scholarly journals ON TIME-DEPENDENT BLACK HOLES AND COSMOLOGICAL MODELS FROM A KALUZA–KLEIN MECHANISM

2009 ◽  
Vol 24 (07) ◽  
pp. 1383-1415
Author(s):  
C. CASTRO ◽  
J. A. NIETO ◽  
L. RUIZ ◽  
J. SILVAS
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Cosmological Model ◽  
Black Hole Entropy ◽  
Time Dependent ◽  
Einstein Field Equations ◽  
Schwarzschild Black Hole ◽  
Field Equations ◽  
Newman Black Hole ◽  
Kaluza Klein

Novel static, time-dependent and spatial–temporal solutions to Einstein field equations, displaying singularities, with and without horizons, and in several dimensions, are found based on a dimensional reduction procedure widely used in Kaluza–Klein-type theories. The Kerr–Newman black hole entropy as well as the Reissner–Nordstrom, Kerr and Schwarzschild black hole entropy are derived from the corresponding Euclideanized actions. A very special cosmological model based on the dynamical interior geometry of a black hole is found that has no singularities at t = 0 due to the smoothing of the mass distribution. We conclude with another cosmological model equipped also with a dynamical horizon and which is related to Vaidya's metric (associated with the Hawking radiation of black holes) by interchanging t ↔ r, which might render our universe a dynamical black hole.

ON (2+2)-DIMENSIONAL SPACE–TIMES, STRINGS AND BLACK HOLES

2007 ◽  
Vol 22 (11) ◽  
pp. 2021-2045 ◽  
Author(s):  
C. CASTRO ◽  
J. A. NIETO
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Homogeneous Spaces ◽  
Dimensional Space ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Dimensional Solution ◽  
Complex Dimensions ◽  
Dimensional Space Time ◽  
Dimensional Boundary

We study black hole-like solutions (space–times with singularities) of Einstein field equations in 3+1 and 2+2 dimensions. We find three different cases associated with hyperbolic homogeneous spaces. In particular, the hyperbolic version of Schwarzschild's solution contains a conical singularity at r = 0 resulting from pinching to zero size r = 0 the throat of the hyperboloid [Formula: see text] and which is quite different from the static spherically symmetric (3+1)-dimensional solution. Static circular symmetric solutions for metrics in 2+2 are found that are singular at ρ = 0 and whose asymptotic ρ→∞ limit leads to a flat (1+2)-dimensional boundary of topology S1 × R2. Finally we discuss the (1+1)-dimensional Bars–Witten stringy black hole solution and show how it can be embedded into our (3+1)-dimensional solutions. Black holes in a (2+2)-dimensional "space–time" from the perspective of complex gravity in 1+1 complex dimensions and their quaternionic and octonionic gravity extensions deserve furher investigation. An appendix is included with the most general Schwarzschild-like solutions in D ≥ 4.

scholarly journals The ‘non-Kerrness’ of domains of outer communication of black holes and exteriors of stars

2011 ◽  
Vol 467 (2130) ◽  
pp. 1701-1718 ◽  
Author(s):  
Thomas Bäckdahl ◽  
Juan A. Valiente Kroon
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Three Dimensional ◽  
Dimensional Manifold ◽  
Geometric Invariant ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Kerr Spacetime ◽  
Killing Spinors ◽  
Initial Dataset

In this paper, we construct a geometric invariant for initial datasets for the vacuum Einstein field equations , such that is a three-dimensional manifold with an asymptotically Euclidean end and an inner boundary with the topology of the 2-sphere. The hypersurface can be thought of being in the domain of outer communication of a black hole or in the exterior of a star. The geometric invariant vanishes if and only if is an initial dataset for the Kerr spacetime. The construction makes use of the notion of Killing spinors and of an expression for a Killing spinor candidate , which can be constructed out of concomitants of the Weyl tensor.

Kaluza–Klein Cosmological Model, Strange Quark Matter, and Time-Varying Lambda

2014 ◽  
Vol 69 (1-2) ◽  
pp. 90-96 ◽  
Author(s):  
Namrata Jain ◽  
Shyamsunder S. Bhoga ◽  
Gowardhan S. Khadekar
Keyword(s):  
Cosmological Model ◽  
Quark Matter ◽  
Strange Quark ◽  
Strange Quark Matter ◽  
Time Varying ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Different Types ◽  
Free Parameters ◽  
Kaluza Klein

In this paper, exact solutions of the Einstein field equations of the Kaluza-Klein cosmological model have been obtained in the presence of strange quark matter. We have considered the timevarying cosmological constant Λ as Λ = αH2 + βR-2, where α and β are free parameters. The solutions are obtained with the help of the equation of state for strange quark matter as per the Bag model, i.e. quark pressure p = 1/3(ρ - 4BC), where BC is Bag’s constant. We also discussed the physical implications of the solutions obtained for the model for different types of universes.

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.

CONTROLLABILITY OF NONHOLONOMIC BLACK HOLES SYSTEMS

2012 ◽  
Vol 10 (02) ◽  
pp. 1250097 ◽  
Author(s):  
CONSTANTIN UDRIŞTE ◽  
VINCENZO CIANCIO
Keyword(s):  
Optimal Control ◽  
Black Holes ◽  
Black Hole ◽  
Vector Fields ◽  
Momentum Tensor ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Stress Energy ◽  
Strongly Connected ◽  
Stress Energy Momentum Tensor

This paper studies the sub-Lorentz–Vrănceanu geometry and the optimal control of nonholonomic black hole systems. This is strongly connected to the possibility of describing a nonholonomic black hole system as kernel of a Gibbs–Pfaff form or by the span of four appropriate vector fields. Joining techniques from sub-Riemannian geometry, optimal control and thermodynamics, we bring into attention new models of black holes systems. These are reflected by the original results: a Lorentz–Vrănceanu geometry on the total space, a new sub-Lorentz–Vrănceanu geometry, a new stress–energy–momentum tensor, original solutions to Einstein field equations, and the controllability of nonholonomic black holes systems by uni-temporal or bi-temporal controls.

scholarly journals Charged fermions tunneling from stationary axially symmetric black holes with generalized uncertainty principle

2019 ◽  
Vol 34 (23) ◽  
pp. 1950184 ◽  
Author(s):  
Muhammad Rizwan ◽  
Muhammad Zubair Ali ◽  
Ali Övgün
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Uncertainty Principle ◽  
Emission Rate ◽  
Generalized Uncertainty Principle ◽  
Axially Symmetric ◽  
Black String ◽  
Fermions Tunneling ◽  
Newman Black Hole ◽  
Kaluza Klein

In this paper, we study the tunneling of charged fermions from the stationary axially symmetric black holes using the generalized uncertainty principle (GUP) via Wentzel, Kramers, and Brillouin (WKB) method. The emission rate of the charged fermions and corresponding modified Hawking temperature of Kerr–Newman black hole, Einstein–Maxwell-dilaton-axion (EMDA) black hole, Kaluza–Klein dilaton black hole, and then, charged rotating black string are obtained and we show that the corrected thermal spectrum is not purely thermal because of the minimal scale length which cause the black hole’s remnant.

scholarly journals On the gravitational entropy of accelerating black holes

2020 ◽  
Vol 29 (05) ◽  
pp. 2050034
Author(s):  
Sarbari Guha ◽  
Samarjit Chakraborty
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Phenomenological Approach ◽  
Entropy Density ◽  
Charged Black Hole ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Gravitational Entropy ◽  
Definition Of ◽  
Black Hole Solutions

In this paper, we have examined the validity of a proposed definition of gravitational entropy in the context of accelerating black hole solutions of the Einstein field equations, which represent the realistic black hole solutions. We have adopted a phenomenological approach proposed in Rudjord et al. [Phys. Scr. 77, 055901 (2008)] and expanded by Romero et al. [Int. J. Theor. Phys. 51, 925 (2012)], in which the Weyl curvature hypothesis is tested against the expressions for the gravitational entropy. Considering the [Formula: see text]-metric for the accelerating black holes, we have evaluated the gravitational entropy and the corresponding entropy density for four different types of black holes, namely, nonrotating black hole, nonrotating charged black hole, rotating black hole and rotating charged black hole. We end up by discussing the merits of such an analysis and the possible reason of failure in the particular case of rotating charged black hole and comment on the possible resolution of the problem.

scholarly journals THE MILNE SPACETIME AND THE HADRONIC RINDLER HORIZON

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1379-1384 ◽  
Author(s):  
H. CULETU
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Time Dependent ◽  
Anisotropic Fluid ◽  
Direct Relation ◽  
Schwarzschild Black Hole ◽  
Black Hole Interior ◽  
Flat Metric ◽  
Shear Tensor ◽  
Hadronic Rindler Horizon

A direct relation between the time-dependent Milne geometry and the Rindler spacetime is shown. Milne's metric corresponds to the region beyond Rindler's event horizon (in the wedge t ≻ |x|). We point out that inside a Schwarzschild black hole and near its horizon, the metric may be Milne's flat metric. It was found that the shear tensor associated to a congruence of fluid particles of the RHIC expanding fireball has the same structure as that corresponding to the anisotropic fluid from the black hole interior, even though the latter geometry is curved.

scholarly journals EXTREMAL BLACK HOLES AND ELEMENTARY STRING STATES

1995 ◽  
Vol 10 (28) ◽  
pp. 2081-2093 ◽  
Author(s):  
ASHOKE SEN
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Black Hole Entropy ◽  
Extremal Black Hole ◽  
Coupling Constant ◽  
Left Handed ◽  
Quantum Numbers ◽  
Independent Parameters ◽  
Elementary String ◽  
Extremal Black Holes

Some of the extremal black hole solutions in string theory have the same quantum numbers as the Bogomol’nyi saturated elementary string states. We explore the possibility that these black holes can be identified with elementary string excitations. It is shown that stringy effects could correct the Bekenstein-Hawking formula for the black hole entropy in such a way that it correctly reproduces the logarithm of the density of elementary string states. In particular, this entropy has the correct dependence on three independent parameters, the mass and the left-handed charge of the black hole, and the string coupling constant.

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