scholarly journals Bianchi Type VI Cosmological Model with Dynamical Cosmological Parameters G and ⩘ in the presence of Bulk Viscous Stress

2019 ◽  
pp. 246-254
Author(s):  
Shilpa Samdurkar ◽  
Seema Bawnerkar
Keyword(s):  
Bianchi Type ◽  
Cosmological Parameters ◽  
Viscosity Coefficient ◽  
Distance Modulus ◽  
Viscous Stress ◽  
Angular Diameter Distance ◽  
Proper Distance ◽  
Gravitational And Cosmological Constants ◽  
Bulk Viscous ◽  
Modulus Curve

In the present study, we have obtained Bianchi type VI anisotropic model of the universe filled with a bulk viscous stress in the presence of variable gravitational and cosmological constants. Here we have assumed the cosmological term in the form Λ∝H to discuss the effect of cosmological variables. It is found that the bulk viscosity coefficient (ξ) is a decreasing function of time. The expression for proper distance, luminosity distance, angular diameter distance, look back time and distance modulus curve have been analyzed and also the distance modulus curve of derived model nearly matches with Supernova Ia (SN Ia) observations.

Bianchi type-III dark energy models with constant deceleration parameter in self-creation cosmology

2014 ◽  
Vol 92 (4) ◽  
pp. 295-301 ◽  
Author(s):  
K.L. Mahanta ◽  
A.K. Biswal ◽  
P.K. Sahoo
Keyword(s):  
Dark Energy ◽  
Deceleration Parameter ◽  
Bianchi Type ◽  
Background Radiation ◽  
Distance Modulus ◽  
Constant Deceleration Parameter ◽  
Eos Parameter ◽  
Type Iii ◽  
Proper Distance ◽  
Type Ia

We have constructed dark energy cosmological models in an anisotropic Bianchi type-III space–time with a variable equation of state (EoS) parameter ω in Barber’s (Gen. Relativ. Gravitation, 14, 117, 1982) second self-creation theory of gravitation. The models are obtained using the special law of variation of Hubble’s parameter that yields a constant value of the deceleration parameter. In the two different models that we have obtained, the EoS parameter ω for dark energy is found to be time dependent. In one model the value of ω is in good agreement with the recent observations of type Ia supernovae (SNe Ia) data, SNe Ia data with cosmic microwave background radiation anisotropy and galaxy clustering statistics. Further we have discussed the well-known astrophysical phenomena, namely, the Hubble parameter H(z), luminosity distance dL, proper distance d(z), distance modulus μ(z), and look-back time with red shift. The expression for jerk parameter and statefinder parameters are also derived.

scholarly journals Two-fluid scenario in Bianchi type-I universe

2020 ◽  
Vol 35 (12) ◽  
pp. 2050086 ◽  
Author(s):  
G. K. Goswami ◽  
Meena Mishra ◽  
Anil Kumar Yadav ◽  
Anirudh Pradhan
Keyword(s):  
Bianchi Type ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
Distance Modulus ◽  
Type I ◽  
Eos Parameter ◽  
Data Set ◽  
Bianchi Type I ◽  
De Formula ◽  
Point Data

In this paper, we study a Bianchi type-I model of universe filled with barotropic and dark energy (DE) type fluids. The present values of cosmological parameters, such as Hubble constant [Formula: see text], DE and anisotropy energy parameters [Formula: see text], [Formula: see text] and [Formula: see text] and Equation of State (EoS) parameter for DE [Formula: see text], are statistically estimated in two ways by taking 38 point data set of Hubble parameter [Formula: see text] and 581 point data set of distance modulus of supernovae in the range [Formula: see text]. It is found that the results agree with the Planck result [Planck Collab. (P. A. R. Ade et al.), Astron. Astrophys. 594, A14 (2016)] and more latest result obtained by Amirhashchi and Amirhashchi [H. Amirhashchi and S. Amirhashchi, arXiv:1811.05400v4]. Various physical properties such as age of the universe, deceleration parameter, etc. have also been investigated.

scholarly journals BIANCHI TYPE I UNIVERSES WITH CAUSAL BULK VISCOUS COSMOLOGICAL FLUID

2002 ◽  
Vol 11 (03) ◽  
pp. 447-462 ◽  
Author(s):  
M. K. MAK ◽  
T. HARKO
Keyword(s):  
Bianchi Type ◽  
Viscosity Coefficient ◽  
State Equation ◽  
Type I ◽  
Bianchi Type I ◽  
Boltzmann Gas ◽  
Bulk Viscous ◽  
Barotropic Equation ◽  
Bulk Viscosity Coefficient ◽  
The Universe

We consider the dynamics of a causal bulk viscous cosmological fluid filled flat constantly decelerating Bianchi type I spacetime. The matter component of the Universe is assumed to satisfy a linear barotropic equation of state and the state equation of the small temperature Boltzmann gas. The resulting cosmological models satisfy the condition of smallness of the viscous stress. The time evolution of the relaxation time, temperature, bulk viscosity coefficient and comoving entropy of the dissipative cosmological fluid is also obtained.

Tilted universe with big rip singularity in Lyra geometry

2020 ◽  
Vol 35 (24) ◽  
pp. 2050196 ◽  
Author(s):  
V. J. Dagwal ◽  
D. D. Pawar ◽  
Y. S. Solanke ◽  
H. R. Shaikh
Keyword(s):  
Flat Space ◽  
Field Vector ◽  
Lyra Geometry ◽  
Distance Modulus ◽  
Field Equations ◽  
Wet Dark Fluid ◽  
Angular Diameter Distance ◽  
Geometrical Properties ◽  
Proper Distance ◽  
Big Rip

We have examined tilted cosmological models by using conformally flat space-time with wet dark fluid in Lyra geometry. In order to solve the field equations we have considered a power law. In this paper we have discussed tilted universe with time-dependent displacement field vector, heat conduction vectors and also discussed big rip singularity. Some physical and geometrical properties are also investigated. We have also extended our work to investigate the consistency of the derived model with observational parameter from the point of astrophysical phenomenon such as look-back time-redshift, proper distance, luminosity distance, angular-diameter distance and distance modulus.

scholarly journals CAUSAL BULK VISCOUS DISSIPATIVE ISOTROPIC COSMOLOGIES WITH VARIABLE GRAVITATIONAL AND COSMOLOGICAL CONSTANTS

2002 ◽  
Vol 11 (08) ◽  
pp. 1265-1283 ◽  
Author(s):  
M. K. MAK ◽  
T. HARKO ◽  
J. A. BELINCHÓN
Keyword(s):  
Cosmological Constant ◽  
Hubble Parameter ◽  
Early Period ◽  
Viscosity Coefficient ◽  
Field Equations ◽  
Gravitational And Cosmological Constants ◽  
Bulk Viscous ◽  
Cosmological Constants ◽  
Bulk Viscosity Coefficient ◽  
The Universe

We consider the evolution of a flat Friedmann–Robertson–Walker Universe, filled with a causal bulk viscous cosmological fluid, in the presence of variable gravitational and cosmological constants. The basic equation for the Hubble parameter, generalizing the evolution equation in the case of constant gravitational coupling and cosmological term is derived, under the supplementary assumption that the total energy of the Universe is conserved. By assuming that the cosmological constant is proportional to the square of the Hubble parameter and a power law dependence of the bulk viscosity coefficient, temperature and relaxation time on the energy density of the cosmological fluid, two classes of exact solutions of the field equations are obtained. In the first class of solutions the Universe ends in an inflationary era, while in the second class of solutions the expan-sion of the Universe is noninflationary for all times. In both models the cosmological "constant" is a decreasing function of time, while the gravitational "constant" increases in the early period of evolution of the Universe and tends in the large time limit to a constant value.

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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