scholarly journals BULK VISCOUS SOLUTIONS TO THE FIELD EQUATIONS AND THE DECELERATION PARAMETER-REVISITED

2002 ◽  
Vol 11 (09) ◽  
pp. 1419-1434 ◽  
Author(s):  
ANIRUDH PRADHAN ◽  
I. AOTEMSHI
Keyword(s):  
Deceleration Parameter ◽  
Gravitational Constant ◽  
Mass Density ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Variable Cosmological Constant ◽  
New Class ◽  
Bulk Viscous Fluid ◽  
Bulk Viscous ◽  
Viscous Solutions

We utilise a form for the Hubble parameter to generate a number of solutions to the Einstein field equations with variable cosmological constant and variable gravitational constant in the presence of a bulk viscous fluid. The Hubble law utilised yields a constant value for the deceleration parameter. A new class of solutions is presented in the Robertson–Walker spacetimes. The coefficient of bulk viscosity is assumed to be a power function of the mass density. For a class of solutions, the deceleration parameter is negative which is consistent with the supernovae Ia observations.

scholarly journals Bianchi Type V Universe and Bulk Viscous Models with Time Dependent Gravitational Constant and Cosmological Constant in General Relativity

2019 ◽  
Vol 9 (1S3) ◽  
pp. 251-256
Keyword(s):  
General Relativity ◽  
Cosmological Constant ◽  
Gravitational Constant ◽  
Bianchi Type ◽  
Relativity Theory ◽  
Field Equations ◽  
Bulk Viscous Fluid ◽  
Bulk Viscous ◽  
Viscous Models ◽  
Bianchi Type V Universe

This paper deals with Bulk Viscous Models and Bianchi type- universe in the standard general relativity theory by assuming where constants, is the density. Einstein field equations ( ) have been solved in the presence of a variable gravitational constant as well as a variable cosmological constant together with a bulk viscous fluid. In order to find a deterministic solution of EFEs, a simple form of Hubble parameter being constant when where has been considered here that shows the signature flip from early deceleration to present acceleration. Moreover, the bulk viscous coefficient is allowed to vary with the density as . The physical and geometrical behavior are described in detail for the obtained model. The model obtained here is in good agreement with the present cosmological observations.

scholarly journals Kaluza–Klein Bulk Viscous Fluid Cosmological Models and the Validity of the Second Law of Thermodynamics in f(R, T) Gravity

2017 ◽  
Vol 72 (4) ◽  
pp. 365-374 ◽  
Author(s):  
Gauranga Charan Samanta ◽  
Ratbay Myrzakulov ◽  
Parth Shah
Keyword(s):  
Cosmological Model ◽  
Viscous Fluid ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Field Equations ◽  
Geometrical Properties ◽  
Bulk Viscous Fluid ◽  
Bulk Viscous ◽  
Two Stages ◽  
Kaluza Klein

Abstract:The authors considered the bulk viscous fluid in f(R, T) gravity within the framework of Kaluza–Klein space time. The bulk viscous coefficient (ξ) expressed as $\xi = {\xi _0} + {\xi _1}{{\dot a} \over a} + {\xi _2}{{\ddot a} \over {\dot a}},$ where ξ0, ξ1, and ξ2 are positive constants. We take p=(γ−1)ρ, where 0≤γ≤2 as an equation of state for perfect fluid. The exact solutions to the corresponding field equations are given by assuming a particular model of the form of f(R, T)=R+2f(T), where f(T)=λT, λ is constant. We studied the cosmological model in two stages, in first stage: we studied the model with no viscosity, and in second stage: we studied the model involve with viscosity. The cosmological model involve with viscosity is studied by five possible scenarios for bulk viscous fluid coefficient (ξ). The total bulk viscous coefficient seems to be negative, when the bulk viscous coefficient is proportional to ${\xi _2}{{\ddot a} \over {\dot a}},$ hence, the second law of thermodynamics is not valid; however, it is valid with the generalised second law of thermodynamics. The total bulk viscous coefficient seems to be positive, when the bulk viscous coefficient is proportional to $\xi = {\xi _1}{{\dot a} \over a},$$\xi = {\xi _1}{{\dot a} \over a} + {\xi _2}{{\ddot a} \over {\dot a}}$ and $\xi = {\xi _0} + {\xi _1}{{\dot a} \over a} + {\xi _2}{{\ddot a} \over {\dot a}},$ so the second law of thermodynamics and the generalised second law of thermodynamics is satisfied throughout the evolution. We calculate statefinder parameters of the model and observed that it is different from the ∧CDM model. Finally, some physical and geometrical properties of the models are discussed.

scholarly journals BIANCHI TYPE I MAGNETOFLUID COSMOLOGICAL MODELS WITH VARIABLE COSMOLOGICAL CONSTANT REVISITED

2004 ◽  
Vol 13 (03) ◽  
pp. 503-516 ◽  
Author(s):  
ANIRUDH PRADHAN ◽  
SANJAY KUMAR SINGH
Keyword(s):  
Magnetic Field ◽  
Bianchi Type ◽  
Mass Density ◽  
Type I ◽  
Variable Cosmological Constant ◽  
Bianchi Type I ◽  
Bulk Viscous ◽  
Tensor Formula ◽  
The Magnetic Field ◽  
Shear Tensor

The behaviour of magnetic field in anisotropic Bianchi type I cosmological model for bulk viscous distribution is investigated. The distribution consists of an electrically neutral viscous fluid with an infinite electrical conductivity. It is assumed that the component [Formula: see text] of shear tensor [Formula: see text] is proportional to expansion (θ) and the coefficient of bulk viscosity is assumed to be a power function of mass density. Some physical and geometrical aspects of the models are also discussed in presence and also in absence of the magnetic field.

scholarly journals The Gravitomagnetism in the Solar System

2017 ◽  
Vol 45 ◽  
pp. 1760052
Author(s):  
Flavia Rocha ◽  
Manuel Malheiro ◽  
Rubens Marinho
Keyword(s):  
Mass Density ◽  
Slow Motion ◽  
Weak Field ◽  
Einstein Equations ◽  
Dipole Potential ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Perihelion Advance ◽  
Motion Approximation

In 1918, Joseph Lense and Hans Thirring discovered the gravitomagnetic (GM) effect of Einstein field equations in weak field and slow motion approximation. They showed that Einstein equations in this approximation can be written as in the same form as Maxwell’s equation for electromagnetism. In these equations the charge and electric current are replaced by the mass density and the mass current. Thus, the gravitomagnetism formalism in astrophysical system is used with the mass assuming the role of the charge. In this work, we present the deduction of gravitoelectromagnetic equations and the analogue of the Lorentz force in the gravitomagnetism. We also discuss the problem of Mercury’s perihelion advance orbit, we propose solutions using GM formalism using a dipole-dipole potential for the Sun-Planet interaction.

KALUZA–KLEIN COSMOLOGICAL MODELS WITH ANISOTROPIC DARK ENERGY

2011 ◽  
Vol 26 (10) ◽  
pp. 739-750 ◽  
Author(s):  
K. S. ADHAV ◽  
A. S. BANSOD ◽  
R. P. WANKHADE ◽  
H. G. AJMIRE
Keyword(s):  
Dark Energy ◽  
Exact Solutions ◽  
Deceleration Parameter ◽  
Hubble Parameter ◽  
Cosmological Models ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Anisotropic Dark Energy ◽  
The Law ◽  
Kaluza Klein

The exact solutions of the Einstein field equations for dark energy in Kaluza–Klein metric under the assumption on the anisotropy of the fluid are obtained by applying the law of variation of Hubble parameter which yields the constant value of deceleration parameter. The isotropy of the fluid, space and expansion are examined.

GENERALIZED SCALAR TENSOR THEORY IN FOUR AND HIGHER DIMENSION

2000 ◽  
Vol 09 (05) ◽  
pp. 543-549 ◽  
Author(s):  
SUBENOY CHAKRABORTY ◽  
ARABINDA GHOSH
Keyword(s):  
Physical Parameters ◽  
Scalar Tensor Theory ◽  
Higher Dimension ◽  
Field Equations ◽  
Bianchi I ◽  
Bulk Viscous Fluid ◽  
Tensor Theory ◽  
Bulk Viscous ◽  
Coupled Field ◽  
Coupled Field Equations

In this paper, we have considered generalized scalar–tensor theory for four-dimensional Bianchi-I model and also for a five-dimensional cosmological model. We have studied both exponential and power law solutions, considering a bulk viscous fluid. To solve the complicated coupled field equations, we have made assumptions among the physical parameters and solutions have been discussed.

scholarly journals Anisotropic Bulk Viscous String Cosmological Model in a Scalar-Tensor Theory of Gravitation

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
D. R. K. Reddy ◽  
Ch. Purnachandra Rao ◽  
T. Vidyasagar ◽  
R. Bhuvana Vijaya
Keyword(s):  
Equations Of State ◽  
Momentum Tensor ◽  
Scalar Tensor Theory ◽  
Field Equations ◽  
Physical Conditions ◽  
Bulk Viscous Fluid ◽  
Tensor Theory ◽  
Highly Nonlinear ◽  
Bulk Viscous ◽  
Theory Of Gravitation

Spatially homogeneous, anisotropic, and tilted Bianchi type-VI0model is investigated in a new scalar-tensor theory of gravitation proposed by Saez and Ballester (1986) when the source for energy momentum tensor is a bulk viscous fluid containing one-dimensional cosmic strings. Exact solution of the highly nonlinear field equations is obtained using the following plausible physical conditions: (i) scalar expansion of the space-time which is proportional to the shear scalar, (ii) the barotropic equations of state for pressure and energy density, and (iii) a special law of variation for Hubble’s parameter proposed by Berman (1983). Some physical and kinematical properties of the model are also discussed.

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