Universe

20 pages, 1263 KiB

Open AccessArticle

Magnetized and Magnetically Charged Particles Motion around Regular Bardeen Black Hole in 4D Einstein Gauss–Bonnet Gravity

by Javlon Rayimbaev, Dilshodbek Bardiev, Farrux Abdulxamidov, Ahmadjon Abdujabbarov and Bobomurat Ahmedov

Universe 2022, 8(10), 549; https://0-doi-org.brum.beds.ac.uk/10.3390/universe8100549 - 21 Oct 2022

Cited by 9 | Viewed by 1265

Abstract

In this paper, we study the horizon properties and scalar invariants of the spacetime around a regular black hole (BH) in 4D Einstein Gauss-Bonnet (4D EGB) gravity. It is observed that the presence of both Gauss-Bonnet (GB) coupling and magnetic charge parameters causes [...] Read more.

In this paper, we study the horizon properties and scalar invariants of the spacetime around a regular black hole (BH) in 4D Einstein Gauss-Bonnet (4D EGB) gravity. It is observed that the presence of both Gauss-Bonnet (GB) coupling and magnetic charge parameters causes the shrinking of the outer horizon. We find that the range of the GB parameter

α / M^{2} \in (- 0.15869, 1)

, and the extreme value of magnetic charge reaches up to

g_{extr} = 0.886 M

, which allows for the existence of a BH horizon, while it is

g_{extr} = 0.7698 M

for pure Bardeen BH. We also investigate the dynamics of magnetized particles around the magnetically charged Bardeen BH, assuming the particle’s motion occurs in the equatorial plane in the proper observation frame, and the direction of the magnetic dipole moment of the particles is always kept radially and its magnitude is constant. Moreover, the dynamics of magnetically charged particles are also studied, and it is shown that both the energy and angular momentum of the particles corresponding to circular orbits increases with the increase of their magnetic charge. Finally, we also study collisions of magnetized, electrically neutral, and magnetically charged particles around the Bardeen BHs, where we provide analyses of critical angular momentum that may allow collision of the particles near-horizon radius, producing enormous values of center of mass energy of the collisions. Full article

(This article belongs to the Special Issue Black Holes in Einstein–Gauss–Bonnet Theories)

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10 pages, 296 KiB

Open AccessArticle

De Sitter Entropy in Higher Derivative Theories of Gravity

by An Gong, Kun Liu and Fu-Wen Shu

Universe 2023, 9(3), 116; https://0-doi-org.brum.beds.ac.uk/10.3390/universe9030116 - 24 Feb 2023

Viewed by 797

Abstract

A theorem on higer-order derivative theories of gravity is proved. We find that the de Sitter/anti-de Sitter metric is always a solution of any generally covariant theory of gravity. With this theorem and a general form of entropy function for de Sitter spacetimes, [...] Read more.

A theorem on higer-order derivative theories of gravity is proved. We find that the de Sitter/anti-de Sitter metric is always a solution of any generally covariant theory of gravity. With this theorem and a general form of entropy function for de Sitter spacetimes, we show how to calculate the entropy of de Sitter spacetime in a generally covariant theory of gravity without knowing the details of the modified metric. As an example, a general formula of dS entropy in Lovelock gravity is obtained. Full article

(This article belongs to the Special Issue Black Holes in Einstein–Gauss–Bonnet Theories)

11 pages, 710 KiB

Open AccessArticle

Holographic p-Wave Superconductor with Excited States in 4D Einstein–Gauss–Bonnet Gravity

by Dong Wang, Xinyi Du, Qiyuan Pan and Jiliang Jing

Universe 2023, 9(2), 104; https://0-doi-org.brum.beds.ac.uk/10.3390/universe9020104 - 17 Feb 2023

Cited by 1 | Viewed by 1024

Abstract

We construct a holographic p-wave superconductor with excited states in the 4D Einstein–Gauss–Bonnet gravity using the Maxwell complex vector field model. In the probe limit, we observe that, the higher curvature correction or the higher excited state can hinder the vector condensate to [...] Read more.

We construct a holographic p-wave superconductor with excited states in the 4D Einstein–Gauss–Bonnet gravity using the Maxwell complex vector field model. In the probe limit, we observe that, the higher curvature correction or the higher excited state can hinder the vector condensate to be formed in the full parameter space, which is different from the holographic s-wave superconductor. Regardless of the choice of the vector mass by selecting the value of

m^{2} L^{2}

or

m^{2} L_{eff}^{2}

, we note that the critical chemical potential becomes evenly spaced for the number of nodes and that the difference of the critical chemical potential between the consecutive states depends on the curvature correction. Moreover, we find that the higher curvature correction or the higher excited state will alter the universal relation of the gap frequency, and the pole and delta function of the conductivity for the excited states can be broadened into the peaks with the finite width as the curvature correction increases. Full article

(This article belongs to the Special Issue Black Holes in Einstein–Gauss–Bonnet Theories)

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13 pages, 414 KiB

Open AccessArticle

Analytical Approximate Solutions for Scalarized AdS Black Holes

by De-Cheng Zou, Bo Meng, Ming Zhang, Sheng-Yuan Li, Meng-Yun Lai and Yun Soo Myung

Universe 2023, 9(1), 26; https://0-doi-org.brum.beds.ac.uk/10.3390/universe9010026 - 30 Dec 2022

Cited by 4 | Viewed by 1017

Abstract

The spontaneous scalarization of Schwarzscild-AdS is investigated in the Einstein-scalar-Gauss–Bonnet (ESGB) theory. Firstly, we construct scalarized AdS black holes numerically. Secondly, making use of the homotopy analysis method (HAM), we obtain analytical approximate solutions for scalarized AdS black holes in the ESGB theory. [...] Read more.

The spontaneous scalarization of Schwarzscild-AdS is investigated in the Einstein-scalar-Gauss–Bonnet (ESGB) theory. Firstly, we construct scalarized AdS black holes numerically. Secondly, making use of the homotopy analysis method (HAM), we obtain analytical approximate solutions for scalarized AdS black holes in the ESGB theory. It is found that scalarized AdS black holes constructed numerically are consistent with analytical approximate solutions in the whole space. Full article

(This article belongs to the Special Issue Black Holes in Einstein–Gauss–Bonnet Theories)

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11 pages, 498 KiB

Open AccessArticle

Phases of Rotating Black Objects in d = 5 Einstein–Gauss–Bonnet Theory

by Burkhard Kleihaus, Jutta Kunz and Eugen Radu

Universe 2023, 9(4), 156; https://0-doi-org.brum.beds.ac.uk/10.3390/universe9040156 - 23 Mar 2023

Viewed by 741

Abstract

We considered several different classes of asymptotically flat, rotating black objects in

d = 5

Einstein–Gauss–Bonnet (EGB) theory. These are black holes with two equal-magnitude angular momenta, in which case extremal configurations are studied as well. Numerical evidence is also given for the [...] Read more.

We considered several different classes of asymptotically flat, rotating black objects in

d = 5

Einstein–Gauss–Bonnet (EGB) theory. These are black holes with two equal-magnitude angular momenta, in which case extremal configurations are studied as well. Numerical evidence is also given for the existence of EGB generalizations of the Myers–Perry black holes with a single plane of rotation and of the Emparan–Reall balanced black rings. All solutions approach asymptotically the Minkowski background and present no singularities outside or on the horizon. The numerical results suggest that, for any mass of the solutions and any topology of the horizon, the rotating configurations exist up to a maximal value of the GB coupling constant, while the solutions with a spherical horizon topology still satisfy the Einstein gravity bound on angular momentum. Full article

(This article belongs to the Special Issue Black Holes in Einstein–Gauss–Bonnet Theories)

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7 pages, 276 KiB

Open AccessArticle

Effects of Quantum Gravity on Thermodynamic Quantities of Gases around a Novel Neutral Four-Dimensional Gauss–Bonnet Black Hole

by Guqiang Li

Universe 2023, 9(6), 253; https://0-doi-org.brum.beds.ac.uk/10.3390/universe9060253 - 26 May 2023

Viewed by 729

Abstract

Taking the generalized uncertainty principle (GUP) into account, we apply the corrected state density to investigate the entropy density, energy density, pressure and equation of state for the perfect relativistic gases of massless particles with an arbitrary spin of s ≤ 2 surrounding [...] Read more.

Taking the generalized uncertainty principle (GUP) into account, we apply the corrected state density to investigate the entropy density, energy density, pressure and equation of state for the perfect relativistic gases of massless particles with an arbitrary spin of s ≤ 2 surrounding a new four-dimensional neutral Gauss–Bonnet black hole. The modifications of these thermodynamic quantities by the gravity correction factor and particle spin are shown, and the expressions have completely different forms from those in flat space-times. For example, the energy density is not proportional to the fourth power of the temperature. In other words, the energy density differs from that of blackbody radiation. The quantum gravity effects reduce these quantities and are proportional to the gravity correction factor. The result that the equation of state is not zero is compatible with the non-vanishing trace of the stress tensor. Full article

(This article belongs to the Special Issue Black Holes in Einstein–Gauss–Bonnet Theories)

12 pages, 423 KiB

Open AccessCommunication

4D Einstein–Gauss–Bonnet Gravity Coupled to Modified Logarithmic Nonlinear Electrodynamics

by Sergey Il’ich Kruglov

Universe 2023, 9(1), 24; https://0-doi-org.brum.beds.ac.uk/10.3390/universe9010024 - 30 Dec 2022

Cited by 1 | Viewed by 1036

Abstract

Spherically symmetric solution in 4D Einstein–Gauss–Bonnet gravity coupled to modified logarithmic nonlinear electrodynamics (ModLogNED) is found. This solution at infinity possesses the charged black hole Reissner–Nordström behavior. We study the black hole thermodynamics, entropy, shadow, energy emission rate and quasinormal modes. It was [...] Read more.

Spherically symmetric solution in 4D Einstein–Gauss–Bonnet gravity coupled to modified logarithmic nonlinear electrodynamics (ModLogNED) is found. This solution at infinity possesses the charged black hole Reissner–Nordström behavior. We study the black hole thermodynamics, entropy, shadow, energy emission rate and quasinormal modes. It was shown that black holes can possess the phase transitions and at some range of event horizon radii black holes are stable. The entropy has the logarithmic correction to the area law. The shadow radii were calculated for variety of parameters. We found that there is a peak of the black hole energy emission rate. The real and imaginary parts of the quasinormal modes frequencies were calculated. The energy conditions of ModLogNED are investigated. Full article

(This article belongs to the Special Issue Black Holes in Einstein–Gauss–Bonnet Theories)

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21 pages, 1145 KiB

Open AccessArticle

Theory and Phenomenology of a Four-Dimensional String–Corrected Black Hole

by Kimet Jusufi and Dejan Stojkovic

Universe 2022, 8(3), 194; https://0-doi-org.brum.beds.ac.uk/10.3390/universe8030194 - 21 Mar 2022

Cited by 7 | Viewed by 2017

Abstract

We construct an effective four-dimensional string-corrected black hole (4D SCBH) by rescaling the string coupling parameter in a D-dimensional Callan–Myers–Perry black hole. From the theoretical point of view, the most interesting findings are that the string corrections coincide with the so-called generalized [...] Read more.

We construct an effective four-dimensional string-corrected black hole (4D SCBH) by rescaling the string coupling parameter in a D-dimensional Callan–Myers–Perry black hole. From the theoretical point of view, the most interesting findings are that the string corrections coincide with the so-called generalized uncertainty principle (GUP) corrections to black hole solutions, Bekenstein–Hawking entropy acquires logarithmic corrections, and that there exists a critical value of the coupling parameter for which the black hole temperature vanishes. We also find that, due to the string corrections, the nature of the central singularity may be altered from space-like to time-like singularity. In addition, we study the possibility of testing such a black hole with astrophysical observations. Since the dilaton field does not decouple from the metric, it is not a priori clear that the resulting 4D SCBH offers only small corrections to the Schwarzschild black hole. We used motion of the S2 star around the black hole at the center of our galaxy to constrain the parameters (the string coupling parameter and ADM mass) of the 4D SCBH. To test the weak gravity regime, we calculate the deflection angle in this geometry and apply it to gravitational lensing. To test the strong field regime, we calculate the black hole shadow radius. While we find that the observables change as we change the string coupling parameter, the magnitude of the change is too small to distinguish it from the Schwarzschild black hole. With the current precision, to the leading order terms, the 4D SCBH cannot be distinguished from the Schwarzschild black hole. Full article

(This article belongs to the Special Issue Black Holes in Einstein–Gauss–Bonnet Theories)

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