Bulk Viscous Cosmological Model Research Articles

Anisotropic bulk viscous cosmological models in a modified gravity

A spatially homogeneous Bianchi type-VI0 space-time is considered in the frame work of f(R,T) gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. Exact solutions of the field equations are obtained both in the absence and in the presence of cosmic strings under some specific plausible physical conditions. Some physical and kinematical properties of the model are, also, studied.

Axially Symmetric Bianchi Type-I Bulk-Viscous Cosmological Models with Time-Dependent Λ and q

The present study deals with spatially homogeneous and anisotropic axially symmetric Bianchi type-I cosmological model with time variable cosmological term Λ in the presence of bulk viscous fluid. The Einstein’s field equations are solved explicitly by time varying deceleration parameter q. Consequences of the four cases of phenomenological decay of Λ have been discussed which are consistent with observations. Physical and kinematical parameters of the models are discussed.

Five dimensional bulk viscous cosmological model with wet dark fluid in general relativity

In this paper, we have constructed a five dimensional LRS Bianchi type I cosmological model with wet dark fluid (WDF) in general relativity with the matter field described as bulk viscosity. It is found that in presence of bulk viscosity an inflationary effective stiff fluid cosmological model is obtained, whereas in absence of bulk viscosity the wet dark fluid degenerate to stiff fluid. Some physical and geometrical properties of the model are also discussed.

Dust Fluid Cosmological Model

Bianchi type I tilted bulk viscous fluid cosmological model filled with dust fluid is investigated. We assume that (constant), where is the coefficient of bulk viscosity and is the expansion in the model. It has been assumed that the expansion in the model is only in two directions; that is, one of the components of Hubble parameters is zero. The physical and geometrical aspects of the model in the presence and absence of bulk viscosity are also discussed. Also, we have discussed two special models and their physical properties. From this, we present a particular example based on dust fluid.

String cosmological models with bulk viscosity in Nordtvedt's general scalar-tensor theory of gravitation

We have obtained and presented spatially homogeneous Bianchi types II, VIII, and IX string cosmological models with bulk viscosity in Nordtvedt's (Astrophys. J. 161:1059, 1970) general scalar-tensor theory of gravitation with the help of a special case proposed by Schwinger. It is observed that only the bulk viscous cosmological model exists in the case of Bianchi type IX universe. Some important features of the models, thus obtained, have been discussed.

Bianchi type-V bulk viscous cosmological models with particle creation in Brans-Dicke theory

The Bianchi type-V cosmological model with viscous fluid and creation particle in Brans-Dicke theory has been considered. The present paper deals with Bianchi type-V cosmological model with bulk viscosity and particle creation described by full causal thermodynamics in Brans-Dicke theory. We have discussed two types of solutions of the average scale factor for a Bianchi type-V model by using a variation law of Hubble’s parameter, which yields a constant value of the deceleration parameter. The exact solutions to the corresponding field equations are obtained in quadrature form. The solutions to the Einstein field equations are obtained for power law and exponential form. The cosmological parameters have been discussed in detail.

Bianchi Types II, VIII and IX String Cosmological Models with Bulk Viscosity in Brans-Dicke Theory of Gravitation

We have obtained and presented spatially homogeneous Bianchi types II, VIII and IX string cosmological models with bulk viscosity in a scalar tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961). It is observed that in case of Bianchi type-IX universe, only bulk viscous cosmological model exists. Some physical and geometrical properties of the models are also discussed.

Bulk Viscous Cosmological Model with Interacting Dark Fluids

The objective of the present work is to study a cosmological model for a spatially flat Universe whose constituents are a dark energy field and a matter field which includes baryons and dark matter. The constituents are supposed to be in interaction and irreversible processes are taken into account through the inclusion of a non-equilibrium pressure. The non-equilibrium pressure is considered to be proportional to the Hubble parameter within the framework of a first order thermodynamic theory. The dark energy and matter fields are coupled by their barotropic indexes, which are considered as functions of the ratio between their energy densities. The free parameters of the model are adjusted from the best fits of the Hubble parameter data. A comparison of the viscous model with the non-viscous one is performed. It is shown that the equality of the dark energy and matter density parameters and the decelerated-accelerated transition occur at earlier times when the irreversible processes are present. Furthermore, the density and deceleration parameters and the distance modulus have the correct behavior which is expected for a viable scenario of the present status of the Universe.

Bianchi type I bulk viscous cosmological models with particle creation in Brans-Dicke theory

This paper is devoted to the study of the role of particle creation and bulk viscosity in the evolution of the homogeneous and anisotropic model of the universe represented by Bianchi type I space-time metric in Brans-Dicke theory. Particle creation and bulk viscosity have been considered as separated irreversible processes. In order to discuss the physical and geometrical behaviour of the model, a new set of exact solutions of field equations have been obtained in non-causal, truncated and full causal theories. The dynamical behaviours of models have also been discussed.

A new class of bulk viscous FRW cosmological models in a scale covariant theory of gravitation

A new class of bulk viscous FRW cosmological models in a scale covariant theory of gravitation

Bianchi Type-III Bulk Viscous and Barotropic Perfect Fluid Cosmological Models in Lyra’s Geometry

We have investigated Bianchi type III bulk viscous and barotropic perfect fluid cosmological models in the frame work of Lyra’s geometry. To get deterministic models of universe, we have assumed the three conditions: (i) shear scalar (σ) is proportional to the expansion (θ). This leads to B=Cn, where B and C are metric potentials. (ii) In presence of viscous fluid, the coefficient of viscosity of dissipative fluid is a power function of mass density ξ=ξ0ρm, where ξ0 and m are constant and (iii) in absence of viscosity, a proportionality relation between pressure and energy density of barotropic perfect fluid p=αρ, where α is a proportionality constant. In all the cases, we observed that the displacement vector β is large at beginning of the universe and reduces fast during its evolution so that its nature coincide with the behavior of cosmological constant Λ.

Bulk Viscous Bianchi-III Models with Time Dependent G and Λ

Bulk Viscous anisotropic Bianchi-III cosmological models are investigated with time dependent gravitational and cosmological constants in the framework of Einstein’s general relativity. In order to get some useful information about the time varying nature of G and Λ, we have assumed an exponentially decaying rest energy density of the universe. The extracted Newtonian gravitational constant G varies with time but its time varying nature depends on bulk viscosity and the anisotropic nature of the model. The cosmological constant Λ is found to decrease with time to a small but positive value for the models.

Anisotropic bulk viscous cosmological models with particle creation

This paper is devoted to the study of role of particle creation and bulk viscosity on evolution of homogeneous and anisotropic model of the universe represented by Bianchi type I space time metric. Particle creation and bulk viscosity have been considered as separated irreversible processes. In order to discuss physical and geometrical behaviour of the model, a new set of exact solutions of Einstein’s field equation have been obtained in non-causal, truncated and full causal theories. Dynamical behaviours of models have also been discussed.

A new class of bulk viscous cosmological models in a scale covariant theory of gravitation

Friedmann Robertson Walker cosmological models with bulk viscosity are constructed in the scale covariant theory of gravitation. A new class of solutions for the field equations of the model is found by applying variable deceleration parameter. Some physical models of these solutions are briefly discussed in this paper.

Bianchi Type V Magnetized String Dust Bulk Viscous Fluid Cosmological Model with Variable Magnetic Permeability

Bianchi Type V magnetized string dust bulk viscous fluid cosmological model with variable magnetic permeability, is investigated. The magnetic field is due to an electric current produced along x-axis. Thus the magnetic fields is in yz-plane and F23 is the only non-vanishing component of electromagnetic field tensor Fij. To get the deterministic model in terms of cosmic time t, we have also assumed the condition ζθ=constant where ζ the coefficient of bulk viscosity and θ the expansion in the model. The behaviour of the model in presence and absence of magnetic field and bulk viscosity and singularities in the model are also discussed.

String Cosmological Model with Bulk Viscosity in Higher Dimensional Space Time

We have investigated the bulk viscous fluid string dust cosmological model in the higher dimensional space-time. To obtain a determinate solution, it is assumed that the coefficient of bulk viscosity is a power function of the scalar of expansion τ = Aθm (t) and the scalar of expansion is proportional to shear scalar, which leads to a relation between metric potentials A = KRn where A and R are function of time. It is also shown that bulk viscosity plays an important role on the evolution of the universe. The physical and geometrical aspects of the model are also discussed.

Bianchi Type-V Bulk Viscous Fluid String Dust Cosmological Model In General Relativity

Bianchi Type-V bulk viscous fluid string dust cosmological model in General Relativity is investigated. It has been shown that if coefficient of bulk viscosity (ζ) is inversely proportional to the expansion (θ) in the model then string cosmological model for Bianchi Type-V space-time is possible. In absence of bulk viscosity (ζ), i.e. when ζ → 0, then there is no string cosmological model for Bianchi Type-V space-time. The physical and geometrical aspects of the model are also discussed.

Bianchi type-I bulk viscous fluid string dust magnetized cosmological model in general relativity

Bianchi Type-I magnetized bulk viscous fluid string dust cosmological model is investigated. To get a determinate model, we have assumed the conditions σ ∝θ andζθ = constant where σ is the shear,θ the expansion in the model andζ the coefficient of bulk viscosity. The behaviour of the model in the presence and absence of magnetic field together with physical and geometrical aspects of the model are also discussed.

Tilted bianchi type v bulk viscous cosmological models in general relativity

Conformally flat tilted Bianchi type V cosmological models in presence of a bulk viscous fluid and heat flow are investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density. Some physical and geometric aspects of the models are also discussed.

Renormalization group approach to causal bulk viscous cosmological models

The renormalization group method is applied to the study of homogeneous and flat Friedmann–Robertson–Walker type universes, filled with a causal bulk viscous cosmological fluid. The starting point of the study is the consideration of the scaling properties of the gravitational field equations, the causal evolution equation of the bulk viscous pressure and the equations of state. The requirement of scale invariance imposes strong constraints on the temporal evolution of the bulk viscosity coefficient, temperature and relaxation time, thus leading to the possibility of obtaining the bulk viscosity coefficient–energy density dependence. For a cosmological model with bulk viscosity coefficient proportional to the Hubble parameter, we perform the analysis of the renormalization group flow around the scale-invariant fixed point, thereby obtaining the long-time behaviour of the scale factor.