Abstract
The evolution of the bulk viscous matter dominated universe has been analysed using the full causal theory for the evolution of the viscous pressure in the context of the recent acceleration of the universe. The form of the viscosity is taken as xi =alpha rho ^{1/2}. We obtained analytical solutions for the Hubble parameter and scale factor of the universe. The model parameters have been computed using the observational data. The evolution of the prominent cosmological parameters was obtained. The age of the universe for the best estimated model parameters is found to be less than observational value. The viscous matter behaves like a stiff fluid in the early phase and evolves to a negative pressure fluid in the later phase. The equation of state is found to be stabilised with value omega >- 1. The local as well as generalised second law of thermodynamics is satisfied. The statefinder diagnostic shows that this model is distinct from the standard varLambda CDM. One of the marked deviations seen in this model to be compared with the corresponding model using the Eckart approach is that in this model the bulk viscosity decreases with the expansion of the universe, while in the Eckart formalism it increases from negative values in the early universe towards positive values.
Highlights
The most successful model of the universe, which explains the recent acceleration of the universe, is the standard ΛCDM model
We investigate the evolution of a bulk viscous matter dominated universe using the Israel–Stewart theory of bulk viscosity
The bulk viscous pressure in Eckart’s theory is of the form Π = −3H ξ, where ξ is the term representing the bulk viscosity of the fluid and as a transport coefficient it can be a function of the Hubble parameter of the universe
Summary
The most successful model of the universe, which explains the recent acceleration of the universe, is the standard ΛCDM model. Later in a more general analysis on bulk viscous matter dominated model of the universe based on the Eckart formalism by Athira and Mathew [13], they have proved that the model has considerably good background evolution and is asymptotically stable if the bulk viscous coefficient is a constant All these analyses were based on the non-causal theory of viscosity. Piattella et al [36] have considered a bulk viscous universe using a full causal theory with the aim of unifying dark matter and dark energy They have found numerical solutions to the gravitational potential using an ansatz for the viscous pressure depends on the density of the viscous fluid and compared it with the standard ΛCDM model.
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