Article
Astronomy & Astrophysics
R. A. Konoplya, J. Kunz, A. Zhidenko
Summary: We studied the Blandford-Znajek process of energy extraction from a slowly rotating black hole using a general parametrization of the black-hole spacetime. We found formulas for magnetic field flux and energy extraction rate which are valid for both Kerr spacetime and its arbitrary deformations, with these quantities mainly depending on a single deformation parameter.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Bobur Turimov, Ozodbek Rahimov
Summary: This article investigates the observational evidence of electromagnetic signals and examines the general relativity and alternative theory of gravity in the strong gravity regime. The orbital and epicyclic motion of test particles in general axially symmetric spacetime are studied, providing a general description to derive exact analytical expressions for the fundamental frequencies. The detailed derivation of the expressions for the orbital and epicyclic frequencies of test particles orbiting around the Kerr-Newman-NUT black hole is also shown.
Article
Physics, Multidisciplinary
Bidyut Bikash Hazarika
Summary: The study introduces an axially symmetric spacetime with closed timelike curves, violating causality, and belonging to type III in the Petrov classification scheme. The matter-energy in this spacetime represents a pure radiation field with a negative cosmological constant, and the spacetime asymptotically approaches anti-de Sitter space in the radial direction.
Article
Mathematics, Applied
Cui Chen, Jiahui Hong, Kai Zhao
Summary: This paper investigates the global propagation of singularities of the viscosity solution to the discounted Hamilton-Jacobi equation. By reducing the original equation to a time-dependent evolutionary Hamilton-Jacobi equation, it is shown that singularities propagate along specific characteristics and time can extend indefinitely. The use of a-compactness of the Euclidean space and the local Lipschitz issue are key technical difficulties in studying the global results.
DISCRETE AND CONTINUOUS DYNAMICAL SYSTEMS
(2022)
Article
Physics, Particles & Fields
J. C. R. de Souza, A. F. Santos
Summary: This paper investigates Ricci-inverse gravity, an alternative theory of gravity that introduces an anti-curvature scalar into the Einstein-Hilbert action. The study focuses on an axially symmetric spacetime with causality violation and explores two classes of models and different sources of matter. The results show that Ricci-inverse gravity allows for the existence of Closed Time-like Curves (CTCs), leading to the violation of causality. A comparison between the results of general relativity and Ricci-inverse gravity is also made. Additionally, spacetimes such as Godel and Godel-type universes, which are exact solutions of general relativity and allow for causality violations, are considered within the framework of Ricci-inverse gravity.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Multidisciplinary
Amnon Moalem, Alexander Gersten
Summary: The study investigates quantum equations for massless particles in stationary uncharged axially symmetric spacetimes. It shows that, up to a normalization function, the angular wave function is independent of the metric and essentially the same as in Minkowski spacetime. The radial wave functions satisfy second order nonhomogeneous differential equations with three nonhomogeneous terms that uniquely depend on time and space curvatures.
Article
Astronomy & Astrophysics
Sanjar Shaymatov, Pankaj Sheoran, Ricardo Becerril, Ulises Nucamendi, Bobomurat Ahmedov
Summary: In this paper, the Penrose process in the vicinity of the axially symmetric magnetized Reissner-Nordstrom black hole is investigated for neutral and charged particles. It is found that there are regions where the g(tt) component of the metric tensor is positive, not only close to the event horizon but also far away in the potential wells. The effect of the magnetic field on the efficiency of the Penrose process for the axially symmetric magnetized black hole case is also examined, and compared with the case of a Kerr black hole.
Article
Mathematics, Applied
Wei Cheng, Jiahui Hong
Summary: This article discusses the importance of strict singular characteristics in the wellposedness issue of singular dynamics on the cut locus of viscosity solutions. We provide an intuitive and rigorous proof of the existence of strict singular characteristics of the Hamilton-Jacobi equation H(x, Du(x), u(x)) = 0 in the two-dimensional case. We also prove that if x is a strict singular characteristic, then the right-differentiability and right-continuity of x hold for every t. Such a strict singular characteristic must give a selection p(t) such that p(t) = argminp. D+ u(x(t)) H(x(t), p, u(x(t))).
NODEA-NONLINEAR DIFFERENTIAL EQUATIONS AND APPLICATIONS
(2023)
Article
Astronomy & Astrophysics
Joshua Baines, Matt Visser
Summary: Thanks to the event horizon telescope, the physical effects of strong-field near-horizon regime for astrophysical black holes can now be tested. The authors discuss a powerful three-function distortion of the Kerr spacetime that can fit observational data and encompass various theoretical models. These spacetimes separate equations and are suitable for modeling real astrophysical black holes. The authors also provide expressions for the horizons' angular velocities, areas, and surface gravities, emphasizing the validity of rigidity results and zeroth laws.
Article
Mathematics, Applied
Yangang Chen, Justin W. L. Wan
Summary: This study explores numerical solutions for HJB and KFP equations in mean field games, proposing a multigrid method for efficient nonlinear discretized system solving. By incorporating artificial viscosity and hybrid full-semi coarsening and kernel preserving biased restriction, the method addresses anisotropy in time and convections in space. Numerical experiments demonstrate that the proposed method has mesh-independent convergence rate and is faster than existing methods.
JOURNAL OF SCIENTIFIC COMPUTING
(2021)
Article
Astronomy & Astrophysics
Vittorio De Falco
Summary: Epicyclic frequencies in the equatorial plane around a general stationary and axially symmetric wormhole are investigated in this study. The existence of the wormholes is distinguished from a Kerr black hole, and a strategy to reconstruct the related metrics is proposed for future observational data on wormholes. The implications of this approach and possible future perspectives are discussed.
Article
Optics
Na Xiao, Chen Xie, Francois Courvoisier, Minglie Hu
Summary: We demonstrate the universality of our theoretical scheme developed for the caustics of abruptly autofocusing vortex beams in all axially symmetric vortex beams. Further analysis reveals the complex compositions of vortex caustics in real space and demonstrates the possibility of tailoring vortex caustics in paraxial optics based on our theory. The excellent agreements between our theoretical results and numerical/experimental results confirm the validity of this scheme.
Article
Mathematics
Wei Cheng, Jiahui Hong
Summary: This paper investigates the local propagation of singularities of viscosity solution to the contact type evolutionary Hamilton-Jacobi equation, focusing on the existence, uniqueness, and regularity of the strict singular characteristic. By applying recent results on variational problems, new findings regarding the local structure of the cut set and existence of smooth strict singular characteristics are presented. Furthermore, a global propagation result for the C-1 singular support in the contact case is obtained.
JOURNAL OF DIFFERENTIAL EQUATIONS
(2022)
Article
Astronomy & Astrophysics
S. Christina, T. Ibungochouba Singh
Summary: This paper investigates the tunneling of vector boson particles across the event horizon of KNdS black hole and the modified Hawking radiation using various methods. The study reveals that the temperatures near the event horizon are dependent on the black hole parameters for both stationary and non-stationary space times.
GENERAL RELATIVITY AND GRAVITATION
(2021)
Article
Astronomy & Astrophysics
Divya Jyoti, Sachin Kumar
Summary: The study investigates the invariant non-static solutions of Einstein's vacuum field equations, which correspond to the most general form of axially symmetric stationary line element representing a non conformally flat semi-Riemannian spacetime in cylindrical coordinates. The Lie symmetry method is utilized for symmetry reduction and obtaining exact solutions involving arbitrary functions. Conservation laws for vacuum equations in axially symmetric gravitational fields are derived. The solutions for the Lewis metric and Chandrasekhar metric are obtained from the derived solutions. The graphical behavior of the solutions is also demonstrated by considering the possibilities of arbitrary functions.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Astronomy & Astrophysics
Torben C. Frost, Volker Perlick
Summary: The C-metric describes an accelerating black hole and in this paper, we discuss the propagation of light rays and lensing features within this metric. By solving the lightlike geodesic equation and introducing an orthonormal tetrad for parameterising the directions of light rays, we derive the shadow's angular radius, formulate a lens equation, and calculate the redshift and travel time of light rays. These theoretical results are relevant for the detection and distinction of accelerating black holes described by the C-metric.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Jan-Menno Memmen, Volker Perlick
Summary: In this study, geometrically thick perfect-fluid tori with constant specific angular momentum, known as 'Polish doughnuts', were analyzed orbiting deformed compact objects with a quadrupole moment. Two different asymptotically flat, static and axisymmetric vacuum solutions to Einstein's field equation with a non-zero quadrupole moment, the q-metric and the Erez-Rosen spacetime, were considered. The main finding is that there is a range of positive quadrupole moments in both metrics which allows for the existence of double tori, with a distinctive fish-shaped cross-section when filled within their Roche lobes, a feature not found in the Schwarzschild spacetime.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Correction
Astronomy & Astrophysics
Mourad Halla, Volker Perlick
GENERAL RELATIVITY AND GRAVITATION
(2021)
Review
Physics, Multidisciplinary
Volker Perlick, Oleg Yu Tsupko
Summary: This article provides a review of current research on black hole shadows, with a focus on analytical studies. It discusses the definition of the shadow, derivation of angular size, and calculation methods under various conditions. Special attention is given to non-asymptotically flat spacetimes and the influence of plasma on black hole shadows.
PHYSICS REPORTS-REVIEW SECTION OF PHYSICS LETTERS
(2022)
Editorial Material
Astronomy & Astrophysics
Volker Perlick
GENERAL RELATIVITY AND GRAVITATION
(2022)
Article
Astronomy & Astrophysics
Mourad Halla, Volker Perlick
Summary: This paper studies the Brill metric, an electrovacuum solution to Einstein's field equation. It depends on three parameters: a mass parameter m, a NUT parameter l, and a charge parameter e. The metric describes a black hole when the charge parameter is small and a wormhole when it is sufficiently big. The paper determines the relevant lensing features in both cases and explores the deflection angle based on the sign of the Gaussian curvature of the optical metric.
Article
Astronomy & Astrophysics
Jay Solanki, Volker Perlick
Summary: This paper derives exact analytical formulas for the evolution of the photon sphere and the angular radius of the shadow in a special Vaidya space-time. The study considers different models based on the choice of the mass function and analyzes the features of the photon sphere and shadow in different coordinate systems by calculating the lightlike geodesics.
Article
Astronomy & Astrophysics
Mourad Halla, Volker Perlick
Summary: We study a class of stationary and axisymmetric wormhole spacetimes that are related to Teo wormholes. We investigate the lensing properties of these wormholes by characterizing the set of lightlike geodesics connecting an observation event to a light source. Our main result shows that under mild conditions, the observer always sees infinitely many images of the light source. We also analyze the qualitative features of these geodesics using potentials that describe the sum of centrifugal and Coriolis forces.
Article
Astronomy & Astrophysics
Wan Cong, Jiri Bicak, David Kubiznak, Robert B. Mann
Summary: A relativistic theory of gravity, such as general relativity, produces phenomena fundamentally different from Newton's theory, including effects like gravitomagnetism. Recent research shows that a detector placed in a slowly rotating shell can distinguish between a static nonrotating shell and a rotating shell, detecting the presence of inertial frame dragging effects even within a finite time interval when light signals cannot convey the rotation.
Article
Physics, Multidisciplinary
Nenad Manojlovic, Volker Perlick, Robertus Potting
Article
Astronomy & Astrophysics
Mourad Halla, Volker Perlick
GENERAL RELATIVITY AND GRAVITATION
(2020)
Article
Astronomy & Astrophysics
Wan Cong, Jiri Bicak, David Kubiznak, Robert B. Mann
