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

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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 September 2023) | Viewed by 22375

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Special Issue Editors

Dr. Luis Acedo

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Guest Editor

Department of Mathematics, University of Extremadura, Badajoz, Spain
Interests: gravitation; modified theories of gravity
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Michael M. Tung

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Guest Editor

Instituto de Matemática Multidisciplinar, Universitat Politècnica de València, Edificio 8-G, 2º piso, Camino de Vera, s/n, 46022 Valencia, Spain
Interests: applied mathematics; theoretical physics

Dr. Golden Gadzirayi Nyambuya

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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 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

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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Open AccessArticle

Stable Exponential Cosmological Type Solutions with Three Factor Spaces in EGB Model with a Λ-Term

Kubantai K. Ernazarov

and

Vladimir D. Ivashchuk

Symmetry 2022, 14(7), 1296; https://doi.org/10.3390/sym14071296 - 22 Jun 2022

Cited by 1 | Viewed by 876

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:

α_{1}

and

α_{2}

. 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:

α_{1}

and

α_{2}

. 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:

H \neq 0

h_{1}

and

h_{2}

, obeying

m H + k_{1} h_{1} + k_{2} h_{2} \neq 0

, corresponding to factor spaces of dimensions

m > 1

k_{1} > 1

and

k_{2} > 1

, respectively, and depending upon sign parameter

ε = \pm 1

, where

ε = 1

corresponds to cosmological case and

ε = - 1

—to static one). We deal with two cases: (i)

m < k_{1} < k_{2}

and (ii)

1 < k_{1} = k_{2} = k

k \neq m

. We show that in both cases the solutions exist if

ε α = ε α_{2} / α_{1} > 0

and

α Λ > 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 \to \pm \infty

. The case

H = 0

is also considered. Full article

(This article belongs to the Special Issue Modified Gravity Theories and Applications to Astrophysics and Cosmology)

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Open AccessArticle

Exact Solution for Relativistic Trajectories Using Modal Transseries

Luis Acedo

Abraham J. Arenas

and

Nicolas De La Espriella

Symmetry 2020, 12(9), 1505; https://doi.org/10.3390/sym12091505 - 13 Sep 2020

Viewed by 1581

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 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

e^{- n θ}

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

(This article belongs to the Special Issue Modified Gravity Theories and Applications to Astrophysics and Cosmology)

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Figure 1

Open AccessArticle

Excluded Volume for Flat Galaxy Rotation Curves in Newtonian Gravity and General Relativity

Rand Dannenberg

Symmetry 2020, 12(3), 398; https://doi.org/10.3390/sym12030398 - 04 Mar 2020

Cited by 2 | Viewed by 1889

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 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

(This article belongs to the Special Issue Modified Gravity Theories and Applications to Astrophysics and Cosmology)

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Review

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Open AccessReview

From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity

Indranil Banik

and

Hongsheng Zhao

Symmetry 2022, 14(7), 1331; https://doi.org/10.3390/sym14071331 - 27 Jun 2022

Cited by 56 | Viewed by 16633

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 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 (

Λ

CDM) 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

(This article belongs to the Special Issue Modified Gravity Theories and Applications to Astrophysics and Cosmology)

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

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