Article
Physics, Particles & Fields
Beatrice Murorunkwere, Joseph Ntahompagaze, Edward Jurua
Summary: In this study, the 1+3 covariant approach and equivalence between f(R) gravity and scalar-tensor theory were applied to analyze cosmological perturbations. Focus was on dust dominated area with perturbation equations applied to a background solution of alpha R+beta R-n model, and the evolution of energy-density perturbations in a dust-dominated universe was found to decay with increasing redshift through numerical solutions.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Multidisciplinary
J. Sadeghi, B. Pourhassan, S. Noori Gashti, S. Upadhyay
Summary: In this paper, a modified f(R) gravitational model is introduced to examine new conditions for inflation models in the expanding universe. By introducing modified cosmological parameters and applying them to the modified f(R) gravitational model, the range of each parameter is determined with respect to observable data such as Planck 2018.
Article
Physics, Particles & Fields
F. M. Belchior, A. R. P. Moreira, R. V. Maluf, C. A. S. Almeida
Summary: In this paper, we investigate the influence of torsion scalar T and boundary term B on the confinement of both the gauge vector and Kalb-Ramond fields in modified teleparallel gravity. We propose a Stueckelberg-like geometrical coupling that non-minimally couples the fields to the torsion scalar and boundary term. We use the first-order formalism and two kinds of superpotential to set up our braneworld models. The geometrical coupling is used to produce a localized zero mode, and we analyze the massive spectrum for both fields to obtain possible resonant massive modes.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Bita Farsi, Ahmad Sheykhi
Summary: This study reveals the effects of an extra longitudinal degree of freedom on the evolution of perturbations in the context of mimetic gravity. By analyzing linear perturbations, it is found that the mimetic potential can act as dark energy and influence the dynamics of matter perturbations and cosmological parameters.
Article
Multidisciplinary Sciences
Bofeng Wu
Summary: A signature invariant geometric algebra framework for spacetime physics is formulated in this paper, including techniques related to relative vector and spacetime split, as well as rotor techniques for Lorentz transformations and relativistic dynamics of a massive particle in curved spacetime. The paper also presents a three-dimensional analogue of Newton's second law for a particle in curved spacetime, and provides a geometric algebra approach to gyroscopic precession in Lense-Thirring spacetime for a gyroscope moving.
SCIENTIFIC REPORTS
(2022)
Article
Astronomy & Astrophysics
Adrian Casado-Turrion, Antonio Dobado, Alvaro de la Cruz-Dombriz
Summary: This study investigates gravitational collapse in the context of f(R) theories of gravity. By generalizing the Oppenheimer-Snyder model to fit within metric f(R) gravity, novel exterior solutions are found, and it is verified that certain vacuum metrics cannot represent spacetime outside a collapsing dust star in metric f(R) gravity. Additionally, it is discovered that the Oppenheimer-Snyder model is incompatible with the junction conditions of the Palatini formulation of f(R) gravity.
Article
Physics, Multidisciplinary
Amir H. Rezaei, T. Azizi, N. Rashidi
Summary: In this paper, an exponential form of modified gravity is considered. The theory is consistent with local tests and various aspects of the model are investigated, including the static solution, scalar field potential, and stability of critical points. The realization of inflation and its graceful exit in this model are also studied.
Article
Astronomy & Astrophysics
Lakhan V. Jaybhaye, Snehasish Bhattacharjee, P. K. Sahoo
Summary: This paper aims to recreate the gravitational baryogenesis epoch in the framework of the f (R, Lm) theory of gravity, where R and Lm are the curvature scalar and the matter Lagrangian, respectively. We examine the model, f (R, Lm) = R2 + L & alpha;m + & zeta;, under the supposition that the universe is saturated with dark energy and perfect fluid, with a non-zero baryon to entropy ratio during a radiation dominance era. Our study found that f (R, Lm) gravity can considerably and steadily make a contribution to the phenomenon of gravitational baryogenesis. & COPY; 2023 Elsevier B.V. All rights reserved.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Particles & Fields
D. Bazeia, D. A. Ferreira, M. A. Marques
Summary: This study investigates thick branes in a single extra dimension modeled by a two-field configuration, including the cuscuton to control one of the fields' dynamics. Results show rich internal structure in branes, with novel geometry behavior governed by the parameter controlling the strength of the cuscuton term. The study also reveals significant modifications in the warp factor and energy density of the branes.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Particles & Fields
D. Bazeia, A. S. Lobao Jr
Summary: In this work, we investigate braneworlds generated by multiple scalar fields. The study focuses on the necessary formalism to examine models and evaluate the stability conditions of the gravitational sector under linear perturbations. Specifically, we develop a mechanism to explore distinct scenarios controlled by two and three fields, with a particular emphasis on how these fields can be utilized to modify the internal structure of the brane.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Multidisciplinary
Maria Shubina
Summary: In this paper, we investigate the metric power-law f(R) similar to Rn- gravity model for the four-dimensional metric tensor with two coordinates. We derive exact analytical vacuum solutions for various values of n, including both non-stationary configurations of the travelling wave type and stationary ones, particularly dependent on one radial variable.
Article
Physics, Multidisciplinary
A. I. Keskin
Summary: This study investigates the inflationary era of the Universe in the context of f(R) gravity, considering scalar perturbation equations and assuming specific parameter values to achieve inflation. The findings suggest that this inflation scenario for the early universe is possible, as observed parameters align with latest observational data.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Astronomy & Astrophysics
Mariaveronica De Angelis, Laria Figurato, Giovanni Montani
Summary: In this study, the canonical quantum dynamics of the isotropic universe in metric f(R) gravity theory is analyzed, with investigations into Schrodinger evolution in both vacuum and scalar field cases. The results show nonspreading wave packet profiles in vacuum and increased localization of universe volume when an external scalar field is present. This suggests a spontaneous mechanism for Universe classicalization in metric f(R) gravity, with implications for the transition from a Planckian Universe to a classical de-Sitter phase.
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, Nuclear
Juan M. Z. Pretel, Takol Tangphati, Ayan Banerjee, Anirudh Pradhan
Summary: Recent advances in nuclear theory and astrophysical observations have raised the need for specific theoretical models to study dense-matter physics phenomena. This study explores the structure of compact stars composed of a charged perfect fluid in the context of f (R,T) gravity, considering the existence of non-nucleonic degrees of freedom predicted by quantum chromodynamics (QCD).
Article
Astronomy & Astrophysics
Zahra Haghani, Nima Khosravi, Shahab Shahidi
CLASSICAL AND QUANTUM GRAVITY
(2015)
Article
Astronomy & Astrophysics
Zahra Haghani, Tiberiu Harko, Hamid Reza Sepangi, Shahab Shahidi
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2015)
Article
Physics, Particles & Fields
Zahra Haghani, Tiberiu Harko, Shahab Shahidi
EUROPEAN PHYSICAL JOURNAL C
(2017)
Article
Physics, Particles & Fields
Zahra Haghani, Tiberiu Harko, Hamid Reza Sepangi, Shahab Shahidi
EUROPEAN PHYSICAL JOURNAL C
(2017)
Article
Astronomy & Astrophysics
Andre Amado, Zahra Haghani, Azadeh Mohammadi, Shahab Shahidi
Article
Astronomy & Astrophysics
Zahra Haghani, Maryam Shiravand, Shahab Shahidi
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2018)
Article
Astronomy & Astrophysics
Zahra Haghani, Tiberiu Harko, Shahab Shahidi
PHYSICS OF THE DARK UNIVERSE
(2018)
Article
Astronomy & Astrophysics
Zahra Haghani, Tiberiu Harko, Hamid Reza Sepangi, Shahab Shahidi
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2014)
Article
Physics, Particles & Fields
Shahab Shahidi, Farid Charmchi, Zahra Haghani, Leila Shahkarami
EUROPEAN PHYSICAL JOURNAL C
(2018)
Article
Physics, Particles & Fields
Shahab Shahidi
EUROPEAN PHYSICAL JOURNAL C
(2019)
Article
Physics, Particles & Fields
Shahab Shahidi
Summary: The theory involves an additional non-minimal coupling between baryonic matter fields and geometry, ensuring conservation of the energy-momentum tensor, with detailed investigation into background cosmological implications and dynamical system analysis. The model parameter is estimated to be small and positive within a 2 sigma confidence interval from observations, showing good agreement with observational data.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Particles & Fields
Shahab Shahidi, Nima Khosravi
Summary: This article introduces a new 4D Einstein-Gauss-Bonnet theory and proposes a new method to consider non-symmetric spacetime by introducing a Lagrange multiplier. The theory has a covariant 4D equation of motion, which is useful for studying less symmetric metrics.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Letter
Astronomy & Astrophysics
Zoltan Kovacs, Tiberiu Harko, Shahab Shahidi
Article
Astronomy & Astrophysics
Shahab Shahidi
Article
Astronomy & Astrophysics
Farid Charmchi, Zahra Haghani, Shahab Shahidi, Leila Shahkarami
