scholarly journals Self similar collapse and the Raychaudhuri equation

2019 ◽  
Vol 79 (12) ◽  
Author(s):  
Shibendu Gupta Choudhury ◽  
Soumya Chakrabarti ◽  
Ananda Dasgupta ◽  
Narayan Banerjee
Keyword(s):  
Scalar Field ◽  
Exact Solutions ◽  
Gravitational Collapse ◽  
Similar Distribution ◽  
Raychaudhuri Equation ◽  
Conformally Flat ◽  
Flat Spacetime ◽  
Imperfect Fluid ◽  
Self Similar

AbstractThe role of the Raychaudhuri equation in studying gravitational collapse is discussed. A self-similar distribution of a scalar field along with an imperfect fluid in a conformally flat spacetime is considered for the purpose. The general focusing condition is found out and verified against the available exact solutions. The connection between the Raychaudhuri equation and the critical phenomena is also explored.

scholarly journals A class of solitons in Maxwell-scalar and Einstein–Maxwell-scalar models

2020 ◽  
Vol 80 (1) ◽  
Author(s):  
Carlos A. R. Herdeiro ◽  
João M. S. Oliveira ◽  
Eugen Radu
Keyword(s):  
Electromagnetic Field ◽  
Scalar Field ◽  
Quantum Gravity ◽  
Exact Solutions ◽  
Point Charge ◽  
Coulomb Field ◽  
Specific Class ◽  
Minimal Coupling ◽  
Flat Spacetime ◽  
Physical Quantities

AbstractRecently, no-go theorems for the existence of solitonic solutions in Einstein–Maxwell-scalar (EMS) models have been established (Herdeiro and Oliveira in Class Quantum Gravity 36(10):105015, 2019). Here we discuss how these theorems can be circumvented by a specific class of non-minimal coupling functions between a real, canonical scalar field and the electromagnetic field. When the non-minimal coupling function diverges in a specific way near the location of a point charge, it regularises all physical quantities yielding an everywhere regular, localised lump of energy. Such solutions are possible even in flat spacetime Maxwell-scalar models, wherein the model is fully integrable in the spherical sector, and exact solutions can be obtained, yielding an explicit mechanism to de-singularise the Coulomb field. Considering their gravitational backreaction, the corresponding (numerical) EMS solitons provide a simple example of self-gravitating, localised energy lumps.

scholarly journals GRAVITATIONAL COLLAPSE OF A MASSLESS SCALAR FIELD AND A PERFECT FLUID WITH SELF-SIMILARITY OF THE FIRST KIND IN 2+1 DIMENSIONS

2008 ◽  
Vol 17 (11) ◽  
pp. 2143-2158 ◽  
Author(s):  
F. I. M. PEREIRA ◽  
R. CHAN
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Perfect Fluid ◽  
Gravitational Collapse ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Self Similarity ◽  
Global Properties ◽  
Self Similar ◽  
Similar Solutions

Self-similar solutions of a collapsing perfect fluid and a massless scalar field with kinematic self-similarity of the first kind in 2+1 dimensions are obtained. The local and global properties of the solutions are studied. It is found that some of them represent gravitational collapse, in which black holes are always formed, and some may be interpreted as representing cosmological models.

A MODEL OF QUANTUM GRAVITATIONAL COLLAPSE

1991 ◽  
Vol 06 (15) ◽  
pp. 2693-2706 ◽  
Author(s):  
J. GREENSITE
Keyword(s):  
Quantum Mechanics ◽  
Scalar Field ◽  
Gravitational Collapse ◽  
Scale Factor ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Intrinsic Time ◽  
Infinite Range ◽  
Metric Scale

Some issues in the quantum mechanics of gravitational collapse are discussed in the framework of a simple minisuperspace model, consisting of a Friedman metric coupled to a massless scalar field. The model illustrates the role of intrinsic time coordinates in parametrizing gravitational collapse through a singularity, and the relevance of quantizing the metric scale factor over an infinite, rather than half-infinite, range.

GRAVITATIONAL COLLAPSE OF A MASSLESS SCALAR FIELD AND A PERFECT FLUID WITH SELF-SIMILARITY OF THE SECOND KIND IN (2 + 1) DIMENSIONS

2006 ◽  
Vol 15 (02) ◽  
pp. 131-152 ◽  
Author(s):  
F. I. M. PEREIRA ◽  
R. CHAN ◽  
AN ZHONG WANG
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Perfect Fluid ◽  
Gravitational Collapse ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Self Similarity ◽  
Global Properties ◽  
Self Similar ◽  
Similar Solutions

Self-similar solutions of a collapsing perfect fluid and a massless scalar field with kinematic self-similarity of the second kind in (2 + 1) dimensions are obtained. The local and global properties of the solutions are studied. It is found that some of them represent gravitational collapse, in which black holes are always formed, and some may be interpreted as representing cosmological models.

scholarly journals ON p – q DUALITY AND EXPLICIT SOLUTIONS IN c ≤ 1 2D GRAVITY MODELS

1995 ◽  
Vol 10 (08) ◽  
pp. 1219-1236 ◽  
Author(s):  
S. KHARCHEV ◽  
A. MARSHAKOV
Keyword(s):  
String Theory ◽  
Exact Solutions ◽  
2D Gravity ◽  
Integral Formula ◽  
Integral Representations ◽  
Gravity Models ◽  
Explicit Solutions ◽  
String Equation ◽  
Duality Transformation

We study the role of integral representations in the description of nonperturbative solutions to c ≤ 1 string theory. A generic solution is determined by two functions, W(x) and Q(x), which behave at infinity like xp and xq respectively. The integral formula for arbitrary (p, q) models is derived, which explicitly realizes a duality transformation between (p, q) and (q, p) 2D gravity solutions. We also discuss the exact solutions to the string equation and reduction condition and present several explicit examples.

CAUSAL BULK VISCOUS COSMOLOGIES IN CONFORMALLY FLAT SPACETIME

2000 ◽  
Vol 09 (04) ◽  
pp. 475-493 ◽  
Author(s):  
M. K. MAK ◽  
T. HARKO
Keyword(s):  
Large Time ◽  
Viscosity Coefficient ◽  
Approximate Solutions ◽  
Conformally Flat ◽  
First Order ◽  
Flat Spacetime ◽  
Bulk Viscous ◽  
Type Differential Equation ◽  
Bulk Viscosity Coefficient ◽  
Large Time Limit

The evolution of a causal bulk viscous cosmological fluid filled open conformally flat spacetime is considered. By means of appropriate transformations the equation describing the dynamics and evolution of the very early Universe can be reduced to a first order Abel type differential equation. In the case of a bulk viscosity coefficient proportional to the square root of the density, ξ~ρ1/2, an exact and two particular approximate solutions are obtained. The resulting cosmologies start from a singular state and generally have a noninflationary behavior, the deceleration parameter tending, in the large time limit, to zero. The thermodynamic consistency of the results is also checked.

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