Black Holes and Gravitational Theory

ROGER PENROSE

doi:10.1038/236377a0

Holographic complexity of the electromagnetic black hole

The European Physical Journal C ◽

10.1140/epjc/s10052-020-7661-z ◽

2020 ◽

Vol 80 (2) ◽

Cited By ~ 5

Author(s):

Jie Jiang ◽

Ming Zhang

Keyword(s):

Growth Rate ◽

Black Holes ◽

Black Hole ◽

Electromagnetic Field ◽

Gravitational Theory ◽

Lagrangian Function ◽

Boundary Term ◽

Late Time ◽

First Order ◽

Boundary Terms

Abstract In this paper, we use the “complexity equals action” (CA) conjecture to evaluate the holographic complexity in some multiple-horzion black holes for the gravitational theory coupled to a first-order source-free electrodynamics. Motivated by the vanishing result of the purely magnetic black hole founded by Goto et al., we investigate the complexity in a static charged black hole with source-free electrodynamics and find that this vanishing feature of the late-time rate is universal for a purely static magnetic black hole. But this result shows some unexpected features of the late-time growth rate. We show how the inclusion of a boundary term for the first-order electromagnetic field to the total action can make the holographic complexity be well-defined and obtain a general expression of the late-time complexity growth rate with these boundary terms. However, the choice of these additional boundary terms is dependent on the specific gravitational theory as well as the black hole geometries. To show this, we apply our late-time result to some explicit cases and show how to choose the proportional constant of the additional boundary term to make the complexity be well-defined in the zero-charge limit. Typically, we investigate the static magnetic black holes in Einstein gravity coupled to a first-order electrodynamics and find that there is a general relationship between the proper proportional constant and the Lagrangian function $$h(\mathcal {F})$$h(F) of the electromagnetic field: if $$h(\mathcal {F})$$h(F) is a convergent function, the choice of the proportional constant is independent on explicit expressions of $$h(\mathcal {F})$$h(F) and it should be chosen as 4/3; if $$h(\mathcal {F})$$h(F) is a divergent function, the proportional constant is dependent on the asymptotic index of the Lagrangian function.

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Charged and Non-Charged Black Hole Solutions in Mimetic Gravitational Theory

Symmetry ◽

10.3390/sym10110559 ◽

2018 ◽

Vol 10 (11) ◽

pp. 559 ◽

Cited By ~ 3

Author(s):

Gamal Nashed

Keyword(s):

Black Holes ◽

General Relativity ◽

Black Hole ◽

Gravitational Theory ◽

Relativity Theory ◽

Charged Black Hole ◽

Field Equations ◽

General Relativity Theory ◽

Mimetic Theory ◽

Black Hole Solutions

In this study, we derive, in the framework of mimetic theory, charged and non-charged black hole solutions for spherically symmetric as well as flat horizon spacetimes. The asymptotic behavior of those black holes behave as flat or (A)dS spacetimes and coincide with the solutions derived before in general relativity theory. Using the field equations of non-linear electrodynamics mimetic theory we derive new black hole solutions with monopole and quadrupole terms. The quadruple term of those black holes is related by a constant so that its vanishing makes the solutions coincide with the linear Maxwell black holes. We study the singularities of those solutions and show that they possess stronger singularity than the ones known in general relativity. Among many things, we study the horizons as well as the heat capacity to see if the black holes derived in this study have thermodynamical stability or not.

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Born–Infeld black holes in 4D Einstein–Gauss–Bonnet gravity

The European Physical Journal C ◽

10.1140/epjc/s10052-020-8246-6 ◽

2020 ◽

Vol 80 (7) ◽

Cited By ~ 7

Author(s):

Ke Yang ◽

Bao-Min Gu ◽

Shao-Wen Wei ◽

Yu-Xiao Liu

Keyword(s):

Black Holes ◽

Black Hole ◽

Black Hole Solution ◽

Gravitational Theory ◽

Charged Black Hole ◽

Spherically Symmetric ◽

The Novel ◽

Singularity Problem ◽

Bonnet Gravity ◽

Symmetric Black Hole

Abstract A novel four-dimensional Einstein-Gauss-Bonnet gravity was formulated by Glavan and Lin (Phys. Rev. Lett. 124:081301, 2020), which is intended to bypass the Lovelock’s theorem and to yield a non-trivial contribution to the four-dimensional gravitational dynamics. However, the validity and consistency of this theory has been called into question recently. We study a static and spherically symmetric black hole charged by a Born–Infeld electric field in the novel four-dimensional Einstein–Gauss–Bonnet gravity. It is found that the black hole solution still suffers the singularity problem, since particles incident from infinity can reach the singularity. It is also demonstrated that the Born-Infeld charged black hole may be superior to the Maxwell charged black hole to be a charged extension of the Schwarzschild-AdS-like black hole in this new gravitational theory. Some basic thermodynamics of the black hole solution is also analyzed. Besides, we regain the black hole solution in the regularized four-dimensional Einstein–Gauss–Bonnet gravity proposed by Lü and Pang (arXiv:2003.11552).

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No inner-horizon theorem for black holes with charged scalar hairs

Journal of High Energy Physics ◽

10.1007/jhep03(2021)263 ◽

2021 ◽

Vol 2021 (3) ◽

Author(s):

Rong-Gen Cai ◽

Li Li ◽

Run-Qiu Yang

Keyword(s):

Black Holes ◽

Scalar Potential ◽

Gravitational Theory ◽

Einstein Gravity ◽

Kinetic Term ◽

Cauchy Horizon ◽

Charged Scalar ◽

Inner Horizon ◽

Scalar Hair ◽

Scalar Potentials

Abstract We establish a no inner-horizon theorem for black holes with charged scalar hairs. Considering a general gravitational theory with a charged scalar field, we prove that there exists no inner Cauchy horizon for both spherical and planar black holes with non-trivial scalar hair. The hairy black holes approach to a spacelike singularity at late interior time. This result is independent of the form of scalar potentials as well as the asymptotic boundary of spacetimes. We prove that the geometry near the singularity takes a universal Kasner form when the kinetic term of the scalar hair dominates, while novel behaviors different from the Kasner form are uncovered when the scalar potential become important to the background. For the hyperbolic horizon case, we show that hairy black hole can only has at most one inner horizon, and a concrete example with an inner horizon is presented. All these features are also valid for the Einstein gravity coupled with neutral scalars.

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The Shadow of the Black Hole

10.1093/oso/9780190650728.001.0001 ◽

2020 ◽

Author(s):

John W. Moffat

Keyword(s):

United States ◽

Black Holes ◽

Black Hole ◽

Neutron Stars ◽

Gravitational Wave ◽

Gravitational Waves ◽

Laser Interferometer ◽

The United States ◽

Gravitational Theory ◽

The People

The author visits one of the two Laser Interferometer Gravitational- Wave Observatory (LIGO) sites in the United States, at Hanford, Washington. This is where scientists are detecting gravitational waves generated by faraway merging black holes and neutron stars. He meets the people who work there and has discussions with some of them. The director gives him a tour of the LIGO experimental installation, describing the work, the technological details of the apparatus, and answers his questions. On the final day of the visit, the author gives a talk to the LIGO group on gravitational waves and on an alternative gravitational theory.

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