Article
Astronomy & Astrophysics
Andrew DeBenedictis, Saga Ilijic, Marko Sossich
Summary: This paper studies the properties that the vacuum must have in the minimal extension of the teleparallel equivalent of general relativity. It is found that the mathematical conditions on the vacuum mimic those of general relativity and that certain restrictions on the existence of smooth horizons and singularities are necessary. The analysis also suggests that static spherical matter distributions may have extra restrictions on their spatial extent and stress-energy bounds to ensure the validity of vacuum solutions.
Article
Astronomy & Astrophysics
Masato Minamitsuji, Antonio De Felice, Shinji Mukohyama, Michele Oliosi
Summary: In this study, static and spherically symmetric solutions are investigated in the minimal theory of bigravity (MTBG). It is found that a pair of Schwarzschild-de Sitter spacetimes with different cosmological constants and black hole masses is a solution in the self-accelerating branch of MTBG, but not in the normal branch. It is also shown that the Schwarzschild-de Sitter solutions can become compatible with the normal branch by using different coordinates. Furthermore, it is confirmed that the self-accelerating branch of MTBG admits static and spherically symmetric general relativity solutions with matter written in the spatially flat coordinates, including neutron stars with arbitrary matter equations of state. Finally, it is demonstrated that nontrivial solutions in the self-accelerating branch are given by the Schwarzschild-de Sitter metrics written in nonstandard coordinates.
Article
Astronomy & Astrophysics
Alexey Golovnev, Maria-Jose Guzman
Summary: We study the properties of static spherically symmetric solutions in f(T) gravity by generalizing Bianchi identities and reducing the search for solutions to two simple equations. One equation is independent of the function f and describes the properties of solutions in any f(T) theory, while the other is the radial equation that identifies which function f is suitable for a chosen solution. Using these equations, we find exact and perturbative solutions for arbitrary and specific choices of f.
Article
Astronomy & Astrophysics
Rui-Hui Lin, Xiang-Hua Zhai
Summary: General relativity can be formulated equivalently with a non-Riemannian geometry involving a nonmetricity Q but vanishing curvature R and torsion T. Modification based on this description leads to f(Q) gravity. The application of f(Q) gravity to spherically symmetric configurations is explored, demonstrating effects on external and internal solutions of compact stars through different modifications.
Article
Astronomy & Astrophysics
G. G. L. Nashed
Summary: The study investigates the non-trivial black hole solutions for neutral and charged spherically symmetric space-times, determines the metric potentials, and calculates the thermodynamic quantities for these black holes, showing consistency with existing literature. Additionally, the validity of the first law of thermodynamics for the black holes is demonstrated.
Article
Astronomy & Astrophysics
Wenyi Wang, Hua Chen, Taishi Katsuragawa
Summary: This study analyzes the theoretical solutions of f(Q) gravity, revealing restrictions on its functional form and studying the properties of Schwarzschild-like solutions in nontrivial f(Q) gravity.
Article
Physics, Particles & Fields
Marco Calza, Lorenzo Sebastiani
Summary: In this paper, we analyze a class of topological static spherically symmetric vacuum solutions in Q-gravity. We consider an Ansatz that ensures these solutions trivially satisfy the field equations when the non-metricity scalar is constant. Specifically, we provide and discuss local solutions in the form of black holes and traversable wormholes.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Nuclear
Moreshwar Tayde, Zinnat Hassan, P. K. Sahoo, Sashideep Gutti
Summary: In this study, we obtain wormhole solutions in the context of f(Q,T) gravity and investigate their properties using different forms of the gravitational Lagrangian.
Article
Physics, Nuclear
Moreshwar Tayde, Sayantan Ghosh, P. K. Sahoo
Summary: In this study, we analyze traversable wormhole solutions within the linear f(Q, T) = alpha Q + beta T gravity framework, ensuring the satisfaction of all energy conditions throughout spacetime. The solutions are obtained through a comprehensive analytical examination of the wormhole model's parameter space, considering the exponents governing redshift and shape functions, the wormhole throat radius (r(0)), redshift function value at the throat (phi(0)), and model parameters (alpha and beta). Bounds on these free parameters are established to guarantee energy condition satisfaction and provide two solutions. Additionally, the stability of a thin-shell around the wormhole is observed using the Israel junction condition. Finally, the null energy condition criteria and the potential for the thin-shell are calculated, along with their variations based on the chosen shape function.
Article
Physics, Multidisciplinary
S. A. Mardan, Umm-e-Farva Moeed, I. Noureen, Adnan Malik
Summary: The main objective of this work is to develop a novel general framework for generating solutions of stellar models in f(R) theory of gravity with class one metric. Such framework is not available in the vicinity of f(R) gravity. The relations of anisotropy factor, which is based on radial and tangential pressure, serve as the main source of generating solutions. The linear equation of state and conformally flat condition for class one metric are used to develop a consistent system of differential equations. We conclude that it is possible to develop generating solutions for the systems in f(R) gravity.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Materials Science, Multidisciplinary
Abu Bakr Mehmood, Fiaz Hussain, Ashfaque H. Bokhari, Muhammad Ramzan, Muhammad Faryad, Tahir Hussain
Summary: This article addresses the problem of finding non-static plane symmetric perfect fluid solutions in the f(R, T) theory of gravity. The authors propose a classification for such spacetimes and calculate solutions within each class, finding both static and non-static geometries. The authors also analyze the Killing symmetries to determine the Lie symmetry groups admitted by the obtained spacetimes, finding a range of Killing vector fields.
RESULTS IN PHYSICS
(2022)
Article
Physics, Multidisciplinary
Sweeti Kiroriwal, Jitendra Kumar, S. K. Maurya, Sourav Chaudhary
Summary: In this study, we examined new spherically symmetric wormhole solutions in modified symmetric teleparallel gravity theory. Constructing traversable wormholes with physically reasonable energy conditions and investigating their stability, we found that violations of energy conditions in gravity theory provide a viable framework for the study of wormholes.
Article
Astronomy & Astrophysics
Vittorio De Falco, Mariafelicia De Laurentis, Salvatore Capozziello
Summary: The study focuses on measuring the epicyclic frequencies to infer information on a given self-gravitating system and the related gravity background, particularly in static and spherically symmetric wormhole spacetimes. These theoretical results can be used to detect the presence of a wormhole, distinguish it from a black hole, and reconstruct wormhole solutions through fitting observational data. The physical implications of the proposed epicyclic method are also discussed.
Article
Physics, Particles & Fields
Erickson Tjoa, Robert B. Mann
Summary: This study investigates the dynamics of an Unruh-DeWitt detector interacting with a massless scalar field in static spherically symmetric spacetimes, deriving specific physical insights and characteristics.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Multidisciplinary
Fiaz Hussain, Murtaza Ali, Muhammad Ramzan, Sabiha Qazi
Summary: In this paper, the classification of static spherically symmetric perfect fluid space-times in the context of f(T) gravity using conformal vector fields (CVFs) is explored. The study reveals that in three cases, the considered space-times have proper CVFs in the framework of f(T) gravity. In one case, the space-time admits proper homothetic vector fields, while in the remaining 16 cases, the space-times either become conformally flat or admit Killing vector fields.
COMMUNICATIONS IN THEORETICAL PHYSICS
(2022)
Article
Astronomy & Astrophysics
G. G. L. Nashed
Summary: The study investigates the non-trivial black hole solutions for neutral and charged spherically symmetric space-times, determines the metric potentials, and calculates the thermodynamic quantities for these black holes, showing consistency with existing literature. Additionally, the validity of the first law of thermodynamics for the black holes is demonstrated.
Article
Multidisciplinary Sciences
Prateek Sharma, Hemwati Nandan, Gamal G. L. Nashed, Shobhit Giri, Amare Abebe
Summary: This article investigates various physical properties of a black hole in the modified general relativity of f(R) gravity, aiming to constrain the values of different parameters. The behavior of particles and photon frequency shift are analyzed to determine the similarity between the studied black hole and astrophysical black holes in general relativity. The findings are crucial for the understanding of gravity.
Article
Astronomy & Astrophysics
G. G. L. Nashed, A. T. Shafeek
Summary: In this study, we derive non-flat cosmological models using Moller's tetradic theory of gravitation and investigate the effects of parameters on the models. We show the impact of non-extensive thermodynamics on the evolution of the universe.
PHYSICS OF THE DARK UNIVERSE
(2022)
Article
Astronomy & Astrophysics
Z. Yousaf, G. G. L. Nashed, M. Z. Bhatti, H. Asad
Summary: The manuscript analyzes hyperbolically symmetric non-static fluid distribution with heat flux and electromagnetic field, constructing a general framework to examine the dynamic regime of matter configuration leading to static spacetime. The presence of negative energy density in the mass function indicates significant quantum implications, and the transport equation reveals the thermodynamic attributes of the fluid.astrophysico objects, Additionally, quasi-homologous constraint is used to construct various models, and valuable applications of astrophysical objects are deduced through evaluating analytical solutions in terms of kinematical variables.
Article
Astronomy & Astrophysics
Gamal Gergess Lamee Nashed
Summary: In this paper, we investigate the spherically symmetric black hole solution of the charged field equation in Rastall gravitational theory. We find that this solution is not affected by the Rastall parameter in the linear case, but when applied to a special form of nonlinear electrodynamics source, a novel solution involving the Rastall parameter is derived. This solution corresponds to the Anti-de-Sitter Reissner-Nordstrom spacetime and coincides with the Reissner-Nordstrom solution when the Rastall parameter vanishes.
Article
Physics, Multidisciplinary
G. G. L. Nashed, S. Nojiri
Summary: In this study, we construct spherically symmetric and static solutions in F(R) gravity coupled with electromagnetic fields. The solutions include new types of black holes with electric and magnetic charges. Our findings show that the higher-derivative terms in F(R) gravity make the curvature singularity softer compared to the charged black holes in Einstein's general relativity. We also calculate thermodynamical quantities of the obtained black holes and confirm the satisfaction of the first law of thermodynamics. Additionally, stability analysis reveals the existence of stable black hole solutions and indicates that the radial speed of the parity-odd mode is the speed of light.
FORTSCHRITTE DER PHYSIK-PROGRESS OF PHYSICS
(2023)
Article
Astronomy & Astrophysics
G. G. L. Nashed
Summary: In this study, modified gravity field equations are applied to millisecond pulsars to examine the matter-geometry coupling and its effects on the star's properties. The explicit forms of the energy-momentum tensor components are derived, and it is shown that the matter-geometry coupling leads to smaller sizes for stars with the same mass under Einstein's general relativity. The hypothesis is validated by observations from additional pulsars.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
G. G. L. Nashed, A. Sheykhi
Summary: We present two new classes of analytical solutions in the framework of f (R) gravity. These solutions describe non-rotating and rotating black holes, respectively, and have non-trivial values of the Ricci scalar. The obtained solutions exhibit strong singularities in spacetime, indicating a change in the causal structure caused by the higher-order derivative terms in f (R) gravity.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Particles & Fields
G. G. L. Nashed
Summary: The equivalence between Rastall's theory of gravity and Einstein's general relativity theory is investigated by applying Rastall's theory to a spacetime with spherical symmetry. Assumptions are made about the form of the metric potential's temporal component and constraints are imposed to eliminate anisotropy, resulting in an isotropic spacetime. The study focuses on obtaining parameters that align with the behavior of pulsars and suggests that Rastall's parameter can play a crucial role in forming realistic compact objects consistent with observational data.
Article
Physics, Particles & Fields
G. G. L. Nashed
Summary: The mimetic gravitational theory has gained attention in cosmology and astrophysics. In this study, it is shown that an isotropic model cannot be derived in the frame of mimetic gravitation theory, leading to the exploration of the theory coupled with a Lagrangian multiplier. The field equations of a static isotropic gravitational system are studied and a new isotropic model is derived, providing consistent results with a realistic isotropic star.
Article
Astronomy & Astrophysics
G. G. L. Nashed
Summary: In this study, a new charged spherically symmetric black hole solution is derived by applying the Gauss-Bonnet equation of motions coupled with the scalar field and potential. The form of the scalar field, the function of the scalar, and the Gauss-Bonnet term are determined successfully. Additional terms, O(r16) and O(r19), are found in this black hole solution compared to the Riessner Nordstrom solution, which are responsible for reproducing the multi-horizon black hole solution. The modified first law of thermodynamics and the corresponding Smarr relation are derived due to the existence of these additional terms.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Particles & Fields
G. G. L. Nashed
Summary: By analyzing observational data from the pulsar PSR J0740+6620, researchers determined the parameter beta in the modified theory of general relativity and used it to model the physical quantities associated with the mass and radius of the pulsar. The results show that, compared to the predictions of general relativity, the modified theory predicts slightly larger sizes for neutron stars.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
G. G. L. Nashed, S. Capozziello
Summary: This study investigates the possible modifications of general relativity at ultraviolet and infrared scales, particularly considering the possibility of parity violation in strong gravity regime. The Chern-Simons gravity theory is used to account for the parity violation. The study shows that for certain spacetime structures, Chern-Simons gravity is equivalent to general relativity, but it is not applicable to (A)dS-Kerr/Kerr black holes. The thermodynamic quantities and geodesic equation of the black hole are also calculated.
Article
Astronomy & Astrophysics
G. G. L. Nashed
Summary: By utilizing the field equations of the modified teleparallel equivalent of general relativity, an exact solution for a static charged black hole in n-dimensions is obtained without imposing any constraints. The solution reveals distinctive dimensional constants associated with mass and electric charge, and the presence of electric charge leads to deviations from the predictions of teleparallel equivalent of general relativity. The study also investigates the thermodynamic properties of the black hole and shows its thermal stability.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Multidisciplinary Sciences
Gamal G. L. Nashed, Sergei D. Odintsov, Vasillis K. Oikonomou
Summary: Using the Gauss-Bonnet gravity framework, this study derives a new internal spherically symmetric solution with specific metric potentials and determines the values of constants based on observational data. The results show stability and satisfactory agreement with observational data.
