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Universe
Special Issues
New Challenges in Modified Gravity at Cosmological and Astrophysical Scales
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New Challenges in Modified Gravity at Cosmological and Astrophysical Scales

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Gravitation".

Deadline for manuscript submissions: closed (10 April 2022) | Viewed by 8798

Special Issue Editors

Dr. Daniele Vernieri

E-Mail Website
Guest Editor
Dipartimento di Fisica “Ettore Pancini”, Università degli Studi di Napoli “Federico II”, Complesso Universitario di Monte Sant'Angelo, Via Cinthia, 21, 80126 Napoli, Italy
Interests: gravitation theory; cosmology; astrophysics
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Salvatore Capozziello

E-Mail Website
Guest Editor
1. Dipartimento di Fisica “E. Pancini”, Università di Napoli “Federico II”, Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, I-80126 Napoli, Italy
2. Istituto Nazionale di Fisica Nucleare (INFN) Sez. di Napoli, Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, I-80126 Napoli, Italy
3. Scuola Superiore Meridionale, Largo S. Marcellino 10, I-80138 Napoli, Italy
Interests: general relativity; cosmology; relativistic astrophysics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In recent decades, a plethora of new theories and toy models of gravity have been proposed in order to address the still unsolved theoretical issues at scales where gravity plays a crucial role, such as the ones connected to quantum gravity, dark energy and dark matter, cosmological constant, and so forth. Moreover, while giving an answer to these fundamental questions, one has also to ensure the viability of the new proposed theories against solar system constraints and the increasing amount of always more precise cosmological data.

This Special Issue aims at collecting and exploring new work with regards to solving methods and analytical solutions in gravitation theory, with applications in astrophysics and cosmology.

Potential topics include, but are not limited to, the following:

  • Symmetries in modified gravity (e.g., Lie and Noether symmetries)
  • New exact and perturbative solving methods of the gravitational field equations
  • Analytical solutions in astrophysical and cosmological background
  • Conformal and disformal transformations connecting different theories of gravity
  • Construction of theories with extra dynamical fields
  • Dynamical systems approaches and methods in higher-order theories

Dr. Daniele Vernieri
Prof. Dr. Salvatore Capozziello
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. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. 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

  • modified gravity
  • cosmology
  • astrophysics
  • exact solutions and symmetries

Published Papers (5 papers)

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Research

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14 pages, 454 KiB  
Communication
Binary X-ray Sources in Massive Brans–Dicke Gravity
by Grigoris Panotopoulos, Ángel Rincón and Ilídio Lopes
Universe 2022, 8(5), 285; https://0-doi-org.brum.beds.ac.uk/10.3390/universe8050285 - 19 May 2022
Cited by 2 | Viewed by 1432
Abstract
This study focuses on the X-ray emission of low-mass black hole binaries in massive Brans–Dicke gravity. First, we compute the accretion disk with the well-known Shakura–Sunyaev model for an optically thick, cool, and geometrically thin disk. Moreover, we assume that the gravitational field [...] Read more.
This study focuses on the X-ray emission of low-mass black hole binaries in massive Brans–Dicke gravity. First, we compute the accretion disk with the well-known Shakura–Sunyaev model for an optically thick, cool, and geometrically thin disk. Moreover, we assume that the gravitational field generated by the stellar-mass black hole is an analogue of the Schwarzschild space-time of Einstein’s theory in massive Brans–Dicke gravity. We compute the most relevant quantities of interest, i.e., (i) the radial velocity, (ii) the energy and surface density, and (iii) the pressure as a function entirely of the radial coordinate. We also compute the soft spectral component of the X-ray emission produced by the disk. Furthermore, we investigate in detail how the mass of the scalar field modifies the properties of the binary as described by the more standard Schwarzschild solution. Full article
(This article belongs to the Special Issue New Challenges in Modified Gravity at Cosmological and Astrophysical Scales)
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8 pages, 248 KiB  
Communication
Renormalizable and Unitary Lorentz Invariant Model of Quantum Gravity
by Sergey A. Larin
Universe 2021, 7(11), 435; https://0-doi-org.brum.beds.ac.uk/10.3390/universe7110435 - 13 Nov 2021
Cited by 1 | Viewed by 1219
Abstract
We analyze the R+R2 model of quantum gravity where terms quadratic in the curvature tensor are added to the General Relativity action. This model was recently proved to be a self-consistent quantum theory of gravitation, being both renormalizable and unitary. [...] Read more.
We analyze the R+R2 model of quantum gravity where terms quadratic in the curvature tensor are added to the General Relativity action. This model was recently proved to be a self-consistent quantum theory of gravitation, being both renormalizable and unitary. The model can be made practically indistinguishable from General Relativity at astrophysical and cosmological scales by the proper choice of parameters. Full article
(This article belongs to the Special Issue New Challenges in Modified Gravity at Cosmological and Astrophysical Scales)
18 pages, 4952 KiB  
Article
Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star
by Duško Borka, Vesna Borka Jovanović, Salvatore Capozziello, Alexander F. Zakharov and Predrag Jovanović
Universe 2021, 7(11), 407; https://0-doi-org.brum.beds.ac.uk/10.3390/universe7110407 - 28 Oct 2021
Cited by 22 | Viewed by 1563
Abstract
After giving a short overview of previous results on constraining of Extended Gravity by stellar orbits, we discuss the Schwarzschild orbital precession of S2 star assuming the congruence with predictions of General Relativity (GR). At the moment, the S2 star trajectory is remarkably [...] Read more.
After giving a short overview of previous results on constraining of Extended Gravity by stellar orbits, we discuss the Schwarzschild orbital precession of S2 star assuming the congruence with predictions of General Relativity (GR). At the moment, the S2 star trajectory is remarkably fitted with the first post-Newtonian approximation of GR. In particular, both Keck and VLT (GRAVITY) teams declared that the gravitational redshift near its pericenter passage for the S2 star orbit corresponds to theoretical estimates found with the first post-Newtonian (pN) approximation. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center and showed that it is close to the GR prediction. Based on this observational fact, we evaluated parameters of the Extended Gravity theories with the Schwarzschild precession of the S2 star. Using the mentioned method, we estimate the orbital precession angles for some Extended Gravity models including power-law f(R), general Yukawa-like corrections, scalar–tensor gravity, and non-local gravity theories formulated in both metric and Palatini formalism. In this consideration, we assume that a gravitational field is spherically symmetric, therefore, alternative theories of gravity could be described only with a few parameters. Specifically, considering the orbital precession, we estimate the range of parameters of these Extended Gravity models for which the orbital precession is like in GR. Then we compare these results with our previous results, which were obtained by fitting the simulated orbits of S2 star to its observed astrometric positions. In case of power-law f(R), generic Yukawa-like correction, scalar–tensor gravity and non-local gravity theories, we were able to obtain a prograde orbital precession, like in GR. According to these results, the method is a useful tool to evaluate parameters of the gravitational potential at the Galactic Center. Full article
(This article belongs to the Special Issue New Challenges in Modified Gravity at Cosmological and Astrophysical Scales)
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8 pages, 521 KiB  
Communication
The Possibility of a Non-Lagrangian Theory of Gravity
by Celia Escamilla-Rivera and Júlio C. Fabris
Universe 2021, 7(7), 230; https://0-doi-org.brum.beds.ac.uk/10.3390/universe7070230 - 06 Jul 2021
Cited by 1 | Viewed by 1941
Abstract
General Relativity resembles a very elegant crystal glass: If we touch its principles, that is, its Lagrangian, there is a risk of breaking everything. Or, if we will, it is like a short blanket: Curing some problems creates new problems. This paper is [...] Read more.
General Relativity resembles a very elegant crystal glass: If we touch its principles, that is, its Lagrangian, there is a risk of breaking everything. Or, if we will, it is like a short blanket: Curing some problems creates new problems. This paper is devoted to bring to light the reasons why we pursue the possibility of a non-Lagrangian theory of gravity under the hypothesis of an extension of the original general relativity with an ansatz inspired in the fundamental principles of classical and quantum physics. Full article
(This article belongs to the Special Issue New Challenges in Modified Gravity at Cosmological and Astrophysical Scales)
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Review

Jump to: Research

18 pages, 471 KiB  
Review
Extended Gravity Constraints at Different Scales
by Stanislav Alexeyev and Vyacheslav Prokopov
Universe 2022, 8(5), 283; https://0-doi-org.brum.beds.ac.uk/10.3390/universe8050283 - 15 May 2022
Viewed by 1706
Abstract
We review a set of the possible ways to constrain extended gravity models at Galaxy clusters scales (the regime of dark energy explanations and comparison with ΛCDM), for black hole shadows, gravitational wave astronomy, binary pulsars, the Solar system and a Large [...] Read more.
We review a set of the possible ways to constrain extended gravity models at Galaxy clusters scales (the regime of dark energy explanations and comparison with ΛCDM), for black hole shadows, gravitational wave astronomy, binary pulsars, the Solar system and a Large Hadron Collider (consequences for high-energy physics at TeV scale). The key idea is that modern experimental and observational precise data provide us with the chance to go beyond general relativity. Full article
(This article belongs to the Special Issue New Challenges in Modified Gravity at Cosmological and Astrophysical Scales)
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