Iterative solutions for relativistic dissipative cosmologies (original) (raw)
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Indian Journal of Physics, 2022
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A new class of exact solutions of Einstein's field equations with a bulk viscous fluid for an LRS Bianchi type-Ia obtained by using a time dependent deceleration parameter and cosmological term Lambda. The coefficient of bulk viscosity is assumed to be a power function of mass density ( xi= xi 0 rho n ). We have obtained a general solution of the field equations from which six models of the universe are derived: exponential, polynomial and sinusoidal form respectively. The behaviour of these models of the universe are also discussed in the frame of reference of recent supernovae Ia observations.
Classical and Quantum Gravity, 2016
We test the physical relevance of the full and truncated versions of the Israel-Stewart theory of irreversible thermodynamics in a cosmological setting. Using a dynamical systems method, we determine the asymptotic future of plane symmetric Bianchi type I spacetimes filled with a viscous γ-fluid, keeping track of the magnitude of relative dissipative fluxes, which determines the applicability of the Israel-Stewart theory. We consider the situations when the dissipative mechanisms of shear and bulk viscosity are involved separately and simultaneously. Also, we apply two different temperature models in the full version of the theory in order to compare the results. We demonstrate that the only case when the fluid asymptotically approaches local equilibrium, and the underlying assumptions of the IS theory are therefore not violated, is that of a dissipative fluid with vanishing bulk viscosity. The truncated Israel-Stewart equations for shear viscosity are found to produce solutions which manifest pathological dynamical features and are in addition strongly sensitive with respect to the choice of initial conditions. The possible role of bulk and shear viscosity in cosmological evolution is also discussed.
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Canadian Journal of Physics, 2010
Assuming that the matter in the background geometry is a free gas and that no phase transitions were occurring in the early Universe, we discuss the thermodynamics of this closed system using classical approaches. We find that essential cosmological quantities, such as the Hubble parameter H, the scaling factor a, and the curvature parameter k, can be derived from this simple model, which on one hand fulfills and entirely obeys the laws of thermodynamics, and on the other hand, its results are compatible with the Friedmann–Robertson–Walker model and the Einstein field equations. Including a finite bulk viscosity coefficient leads to important changes in all these cosmological quantities. Accordingly, our picture about the evolution of the Universe and its astrophysical consequences seems to undergoing a radical revision. We find that k strongly depends on the thermodynamics of background matter. The time scale at which negative curvature might take place depends on the relation betw...
Indian Journal of Physics, 2013
Exact solutions of Einstein's field equations are obtained in a spatially homogeneous and anisotropic Bianchi type-I space-time in presence of a dissipative fluid with constant and time dependent cosmological term K. Einstein's field equations are solved by considering a time dependent deceleration parameter, which affords a late time acceleration in the universe. The cosmological constant K is found to be a decreasing function of time and it approaches a small positive value at present epoch, which is corroborated by consequences from recent supernovae I a observations. To get the deterministic solution a barotropic equation of state together with shear viscosity, proportional to expansion scalar, is also assumed. It is observed that initial nature of singularity is not changed due to presence of viscous fluid. The basic equation of thermodynamics is deduced and thermodynamic aspects of models are discussed. Physical and geometric properties of cosmological models are also discussed.
A new class of bulk viscous universe with time dependent deceleration parameter and Λ-term
Astrophysics and Space Science, 2007
A new class of exact solutions of Einstein's field equations with a bulk viscous fluid for an LRS Bianchi type-Ia obtained by using a time dependent deceleration parameter and cosmological term . The coefficient of bulk viscosity is assumed to be a power function of mass density (ξ = ξ 0 ρ n ). We have obtained a general solution of the field equations from which six models of the universe are derived: exponential, polynomial and sinusoidal form respectively. The behaviour of these models of the universe are also discussed in the frame of reference of recent supernovae Ia observations.
Friedmann model with viscous cosmology in modified f(R,T) gravity theory
In this paper, we introduce the bulk viscosity in the formalism of modified gravity theory in which the gravitational action contains a general function f (R, T ), where R and T denote the curvature scalar and the trace of the energy-momentum tensor, respectively, within the framework of a flat Friedmann-Robertson-Walker model. As an equation of state for a prefect fluid, we take p = (γ − 1)ρ, where 0 ≤ γ ≤ 2 and a viscous term as a bulk viscosity due to the isotropic model, of the form ζ = ζ 0 + ζ 1 H , where ζ 0 and ζ 1 are constants, and H is the Hubble parameter. The exact non-singular solutions to the corresponding field equations are obtained with non-viscous and viscous fluids, respectively, by assuming a simplest particular model of the form of f (R, T ) = R + 2 f (T ), where f (T ) = αT (α is a constant). A big-rip singularity is also observed for γ < 0 at a finite value of cosmic time under certain constraints. We study all possible scenarios with the possible positive and negative ranges of α to analyze the expansion history of the universe. It is observed that the universe accelerates or exhibits a transition from a decelerated phase to an accelerated phase under certain constraints of ζ 0 and ζ 1 . We compare the viscous models with the non-viscous one through the graph plotted between the scale factor and cosmic time and find that the bulk viscosity plays a major role in the expansion of the universe. A similar graph is plotted for the deceleration parameter with non-viscous and viscous fluids and we find a transition from decelerated to accelerated phase with some form of bulk viscosity.