Some Homogeneous Bianchi Type IX Viscous Fluid Cosmological Models with a varying $\Lambda$

TL;DR

This paper investigates Bianchi type IX viscous fluid cosmological models with a time-varying cosmological constant, analyzing their physical properties and how viscosity and expansion influence the models' evolution.

Contribution

It introduces new solutions for Bianchi type IX models incorporating bulk and shear viscosity with a decreasing cosmological constant over time.

Findings

The cosmological constant $mbda$ is positive and decreases over time.

Viscosity coefficients are modeled as functions of density and expansion.

Models exhibit physical and geometric properties consistent with observations.

Abstract

Some Bianchi type IX viscous fluid cosmological models are investigated. To get a solution a supplementary condition between metric potentials is used. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density whereas the coefficient of shear viscosity is considered as proportional to scale of expansion in the model. The cosmological constant $\Lambda$ is found to be positive and is a decreasing function of time which is supported by results from recent supernova observations. Some physical and geometric properties of the models are also discussed.