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9 pages, 262 KiB

Open AccessArticle

Double Hawking Temperature: From Black Hole to de Sitter

by Grigory E. Volovik

Universe 2022, 8(12), 639; https://doi.org/10.3390/universe8120639 - 1 Dec 2022

Cited by 8 | Viewed by 1751

The double Hawking temperature

T = 2 T_{H}

The double Hawking temperature

T = 2 T_{H}

appears in some approaches to the Hawking radiation when the radiation is considered in terms of the quantum tunneling. We consider the origin of such unusual temperature for the black hole horizon and also for the cosmological horizon in de Sitter spacetime. In the case of the black hole horizon, there are two contributions to the tunneling process of radiation, each being governed by the temperature

T = 2 T_{H}

. These processes are coherently combined to produce the radiation with the Hawking temperature

T_{H}

. This can be traditionally interpreted as the pair creation of two entangled particles, of which one goes towards the center of the black hole, while the other one escapes from the black hole. In the case of the cosmological horizon, the temperature

T = 2 T_{H}

is physical. While the creation of the entangled pair is described by the Hawking temperature, the de Sitter spacetime allows for another process, in which only a single (non-entangled) particle inside the cosmological horizon is created. This process is characterized by the local temperature

T = 2 T_{H}

. The local single-particle process also takes place outside the black hole horizon, but it is exponentially suppressed. Full article

(This article belongs to the Section Cosmology)

24 pages, 384 KiB

Open AccessEditor’s ChoiceArticle

Spherically Symmetric Exact Vacuum Solutions in Einstein-Aether Theory

by Jacob Oost, Shinji Mukohyama and Anzhong Wang

Universe 2021, 7(8), 272; https://doi.org/10.3390/universe7080272 - 28 Jul 2021

Cited by 14 | Viewed by 2895

Abstract

We study spherically symmetric spacetimes in Einstein-aether theory in three different coordinate systems, the isotropic, Painlevè-Gullstrand, and Schwarzschild coordinates, in which the aether is always comoving, and present both time-dependent and time-independent exact vacuum solutions. In particular, in the isotropic coordinates we find [...] Read more.

c_{14}

in closed forms, which satisfies all the current observational constraints of the theory, and reduces to the Schwarzschild vacuum black hole solution in the decoupling limit (

c_{14} = 0

). However, as long as

c_{14} \neq 0

, a marginally trapped throat with a finite non-zero radius always exists, and on one side of it the spacetime is asymptotically flat, while on the other side the spacetime becomes singular within a finite proper distance from the throat, although the geometric area is infinitely large at the singularity. Moreover, the singularity is a strong and spacetime curvature singularity, at which both of the Ricci and Kretschmann scalars become infinitely large. Full article

(This article belongs to the Special Issue Inflation, Black Holes and Gravitational Waves)

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16 pages, 898 KiB

Open AccessArticle

Classical Limit for Dirac Fermions with Modified Action in the Presence of a Black Hole

by Meir Lewkowicz and Mikhail Zubkov

Symmetry 2019, 11(10), 1294; https://doi.org/10.3390/sym11101294 - 15 Oct 2019

Cited by 6 | Viewed by 2226

Abstract

We consider the model of Dirac fermions coupled to gravity as proposed, in which superluminal velocities of particles are admitted. In this model an extra term is added to the conventional Hamiltonian that originates from Planck physics. Due to this term, a closed Fermi surface is formed in equilibrium inside the black hole. In this paper we propose the covariant formulation of this model and analyse its classical limit. We consider the dynamics of gravitational collapse. It appears that the Einstein equations admit a solution identical to that of ordinary general relativity. Next, we consider the motion of particles in the presence of a black hole. Numerical solutions of the equations of motion are found which demonstrate that the particles are able to escape from the black hole. Full article

(This article belongs to the Special Issue Modified Theories of Gravity)

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