Bulk Viscous Cosmological Model Research Articles

Time Variable G and Λ in Five Dimensional Bulk Viscous Cosmological Model with Functional form of Hubble Parameter

Abstract In this article, we have constructed a spatially-flat Kaluza-Klein type cosmological model with the matter field narrated as bulk viscous fluid united with time dependent gravitational constant G and cosmological term Λ. The viscous coefficient η is taken as a quadratic form of Hubble parameter H (i.e. η = η 0 + η 1 H + η 2 H 2, where η 0 (≥ 0), η 1 and η 2 are constants). Exact generic solutions of the field equations are acquired with help of functional form of Hubble’s parameter, which yields initial deceleration to current time acceleration of the universe. Some geometrical and kinematical behaviours are analyzed.

Bulk Viscous Bianchi Type-V Cosmological Model in f(R, T) Theory of Gravity

This paper deals with the bulk viscous Bianchi type-V cosmological model with an exponential scale factor in Lyra geometry based on f(R, T) gravity, by considering a time dependent displacement field. To determine the nature and physical properties of the model, we considered Harko et al. (Harko et al., Phys. Rev. D, 2011, 84, 024020) [proposed the linear form f(R, T) = f1(R) + f2(T)], in which the barotropic equation of state for pressure, density, and bulk viscous pressure is proportional to energy density. The kinematical properties of the model are also discussed in the presence of bulk viscosity. Evolution of energy conditions is also studied and examined the behaviour of that in examined in order to explain the late-time cosmic acceleration.

Viscous cosmology in the Weyl-type f(Q,\xa0T) gravity

Bulk viscosity is the only viscous influence that can change the background dynamics in a homogeneous and isotropic universe. In the present work, we analyze the bulk viscous cosmological model with the bulk viscosity coefficient of the form zeta =zeta _0+zeta _1H+zeta _2left( frac{dot{H}}{H}+Hright) where, zeta _0, zeta _1 and zeta _2 are bulk viscous parameters, and H is the Hubble parameter. We investigate the impact of the bulk viscous parameter on dynamics of the universe in the recently proposed Weyl-type f(Q, T) gravity, where Q is the non-metricity, and T is the trace of the matter energy–momentum tensor. The exact solutions to the corresponding field equations are obtained with the viscous fluid and the linear model of the form f(Q, T)=alpha Q+frac{beta }{6kappa ^2}T, where alpha and beta are model parameters. Further, we constrain the model parameters using the 57 points Hubble dataset the recently released 1048 points Pantheon sample and the combination Hz + BAO + Pantheon, which shows our model is good congeniality with observations. We study the possible scenarios and the evolution of the universe through the deceleration parameter, the equation of state (EoS) parameter, the statefinder diagnostics, and the Om diagnostics. It is observed that the universe exhibits a transition from a decelerated to an accelerated phase of the universe under certain constraints of model parameters.

Bianchi type-I bulk viscous cosmological model with inhomogeneous equation of state

In the present paper we investigate Bianchi type-I Cosmological model with inhomogeneous equation of state (EoS) in the presence of variable bulk viscous fluid(ζ) in the framework of general theory of relativity. In order to find exact solutions of the Einstein’s field equations, we have assumed a special law of variation for Hubble parameter H i. e. . The nature of model is discussed for α ≠ 0 and α = 0. Some physical and kinematical aspects of model are also discussed for both the conditions.

Axially Symmetric Bulk Viscous Cosmological Model in F(R, T) Theory of Gravity

In this paper, axially symmetric space-time in presence of perfect fluid with viscosity has been considered and studied within the framework of F(R, T) theory of gravity proposed by (Harko et al. [14]). The solutions of the field equations axe evaluated by assuming the proportionality of expansion (θ) to the shear scalar (σ). The physical and kinematical aspects of the model have also been discussed.

Bulk viscous cosmological model in f(R,T) theory of gravity

In this paper, we have presented bulk viscous cosmological model of the universe in the modified gravity theory in which the Lagragian of the gravitational action contains a general function [Formula: see text], where [Formula: see text] and [Formula: see text] denote the curvature scalar and the trace of the energy–momentum tensor, respectively, in the framework of a flat Friedmann–Robertson–Walker model with isotropic fluid. We obtain cosmological solution in [Formula: see text] theory of gravity, specially of particular choice [Formula: see text], where [Formula: see text] is a constant, in the presence of bulk viscosity that are permitted in Eckart theory, Truncated Israel Stewart (TIS) theory and Full Israel Stewart (FIS) theory. The physical and geometrical properties of the models in Eckart, TIS theory and FIS theory are studied in detail. The analysis of the variation of bulk viscous pressure, energy density, scale factor, Hubble parameter and deceleration parameter with cosmic evolution is done in the respective theories. The models are analyzed by comparison with recent observational data. The cosmological models are compatible with observations.

LRS Bianchi Type-I Bulk Viscous Cosmological Models in f(R, T) Gravity

We have studied the locally rotationally symmetric (LRS) Bianchi type-I cosmological model in $f(R,T)$ gravity ($R$ is the Ricci scalar and $T$ is the trace of the stress energy tensor) with Bulk viscous fluid as matter content. The model is constructed for the linear form $f(R,T)=R+2f(T)$. The exact solution of field equations is obtained by using a time varying deceleration parameter $q$ for a suitable choice of the function $f(T)$. In this work, the bulk viscous pressure $\bar{p}$ is found to be negative and energy density $\rho$ is found to be positive. The obtained model is anisotropic, accelerating and compatible with the results of astronomical observations. Also, some important features of physical parameters of this model have been discussed.

Bulk Viscous Cosmological Model in Brans-Dicke Theory with New Form of Time Varying Deceleration Parameter

We have presented FRW cosmological model in the framework of Brans-Dicke theory. This paper deals with a new proposed form of deceleration parameter and cosmological constant Λ. The effect of bulk viscosity is also studied in the presence of modified Chaplygin gas equation of state (p=Aρ-B/ρn). Furthermore, we have discussed the physical behaviours of the models.

Hypersurface-Homogeneous Bulk Viscous Cosmological Models with Particle Creation in General Relativity

This article deals with the study of particle creation and bulk viscous stress for the hypersurface-homogeneous cosmological model in the context of general theory of relativity. Here, the solutions of the Einstein’s field equations are reduced to a simple integration for arbitrary choice of the metric potential A(t). We have obtained the coefficient of bulk viscosity for truncated theory, full casual theory, and non-casual theory. A set of models have been taken into consideration based on the plausible relations among the variables. In addition, we have studied the physical and kinematical properties of the models.

Five dimensional FRW bulk viscous cosmological models in Brans–Dicke theory of gravitation

Five dimensional FRW space-time is considered in the presence of bulk viscous fluid in the frame work of Brans and Dicke (Phys. Rev. 124:925, 1961) scalar–tensor theory of gravitation. To obtain determinate solution of the field equations we have used a power law between scalar field and the scale factor of the universe. Radiating flat, closed and open models are also presented. Physical properties of the models are also discussed.

On Kantowski-Sachs Viscous Fluid Model in Bimetric Relativity

Kantowski-Sachs plane symmetric models are investigated in bimetric theory of gravitation proposed by Rosen [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400310035003100330038003900340034000000 in the context of bulk viscous fluid. Taking conservation law and the equation of state, two different models of the universe are obtained. It is observed that Kantowski-Sachs vacuum model obtained in first case and bulk viscous fluid model obtained in second case. It is also observed that the bulk viscous cosmological model always represents an accelerated universe and consistent with the recent observations of type-1a supernovae. Some physical and geometrical features of the viscous fluid model are studied.

Bulk Viscous Anisotropic Cosmological Models with Generalized Chaplygin Gas with Time Varying Gravitational and Cosmological Constants

This paper is devoted to studying the generalized Chaplygin gas models in Bianchi type III space- time geometry with time varying bulk viscosity, cosmological and gravitational constants. We are considering the condition on metric potential . Also to obtain deterministic models we have considered physically reasonable relations like , and the equation of state for generalized Chaplygin gas given by . A new set of exact solutions of Einstein’s field equations has been obtained in Eckart theory, truncated theory and full causal theory. Physical behaviour of the models has been discussed.

Accelerating Bianchi type-VI0 bulk viscous cosmological models in Lyra geometry

The present study deals with spatially homogeneous and totally anisotropic Bianchi type-VI0 bulk viscous cosmological models in Lyra geometry. The Einstein’s field equations have been solved exactly by taking the shear (σ) in the model proportional to expansion scalar ( θ ) which leads to A = Bn, where A and B are metric functions and n is a positive constant (n > 1). We also adopt a condition ζ θ = L (constant) where ζ is the coefficient of bulk viscosity. It has been found that the displacement vector (β) is a decreasing function of time and it approaches to a small positive value at late time which is supported by recent observations. It is also found that the distance modulus curve of derived model matches with observations perfectly.

Bulk viscous cosmological models in f(R,T) theory of gravity

We have constructed Locally Rotationally Symmetric Bianchi type I (LRSBI) cosmological models in the f(R,T) theory of gravity when the source of gravitation is the bulk viscous fluid. The models are constructed for f(R,T)=R+2f(T) and f(R,T)=f1(R)+f2(T). We found that in the first case the model degenerates into effective stiff fluid model of the universe. In the second case we obtained degenerate effective stiff fluid model as well as general bulk viscous models of the universe. Some physical and kinematical properties of the models are also discussed.

Bianchi type V bulk viscous cosmological models with particle creation in general relativity

In this paper, a spatially homogeneous and anisotropic Bianchi type V model filled with an imperfect fluid with bulk viscosity and particle creation, is investigated within the framework of General Relativity. Particle creation and bulk viscosity have been considered as separate irreversible processes. The energy- momentum tensor is modified to accommodate the viscous pressure and creation pressure which is associated with creation of matter out of gravitational field. Exact solutions of the field equations are obtained by applying a special law of variation of Hubble parameter. Using this assumption, we obtain two types of cosmological models. We find a singularity in the first model whereas second model is non-singular. Further we separately study the bulk viscosity and particle creation in each model considering four different cases. The bulk viscosity coefficient $\zeta$ is obtained for Truncated, Full Causal and Eckart theories in all cases. All physical parameters are calculated and thoroughly discussed in both models.

Kantowski–Sachs bulk viscous cosmological model in a scalar–tensor theory of gravitation

Field equations are obtained in the scalar–tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986) with the aid of spatially homogenous and anisotropic Kantowski–Sachs space–time in the presence of bulk viscous fluid containing one dimensional cosmic strings. A determinate solution of the field equations is obtained, using some plausible physical conditions, which represents a Kantowski–Sach’s bulk viscous Cosmological model in the new scalar–tensor theory. Physical and kinematical properties of the model are also discussed.

Axially Symmetric Bianchi Type-I Bulk Viscous Cosmological Model with Time Varying Gravitational and Cosmological Constants

The present study deals with spatially homogeneous and anisotropic axially symmetric Bianchi type-I cosmological model with time variable G and Λ in the presence of bulk viscous fluid. The coefficient of bulk viscosity ζ is considered as a quadratic function of Hubble parameter H (i.e. ζ = ζ0 + ζ1H + ζ2H2, where ζ0, ζ1 and ζ2 are constants). The Einstein’s field equations are solved explicitly by using a law of variation for the Hubble parameter, which gives a constant value of deceleration parameter. The law generates power law and exponential form of average scale factor in terms of cosmic time. The physical and kinematical properties of the models are discussed.

Viscous cold dark matter in agreement with observations

We discuss bulk viscous cosmological models. Since the bulk viscous pressure is negative, viable viscous cosmological scenarios with late time accelerated expansion can in principle be constructed. After discussing some alternative models based on bulk viscous effects we will focus on a model very similar to the standard ΛvCDM. We argue that a ΛvCDM model, where we assign a very small (albeit perceptible) bulk viscosity to dark matter is in agreement with available cosmological observations. Hence, we work with the concept of viscous Cold Dark Matter (vCDM). At the level of the perturbations, the growth of vCDM structures is slightly suppressed when compared with the standard CDM ones. Having in mind that the small scale problems of the ΛCDM model are related to an excess of clustering, our proposal seems to indicate a possible direction for solving the serious drawbacks of the CDM paradigm within the standard cosmological model.

Polytropic Bulk Viscous Cosmological Model with Variable G and Λ

We consider a Bianchi type-I Polytropic bulk viscous fluid cosmological model with variable G and Λ. To get a deterministic model, it is assumed that and , , , where is the pressure, ρ is the energy density, η is the coefficient of bulk viscosity, α, k, γ and ηo are constants, H is Hubble constant, where k1 > 0, k2 > 0. The solution obtained lead to inflationary phase and the results obtained match with the observations [31] [32]. The case n = 1 for α = 1 is also discussed, relating the results with the observations.

Bianchi types I and V bulk viscous fluid cosmological models in f(R, T) gravity theory

AbstractIn this paper we present non-singular Bianchi types I and V cosmological models, in the presence of bulk viscous fluid and within the framework of f(R,T) gravity theory. Exact solutions to the field equations are obtained by choosing a particular form of the function f(R,T) and a special value for the average scale factor of the model, which corresponds to a time- dependent deceleration parameter. The cosmological models initially accelerate for a certain period of time and thereafter decelerate. The physical and kinematical properties of the models of the universe are discussed.