Bianchi type I universe with viscous fluid

TL;DR

This paper investigates how viscous fluids and a cosmological constant influence the evolution and singularity behavior of a Bianchi type-I universe, revealing conditions for singularity avoidance and oscillatory expansion modes.

Contribution

It introduces new insights into the effects of viscosity and b3b5 on the evolution of anisotropic universes, including singularity elimination and oscillatory solutions.

Findings

Viscosity influences solution behavior near singularity.

b3b5b5 can help eliminate cosmological singularity.

Oscillatory expansion modes are possible with specific viscosity and b3b5 values.

Abstract

We study the evolution of a homogeneous, anisotropic Universe given by a Bianchi type-I cosmological model filled with viscous fluid, in the presence of a cosmological constant $\Lambda$. The role of viscous fluid and $\Lambda$ term in the evolution the BI space-time is studied. Though the viscosity cannot remove the cosmological singularity, it plays a crucial part in the formation of a qualitatively new behavior of the solutions near singularity. It is shown that the introduction of the $\Lambda$ term can be handy in the elimination of the cosmological singularity. In particular, in case of a bulk viscosity, it provides an everlasting process of evolution ($\Lambda < 0$), whereas, for some positive values of $\Lambda$ and the bulk viscosity being inverse proportional to the expansion, the BI Universe admits a singularity-free oscillatory mode of expansion. In case of a constant bulk viscosity and share viscosity being proportional to expansion, the model allows oscillatory mode accompanied by an exponential growth even with a negative $\Lambda$. Space-time singularity in this case occurs at $t \to -\infty$.