scholarly journals Scalar field collapse in a conformally flat spacetime

2017 ◽  
Vol 77 (3) ◽  
Author(s):  
Soumya Chakrabarti ◽  
Narayan Banerjee
Keyword(s):  
Scalar Field ◽  
Conformally Flat ◽  
Flat Spacetime

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.

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.

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.

Dynamical system analysis of a nonminimally coupled scalar field

2019 ◽  
Vol 28 (15) ◽  
pp. 1950173 ◽  
Author(s):  
Subhajyoti Pal ◽  
Sudip Mishra ◽  
Subenoy Chakraborty
Keyword(s):  
Scalar Field ◽  
Critical Points ◽  
Center Manifold ◽  
System Analysis ◽  
Nonlinear Differential Equations ◽  
Center Manifold Theory ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Flat Spacetime ◽  
Manifold Theory

This paper deals with a nonminimally coupled scalar field in the background of homogeneous and isotropic Friedmann–Lemaître–Robertson–Walker (FLRW) flat spacetime. As Einstein field equations are coupled second-order nonlinear differential equations, it is very hard to find exact solutions. By suitable choice of variables, we transform Einstein field equations to an autonomous system and critical points are determined. We use center manifold theory to characterize nonhyperbolic critical points and are found to be saddle in nature. We discuss possible bifurcation scenarios, which indicate the existence of the cosmological bouncing model.

scholarly journals On the flat spacetime Galileons and the Born–Infeld type structures

2015 ◽  
Vol 24 (06) ◽  
pp. 1550041
Author(s):  
Cuauhtemoc Campuzano ◽  
Rubén Cordero ◽  
Miguel Cruz ◽  
Efraín Rojas
Keyword(s):  
Scalar Field ◽  
Variational Analysis ◽  
Momentum Density ◽  
Type Structure ◽  
Field Theories ◽  
Flat Spacetime ◽  
Arbitrary Dimensions ◽  
Derivatives Of ◽  
Galileon Field

We show how the flat spacetime Galileon field theories (FSGFT) in arbitrary dimensions can be obtained through a Born–Infeld (BI) type structure. This construction involves a brane metric and nonlinear combinations of derivatives of a scalar field. Our setup gives rise to some Galileon tensors and vectors useful for the variational analysis which are related to the momentum density of the probe Lovelock branes floating in a N-dimensional flat bulk. We find further that the Noether currents associated to these Galileon theories may be written in terms of such tensors.

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