volume of the vacuum is then excluded, with no averaging process. A rationale then follows for why these terms would become important on the galactic scale. Then, a modification of General Relativity, motivated by the Newtonian solutions, that are equivalent to a charge void, is partially defined and discussed in terms of a least action principle. Full article
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Review

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Review
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity
Symmetry 2022, 14(7), 1331; https://doi.org/10.3390/sym14071331 - 27 Jun 2022
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Abstract
Astronomical observations reveal a major deficiency in our understanding of physics—the detectable mass is insufficient to explain the observed motions in a huge variety of systems given our current understanding of gravity, Einstein’s General theory of Relativity (GR). This missing gravity problem may [...] Read more.
Astronomical observations reveal a major deficiency in our understanding of physics—the detectable mass is insufficient to explain the observed motions in a huge variety of systems given our current understanding of gravity, Einstein’s General theory of Relativity (GR). This missing gravity problem may indicate a breakdown of GR at low accelerations, as postulated by Milgromian dynamics (MOND). We review the MOND theory and its consequences, including in a cosmological context where we advocate a hybrid approach involving light sterile neutrinos to address MOND’s cluster-scale issues. We then test the novel predictions of MOND using evidence from galaxies, galaxy groups, galaxy clusters, and the large-scale structure of the universe. We also consider whether the standard cosmological paradigm (LCDM) can explain the observations and review several previously published highly significant falsifications of it. Our overall assessment considers both the extent to which the data agree with each theory and how much flexibility each has when accommodating the data, with the gold standard being a clear a priori prediction not informed by the data in question. Our conclusion is that MOND is favoured by a wealth of data across a huge range of astrophysical scales, ranging from the kpc scales of galactic bars to the Gpc scale of the local supervoid and the Hubble tension, which is alleviated in MOND through enhanced cosmic variance. We also consider several future tests, mostly at scales much smaller than galaxies. Full article

Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Excluded Volume for Flat Galaxy Rotation Curves in Newtonian Gravity and General Relativity
Authors: Rand Dannenberg
Affiliation: Optical Physics Company
Abstract: Adding classical vacuum solutions to Newtonian gravity that do not explicitly involve matter, dark matter, or the gravitational constant, then averaged over angular orientation, admits a form of gravity possibly pertinent to the flattening of galaxy rotation curves. The latter resembles the solution found if the vacuum is assigned a gravitational field density, and a volume of the vacuum is then excluded, with no averaging process. A rationale then follows for why these terms would become important on the galactic scale. Then, a modification of General Relativity, motivated by the Newtonian solutions, that are equivalent to a charge void, is partially defined and discussed in terms of a least action principle.

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