Article
Astronomy & Astrophysics
Li Li
Summary: The presence of a scalar hair in black holes leads to an additional contribution to the first law of black hole thermodynamics, which requires modification including new thermodynamic conjugate variables phi(s) and (O). The study provides a deeper understanding of the thermodynamics of AdS black holes in Einstein-scalar gravity and sheds light on the behavior of the scalar field near the AdS boundary.
Article
Multidisciplinary Sciences
Yves Brihaye, Felipe Console, Betti Hartmann
Summary: In this paper, the phenomenon of topological inflation and its non-topological counterpart are studied in a simple model involving gravity, electromagnetic field, and a complex scalar field. The existence of globally regular solutions such as boson stars, and black holes with scalar hair, are found in the presence of unbroken U(1) symmetry.
Article
Astronomy & Astrophysics
Zhong-Ying Fan
Summary: In this work, a universal picture is developed to describe first order phase transitions of black holes in the thermodynamic parameters space using topology. Two types of topological defects are identified, one normal and one exotic, with different properties and behaviors. The study shows that first order transitions can be viewed as the interchange of winding numbers between black holes and exotic defects, or as virtual collisions between black holes and exotic defects. The critical point of the transition can be determined by the meeting of all the defects in the parameters space, where universal behaviors can be observed.
Article
Astronomy & Astrophysics
De-Cheng Zou, Yun Soo Myung
Summary: The tachyonic instability of Kerr black holes is analyzed in the Einstein-scalar theory with different couplings, deriving threshold curves for stable and unstable Kerr black holes. A new bound for unstable Kerr black holes with negative coupling is also found.
Article
Astronomy & Astrophysics
Stella Kiorpelidi, George Koutsoumbas, Andri Machattou, Eleftherios Papantonopoulos
Summary: In this study, we investigate the stability of topological black holes in the presence of a cosmological constant and a scalar field coupled to the Gauss-Bonnet term. We find two competing effects and observe a phase transition to a scalarized topological black hole induced by curvature effects.
Article
Astronomy & Astrophysics
Lucas G. Collodel, Daniela D. Doneva, Stoytcho S. Yazadjiev
Summary: In this work, we analyze the solutions of Kerr black holes with scalar hair that are of special interest for extreme mass ratio inspirals (EMRIs) in gravitational wave events. The off-center distribution of energy density in these spacetimes causes nonmonotonic behavior in the metric functions, which has a significant impact on the orbital parameters and signals from EMRIs. By investigating circular orbit parameters, we identify qualitative features in the signals that are distinct from Kerr black holes, and we simulate inspirals using the quadrupole formula approximation. We find that the emitted signal frequencies exhibit nonmonotonic behavior, including backward chirp, and can fall below the sensitivity range of LISA in some cases. Additionally, we present waveforms of a noncircular EMRI where the compact object follows a geodesic motion typically associated with spacetimes containing a static ring.
Article
Astronomy & Astrophysics
K. A. Bronnikov
Summary: Simpson and Visser proposed a phenomenological way to avoid space-time singularities by replacing a parameter corresponding to singularity with a nonzero expression. This method can lead to a regular minimum beyond a black hole horizon and potentially mimic quantum gravity effects. The authors applied this method to regularize various metrics and obtained exact solutions in general relativity.
Article
Physics, Multidisciplinary
Hui-Hua Zhao, Li-Chun Zhang, Fang Liu
Summary: The study discusses black hole solutions in Einstein-Lambda gravity with nonlinear electrodynamics in dS spacetime. It shows that the nonlinearity parameter alpha affects the thermodynamic properties of the system, especially in critical state and when the effective temperature is below the critical temperature, influencing the phase structure of the system. The critical phase transition is proven to be a second-order equilibrium phase transition using the Gibbs free energy criterion and Ehrenfest equations.
COMMUNICATIONS IN THEORETICAL PHYSICS
(2021)
Article
Physics, Multidisciplinary
Shao-Wen Wei, Yu-Xiao Liu, Robert B. Mann
Summary: This article treats black hole solutions as defects in the thermodynamic parameter space and investigates the relationship between the topological number and the thermodynamic properties of black holes. By using the topological number, different black hole systems can be better distinguished and understood.
PHYSICAL REVIEW LETTERS
(2022)
Article
Astronomy & Astrophysics
Yves Brihaye, Betti Hartmann
Summary: We study the black hole solutions with scalar hair in the Einstein-Maxwell theory coupled to a complex scalar field. We find that new solutions exist for sufficiently large gravitational coupling and sufficiently small electromagnetic coupling. The scalar hair takes the form of a spatially oscillating 'wave packet' and affects the space-time such that the Ricci and Kretschmann scalars show similar oscillations.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
Di Wu
Summary: In this paper, the topological numbers for singly rotating Kerr black holes in all dimensions and the four-dimensional Kerr-Newman black hole are investigated. It is found that the rotation parameter has a significant effect on the topological number for uncharged black holes, and the dimension of spacetimes also has a remarkable effect on the topological number for rotating black holes. Additionally, it is discovered that the topological numbers of the four-dimensional Kerr and Kerr-Newman black holes are the same, suggesting that the electric charge parameter does not affect the topological number of rotating black holes. The research provides more evidence for the conjecture proposed in Wei et al. [Phys. Rev. Lett., 129, 191101(2022)] that all black hole solutions should be separated into three different topological classes, at least in the pure Einstein-Maxwell gravity theory.
Article
Physics, Particles & Fields
Yu-Ping An, Li Li
Summary: We have proven the absence of charged scalar hair for static black holes in de-Sitter spacetime between the event horizon and the cosmological horizon. The proof is not dependent on the assumption of spherical symmetry and allows for general non-minimal coupling functions and higher curvature term corrections. This result has implications for the possibility of spontaneous scalarization around charged de-Sitter black holes.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Keitaro Tomikawa, Tsutomu Kobayashi
Summary: In this study, we investigate odd parity perturbations of spherically symmetric black holes with time-dependent scalar hair in shift-symmetric higher-order scalar-tensor theories without assuming degeneracy conditions. By analyzing the general form of the quadratic Lagrangian and refining the stability conditions, we obtain insights into the behavior of these perturbations. This research also extends to include the matter energy-momentum tensor as a source term, providing a more comprehensive understanding of the dynamics involved.
Article
Astronomy & Astrophysics
Shahar Hod
Summary: Recent research has shown that magnetized black holes with a negative coupling of the scalar field to the Gauss-Bonnet curvature can support spatially regular scalar hairy configurations. The onset of spontaneous scalarization in these magnetized black holes is marked by a critical magnetic field strength, and the phenomenon is restricted to the black hole poles with a unique angular relation.
Article
Astronomy & Astrophysics
Xiao Yan Chew, Dong-han Yeom, Jose Luis Blazquez-Salcedo
Summary: This study investigates the properties of black holes and scalarons in Einstein gravity coupled to a scalar field with an asymmetric potential. The potential has been used in cosmology to describe quantum tunneling between vacuum states and contains local and global minima. The study focuses on asymptotically flat solutions and shows the existence of hairy black hole solutions that can converge to particlelike solutions in the small horizon limit. It also demonstrates the instability of both black holes and scalarons under radial perturbations.
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.