scholarly journals EXTRA DIMENSIONS AND POSSIBLE SPACE-TIME SIGNATURE CHANGES

1995 ◽  
Vol 04 (04) ◽  
pp. 491-516 ◽  
Author(s):  
K.A. BRONNIKOV
Keyword(s):  
Black Hole ◽  
Extra Dimensions ◽  
Field Potential ◽  
Space Time ◽  
Spherically Symmetric ◽  
Vector Coupling ◽  
Special Cases ◽  
Dimensional Gravity ◽  
Time Changes ◽  
A Chain

Exact static, spherically symmetric solutions to the Einstein-Maxwell-scalar equations, with a dilatonic-type scalar-vector coupling, in D-dimensional gravity with a chain of n Ricci-flat internal spaces are considered, with the Maxwell field potential having two nonzero components: the temporal, Coulomb-like one and the one pointing to one of the extra dimensions. The properties and special cases of the solutions are discussed, in particular, those when there are horizons in the space-time. Two types of horizons are distinguished: the conventional black-hole (BH) ones and those at which the physical section of the space-time changes its signature (the latter are called T-horizons). Two theorems are proved, one fixing the BH- and T-horizon existence conditions, the other claiming that the system under study cannot have a regular center. The stability of a selected family of solutions under spherically symmetric perturbations is studied. It is shown that only black-hole solutions are stable, while all others, in particular, those with T-horizons are unstable.

NONCOMMUTATIVE D-BRANE WORLD, BLACK HOLES AND EXTRA DIMENSIONS

2009 ◽  
Vol 24 (18n19) ◽  
pp. 3571-3576 ◽  
Author(s):  
SUPRIYA KAR
Keyword(s):  
Black Holes ◽  
String Theory ◽  
Extra Dimensions ◽  
Space Time ◽  
Brane World ◽  
Spherically Symmetric ◽  
Axially Symmetric ◽  
Ordinary Space ◽  
Classical Black Holes ◽  
Type Iib String Theory

Inspired by the space-time noncommutativity on a D5-brane world, in a type IIB string theory, we explore the possibility of an emergent 4D ordinary space-time in the formalism. In particular, a curved D3-brane dynamics is worked out to obtain an axially symmetric and a spherically symmetric AdS and dS black holes. Extremal geometries are analyzed, using the noncommutative scaling. The emerging two dimensional semi-classical black holes are investigated to yield evidence for extra dimensions in the curved brane-world. Interestingly, a tunneling between dS to AdS vacua in the formalism is briefly discussed by incorporating the Hagedorn transitions in string theory.

scholarly journals Black hole and naked singularity geometries supported by three-form fields

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
Bruno J. Barros ◽  
Bogdan Dǎnilǎ ◽  
Tiberiu Harko ◽  
Francisco S. N. Lobo
Keyword(s):  
Black Hole ◽  
Killing Vector ◽  
Field Potential ◽  
Naked Singularity ◽  
Radial Coordinate ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Metric Tensor ◽  
Killing Horizon ◽  
Form Field

Abstract We investigate static and spherically symmetric solutions in a gravity theory that extends the standard Hilbert–Einstein action with a Lagrangian constructed from a three-form field $$A_{\alpha \beta \gamma }$$Aαβγ, which is related to the field strength and a potential term. The field equations are obtained explicitly for a static and spherically symmetric geometry in vacuum. For a vanishing three-form field potential the gravitational field equations can be solved exactly. For arbitrary potentials numerical approaches are adopted in studying the behavior of the metric functions and of the three-form field. To this effect, the field equations are reformulated in a dimensionless form and are solved numerically by introducing a suitable independent radial coordinate. We detect the formation of a black hole from the presence of a Killing horizon for the timelike Killing vector in the metric tensor components. Several models, corresponding to different functional forms of the three-field potential, namely, the Higgs and exponential type, are considered. In particular, naked singularity solutions are also obtained for the exponential potential case. Finally, the thermodynamic properties of these black hole solutions, such as the horizon temperature, specific heat, entropy and evaporation time due to the Hawking luminosity, are studied in detail.

AN ANSWER TO THE MAIN BLACK HOLE PATHOLOGY: FORMING NONSINGULAR BLACK HOLES FROM DUST COLLAPSE

2009 ◽  
Vol 18 (14) ◽  
pp. 2221-2229 ◽  
Author(s):  
R. MAIER ◽  
I. DAMIÃO SOARES
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Event Horizon ◽  
Nonlinear Resonance ◽  
Space Time ◽  
Low Energy ◽  
Spherically Symmetric ◽  
Energy Limit ◽  
Exterior Space

The dynamics of gravitational collapse is examined in the realm of string-based formalism of D-branes which encompasses general relativity as a low energy limit. A complete analytical solution is given to the spherically symmetric collapse of a pure dust star, including its matching with a corrected Schwarzschild exterior space–time. The collapse forms a black hole (an exterior event horizon) enclosing not a singularity but perpetually bouncing matter in the infinite chain of space–time maximal analytical extensions inside the outer event horizon. This chain of analytical extensions has a structure analogous to that of the Reissner–Nordstrom solution. The interior trapped bouncing matter has the possibility of being expelled by disruptive nonlinear resonance mechanisms.

scholarly journals NONEXTREME BLACK HOLES FROM INTERSECTING M-BRANES

1998 ◽  
Vol 13 (08) ◽  
pp. 1305-1328 ◽  
Author(s):  
NOBUYOSHI OHTA ◽  
TAKASHI SHIMIZU
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Higher Dimensions ◽  
Symmetric Case ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Deformation Parameters ◽  
Special Cases ◽  
Two Parameter ◽  
Black Hole Solutions

We investigate the possibility of extending nonextreme black hole solutions made of intersecting M-branes to those with two nonextreme deformation parameters, similar to Reissner–Nordstrøm solutions. General analysis of possible solutions is carried out to reduce the problem of solving field equations to a simple algebraic one for static spherically-symmetric case in D dimensions. The results are used to show that the extension to two-parameter solutions is possible for D= 4,5 dimensions but not for higher dimensions, and that the area of horizon always vanishes in the extreme limit for black hole solutions for D≥6 except for two very special cases which are identified. Various solutions are also summarized.

scholarly journals Loop Quantum Black Hole Extensions Within the Improved Dynamics

2021 ◽  
Vol 8 ◽  
Author(s):  
Rodolfo Gambini ◽  
Javier Olmedo ◽  
Jorge Pullin
Keyword(s):  
Black Hole ◽  
Quantum Gravity ◽  
Loop Quantum Gravity ◽  
Space Time ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Quantization Scheme ◽  
White Hole ◽  
Quantum Black Hole ◽  
Black Hole Singularity

We continue our investigation of an improved quantization scheme for spherically symmetric loop quantum gravity. We find that in the region where the black hole singularity appears in the classical theory, the quantum theory contains semi-classical states that approximate general relativity coupled to an effective anisotropic fluid. The singularity is eliminated and the space-time can be continued into a white hole space-time. This is similar to previously considered scenarios based on a loop quantum gravity quantization.

scholarly journals Absence of Singularity in Schwarzschild Metric in the Vector Model for Gravitational Field

2012 ◽  
Vol 18 (3) ◽  
pp. 175-184
Author(s):  
Vo Van On
Keyword(s):  
Black Hole ◽  
Gravitational Field ◽  
General Theory ◽  
Space Time ◽  
Symmetric Body ◽  
Vector Model ◽  
Spherically Symmetric ◽  
Theory Of Relativity ◽  
General Theory Of Relativity ◽  
Schwarzschild Metric

In this paper, based on the vector model for gravitational field we deduce an equation to determinate the metric of space-time. This equation is similar to equation of Einstein. The metric of space-time outside a static spherically symmetric body is also determined. It gives a small supplementation to the Schwarzschild metric in General theory of relativity but the singularity does not exist. Especially, this model predicts the existence of a new universal body after a black hole.

scholarly journals Genericity aspects of black hole formation in the collapse of spherically symmetric slightly inhomogeneous perfect fluids

2016 ◽  
Vol 25 (02) ◽  
pp. 1650023 ◽  
Author(s):  
Seema Satin ◽  
Daniele Malafarina ◽  
Pankaj S. Joshi
Keyword(s):  
Black Hole ◽  
Perfect Fluid ◽  
Naked Singularity ◽  
Spherically Symmetric ◽  
Final State ◽  
Naked Singularities ◽  
Perfect Fluids ◽  
Special Cases ◽  
Collapse Models ◽  
Mass Profile

We study the complete gravitational collapse of a class of spherically symmetric inhomogeneous perfect fluid models obtained by introducing small radial perturbations in an otherwise homogeneous matter cloud. Our aim here is to study the genericity and stability of the formation of black holes and locally naked singularities in collapse. While the occurrence of naked singularities is known for many models of collapse, the key issue now in focus is genericity and stability of these outcomes. Towards this purpose, we study how the introduction of a somewhat general class of small inhomogeneities in homogeneous collapse leading to a black hole can change the final outcome to a naked singularity. The key feature that we assume for the perturbation profile is that of a mass profile that is separable in radial and temporal coordinates. The known models of dust and homogeneous perfect fluid collapse can be obtained from this choice of the mass profile as special cases. This choice is very general and physically well motivated and we show that this class of collapse models leads to the formation of a naked singularity as the final state.

scholarly journals SPHERICALLY SYMMETRIC SPACE–TIME WITH REGULAR DE SITTER CENTER

2003 ◽  
Vol 12 (06) ◽  
pp. 1015-1034 ◽  
Author(s):  
IRINA DYMNIKOVA
Keyword(s):  
Black Hole ◽  
Energy Condition ◽  
Space Time ◽  
Cosmological Term ◽  
Spherically Symmetric ◽  
De Sitter ◽  
Sitter Group ◽  
Class Invariant ◽  
Time Symmetry ◽  
De Sitter Vacuum

We formulate the requirements which lead to the existence of a class of globally regular solutions of the minimally coupled GR equations asymptotically de Sitter at the center. The source term for this class, invariant under boosts in the radial direction, is classified as spherically symmetric vacuum with variable density and pressure [Formula: see text] associated with an r-dependent cosmological term [Formula: see text], whose asymptotic at the origin, dictated by the weak energy condition, is the Einstein cosmological term Λgμν, while asymptotic at infinity is de Sitter vacuum with λ < Λ or Minkowski vacuum. For this class of metrics the mass m defined by the standard ADM formula is related to both the de Sitter vacuum trapped at the origin and the breaking of space–time symmetry. In the case of the flat asymptotic, space–time symmetry changes smoothly from the de Sitter group at the center to the Lorentz group at infinity through radial boosts in between. Geometry is asymptotically de Sitter as r → 0 and asymptotically Schwarzschild at large r. In the range of masses m ≥ m crit , the de Sitter–Schwarzschild geometry describes a vacuum nonsingular black hole (ΛBH), and for m < m crit it describes G-lump — a vacuum selfgravitating particle-like structure without horizons. In the case of de Sitter asymptotic at infinity, geometry is asymptotically de Sitter as r → 0 and asymptotically Schwarzschild–de Sitter at large r. Λμν geometry describes, dependently on parameters m and [Formula: see text] and choice of coordinates, a vacuum nonsingular cosmological black hole, self-gravitating particle-like structure at the de Sitter background λgμν, and regular cosmological models with cosmological constant evolving smoothly from Λ to λ.

scholarly journals THE ENERGY DISTRIBUTION IN A STATIC SPHERICALLY SYMMETRIC NONSINGULAR BLACK HOLE SPACE–TIME

2000 ◽  
Vol 15 (11n12) ◽  
pp. 803-807 ◽  
Author(s):  
I. RADINSCHI
Keyword(s):  
Black Hole ◽  
Energy Distribution ◽  
Space Time ◽  
Spherically Symmetric ◽  
Cartesian Coordinates ◽  
Momentum Complex

We calculate the energy distribution in a static spherically symmetric nonsingular black hole space–time by using the Tolman's energy–momentum complex. All the calculations are performed in quasi-Cartesian coordinates. The energy distribution is positive everywhere and equal to zero at the origin. We get the same result as obtained by I.-C. Yang by using the Einstein's and Weinberg's prescriptions.

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