Article
Physics, Particles & Fields
M. Z. Bhatti, S. Ijaz, Bander Almutairi, A. S. Khan
Summary: This paper analyzes the characteristics of a non-static sphere with an anisotropic fluid distribution in the background of modified f (G) theory. The presence of a conformal Killing vector allows for the computation of reliable results for the modified field equations. Various precise analytical solutions are obtained for both non-dissipative and dissipative systems by making different choices of the conformal Killing vector. The matching conditions in the context of f (G) gravity are computed and specific constraints are applied to determine significant results. The results of this study help in understanding the properties of astrophysical objects.
EUROPEAN PHYSICAL JOURNAL C
(2023)
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
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
Physics, Multidisciplinary
Tee-How Loo, Avik De, Sanjay Mandal, P. K. Sahoo
Summary: In this paper, a projectively flat spacetime solution of F(R)-gravity theory is examined, revealing that projective flatness leads to matter field with constant energy density and isotropic pressure. The effects of projectively harmonic spacetime geometry in F(R)-gravity theory are discussed, showing a reduction to a generalized Robertson-Walker spacetime. The role of conharmonic curvature tensor in spacetime geometry is briefly discussed alongside analysis in terms of F(R)-gravity models.
Article
Astronomy & Astrophysics
S. D. Odintsov, V. K. Oikonomou
Summary: The deformed R-2 model closely approximates the R-2 model during inflation, but exhibits stronger gravity and can incorporate an early dark energy term to control late-time dynamics.
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.
Editorial Material
Biochemistry & Molecular Biology
Weiming Tang, Dan Wu, Fan Yang, Cheng Wang, Wenfeng Gong, Kurt Gray, Joseph D. Tucker
Summary: During the COVID-19 pandemic, pay-it-forward programs have become more widespread, offering healthcare providers an opportunity to reduce costs, increase uptake of interventions like testing and vaccines, and promote sustainability through gift-giving.
Article
Physics, Particles & Fields
Asier Alonso-Bardaji, David Brizuela
Summary: This study introduces the application of Loop quantum gravity theory in spherically symmetric spacetimes, proposing holonomy and inverse-triad corrections and developing anomaly-free effective constraints encoding these corrections. By modifying the Hamiltonian constraint, a modified Hamiltonian in the form of a first-class algebra is obtained, constructing a family of consistent deformations of spherical general relativity. The analysis also explores the cases of vacuum model and two matter models, concluding that holonomy corrections are not allowed under certain matter fields.
EUROPEAN PHYSICAL JOURNAL C
(2021)
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, 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
Asier Alonso-Bardaji, David Brizuela, Raul Vera
Summary: This study examines spherical charged black holes in the presence of a cosmological constant with corrections based on loop quantum gravity theory. The effective theory is constructed at the Hamiltonian level by introducing certain correction terms that satisfy a closed algebra for modified constraints. The resulting geometry, characterized by four parameters, exhibits singularity depending on the parameter values, with explicit ranges of singularity-free spacetimes identified. The conditions for nonsingular geometry include nonnegative mass and cosmological constant, and a bounded amount of charge.
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
Computer Science, Software Engineering
Hanxiao Shen, Leyi Zhu, Ryan Capouellez, Daniele Panozzo, Marcel Campen, Denis Zorin
Summary: This paper describes a method for generating seamless surface parametrizations with guaranteed local injectivity and full control over holonomy. The ability to control holonomy is crucial for guiding isocurves based on directional information and topological constraints on the parametrization.
ACM TRANSACTIONS ON GRAPHICS
(2022)
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
Astronomy & Astrophysics
Jaume Haro, Weigiang Yang, Supriya Pan
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2019)
Article
Astronomy & Astrophysics
Jaume de Haro, Llibert Areste Salo, Supriya Pan
GENERAL RELATIVITY AND GRAVITATION
(2019)
Article
Physics, Particles & Fields
Jaume Haro, Jaume Amoros, Supriya Pan
EUROPEAN PHYSICAL JOURNAL C
(2020)
Letter
Physics, Particles & Fields
Jaume Haro
EUROPEAN PHYSICAL JOURNAL C
(2020)
Article
Astronomy & Astrophysics
Jaume Haro Cases, Llibert Areste Salo
Article
Astronomy & Astrophysics
Jaume Haro, Llibert Areste Salo
GENERAL RELATIVITY AND GRAVITATION
(2020)
Article
Physics, Particles & Fields
Llibert Areste Salo, Jaume Haro
Summary: For exponential type potentials used to depict quintessential inflation, solutions with large n values do not belong to the basin of attraction of the scaling solution. A late time mechanism to exit this behavior and depict correctly the current cosmic acceleration is not needed, but an improvement introducing another parameter is required to deal with the late time acceleration of our universe.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
L. Areste Salo, D. Benisty, E. Guendelman, J. D. Haro
Summary: A new type of quintessential inflation based on the Lorentzian distribution has been introduced, with a simple potential that aligns with recent observations and depicts the acceleration of the universe, including reheating constraints.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Jaume de Haro, Llibert Areste Salo
Summary: The study details important inflation models that can explain the accelerated expansion of the universe and reheating process, ultimately aligning with the theory of the Hot Big Bang universe.
Article
Astronomy & Astrophysics
Llibert Areste Salo, Jaume de Haro
Summary: This study numerically calculates the reheating temperature caused by the gravitational production of conformally-coupled superheavy particles during the phase transition from the end of inflation to the beginning of kination in two different quintessential inflation scenarios. It shows that the reheating temperature in both scenarios is higher than expected, contrary to traditional beliefs.
Article
Astronomy & Astrophysics
L. Areste Salo, D. Benisty, E. Guendelman, J. d Haro
Summary: An exponential kind of quintessential inflation potential motivated by supergravity is studied, which belongs to the class of alpha-attractor models. The model accurately depicts the early- and late-time acceleration of the Universe and is compatible with recent observations, showing an effective equation of state equal to -1 for late time cosmic acceleration.
Article
Astronomy & Astrophysics
Weiqiang Yang, Supriya Pan, Llibert Areste Salo, Jaume de Haro
Summary: The study focuses on the energy flow interaction between dark matter and dark energy, using various interaction functions in four distinct cosmic scenarios. The analysis reveals the importance of handling these interaction models with caution.
Article
Astronomy & Astrophysics
Supriya Pan, Jaume de Haro, Weiqiang Yang, Jaume Amoros
Article
Astronomy & Astrophysics
Jaume Haro, Llibert Areste Salo
Article
Astronomy & Astrophysics
Jaume Haro