Bulk Viscous Research Articles

Exploration of bulk viscous Bianchi type cosmological model in f(T) theory of gravity

In the present paper, the expansion of Locally Rotational Symmetric (LRS) Bianchi type - I cosmological model have been investigated with Bulk Viscous matter in the context of f(T) theory of gravity, where T signifies the torsion scalar. The power model, exponential model and linear functional model of the universe have been discussed for choices of f(T)with utilization of the special form of time dependent varying deceleration parameter. The discussion involves the examination of the dynamical behaviour of these models using some dynamical parameters and its graphical representation.

Certain Investigations on Bulk Viscous String Models of the Universe with BVDP

Certain Investigations on Bulk Viscous String Models of the Universe with BVDP

Five Dimensional FRW Radiating Cosmological Model in Presence of Bulk Viscous Fluid in Scalar Tensor Theory of Gravitation

In this paper using the Saez-Ballester scalar-tensor theory of gravitation, we examined a 5-dimensional FRW cosmic space-time in a source of bulk viscous fluid in the article. To examine determinate solutions of the field equations, we used a power law between a scalar field and the universe's scale factor. Our research considers radiating flat, closed, and open models. The physical and kinematical properties of the models were explored in each scenario. In this study, we show that our model expands and is free of initial singularities, as well as that our models decelerate in a conventional manner.
 HIGHLIGHTS
 
 Using the Saez-Ballester theory and a 5-dimensional FRW space-time as a source of bulk viscous fluid, we have obtained cosmological models that can be assumed to be equivalent radiating models in closed, open, and flat space-times
 We have obtained models that are expanding and free of initial singularity
 We used a power law between a scalar field and the universe's scale factor

Bulk Viscous Bianchi Type VI Cosmological Model In Extended Gravity With Exponential Function

We have constructed bulk viscous Bianchi Type VI cosmological model with an exponential scale factor based on 𝑓(𝑅, 𝑇) gravity. To determine the nature and physical properties of the model, we considered 𝑓(𝑅, 𝑇) = 𝑅 + 2𝛬0 + 2𝛽𝑇. We have made use of exponential scale factor to find the physical properties. Evolution of energy conditions is also studied and examined the behavior of that in examined. The kinematical and geometrical parameters are derived and analyzed in detail. The cosmological constant and coupling constant, is likely to experience an expansion at the late time of cosmic acceleration. Keywords: Bianchi type-VI, Bulk viscous, Exponential scale factor, Modified gravity, Effective cosmological constant.

Higher Dimensional LRS Bianchi Type-I String Cosmological Model with Bulk Viscosity in General Relativity

Objective: To present a new solution to the field equations obtained for higher dimensional LRS Bianchi type-I universe generated by means of a cloud of strings with particles connected to them with bulk viscosity in general relativity. Methods: To obtain the solutions of field equations of higher dimensional LRS Bianchi type-I universe we consider that the shear scalar of the model is proportional to the scalar expansion of the model (saq ), which leads to, c=b^n. The physical and geometrical behaviors of the model universe are studied by comparing with the present cosmological scenario and observations. Findings: It is observed that our model is anisotropic, expanding and decelerates at early stage and then accelerates in late universe giving the inflation model universe. Novelty: We obtained new solution to the field equations for higher dimensional LRS Bianchi type-I generated by means of a cloud of strings with bulk viscous fluid in general relativity. Keywords: LRS Bianchi TypeI Metric; Bulk Viscous Fluid; Strings

Dynamics of Bulk Viscous String Cosmological Model in f(R,G) Theory of Gravity

Existing investigations dedicated to the self-propelling investigation of dynamics of bulk viscous string in LRS Bianchi type-I cosmological model within the circumstance of alternative theory of gravity with Langrangian be the impulsive perform of Ricci scalar R and Gouss-Bonnet invariant G , say f(R,G) gravity. Exact solutions of the field equations correspond to special law of variation which provides singular model. Also some physical and kinematical aspects and its behavior with the present day universe of the cosmological model have been discussed.

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.

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

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.

Some Bianchi Type Bulk Viscous String Cosmological Models in f(R) Gravity

In this paper, we investigate bianchi type II, V III and IX Bulk viscous string cosmological models in the context of f(R) gravity. Here, we obtained the solutions of the field equations in the presence of cosmic strings under some specific possible physical conditions. Some physical and geometrical features of the models are also discussed.

Dynamical Stability of Bulk Viscous Isotropic and Homogeneous Universe

In this paper, we study the phase space portrait of homogeneous and isotropic universe by taking different coupling functions between dark energy models and bulk viscous dark matter. The dimensionless quantities are introduced to establish an autonomous set of equations. To analyze the stability of the cosmos, we evaluate critical points and respective eigenvalues for different dynamical quantities. For bulk viscous matter and radiation in tachyon coupled field, these points show stable evolution when γ ≫ δ but accelerated expansion of the universe for δ > 1 9 . The stability of the universe increases for some stationary points which may correspond to the late-time expansion for the coupled phantom field.

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

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-I Bulk Viscous String Model in f(R) Gravity

ABSTRACTField equations of f(R) theory of gravity are obtained with the aid of locally rotationally symmetric (LRS) Bianchi type-I metric when the matter source is a bulk viscous fluid containing one dimensional cosmic strings. Applying some physically possible conditions, we have obtained a determinate solution of the field equations. The deceleration parameter of our model exhibits a smooth transition from early decelerated phase to late time accelerating phase. We also find that the realistic energy conditions p ≥ 0 and pp ≤ 0 are satisfied in our model. Some other properties of the model are also discussed.

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.

Stability Analysis of Bulk Viscous Cosmology

In this paper, we study phase space analysis of FRW universe model by taking a power-law model for bulk viscosity coefficient. An autonomous system of equations is developed by defining normalized dimensionless variables. We find corresponding critical points for di.erent values of the parameters to investigate stability of the system. It is found that the presence of power-law model of bulk viscosity appears as an e.ective ingredient to enhance the stability of the respective universe model.

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

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 ξ = ξ 0 + ξ 1 a ˙ a + ξ 2 a ¨ a ˙ , $\xi = {\xi _0} + {\xi _1}{{\dot a} \over a} + {\xi _2}{{\ddot a} \over {\dot a}},$ where ξ 0, ξ 1, and ξ 2 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 ξ 2 a ¨ a ˙ , ${\xi _2}{{\ddot a} \over {\dot a}},$ 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 ξ = ξ 1 a ˙ a , $\xi = {\xi _1}{{\dot a} \over a},$ ξ = ξ 1 a ˙ a + ξ 2 a ¨ a ˙ $\xi = {\xi _1}{{\dot a} \over a} + {\xi _2}{{\ddot a} \over {\dot a}}$ and ξ = ξ 0 + ξ 1 a ˙ a + ξ 2 a ¨ a ˙ , $\xi = {\xi _0} + {\xi _1}{{\dot a} \over a} + {\xi _2}{{\ddot a} \over {\dot a}},$ 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.

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.

Anisotropic Bianchi Type-I and Type-II Bulk Viscous String Cosmological Models Coupled with Zero Mass Scalar Field

The LRS Bianchi type-I and type-II string cosmological models are studied when the source for the energy momentum tensor is a bulk viscous stiff fluid containing one dimensional strings together with zero-mass scalar field. We have obtained the solutions of the field equations assuming a functional relationship between metric coefficients when the metric is Bianchi type-I and constant deceleration parameter in case of Bianchi type-II metric. The physical and kinematical properties of the models are discussed in each case. The effects of Viscosity on the physical and kinematical properties are also studied.

Spherically Symmetric Bulk Viscous Fluid in Bimetric Relativity

In this paper, cylindrically symmetric space-time is studied with bulk viscous fluid in the context of

Axially Symmetric Bulk Viscous String Cosmological Models in GR and Brans-Dicke Theory of Gravitation

Axially symmetric string cosmological models with bulk viscosity in Brans-Dicke (1961) and general relativity (GR) have been studied. The field equations have been solved by using the anisotropy feature of the universe in the axially symmetric space-time. Some important features of the models, thus obtained, have been discussed. We noticed that the presence of scalar field does not affect the geometry of the space-time but changes the matter distribution, and as a special case, it is always possible to obtain axially symmetric string cosmological model with bulk viscosity in general relativity.

Five Dimensional Bulk Viscous String Cosmological Models in Saez and Ballester Theory of Gravitation

LRS Bianchi type-I bulk viscous string cosmological models are obtained in scalar tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). It is shown that cosmic string does not survive for ρ+λ=0 whereas it survives for the equations of state ρ=(1+ω)λ (Takabayasi string) and ρ=λ (Geometric string). Some physical and geometrical properties of the exhibited model are discussed.