Viscous cosmological models and accelerated Universes

TL;DR

This paper explores viscous cosmological models where a non-equilibrium pressure term allows for a universe that transitions from past deceleration to current acceleration, with dark energy decaying slowly over time.

Contribution

It introduces a model incorporating non-equilibrium pressure in the energy-momentum tensor to explain accelerated expansion with a decelerated past.

Findings

Dark energy density decays more slowly than matter density.

Non-equilibrium pressure reduces the duration of past deceleration.

Model supports a universe transitioning from deceleration to acceleration.

Abstract

It is shown that a present acceleration with a past deceleration is a possible solution of the Friedmann equation by considering the Universe as a mixture of a scalar with a matter field and by including a non-equilibrium pressure term in the energy-momentum tensor. The dark energy density decays more slowly with respect to the time than the matter energy density does. The inclusion of the non-equilibrium pressure leads to a less pronounced decay of the matter field with a shorter period of past deceleration.