Article
Astronomy & Astrophysics
Cristobal Corral, Daniel Flores-Alfonso, Gaston Giribet, Julio Oliva
Summary: This paper discusses the higher-dimensional generalizations of the Eguchi-Hanson gravitational instanton in the presence of higher-curvature deformations of general relativity. It analyzes different aspects of these solutions, including the regularization of the on-shell Euclidean action by means of the addition of topological invariants, and the explicit construction of Eguchi-Hanson type solutions with higher-curvature corrections to the gravity action.
Article
Physics, Particles & Fields
Yekun Yang, Xiao Zhang
Summary: Geodesic equations can be solved on scalar flat metrics of Eguchi-Hanson type when certain variables are constant. However, explicit solutions are not available yet under certain conditions.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Turkuler Durgut, Robie A. Hennigar, Hari K. Kunduri, Robert B. Mann
Summary: The Eguchi-Hanson-AdS(5) spacetimes are static, geodesically complete asymptotically locally AdS(5) soliton solutions with negative mass and parameterized by an integer p >= 3. They have a conformal boundary with spatial topology L(p, 1). We study the mode solutions of the scalar wave equation on this background and find a normal mode spectrum, similar to AdS(5). We also explore other geometric properties, such as causal geodesics and thermodynamic properties, and discover a surprising connection with the AdS soliton.
JOURNAL OF HIGH ENERGY PHYSICS
(2023)
Article
Physics, Multidisciplinary
Zhuohua Cai, Xiao Zhang
Summary: We study parallel spinors on the Eguchi-Hanson metrics and find that the space of complex parallel spinors is complex two-dimensional. For the metrics of Eguchi-Hanson type with zero scalar curvature, we separate variables for the harmonic spinors and obtain explicit solutions.
COMMUNICATIONS IN THEORETICAL PHYSICS
(2023)
Article
Mathematics, Applied
Nasser Bin Turki, Uday Chand De, Abdallah Abdelhameed Syied, Gabriel-Eduard Vilcu
Summary: This paper investigates space-times with W-2 curvature tensor in f (R, G) modified theory of gravity and space-times with divergence-free W-2 curvature tensor in f (R, G) gravity. It is found that space-times with W-2 curvature tensor represent inflation and have constant isotropic pressure and energy density. For space-times with divergence-free W-2 curvature tensor, it is proven that if the energy-momentum tensor is bi-recurrent, then either the space-times represent inflation or have constant isotropic pressure and energy density.
JOURNAL OF GEOMETRY AND PHYSICS
(2023)
Article
Mathematics, Applied
Junwen Chen, Xiao Zhang
Summary: Two types of Eguchi-Hanson metrics with negative constant scalar curvature are constructed in this study. Type I metrics are Kahler, while type II metrics are ALH and can have negative total energy.
JOURNAL OF GEOMETRY AND PHYSICS
(2021)
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
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
C. R. Muniz, R. V. Maluf
Summary: This paper investigates generalized Ellis-Bronikov (E-B) traversable wormholes in f (R) extended gravity, assuming the support of anisotropic dark matter (DM) and discussing different DM models and the feasibility of the wormhole-dark matter system.
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
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
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
Astronomy & Astrophysics
Jerry Wu, Robert B. Mann
Summary: We present the first examples of phase transitions in asymptotically flat black hole solutions. We find stable temperature regions for otherwise unstable neutral black holes, indicating the existence of multiple stable phases that can coexist at multi-critical points. For charged black holes, multiple first order phase transitions can occur on the stable Gibbs free energy branch, similar to anti-de Sitter (AdS) black holes. The changes in Gibbs free energy are investigated and compared to pressure changes for AdS black hole systems.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Astronomy & Astrophysics
Jerry Wu, Robert B. Mann
Summary: We find that there are multi-critical points, where more than three phases coalesce, in multiply rotating Kerr-anti de Sitter black holes in d-dimensions. Specifically, we present a quadruple point for a triply rotating black hole in d = 8 and a quintuple point for a quadruply rotating black hole in d = 10. The maximal number of distinct phases n is one larger than the maximal number of independent rotations, and we outline a method for obtaining the associated n-tuple point. There are also situations where more than three phases merge at sub-maximal multi-critical points. Our results indicate that multi-critical points in black hole thermodynamics are more common than previously believed, as long as there are a sufficient number of thermodynamic variables.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Physics, Multidisciplinary
B. Eslam Panah
Summary: In this paper, general uncharged accelerating BTZ black hole solutions are extracted and some of their properties are studied. The analysis reveals that the spacetime's asymptotic behavior depends on four parameters: the cosmological constant, mass, acceleration, and topological constant. The temperature of these black holes is found to be always positive for AdS spacetime. Charged accelerating BTZ black hole solutions in the presence of a conformally invariant Maxwell field are also investigated. The findings show a coupling between the electrical charge and other quantities of the accelerating BTZ black holes. The asymptotic behavior and temperature of charged accelerating BTZ black holes are studied, with the temperature depending on the electrical charge, accelerating parameter, and cosmological constant.
FORTSCHRITTE DER PHYSIK-PROGRESS OF PHYSICS
(2023)
Article
Physics, Multidisciplinary
S. H. Hendi, S. Hajkhalili, S. Mahmoudi
Summary: A new model of regular black hole in 2+1 dimensions is proposed by considering an appropriate matter field as the energy-momentum tensor. The model introduces an upper bound on the radius of the event horizon and a lower bound on the mass, motivated by astrophysical black holes. The solutions obtained are investigated for their geometric properties and found to be thermally stable in the mentioned admissible domain.
FORTSCHRITTE DER PHYSIK-PROGRESS OF PHYSICS
(2023)
Article
Astronomy & Astrophysics
S. H. Hendi, Kh Jafarzade, B. Eslam Panah
Summary: The recent observations of M87* by the EHT have sparked interest in studying the shadow of black holes, as well as investigating the time evolution and lifetime of black holes to refine theoretical models in gravitating systems. In this study, we focus on the optical features of a charged AdS black hole in dRGT massive gravity, such as its shadow geometrical shape and energy emission rate, to narrow down the free parameters of the theory. Our main goal is to compare the rotating counterpart of the static black hole solution in dRGT massive gravity with EHT data to determine the allowed regions of the model parameters. Additionally, we analyze how the rotation factor and other parameters impact the emission of particles around the black holes.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Multidisciplinary
Jack Davis, Robie A. Hennigar, Robert B. Mann, Shohini Ghose
Summary: The Majorana stellar representation is used to characterize spin states with maximally negative Wigner quasiprobability distributions. These states exhibit partial symmetry within their star configurations and do not follow an obvious geometric pattern with increasing dimension. They are also different from states that maximize other measures of nonclassicality. Random states have a relatively high amount of negativity, but extremal states and those with similar negativity are statistically rare in Hilbert space. Spin coherent states of arbitrary dimension have non-zero Wigner negativity, suggesting that all pure spin states have non-zero Wigner negativity. These results can be applied to permutation invariant qubit ensembles.
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
(2023)
Article
Astronomy & Astrophysics
B. Eslam Panah
Summary: By considering a three-dimensional C-metric and introducing energy dependence, we construct a three-dimensional energy-dependent C-metric. We then obtain accelerating BTZ black hole solutions in gravity's rainbow. Moreover, we find that (A)dS black holes have an event horizon depending on all the parameters of this theory. The temperature and entropy of these black holes are calculated and analyzed, with the heat capacity indicating different behaviors based on the cosmological energy-dependent constant. Finally, we show that accelerating AdS BTZ black holes can satisfy both physical conditions and local stability.
Article
Physics, Multidisciplinary
B. Eslam Panah, M. Khorasani, J. Sedaghat
Summary: In this article, we investigated the three-dimensional C-metric in the F(R) theory of gravity with and without a matter field, and obtained exact solutions for accelerating black holes. The effects of various parameters on the metric function, roots, and temperature of the black holes were studied. We also considered the coupling of nonlinear electrodynamics as a matter field to obtain charged black hole solutions and evaluated the effects of different parameters on the solutions, roots, and temperature. The results showed a dependency on various parameters, and the temperature of the black holes was positive after a certain root.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Astronomy & Astrophysics
Jerry Wu, Robert B. Mann
Summary: We demonstrate that black holes in Lovelock gravity with order N≥4 can exhibit multicritical phase behavior. We provide explicit examples of quadruple points in d=10 fourth-order Lovelock gravity and quintuple points in d=14 sixth-order Lovelock gravity. We also show that multicriticality can be realized for uncharged, nonrotating black holes by introducing a new type of multicritical point between black holes and thermal radiation. Additionally, we discuss the methodology used and compare it to other black hole multicritical points in terms of the Gibbs phase rule.
Article
Astronomy & Astrophysics
Ahmed Shalabi, Laura J. Henderson, Robert B. Mann
Summary: The potential breakdown of the metric at high energy scales could suggest a fundamental minimal length scale. One approach to this minimum length scale is to construct a quantum field theory with a bandlimit on the field. We investigate the effects of implementing such a bandlimit on a field in a curved and compact spacetime, and how to detect it.
Article
Astronomy & Astrophysics
Manar Naeem, Kensuke Gallock-Yoshimura, Robert B. Mann
Summary: We studied the mutual information harvesting protocol for two uniformly accelerated particle detectors. Our numerical calculations demonstrate that, although a single detector behaves as if it is in a thermal bath, the quantum mutual information between two accelerating detectors differs from that of two inertial detectors in a thermal bath. This discrepancy arises because the Wightman function along the trajectory of a single uniformly accelerating detector is the same as that of a detector in a thermal bath, but a pair of detectors in the respective cases have different Wightman functions.
Article
Astronomy & Astrophysics
Brayden R. Hull, Robert B. Mann
Summary: We demonstrate the existence of asymptotically de Sitter black holes of negative mass in Lovelock gravity. These black holes have horizon geometries with nonconstant curvature and are known as exotic black holes. We specifically study the case of Gauss-Bonnet gravity. We discuss the impact of transverse space geometry on the existence of black holes for both positive and negative mass solutions and provide closed form bounds for geometric parameters.
Article
Astronomy & Astrophysics
Amjad Ashoorioon, Mohammad Bagher Jahani Poshteh, Robert B. Mann
Summary: Accelerating black holes, connected to cosmic strings, could evolve into supermassive black holes. However, the acceleration should be small in order for them to participate in structure formation and reside at the center of galaxies. Although this slow acceleration does not significantly change the shadow or image position in gravitational lensing, it does significantly affect the time delay associated with these images.
Article
Physics, Particles & Fields
S. N. Sajadi, Ali Hajilou, S. H. Hendi
Summary: In this paper, analytical approximate black hole solutions are derived in the framework of f (R) gravity without a cosmological constant. The equations of motion are applied to a spherically symmetric spacetime with one unknown function, resulting in black hole solutions that are not constrained by the Ricci scalar. Near horizon and asymptotic solutions are obtained and combined using a continued-fraction expansion to yield a complete solution. The stability of the solutions is then investigated through the use of thermodynamics and quasi-normal modes.
EUROPEAN PHYSICAL JOURNAL C
(2023)
