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
Astronomy & Astrophysics
Younes Younesizadeh
Summary: The study focuses on obtaining the exact rotating black hole solution in the f(R)-gravity model and analyzing its thermodynamics, including comparison with the BTZ black hole solution. The validity of the first law of thermodynamics was demonstrated, and the stability of the obtained solution was investigated. No evidence of P-V criticality similar to the ordinary BTZ case was found.
PHYSICS OF THE DARK UNIVERSE
(2021)
Article
Multidisciplinary Sciences
Yaroslav Erisov, Sergei Surudin, Fedor Grechnikov, Elena Lyamina
Summary: An axisymmetric boundary value problem for the flow of an incompressible material obeying Hill's orthotropic quadratic yield criterion and its associated flow rule is formulated and solved, with numerical techniques only necessary for evaluating ordinary integrals. The solution may exhibit singular behavior near the friction surface, with some strain rate components and plastic work rate approaching infinity. The effect of plastic anisotropy on the solution's behavior is discussed in detail.
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, Particles & Fields
K. Dialektopoulos, G. Leon, A. Paliathanasis
Summary: The Noether symmetry analysis is used to investigate a multiscalar field cosmological model in teleparallel gravity. Specifically, the study focuses on two scalar fields interacting in scalar-torsion theory. The field equations are described in a minisuperspace framework, and the evolution of physical variables depends on the potential function governing the dynamics of the scalar fields. By requiring the field equations to possess non-trivial Noether point symmetries and utilizing the first theorem of Noether, restrictions are imposed on the functional forms of the potential. Finally, symmetry vectors and corresponding conservation laws are employed to determine exact and analytic solutions in multiscalar-torsion cosmology.
EUROPEAN PHYSICAL JOURNAL C
(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
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
Iqra Nawazish, M. Sharif
Summary: This paper studies cosmic evolutionary stages in the background of a modified theory allowing for non-minimal coupling between various cosmological quantities. Different cosmic models are considered and analyzed, and exact solutions with different symmetries and conserved properties are derived. These solutions are found to be consistent with observational data and viability conditions, providing a successful explanation for cosmic accelerated expansion.
Article
Physics, Mathematical
G. Abbas, S. Taj, Aisha Siddida, Zohra Arbab
Summary: This study investigates the tunnel-like structures proposed by Morris and Thorne using the f(R, T) framework. The solutions of static wormholes supported by matter with van der Waals equation of state are derived through two possible schemes. The shape function and various energy conditions are explored, and the radius of the wormhole's throat is calculated to satisfy the energy conditions. Graphical illustrations of the solutions are also presented.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Astronomy & Astrophysics
Yuri Makeenko
Summary: This article investigates the two-dimensional four-derivative conformal theory derived from the Nambu-Goto string by path-integration. By using the method of singular products, the author demonstrates that the one-loop approximation provides an exact solution. The solution can be conveniently described using minimal models, where the central charge c in the Kac spectrum depends on the parameters of the four-derivative action. This relation is nonlinear, allowing the mapping of the domain of physical parameters to c < 1, bypassing the KPZ barrier of the Liouville action.
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
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, Particles & Fields
Hamid R. Bakhtiarizadeh
Summary: We investigate new solutions to the Einstein-Maxwell equations with the presence of mimetic field in D dimensions, with a focus on the asymptotically anti-de Sitter case. We derive the solutions in detail in a five-dimensional spacetime and generalize them to higher dimensions. The solutions describe charged static and rotating solutions with different types of horizons and can be interpreted as black holes or black strings/branes based on their global features. We also examine various physical properties of the solutions, including horizons, singularities, entropy, mass, and angular momenta of rotating solutions.
EUROPEAN PHYSICAL JOURNAL C
(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, Particles & Fields
Isil Basaran Oz, Kazuharu Bamba
Summary: The solutions for the field equations of f(R) gravity in static cylindrically symmetric space-time were investigated. Unknown values of the equations of state parameter were determined through the analysis of constraints obtained by using the Noether symmetry method. Several new exact solutions for cases of General Relativity in static cylindrically symmetrical space-time for the non-dust matter were discovered.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Engineering, Multidisciplinary
Hector Puebla, Eliseo Hernandez-Martinez, Mariana Rodriguez-Jara, Cesar S. Lopez-Monsalvo
MATHEMATICAL PROBLEMS IN ENGINEERING
(2017)
Article
Astronomy & Astrophysics
Alessandro Bravetti, Christine Gruber, Cesar S. Lopez-Monsalvo, Francisco Nettel
Article
Engineering, Electrical & Electronic
Irvin Lopez-Garcia, Cesar S. Lopez-Monsalvo, Francisco Beltran-Carbajal, Eduardo Campero-Littlewood
IET GENERATION TRANSMISSION & DISTRIBUTION
(2018)
Article
Astronomy & Astrophysics
Antonio C. Gutierrez-Pineres, Hernando Quevedo
CLASSICAL AND QUANTUM GRAVITY
(2019)
Article
Engineering, Electrical & Electronic
Irvin Lopez-Garcia, Cesar S. Lopez-Monsalvo, Francisco Beltran-Carbajal, Rafael Escarela-Perez, Juan C. Olivares-Galvan
IET GENERATION TRANSMISSION & DISTRIBUTION
(2019)
Article
Physics, Multidisciplinary
C. S. Lopez-Monsalvo, D. Garcia-Pelaez, A. Rubio-Ponce, R. Escarela-Perez
Article
Astronomy & Astrophysics
J. A. Arrieta-Villamizar, J. M. Velasquez-Cadavid, O. M. Pimentel, F. D. Lora-Clavijo, A. C. Gutierrez-Pineres
Summary: This study examines the shadow produced by a compact object described by the q-metric, revealing the existence of naked singularities at specific parameter values. By analyzing the eigenvalues of the Riemann tensor using a specific representation, the study identifies regions where repulsive effects may occur. Numerical solutions for the motion equations show the gravitational lensing effects and the impact of different values of q on the system's behavior.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Physics, Multidisciplinary
C. S. Lopez-Monsalvo, F. Nettel, V Pineda-Reyes, L. F. Escamilla-Herrera
Summary: In this work, a set of Riemannian and pseudo-Riemannian metrics are constructed on a contact manifold by introducing almost contact and para-contact structures, and their isometries are analyzed. It is found that it is not possible to find a class of metric tensors which fulfill two specific properties, leading to the necessity of abandoning the idea of an associated metric to an almost contact or para-contact structure in order to define a Riemannian structure with desired properties.
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
(2021)
Article
Astronomy & Astrophysics
Daniel Flores-Alfonso, Cesar S. Lopez-Monsalvo, Marco Maceda
Summary: The article discusses the relationship between three-dimensional e-contact manifolds and electromagnetism equations, showing that manifolds satisfying specific conditions are solutions to certain gravity actions. An example of a contact manifold with an associated metric tensor is analyzed to demonstrate the conclusions presented.
Article
Physics, Multidisciplinary
Daniel Flores-Alfonso, Cesar S. Lopez-Monsalvo, Marco Maceda
Summary: The study demonstrates that the three-dimensional Thurston geometries are vacuum solutions to the 3D new massive gravity equations, and also analyzes their Lorentzian counterparts.
PHYSICAL REVIEW LETTERS
(2021)
Article
Astronomy & Astrophysics
Antonio C. Gutierrez-Pineres, Hernando Quevedo
Summary: This study applies different matching conditions to three spherically symmetric spacetimes and finds that the Darmois matching conditions are satisfied in all cases, while the C (3) conditions are not fulfilled. The difference is argued to be due to a non-physical behavior of the pressure on the matching surface.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Physics, Mathematical
D. Garcia-Pelaez, C. S. Lopez-Monsalvo, A. Rubio Ponce
Summary: In this work, we demonstrate the orthogonality between rays and fronts of light propagation in a medium, and show that the inclusion of interfaces invalidates this orthogonality, leading to optical aberrations and potential total internal reflection.
JOURNAL OF MATHEMATICAL PHYSICS
(2022)
Article
Mathematics
Irvin Lopez-Garcia, Cesar S. Lopez-Monsalvo, Oscar Gomez-Gonzalez, Mauricio Sanabria-Villamizar, Francisco Beltran-Carbajal, Rafael Escarela-Perez
Summary: In this study, we determine the upper and lower bounds of the wind speed interval in which a wind energy conversion system (WECS) can be regulated similarly to a conventional power generation plant. We conducted a steady-state analysis of a wind turbine coupled with a doubly fed induction generator (DFIG) that delivers power in a safe manner according to the electric grid requirements. Our main contributions involve expanding the secure operation window by adjusting the gearbox ratio, thus improving the reliability of grid integration, and controlling the WECS within new, safe wind speed intervals using a passivity-based controller and a proportional-integral controller, both of which show satisfactory performance.
Proceedings Paper
Astronomy & Astrophysics
A. C. Gutierrez-Pineres, E. A. Montoya, L. A. Nunez
70 & 70 GRAVITATION FEST
(2017)
Proceedings Paper
Astronomy & Astrophysics
C. S. Lopez-Monsalvo, I. Lopez-Garcia, F. Beltran-Carbajal, R. Escarela-Perez
70 & 70 GRAVITATION FEST
(2017)
Article
Astronomy & Astrophysics
Nelson R. F. Braga, Octavio C. Junqueira
Summary: This study investigates the influence of rotation on the transition temperature of strongly interacting matter produced in non-central heavy ion collisions. By using a holographic description of an AdS black hole, the authors extend the analysis to the more realistic case where the matter spreads over a region around the rotational axis. The results show the coexistence of confined and deconfined phases and are consistent with the concept of local temperature in rotating frames developed by Tolman and Ehrenfest.
Article
Astronomy & Astrophysics
Bing Sun, Jiachen An, Zhoujian Cao
Summary: This paper investigates the effect of gravitational constant variation on the propagation of gravitational waves. By employing two analytical methods, the study finds that variations in the gravitational constant result in amplitude and phase corrections for gravitational waves, and the time variation of the gravitational constant can be constrained through the propagation of gravitational waves.
Article
Astronomy & Astrophysics
Abdellah Touati, Zaim Slimane
Summary: This letter presents the first study of Hawking radiation as a tunneling process within the framework of non-commutative gauge theory of gravity. The non-commutative Schwarzschild black hole is reconstructed using the Seiberg-Witten map and the star product. The emission spectrum of outgoing massless particles is computed using the quantum tunneling mechanism. The results reveal pure thermal radiation in the low-frequency scenario, but a deviation from pure thermal radiation in the high-frequency scenario due to energy conservation. It is also found that noncommutativity enhances the correlations between successively emitted particles.
Article
Astronomy & Astrophysics
Shahar Hod
Summary: The travel times of light signals between two antipodal points on a compact star's surface are calculated for two different trajectories. It is shown that, for highly dense stars, the longer trajectory along the surface may have a shorter travel time as measured by asymptotic observers. A critical value of the dimensionless density-area parameter is determined for constant density stars to distinguish cases where crossing through the star's center or following a semi-circular trajectory on the surface has a shorter travel time as measured by asymptotic observers.
