scholarly journals The Quantum Regularization of Singular Black-Hole Solutions in Covariant Quantum Gravity

Entropy ◽  
2021 ◽  
Vol 23 (3) ◽  
pp. 370
Author(s):  
Massimo Tessarotto ◽  
Claudio Cremaschini
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Form Factor ◽  
Quantum Gravity ◽  
Metric Tensor ◽  
Covariant Approach ◽  
Covariant Quantum ◽  
Background Space ◽  
Hamilton Equations ◽  
Black Hole Solutions

An excruciating issue that arises in mathematical, theoretical and astro-physics concerns the possibility of regularizing classical singular black hole solutions of general relativity by means of quantum theory. The problem is posed here in the context of a manifestly covariant approach to quantum gravity. Provided a non-vanishing quantum cosmological constant is present, here it is proved how a regular background space-time metric tensor can be obtained starting from a singular one. This is obtained by constructing suitable scale-transformed and conformal solutions for the metric tensor in which the conformal scale form factor is determined uniquely by the quantum Hamilton equations underlying the quantum gravitational field dynamics.

BH solutions with toroidal horizon in dilaton gravity inspired by power-law electrodynamics: PV criticality and quasinormal modes

2020 ◽  
Vol 35 (27) ◽  
pp. 2050172
Author(s):  
Younes Younesizadeh ◽  
Ali Hassan Ahmed ◽  
Amir A. Ahmad ◽  
Feyzollah Younesizadeh ◽  
Morad Ebrahimkhas
Keyword(s):  
Black Hole ◽  
Equation Of State ◽  
Electric Field ◽  
Quasinormal Modes ◽  
Dilaton Field ◽  
Dilaton Gravity ◽  
Field Representation ◽  
Background Space ◽  
Key Factor ◽  
Black Hole Solutions

In this work, a new class of black hole solutions in dilaton gravity has been obtained where the dilaton field is coupled with nonlinear Maxwell invariant as a source. The background space–time in this works is considered as the [Formula: see text]-dimensional toroidal metric. In the presence of the dilaton field (for some unique values of [Formula: see text][Formula: see text] a ), the electric field increases as we got farther away from the origin. In the absence of the dilaton field [Formula: see text], the electric field always decreases as one goes farther away from the origin. In the thermodynamical analysis, we obtain the Smarr formula for our solution. We find that the presence of the dilaton field makes the solutions to be locally stable near the origin. Also, this field vanishes the global stability near the origin compared to the no dilaton field case [Formula: see text]. We can say that the dilaton field has a crucial impact on the thermodynamical stability and it is a key factor in stability analysis. We study the quasinormal modes (QNMs) of black hole solutions in dilaton gravity. For this purpose, we use the WKB approximation method upto first order corrections. We have shown the perturbations decay in corresponding diagrams when the dilaton parameter [Formula: see text] and coupling constant [Formula: see text] change. Motivated by the thermodynamical analogy of black holes and Van der Waals liquid/gas systems, in this work, we investigate PV criticality of the obtained solution. We extend the phase space by considering the cosmological constant as thermodynamic pressure. We obtain the equation of state (EOS) and plot the relevant PV [Formula: see text] diagrams. We also present a class of interior solutions corresponding to the exterior solution in dilaton gravity. The solution which is obtained for a linear equation of state is regular and well-behaved at the stellar interior. a Dilaton field representation.

scholarly journals Constructing black hole solutions in supergravity theories

2019 ◽  
Vol 34 (35) ◽  
pp. 1930017 ◽  
Author(s):  
Antonio Gallerati
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Supergravity Models ◽  
Detailed Analysis ◽  
Black Hole Solution ◽  
Explicit Construction ◽  
General Introduction ◽  
Supersymmetric Theories ◽  
Black Hole Solutions

We perform a detailed analysis of black hole solutions in supergravity models. After a general introduction on black holes in general relativity and supersymmetric theories, we provide a detailed description of ungauged extended supergravities and their dualities. Therefore, we analyze the general form of black hole configurations for these models, their near-horizon behavior and characteristic of the solution. An explicit construction of a black hole solution with its physical implications is given for the STU-model. The second part of this review is dedicated to gauged supergravity theories. We describe a step-by-step gauging procedure involving the embedding tensor formalism to be used to obtain a gauged model starting from an ungauged one. Finally, we analyze general black hole solutions in gauged models, providing an explicit example for the [Formula: see text], [Formula: see text] case. A brief review on special geometry is also provided, with explicit results and relations for supersymmetric black hole solutions.

scholarly journals A SLOWLY ROTATING CHARGED BLACK HOLE IN FIVE DIMENSIONS

2006 ◽  
Vol 21 (09) ◽  
pp. 751-757 ◽  
Author(s):  
A. N. ALIEV
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
System Of Equations ◽  
Maxwell System ◽  
Five Dimensions ◽  
Four Dimensions ◽  
Higher Dimensional ◽  
Long Time ◽  
Electrically Charged ◽  
Black Hole Solutions

Black hole solutions in higher dimensional Einstein and Einstein–Maxwell gravity have been discussed by Tangherlini as well as Myers and Perry a long time ago. These solutions are the generalizations of the familiar Schwarzschild, Reissner–Nordström and Kerr solutions of four-dimensional general relativity. However, higher dimensional generalization of the Kerr–Newman solution in four dimensions has not been found yet. As a first step in this direction we shall report on a new solution of the Einstein–Maxwell system of equations that describes an electrically charged and slowly rotating black hole in five dimensions.

scholarly journals ON GENERATING SOME KNOWN BLACK HOLE SOLUTIONS

2010 ◽  
Vol 25 (10) ◽  
pp. 835-842 ◽  
Author(s):  
F. RAHAMAN ◽  
MUBASHER JAMIL ◽  
A. GHOSH ◽  
K. CHAKRABORTY
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Alternative Theories Of Gravity ◽  
Dimensional Parameters ◽  
Theories Of Gravity ◽  
Alternative Theories ◽  
Black Hole Solutions

In this paper, we have presented an algorithm to generate various black hole solutions in general relativity and alternative theories of gravity. The algorithm involves few dimensional parameters that are assigned suitable values to specify the required black hole.

scholarly journals Physical Properties of Schwarzschild–deSitter Event Horizon Induced by Stochastic Quantum Gravity

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 511
Author(s):  
Claudio Cremaschini ◽  
Massimo Tessarotto
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Quantum Gravity ◽  
Event Horizon ◽  
Field Equations ◽  
Central Mass ◽  
Event Horizons ◽  
Covariant Quantum ◽  
Gravitational Fields ◽  
New Type

A new type of quantum correction to the structure of classical black holes is investigated. This concerns the physics of event horizons induced by the occurrence of stochastic quantum gravitational fields. The theoretical framework is provided by the theory of manifestly covariant quantum gravity and the related prediction of an exclusively quantum-produced stochastic cosmological constant. The specific example case of the Schwarzschild–deSitter geometry is looked at, analyzing the consequent stochastic modifications of the Einstein field equations. It is proved that, in such a setting, the black hole event horizon no longer identifies a classical (i.e., deterministic) two-dimensional surface. On the contrary, it acquires a quantum stochastic character, giving rise to a frame-dependent transition region of radial width δr between internal and external subdomains. It is found that: (a) the radial size of the stochastic region depends parametrically on the central mass M of the black hole, scaling as δr∼M3; (b) for supermassive black holes δr is typically orders of magnitude larger than the Planck length lP. Instead, for typical stellar-mass black holes, δr may drop well below lP. The outcome provides new insight into the quantum properties of black holes, with implications for the physics of quantum tunneling phenomena expected to arise across stochastic event horizons.

scholarly journals Charged spherically symmetric Taub–NUT black hole solutions in $f(R)$ gravity

2020 ◽  
Vol 2020 (4) ◽  
Author(s):  
G G L Nashed ◽  
Kazuharu Bamba
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Free Energy ◽  
Black Hole Solution ◽  
Energy Conditions ◽  
Thermodynamic Quantities ◽  
Spherically Symmetric ◽  
Dimensional Parameter ◽  
Charged Black Holes ◽  
Black Hole Solutions

Abstract $f(R)$ theory is a modification of Einstein’s general relativity which has provided many interesting results in cosmology and astrophysics. To derive a black hole solution in this theory is difficult due to the fact that it contains fourth-order differential equations. In this study, we use the first reliable deviation from general relativity which is given by the quadratic form of $f(R)=R+\beta R^2$, where $\beta$ is a dimensional parameter. We calculate the energy conditions of charged black holes and show that they are all satisfied for the Taub–NUT spacetime. Finally, we study some thermodynamic quantities such as entropy, temperature, specific heat, and Gibbs free energy. The calculations of heat capacity and free energy show that the charged Taub–NUT black hole has positive values, which means that it has thermal stability.

Black to white hole tunneling: An exact classical solution

2015 ◽  
Vol 30 (28n29) ◽  
pp. 1545015 ◽  
Author(s):  
Hal M. Haggard ◽  
Carlo Rovelli
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Quantum Theory ◽  
Quantum Gravity ◽  
Quantum Tunneling ◽  
Einstein Equations ◽  
White Hole ◽  
Small Quantum ◽  
Pile Up ◽  
Over Time

We present a metric that describes conventional matter collapsing into a black hole, bouncing and emerging from a white hole, and that satisfies the vacuum Einstein equations everywhere, including in the interior of the black hole and the subsequent white hole, except for a small compact 4d “quantum tunneling” zone. This shows that a black hole can tunnel into a white hole without violating classical general relativity where this can be trusted. We observe that quantum gravity can affect the metric in a region outside the horizon without violating causality because small quantum effects might pile up over time. We study how quantum theory can determines the bouncing time.

GEOMETRIC DUALITY AND CHERN–SIMONS MODIFIED GRAVITY

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1323-1327 ◽  
Author(s):  
L. A. CABRAL
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Modified Gravity ◽  
Kerr Metric ◽  
Nontrivial Solutions ◽  
Topological Current ◽  
Chern Simons ◽  
Hilbert Action ◽  
Black Hole Solutions ◽  
Geometric Duality

We consider a theory which involves an extension of general relativity known as Chern–Simons modified gravity (CSMG). In this theory the standard Einstein–Hilbert action is extended with a gravitational Pontryagin density that is obtained from a divergence of a Chern–Simons topological current. The extended theory has the standard Schwarzchild metric as solution, however, only a perturbed Kerr metric holds solution. From the exact Kerr metric we construct dual metrics to search for rotating black hole solutions. The conditions on the Killing tensors associated with dual metrics entail nontrivial solutions to CSMG.

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