scholarly journals Exploration of a singular fluid spacetime

2021 ◽  
Vol 53 (11) ◽  
Author(s):  
Grant N. Remmen
Keyword(s):  
Arbitrary Constant ◽  
Special Function ◽  
Naked Singularity ◽  
State Parameter ◽  
Singular Solutions ◽  
Spherically Symmetric ◽  
Spatial Homogeneity ◽  
Love Numbers ◽  
Geodesic Structure ◽  
Double Copy

AbstractWe investigate the properties of a special class of singular solutions for a self-gravitating perfect fluid in general relativity: the singular isothermal sphere. For arbitrary constant equation-of-state parameter $$w=p/\rho $$ w = p / ρ , there exist static, spherically-symmetric solutions with density profile $$\propto 1/r^2$$ ∝ 1 / r 2 , with the constant of proportionality fixed to be a special function of w. Like black holes, singular isothermal spheres possess a fixed mass-to-radius ratio independent of size, but no horizon cloaking the curvature singularity at $$r=0$$ r = 0 . For $$w=1$$ w = 1 , these solutions can be constructed from a homogeneous dilaton background, where the metric spontaneously breaks spatial homogeneity. We study the perturbative structure of these solutions, finding the radial modes and tidal Love numbers, and also find interesting properties in the geodesic structure of this geometry. Finally, connections are discussed between these geometries and dark matter profiles, the double copy, and holographic entropy, as well as how the swampland distance conjecture can obscure the naked singularity.

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.

scholarly journals GENERALIZED MODEL FOR Λ DARK ENERGY

2009 ◽  
Vol 18 (03) ◽  
pp. 389-396 ◽  
Author(s):  
UTPAL MUKHOPADHYAY ◽  
P. C. RAY ◽  
SAIBAL RAY ◽  
S. B. DUTTA CHOUDHURY
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Model ◽  
A Priori ◽  
State Parameter ◽  
Spherically Symmetric ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Two Fluid

Einstein field equations under spherically symmetric space–times are considered here in connection with dark energy investigation. A set of solutions is obtained for a kinematic Λ model, viz. [Formula: see text], without assuming any a priori value for the curvature constant and the equation-of-state parameter ω. Some interesting results, such as the nature of cosmic density Ω and deceleration parameter q, have been obtained with the consideration of two-fluid structure instead of the usual unifluid cosmological model.

scholarly journals Self-similar Langmuir collapse at critical dimension

1991 ◽  
Vol 9 (2) ◽  
pp. 363-370 ◽  
Author(s):  
L. Bergé ◽  
PH. Dousseau ◽  
G. Pelletier ◽  
D. Pesme
Keyword(s):  
Control Parameter ◽  
Linear Time ◽  
Critical Dimension ◽  
Singular Solutions ◽  
Spherically Symmetric ◽  
Scalar Model ◽  
Contraction Rate ◽  
Self Similar ◽  
Similar Solutions ◽  
Time Contraction

Two spherically symmetric versions of a self-similar collapse are investigated within the framework of the Zakharov equations, namely, one relative to a vectorial electric field and the other corresponding to a scalar modeling of the Langmuir field. Singular solutions of both of them depend on a linear time contraction rate Ξ(t) = V(t* – t), where t* and V = – Ξ denote, respectively, the collapse time and the constant collapse velocity. We show that under certain conditions, only the scalar model admits self-similar solutions, varying regularly as a function of the control parameter V from the subsonic (V ≪ 1) to the supersonic (V ≫ 1) regime.

scholarly journals Generic Three-Parameter Wormhole Solution in Einstein-Scalar Field Theory

Particles ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 1-11
Author(s):  
Bobur Turimov ◽  
Ahmadjon Abdujabbarov ◽  
Bobomurat Ahmedov ◽  
Zdeněk Stuchlík
Keyword(s):  
Field Theory ◽  
Scalar Field ◽  
Exact Analytical Solution ◽  
Naked Singularity ◽  
Radial Coordinate ◽  
Spherically Symmetric ◽  
Einstein Field Equations ◽  
Wormhole Solution ◽  
Field Equations ◽  
Scalar Field Theory

An exact analytical, spherically symmetric, three-parametric wormhole solution has been found in the Einstein-scalar field theory, which covers the several well-known wormhole solutions. It is assumed that the scalar field is massless and depends on the radial coordinate only. The relation between the full contraction of the Ricci tensor and Ricci scalar has been found as RαβRαβ=R2. The derivation of the Einstein field equations have been explicitly shown, and the exact analytical solution has been found in terms of the three constants of integration. The several wormhole solutions have been extracted for the specific values of the parameters. In order to explore the physical meaning of the integration constants, the solution has been compared with the previously obtained results. The curvature scalar has been determined for all particular solutions. Finally, it is shown that the general solution describes naked singularity characterized by the mass, the scalar quantity and the throat.

scholarly journals STATIC SPHERICALLY SYMMETRIC SCALAR FIELD SPACETIMES WITH C0 MATCHING

2011 ◽  
Vol 26 (17) ◽  
pp. 1281-1290 ◽  
Author(s):  
SWASTIK BHATTACHARYA ◽  
PANKAJ S. JOSHI
Keyword(s):  
Scalar Field ◽  
Naked Singularity ◽  
Scalar Fields ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Spherically Symmetric ◽  
Curvature Singularity ◽  
Einstein Theory ◽  
Full Class ◽  
Strong Curvature

All the classes of static massless scalar field models currently available in the Einstein theory of gravity necessarily contain a strong curvature naked singularity. We obtain here a family of solutions for static massless scalar fields coupled to gravity, which does not have any strong curvature singularity. This class of models contain a thin shell of singular matter, which has a physical interpretation. The central curvature singularity is, however, avoided which is common to all static massless scalar field spacetime models known so far. Our result thus points out that the full class of solutions in this case may contain non-singular models, which is an intriguing possibility.

scholarly journals Regular and singular solutions for charged dust distributions in the Einstein-Maxwell theory

2007 ◽  
Vol 85 (9) ◽  
pp. 957-965
Author(s):  
D Horvat ◽  
S Ilijić
Keyword(s):  
Distinctive Feature ◽  
Total Mass ◽  
Singular Solutions ◽  
Charged Dust ◽  
Spherically Symmetric ◽  
Regular Solutions ◽  
Maxwell Theory ◽  
Metric Tensor ◽  
Net Charge ◽  
Adm Mass

Solutions for the static spherically symmetric extremally charged dust in the Majumdar–Papapetrou system have been found. For a certain amount of the allocated mass and (or) charge, the solutions have singularities of a type that could render them physically unacceptable, since the corresponding physically relevant quantities are singular as well. These solutions, with a number of zero-nodes in the metric tensor, are regularized through the δ-shell formalism, thus redefining the mass and (or) charge distributions. The bifurcating behaviour of regular solutions found before is no longer present in these singular solutions, but quantized-like behaviour in the total mass is observed. The spectrum of regularized solutions restores the equality of the Tolman–Whittaker and Arnowitt–Deser–Misner (ADM) mass, as well the equality of the net charge and ADM mass, which is the distinctive feature of Majumdar–Papapetrou systems.PACS No.:04.40.Nr

scholarly journals COSMOLOGICAL CONSTANT IN LOW ENERGY d = 4 STRING LEADS TO (STATIC SPHERICALLY SYMMETRIC) NAKED SINGULARITY

1995 ◽  
Vol 10 (10) ◽  
pp. 789-797 ◽  
Author(s):  
S. KALYANA RAMA
Keyword(s):  
Cosmological Constant ◽  
Sigma Model ◽  
Naked Singularity ◽  
Point Of View ◽  
Low Energy ◽  
Tree Level ◽  
Spherically Symmetric ◽  
Naked Singularities ◽  
Noncritical Strings ◽  
Β Function

In the sigma model approach, the β-function equations for noncritical strings contain a term which acts like a tree level cosmological constant, Λ. We analyze the static, spherically symmetric solutions to these equations in d = 4 space-time, which will describe the gravitational field of a point star up to a distance r*, of the order of parsecs. We show that the curvature scalar seen by the strings is singular in these solutions if Λ ≠ 0. This singularity is naked. Requiring its absence up to a distance r* imposes the constraint [Formula: see text] in natural units. Thus if r* ≃ 1 Mpc then |Λ| < 10−114, and if r* extends all the way up to the edge of the universe (1028 cm) then |Λ| < 10−122 in natural units. From another point of view, our analysis implies that low energy d = 4 noncritical strings in the sigma model formulation lead to naked singularities.

scholarly journals Bounded orbits for photons as a consequence of extra dimensions

2017 ◽  
Vol 32 (32) ◽  
pp. 1750173 ◽  
Author(s):  
P. A. González ◽  
Marco Olivares ◽  
Yerko Vásquez
Keyword(s):  
Extra Dimension ◽  
Extra Dimensions ◽  
Symmetric Solution ◽  
Spherically Symmetric ◽  
Spherically Symmetric Solution ◽  
Geodesic Structure

In this paper, we study the geodesic structure for a geometry described by a spherically symmetric four-dimensional (4D) solution embedded in a five-dimensional (5D) space known as a brane-based spherically symmetric solution. Mainly, we have found that the extra dimension contributes to the existence of bounded orbits for the photons, such as planetary and circular stable orbits that have not been observed for other geometries.

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