Advances and Limitations of Modified Gravity

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

Deadline for manuscript submissions: 31 March 2024 | Viewed by 2220

Special Issue Editors

Departamento de Física, Campus do Pici, Universidade Federal do Ceará, Fortaleza 60455-760, CE, Brazil
Interests: modified gravity
Departamento de Física, CCT, Universidade Estadual do Ceará, Fortaleza 60714-903, Brazil
Interests: classical and quantum field theory; quantum mechanics; modified theory of gravity; cosmology; black holes
Departamento de Física, Universidade Federal do Cariri (UFCA), Av. Tenente Raimundo Rocha, Cidade Universitária, Juazeiro do Norte 63048-080, Brazil
Interests: classical and quantum field theory; finite temperature field theory; modified theories of gravity; black holes; wormholes; black strings; analogue models for gravity

Special Issue Information

Dear Colleagues,

Despite the enormous success of general relativity, some questions remain unanswered, such as problems related to dark energy, dark matter, inflation, and quantum description of gravity, among others. The new era of high-precision tests of general relativity, with LIGO, VIRGO, EHT, and JWST, has attracted renewed interest among the community in alternative theories of gravity. There are several modified theories of gravity proposed in the literature so far; thus, a Special Issue on the advances and limitations of modified theories of gravity is of great importance. This Special Issue will be hosted in an open access, peer-reviewed journal which publishes original and quality research on all aspects of gravitational physics and cosmology.

Dr. Geová Maciel De Alencar
Dr. Marcony Silva Cunha
Prof. Dr. Job Saraiva Furtado
Guest Editors

Manuscript Submission Information

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Published Papers (2 papers)

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38 pages, 3836 KiB  
Article
Geometric Origin of the Galaxies’ Dark Side
by Leonardo Modesto, Tian Zhou and Qiang Li
Universe 2024, 10(1), 19; https://doi.org/10.3390/universe10010019 - 29 Dec 2023
Cited by 3 | Viewed by 871
Abstract
We show that Einstein’s conformal gravity can explain, simply, and on the geometric ground, galactic rotation curves, without the need to introduce any modification in both the gravitational as well as in the matter sector of the theory. The geometry of each galaxy [...] Read more.
We show that Einstein’s conformal gravity can explain, simply, and on the geometric ground, galactic rotation curves, without the need to introduce any modification in both the gravitational as well as in the matter sector of the theory. The geometry of each galaxy is described by a metric obtained, making a singular rescaling of Schwarzschild’s spacetime. The new exact solution, asymptotically anti-de Sitter, manifests an unattainable singularity at infinity that cannot be reached in finite proper time; namely, the spacetime is geodetically complete. It deserves to be noticed that, in this paper, we have a different opinion from the usual one. Indeed, instead of making the metric singularity-free, we make it apparently but harmlessly even more singular than Schwarzschild’s. Finally, it is crucial to point out that Weyl’s conformal symmetry is spontaneously broken into the new singular vacuum rather than the asymptotically flat Schwarzschild’s one. The metric is unique according to the null energy condition, the zero acceleration for photons in the Newtonian regime, and the homogeneity of the Universe at large scales. Once the matter is conformally coupled to gravity, the orbital velocity for a probe star in the galaxy turns out to be asymptotically constant consistent with the observations and the Tully–Fisher relation. Therefore, we compare our model with a sample of 175 galaxies and show that our velocity profile very well interpolates the galactic rotation curves after a proper choice of the only free parameter in the metric. The mass-to-luminosity ratios of galaxies turn out to be close to 1, consistent with the absence of dark matter. Full article
(This article belongs to the Special Issue Advances and Limitations of Modified Gravity)
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10 pages, 371 KiB  
Article
Neutron Stars in the Context of f(T,T) Gravity
by Clésio E. Mota, Luis C. N. Santos, Franciele M. da Silva, César V. Flores, Iarley P. Lobo and Valdir B. Bezerra
Universe 2023, 9(6), 260; https://doi.org/10.3390/universe9060260 - 29 May 2023
Cited by 1 | Viewed by 732
Abstract
In this work, we investigate the existence of neutron stars (NS) in the framework of f(T,T) gravity, where T is the torsion tensor and T is the trace of the energy–momentum tensor. The hydrostatic equilibrium equations are obtained, [...] Read more.
In this work, we investigate the existence of neutron stars (NS) in the framework of f(T,T) gravity, where T is the torsion tensor and T is the trace of the energy–momentum tensor. The hydrostatic equilibrium equations are obtained, however, with p and ρ quantities passed on by effective quantities p¯ and ρ¯, whose mass–radius diagrams are obtained using modern equations of state (EoS) of nuclear matter derived from relativistic mean field models and compared with the ones computed by the Tolman–Oppenheimer–Volkoff (TOV) equations. Substantial changes in the mass–radius profiles of NS are obtained even for small changes in the free parameter of this modified theory. The results indicate that the use of f(T,T) gravity in the study of NS provides good results for the masses and radii of some important astrophysical objects, as, for example, the NS of low-mass X-ray binary in NGC 6397, the millisecond pulsar PSR J0740+6620 and the GW170817 event. In addition, radii results inferred from the Lead Radius Experiment (PREX-2) can also be described for certain parameter values. Full article
(This article belongs to the Special Issue Advances and Limitations of Modified Gravity)
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