Rip/singularity free cosmology models with bulk viscosity

TL;DR

This paper introduces two bulk viscosity cosmological models that explain the universe's accelerated expansion without dark energy, fitting observational data and avoiding future singularities or rip scenarios.

Contribution

The paper presents novel bulk viscosity models with exact solutions that fit observational data, offering an alternative to dark energy in explaining cosmic acceleration.

Findings

Models fit observational data well

Universe evolution avoids future singularities

Bulk viscosity provides a realistic cosmological scenario

Abstract

In this paper we present two concrete models of non-perfect fluid with bulk viscosity to interpret the observed cosmic accelerating expansion phenomena, avoiding the introduction of exotic dark energy. The first model we inspect has a viscosity of the form ${\zeta} = {\zeta}_0 + ({\zeta}_1-{\zeta}_2q)H$ by taking into account of the decelerating parameter q, and the other model is of the form ${\zeta} = {\zeta}_0 + {\zeta}_1H + {\zeta}_2H^2$. We give out the exact solutions of such models and further constrain them with the latest Union2 data as well as the currently observed Hubble-parameter dataset (OHD), then we discuss the fate of universe evolution in these models, which confronts neither future singularity nor little/pseudo rip. From the resulting curves by best fittings we find a much more flexible evolution processing due to the presence of viscosity while being consistent with the observational data in the region of data fitting. With the bulk viscosity considered, a more realistic universe scenario is characterized comparable with the {\Lambda}CDM model but without introducing the mysterious dark energy.