scholarly journals On causal structure of 4D-Einstein–Gauss–Bonnet black hole

2020 ◽  
Vol 80 (9) ◽  
Author(s):  
Naresh Dadhich
Keyword(s):  
Black Hole ◽  
Black Hole Solution ◽  
Causal Structure ◽  
Equation Of Motion ◽  
Cauchy Horizon ◽  
Coupling Constant ◽  
Schwarzschild Black Hole ◽  
Effective Equation ◽  
Central Singularity ◽  
Static Black Hole

AbstractThe recently proposed effective equation of motion for the 4D-Einstein–Gauss–Bonnet gravity admits a static black hole solution that has, like the Rissner–Nordström charged black hole, two horizons instead of one for the Schwarzschild black hole. This means that the central singularity is timelike instead of spacelike. It should though be noted that in $$D\ge 5$$ D ≥ 5 , the solution always admits only one horizon like the Schwarzshild solution. In the equation defining the horizon, the rescaled Gauss–Bonnet coupling constant appears as a new ‘gravitational charge’ with a repulsive effect to cause in addition to event horizon a Cauchy horizon. Thus it radically alters the causal structure of the black hole.

scholarly journals Causality of black holes in 4-dimensional Einstein–Gauss–Bonnet–Maxwell theory

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
Xian-Hui Ge ◽  
Sang-Jin Sin
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Shear Viscosity ◽  
Upper Bound ◽  
Causal Structure ◽  
Density Ratio ◽  
Entropy Density ◽  
Coupling Constant ◽  
Maxwell Theory ◽  
Black Hole Solutions

Abstract We study charged black hole solutions in 4-dimensional (4D) Einstein–Gauss–Bonnet–Maxwell theory to the linearized perturbation level. We first compute the shear viscosity to entropy density ratio. We then demonstrate how bulk causal structure analysis imposes an upper bound on the Gauss–Bonnet coupling constant in the AdS space. Causality constrains the value of Gauss–Bonnet coupling constant $$\alpha _{GB}$$αGB to be bounded by $$\alpha _{GB}\le 0$$αGB≤0 as $$D\rightarrow 4$$D→4.

scholarly journals Black holes in magnetic monopoles with a dark halo

2019 ◽  
Vol 34 (01) ◽  
pp. 1950002 ◽  
Author(s):  
A. Lugo ◽  
J. M. Pérez Ipiña ◽  
F. A. Schaposnik
Keyword(s):  
Black Hole ◽  
Black Hole Solution ◽  
Scalar Potential ◽  
Magnetic Monopoles ◽  
Dark Halo ◽  
Higgs Potential ◽  
Coupling Constant ◽  
Horizon Radius ◽  
Yang Mills ◽  
Higgs Portal

We study a spontaneously broken Einstein–Yang–Mills–Higgs model coupled via a Higgs portal to an uncharged scalar [Formula: see text]. We present a phase diagram of self-gravitating solutions showing that depending on the choice of parameters of the [Formula: see text] scalar potential and the Higgs portal coupling constant [Formula: see text], one can identify different regions: If [Formula: see text] is sufficiently small, a [Formula: see text] halo is created around the monopole core which in turn surrounds a black hole. For larger values of [Formula: see text], no halo exists and the solution is just a black hole monopole one. When the horizon radius grows and becomes larger than the monopole radius, solely a black hole solution exists. Because of the presence of the [Formula: see text] scalar, a bound for the Higgs potential coupling constant exists and when it is not satisfied, the vacuum is unstable and no nontrivial solution exists. We briefly comment on possible connections of our results with those found in recent dark matter axion models.

scholarly journals Exact black hole solutions with nonlinear electrodynamic field

2020 ◽  
Vol 29 (05) ◽  
pp. 2050032
Author(s):  
Shuang Yu ◽  
Changjun Gao
Keyword(s):  
Black Hole ◽  
Cosmological Constant ◽  
Electric Charge ◽  
Single Phase ◽  
Causal Structure ◽  
Nonlinear Electrodynamic ◽  
Coupling Constant ◽  
De Sitter ◽  
Black Hole Solutions ◽  
Three Phases

We construct exact black hole solutions to Einstein gravity with nonlinear electrodynamic field. In these solutions, there are, in general, four parameters. They are physical mass, electric charge, cosmological constant and the coupling constant. These solutions differ significantly from the Reissner–Nordström–de Sitter solution in Einstein–Maxwell gravity with a cosmological constant, due to the presence of coupling constant. For example, some of them are endowed with a topological defect on angle [Formula: see text] and the electric charge of some can be much larger or smaller than their mass by varying the coupling constant. On the other hand, these spacetimes are all asymptotically de Sitter (or anti-de Sitter). As a result, their causal structure is similar to the Reissner–Nordström–de Sitter spacetime. Finally, the investigations on the thermodynamics reveal that the coupling constant except for solution-4 has the opposite effect as temperature on the phase, structure of black holes. Concretely, the phase-space changes from single phase to three phases with the decrease of temperature. On the contrary, it changes from three phases to a single phase with the decrease of coupling constant.

scholarly journals ORIGIN OF MATTER OUT OF PURE CURVATURE

2008 ◽  
Vol 17 (03n04) ◽  
pp. 513-518 ◽  
Author(s):  
NARESH DADHICH ◽  
HIDEKI MAEDA
Keyword(s):  
Black Hole ◽  
Black Hole Solution ◽  
Space Time ◽  
De Sitter ◽  
Matter Distribution ◽  
Static Black Hole ◽  
Negative Constant ◽  
Usual Formula ◽  
The Universe ◽  
Kaluza Klein

We propose a mechanism for the origin of matter in the universe in the framework of Einstein–Gauss–Bonnet gravity in higher dimensions. The new static black hole solution recently discovered by the authors,1 with the Kaluza–Klein split of space–time as a product of the usual [Formula: see text] with a space of negative constant curvature, is indeed a pure gravitational creation of a black hole which is also endowed with a Maxwell-like gravitational charge in four-dimensional vacuum space–time. This solution has been further generalized to include radially flowing radiation, which means that extra-dimensional curvature also produces matter distribution asymptotically, resembling charged null dust. The static black hole could thus be envisioned as being formed from anti–de Sitter space–time by the collapse of radially inflowing charged null dust. It thus establishes the remarkable reciprocity between matter and gravity — as matter produces gravity (curvature), gravity produces matter. After the Kaluza–Klein generation of the Maxwell field, this is the first instance of realization of matter without matter in the classical framework.

scholarly journals Spatially homogeneous black hole solutions in $$z=4$$ Hořava–Lifshitz gravity in $$(4+1)$$ dimensions with Nil geometry and $$H^2\times R$$ horizons

2021 ◽  
Vol 81 (10) ◽  
Author(s):  
F. Naderi ◽  
A. Rezaei-Aghdam ◽  
Z. Mahvelati-Shamsabadi
Keyword(s):  
Black Hole ◽  
Black Hole Solution ◽  
Three Dimensional ◽  
Hamiltonian Formalism ◽  
Coupling Constant ◽  
Especial Case ◽  
Gravity Equations ◽  
Spatially Homogeneous ◽  
Black Hole Solutions ◽  
Bianchi Types

AbstractIn this paper, we present two new families of spatially homogeneous black hole solution for $$z=4$$ z = 4 Hořava–Lifshitz Gravity equations in $$(4+1)$$ ( 4 + 1 ) dimensions with general coupling constant $$\lambda $$ λ and the especial case $$\lambda =1$$ λ = 1 , considering $$\beta =-1/3$$ β = - 1 / 3 . The three-dimensional horizons are considered to have Bianchi types II and III symmetries, and hence the horizons are modeled on two types of Thurston 3-geometries, namely the Nil geometry and $$H^2\times R$$ H 2 × R . Being foliated by compact 3-manifolds, the horizons are neither spherical, hyperbolic, nor toroidal, and therefore are not of the previously studied topological black hole solutions in Hořava–Lifshitz gravity. Using the Hamiltonian formalism, we establish the conventional thermodynamics of the solutions defining the mass and entropy of the black hole solutions for several classes of solutions. It turned out that for both horizon geometries the area term in the entropy receives two non-logarithmic negative corrections proportional to Hořava–Lifshitz parameters. Also, we show that choosing some proper set of parameters the solutions can exhibit locally stable or unstable behavior.

scholarly journals Spherically symmetric black holes with electric and magnetic charge in extended gravity: physical properties, causal structure, and stability analysis in Einstein’s and Jordan’s frames

2020 ◽  
Vol 80 (2) ◽  
Author(s):  
E. Elizalde ◽  
G. G. L. Nashed ◽  
S. Nojiri ◽  
S. D. Odintsov
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Stability Analysis ◽  
Physical Properties ◽  
Causal Structure ◽  
Hawking Temperature ◽  
The Novel ◽  
Extended Gravity ◽  
Static Black Hole ◽  
Black Hole Solutions

Abstract Novel static black hole solutions with electric and magnetic charges are derived for the class of modified gravities: $$f({{{\mathcal {R}}}})={{{\mathcal {R}}}}+2\beta \sqrt{{{\mathcal {R}}}}$$f(R)=R+2βR, with or without a cosmological constant. The new black holes behave asymptotically as flat or (A)dS space-times with a dynamical value of the Ricci scalar given by $$R=\frac{1}{r^2}$$R=1r2 and $$R=\frac{8r^2\Lambda +1}{r^2}$$R=8r2Λ+1r2, respectively. They are characterized by three parameters, namely their mass and electric and magnetic charges, and constitute black hole solutions different from those in Einstein’s general relativity. Their singularities are studied by obtaining the Kretschmann scalar and Ricci tensor, which shows a dependence on the parameter $$\beta $$β that is not permitted to be zero. A conformal transformation is used to display the black holes in Einstein’s frame and check if its physical behavior is changed w.r.t. the Jordan one. To this end, thermodynamical quantities, as the entropy, Hawking temperature, quasi-local energy, and the Gibbs free energy are calculated to investigate the thermal stability of the solutions. Also, the casual structure of the new black holes is studied, and a stability analysis is performed in both frames using the odd perturbations technique and the study of the geodesic deviation. It is concluded that, generically, there is coincidence of the physical properties of the novel black holes in both frames, although this turns not to be the case for the Hawking temperature.

scholarly journals Cosmological isotropic matter–energy generalizations of Schwarzschild and Kerr metrics

2016 ◽  
Vol 25 (10) ◽  
pp. 1650088
Author(s):  
Metin Arik ◽  
Yorgo Senikoglu
Keyword(s):  
Black Hole ◽  
Dark Energy ◽  
Black Hole Solution ◽  
State Parameter ◽  
Time Dependent ◽  
Schwarzschild Black Hole ◽  
Field Equations ◽  
Rotating Black Hole ◽  
Special Solutions ◽  
Matter Energy

We present a time-dependent isotropic fluid solution around a Schwarzschild black hole. We offer the solutions and discuss the effects on the field equations and the horizon. We derive the energy density, pressure and the equation of state parameter. In the second part, we generalize the rotating black hole solution to an expanding universe. We derive from the proposed metric the special solutions of the field equations for the dust approximation and the dark energy solution. We show that the presence of a rotating black hole does not modify the scale factor [Formula: see text] law for dust, nor [Formula: see text] and [Formula: see text] for dark energy.

The Wheeler–Dewitt Equation for the Superstring World Sheet

1997 ◽  
Vol 06 (01) ◽  
pp. 91-105 ◽  
Author(s):  
M. D. Pollock
Keyword(s):  
Black Hole ◽  
Ground State ◽  
Total Mass ◽  
Equation Of Motion ◽  
Schwarzschild Black Hole ◽  
World Sheet ◽  
Integral Expression ◽  
Higher Derivative ◽  
The World ◽  
The Universe

The Wheeler–DeWitt equation for the wave function ψ is obtained from the two-dimensional world-sheet action for the bosonic string and the superstring, including higher-derivative terms, as the Schrödinger equation i ∂ ψ/ ∂τ = V(τ)ψ. The potential is given by the rate at which the world-sheet area is swept out, V(τ) = dA(τ)/dτ, and is positive semi-definite, allowing the existence of a ground state, corresponding to the absence of the string, with a non-vanishing probability density ψ ψ*. Integration of this equation yields the solution [Formula: see text], where [Formula: see text] is the action, minus the higher-derivative terms [Formula: see text] (and terms involving ∊ab in the case of the superstring), which, however, are constrained to vanish semi-classically, being constructed from the square of the equation of motion for the bosonic coordinates XA derived from [Formula: see text] alone. This path-integral expression for ψ is consistent with the operator replacements for the canonical momenta used in its derivation, and forms the basis of the approach due to Polyakov of summing over random surfaces. Comparison is made with the Schrödinger equations derived previously from the reduced, four-dimensional effective action for the heterotic superstring, and for the Schwarzschild black hole (by Tomimatsu), where the potential is also positive semi-definite, being (twice) the total mass of the Universe and the mass of the black hole, respectively, showing the unity of the method.

scholarly journals Probing the parameters of a Schwarzschild black hole surrounded by quintessence and cloud of strings through four standard astrophysical tests

2021 ◽  
Vol 81 (10) ◽  
Author(s):  
Víctor H. Cárdenas ◽  
Mohsen Fathi ◽  
Marco Olivares ◽  
J. R. Villanueva
Keyword(s):  
Black Hole ◽  
Time Delay ◽  
Observational Data ◽  
Gravitational Redshift ◽  
Schwarzschild Black Hole ◽  
Gravitational Perturbations ◽  
Deflection Of Light ◽  
Static Black Hole ◽  
Planetary Orbits ◽  
General Relativistic

AbstractIn this paper, we concern about applying general relativistic tests on the spacetime produced by a static black hole associated with cloud of strings, in a universe filled with quintessence. The four tests we apply are precession of the perihelion in the planetary orbits, gravitational redshift, deflection of light, and the Shapiro time delay. Through this process, we constrain the spacetime’s parameters in the context of the observational data, which results in about $$\sim 10^{-9}$$ ∼ 10 - 9 for the cloud of strings parameter, and $$\sim 10^{-20}$$ ∼ 10 - 20  m$$^{-1}$$ - 1 for that of quintessence. The response of the black hole to the gravitational perturbations is also discussed.

scholarly journals Thermodynamic properties of Bardeen black holes in dRGT massive gravity

2021 ◽  
Author(s):  
R P Singh ◽  
B K Singh ◽  
B R K Gupta ◽  
S Sachan
Keyword(s):  
Heat Capacity ◽  
Black Hole ◽  
Free Energy ◽  
Black Hole Solution ◽  
Massive Gravity ◽  
Schwarzschild Black Hole ◽  
Regular Black Hole ◽  
Horizon Radius ◽  
Canonical Ensembles ◽  
Grand Canonical

The Bardeen black hole solution is the first spherically symmetric regular black hole based on the Sakharov and Gliner proposal which is the modification of the Schwarzschild black hole. We present the Bardeen black hole solution in presence of the dRGT massive gravity, which is regular everywhere in the presence of a nonlinear source. The obtained solution interpolates with the Bardeen black hole in the absence of massive gravity parameter and the Schwarzschild black hole in the limit of magnetic charge g=0. We investigate the thermodynamical quantities viz. mass (M), temperature (T), entropy (S) and free energy (F) in terms of horizon radius for both canonical and grand canonical ensembles. We check the local and global stability of the obtained solution by studying the heat capacity and free energy. The heat capacity flips the sign at r = r<sub>c</sub>. The black hole is thermodynamically stable with positive heat capacity C>0 for i.e., globally preferred with negative free energy F < 0. In addition, we also study the phase structure of the obtained solution in both ensembles.

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