Article
Physics, Particles & Fields
M. Z. Bhatti, Z. Yousaf, F. Hussain
Summary: This article investigates the effects of electromagnetic field on the generalization of Lemaitre-Tolman-Bondi (LTB) spacetime while considering Palatini f(R) gravity and dissipative dust fluid. By exploring modified field equations and establishing evolution equations, the study delves into the dynamics of an inhomogeneous universe, with a focus on the scalar functions associated with metric coefficients. The properties of generalized LTB spacetime under the influence of charge and Palatini f(R) curvature terms are compared and analyzed, with symmetric properties also studied using streaming out and diffusion approximations.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
A. B. Lahanas
Summary: In this study, we investigate R2 inflation in Palatini gravity with scalar fields coupled to gravity. We explore the similarities between these theories, in the Einstein frame, and K-inflation models. Additionally, we examine single-field inflationary models with monomial potentials V similar to hn, where n is a positive even integer. The analysis also includes the study of the Higgs model with nonminimal coupling to gravity. Through constraints from cosmological data, we find bounds on the inflationary scale Ms similar to 1/√(alpha) and the reheating temperature of the Universe.
Article
Physics, Multidisciplinary
Stefano Camera, Salvatore Capozziello, Lorenzo Fatibene, Andrea Orizzonte
Summary: We investigate how the cosmological equation of state can be used to scrutinize extended theories of gravity, specifically the Palatini f(R) gravity. The effective equation of state produced by a given model is studied, and the inverse problem of determining which models are compatible with a given effective equation of state is also considered. We find that power-law models are capable of transforming barotropic Equations of State into effective barotropic ones, and the form of equation of state is preserved only for f(R) = R. Additionally, quadratic and non-homogeneous effective Equations of State contain the Starobinsky model and other models.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Physics, Particles & Fields
Mutasem Z. Bani-Fwaz, M. Z. Bhatti, Z. Yousaf, U. Farwa, Ahmed M. Galal
Summary: This paper investigates the continuation of LTB space-time for dissipative dust configuration in the direction of Palatini f(R) theory. The effects of kinematical variables and curvature invariant on the proposed fluid configuration are explored. The significance of computing Palatini f(R) scalar variables for dissipative dust spheres through the orthogonal splitting of Riemann-tensor is reported. Two subcases of LTB space-time are carried out to note down its symmetric aspects.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
Joao C. Lobato, Isabela S. Matos, Mauricio O. Calvao, Ioav Waga
Summary: The study introduces an alternative choice of variables for treating f(R) models in their Palatini formulation, leading to the derivation of general results and a complete description of the phase space for exponential gravity. It is shown that Palatini exponential gravity theories have a final attractor critical point with specific effective equation of state parameters. Comparison of analytical results with numerical solutions of the field equations is also conducted.
Article
Astronomy & Astrophysics
Jaakko Annala, Syksy Rasanen
Summary: In this study, we investigate inflation using the most general non-degenerate gravitational action, involving the symmetric part of the Ricci tensor coupled to a scalar field in the Palatini formulation of gravity. By employing field redefinitions, we manage to shift the impact of the Ricci terms from gravity to the scalar field, specifically focusing on slow-roll inflation. As exemplified by cases of actions quadratic and cubic in the Ricci tensor, we find that in the quadratic scenario, the tensor-to-scalar ratio r can be suppressed with no effect on the scalar spectrum, while in the cubic scenario, r can be suppressed by at most 2/9, with significant changes in the scalar spectral index n(s).
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Physics, Particles & Fields
Julio C. Fabris, Ednaldo L. B. Junior, Manuel E. Rodrigues
Summary: This article investigates the implementation of black bounce solutions in f(R) theories. It is found that violation of the energy conditions still occurs in these solutions, albeit less severe than in General Relativity (GR) cases. The authors propose a zero-density model with horizons and present a model with positive energy density, which differs from GR.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Joao Luis Rosa, D. A. Ferreira, Dionisio Bazeia, Francisco S. N. Lobo
Summary: The study focuses on 5-dimensional braneworld scenarios within the scalar-tensor representation of the generalized hybrid metric-Palatini gravitational theory. It shows that all models are stable against small fluctuations of the metric and that the gravitational zero mode profile can be controlled by the model's parameters, particularly in the presence of an additional scalar field.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Particles & Fields
Georg Herzog, Helios Sanchis-Alepuz
Summary: The study focuses on solutions of stellar structure equations in modified theories of gravity, particularly in the context of neutron stars. By exploring a range of viable values of alpha and beta, the potential impacts of R-2 and Q terms are illustrated. Results suggest that modifications of general relativity can have a significant effect on the properties of stars under certain combinations of parameters and equations of state, indicating that astrophysical observations may serve as discriminators of modifications of General Relativity as the accuracy of determination of neutron star equations of state increases.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
D. Demir, K. Gabriel, A. Kasem, S. Khalil
Summary: This study investigates the impact of the geometric Proca field on gravitational waves. The results show significant signatures of the geometric Proca in the gravitational wave signal, with a detectable gravitational wave energy density by the next generation of detectors. This could indicate that gravity has a non-Riemannian nature.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Hamidreza Saiedi
Summary: In this study, the thermodynamic behavior of time-dependent wormhole geometries is investigated within the Palatini approach to modified f(R) theories of gravity. By redefining energy density and pressure, the continuity equation is satisfied, leading to the exploration of total entropy variation and the validity of the generalized second law of thermodynamics in relation to apparent and event horizons of evolving wormholes.
GENERAL RELATIVITY AND GRAVITATION
(2021)
Article
Astronomy & Astrophysics
Andreu Maso-Ferrando, Nicolas Sanchis-Gual, Jose A. Font, Gonzalo J. Olmo
Summary: In the Palatini formulation of f (R) gravity, equilibrium solutions of spherically symmetric boson stars were explored. The study compared solutions of the quadratic theory f (R) = R + xi R-2 with those in general relativity, showing similar existence curves but significant differences for negative coupling parameters leading to repulsive gravitational components. Introducing self-interactions further emphasized the similarities between f (R) and general relativity, making observational discrimination between the two theories challenging.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Physics, Multidisciplinary
Hamidreza Saiedi
Summary: This study investigates traversable wormhole spacetimes constructed in the Palatini version of modified f(R) gravity theory, with the requirement that the matter supporting these spacetimes satisfies specific conditions. The results demonstrate significant differences in the gravitational field equations between the Palatini approach and general relativity/f(R) metric approach, and show that the matter stress-energy tensor meets the NEC and WEC criteria in this framework.
INDIAN JOURNAL OF PHYSICS
(2022)
Article
Physics, Particles & Fields
Fernanda Alvarim Silveira, Rodrigo Maier, Santiago Esteban Perez Bergliaffa
Summary: This study presents a model that generalizes Schwarzschild's homogeneous star by adding a transition zone for the density near the surface, and numerically integrates the modified TOV equations for the f(R)=R+lambda R2 Palatini theory to obtain finite configurations. Depending on the values of the relevant parameters, objects more compact, less compact, or equally compact as those obtained in GR with the same density profile have been shown to exist. Particularly, in some region of the parameter space, the compactness is close to that set by the Buchdahl limit.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Dhruba Jyoti Gogoi, Umananda Dev Goswami
Summary: This study investigates the behavior of dark energy f(R) gravity models along with two other cosmological models under the Palatini formalism. The results show that the new model behaves similarly to the other models in the early stages of the universe but has a unique prediction for the future history of the universe. All models show good agreement with observational data within a constrained range of parameters, with the new model showing particularly satisfactory agreement throughout its allowed parameter range.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Physics, Multidisciplinary
K. Atazadeh
Article
Astronomy & Astrophysics
Y. Heydarzade, F. Darabi, K. Atazadeh
ASTROPHYSICS AND SPACE SCIENCE
(2016)
Article
Physics, Particles & Fields
K. Atazadeh, F. Darabi, M. Mousavi
EUROPEAN PHYSICAL JOURNAL C
(2016)
Article
Astronomy & Astrophysics
Akram Sadat Sefiedgar
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2016)
Article
Physics, Multidisciplinary
A. S. Sefiedgar, A. Ashrafinejad
Article
Physics, Multidisciplinary
A. S. Sefiedgar
Article
Astronomy & Astrophysics
Akram Sadat Sefiedgar, Majid Daghigh
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2017)
Article
Astronomy & Astrophysics
K. Atazadeh, F. Darabi
PHYSICS OF THE DARK UNIVERSE
(2017)
Article
Physics, Particles & Fields
K. Atazadeh
EUROPEAN PHYSICAL JOURNAL C
(2018)
Article
Physics, Mathematical
F. Darabi, K. Atazadeh
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2018)
Article
Physics, Multidisciplinary
F. Darabi, K. Atazadeh, Y. Heydarzade
EUROPEAN PHYSICAL JOURNAL PLUS
(2018)
Article
Physics, Multidisciplinary
A. S. Sefiedgara, A. Yoonesyaanb
EUROPEAN PHYSICAL JOURNAL PLUS
(2018)
Article
Physics, Particles & Fields
A. S. Sefiedgar, M. Mirzazadeh
ADVANCES IN HIGH ENERGY PHYSICS
(2018)
Article
Astronomy & Astrophysics
A. S. Sefiedgar, M. Mirzazadeh
MODERN PHYSICS LETTERS A
(2020)
Article
Physics, Multidisciplinary
A. S. Sefiedgar, A. Gharibi Ziarati