An example of rotating cosmological universe in modified gravity

Ahmed, F.; de Souza, J. C. R.; Santos, A. F.

doi:10.1140/epjp/s13360-024-05240-w

Eur. Phys. J. Plus

2024

DOI: 10.1140/epjp/s13360-024-05240-w

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An example of rotating cosmological universe in modified gravity

F. Ahmed,

J. C. R. de Souza,

A. F. Santos

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2024

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Cited by 6 publications

References 59 publications

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Fermion localization on the brane in Ricci-inverse gravity

Moreira,

Ahmed,

Dong

2024

Annals of Physics

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Fermion localization on the brane in Ricci-inverse gravity

Moreira,

Ahmed,

Dong

2024

Annals of Physics

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Time-machines construct in f(ℛ, 𝒜, A^μν A_μν ) and f(ℛ) modified gravity theories

Ahmed,

de Souza,

Santos

2024

J. Cosmol. Astropart. Phys.

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In this paper, our objective is to explore a time-machine space-time formulated in general relativity, as introduced by Li (Phys. Rev. D 59, 084016 (1999)), within the context of modified gravity theories. We consider Ricci-inverse gravity of all Classes of models, i.e., (i) Class-I: f(ℛ, 𝒜) = (ℛ + κℛ2 + β 𝒜), (ii) Class-II: f(ℛ, Aμν Aμν ) = (ℛ + κℛ2 + γ Aμν Aμν ) model, and (iii) Class-III: f(ℛ, 𝒜, Aμν Aμν ) = (ℛ + κℛ2 + β𝒜 + δ𝒜2 + γ Aμν Aμν ) model, where Aμν is the anti-curvature tensor, the reciprocal of the Ricci tensor, Rμν , 𝒜 = gμν Aμν is its scalar, and β, κ, γ, δ are the coupling constants. Moreover, we consider f(ℛ) modified gravity theory and investigate the same time-machine space-time. In fact, we show that Li time-machine space-time serve as valid solutions both in Ricci-inverse and f(ℛ) modified gravity theories. Thus, both theory allows the formation of closed time-like curves analogue to general relativity, thereby representing a possible time-machine model in these gravity theories theoretically.

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Axially symmetric solutions in Ricci-inverse modified gravity

Ahmed,

de Souza,

Santos

2024

Eur. Phys. J. C

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We investigate a family of axial symmetry solution constructed in general relativity (GR) within the framework of Ricci-inverse (RI) gravity theory. In GR, these solutions admitted closed time-like curves at an instant of time from an initial spacelike hypersurface in a causally well-behaved manner, thus, violates the causality condition. Our aim is to examine these axial symmetry solutions within the context of Ricci-inverse gravity theory to determine whether closed time-like curves still appear in this new gravity theory. We consider two Classes of RI-gravity models: (i) Class-II models defined by a function $$f=f({\mathcal {R}}, A^{\mu \nu }\,A_{\mu \nu })$$ f = f ( R , A μ ν A μ ν ) gravity and (ii) Class-III models defined by $$f=f({\mathcal {R}},{\mathcal {A}}, A^{\mu \nu }\,A_{\mu \nu })$$ f = f ( R , A , A μ ν A μ ν ) , where $$A^{\mu \nu }$$ A μ ν is the anti-curvature tensor, $${\mathcal {A}}=g_{\mu \nu }\,A^{\mu \nu }$$ A = g μ ν A μ ν as its scalar, and $$R^{\mu \nu }$$ R μ ν is the Ricci tensor. We are able solved the modified field equations considering these axial symmetry solutions as background in RI-gravity with null radiation as the matter content and the cosmological constant. This confirms that the chosen family of axial symmetry solutions are valid solutions in RI-gravity theory and, consequently, closed time-like curves is still form, analogous to their formation in GR.

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An example of rotating cosmological universe in modified gravity

Cited by 6 publications

References 59 publications

Fermion localization on the brane in Ricci-inverse gravity

Fermion localization on the brane in Ricci-inverse gravity

Time-machines construct in f(ℛ, 𝒜, A^μν A_μν ) and f(ℛ) modified gravity theories

Axially symmetric solutions in Ricci-inverse modified gravity

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An example of rotating cosmological universe in modified gravity

Cited by 6 publications

References 59 publications

Fermion localization on the brane in Ricci-inverse gravity

Fermion localization on the brane in Ricci-inverse gravity

Time-machines construct in f(ℛ, 𝒜, Aμν Aμν ) and f(ℛ) modified gravity theories

Axially symmetric solutions in Ricci-inverse modified gravity

Contact Info

Product

Resources

About

Time-machines construct in f(ℛ, 𝒜, A^μν A_μν ) and f(ℛ) modified gravity theories