Some Bianchi Type I Viscous Fluid Cosmological Models with a Variable Cosmological Constant

TL;DR

This paper explores Bianchi type I cosmological models with viscous fluids and a variable cosmological constant, analyzing their physical properties and how the cosmological constant decreases over time, aligning with supernova observations.

Contribution

It introduces new Bianchi type I models with specific viscous fluid assumptions and a decreasing cosmological constant, expanding understanding of anisotropic cosmologies.

Findings

Cosmological constant is positive and decreases over time.

Models support recent supernovae Ia observations.

Physical and geometric properties of the models are discussed.

Abstract

Some Bianchi type I viscous fluid cosmological models with a variable cosmological constant are investigated in which the expansion is considered only in two direction i.e. one of the Hubble parameter $(H_{1} = \frac{A_{4}}{A})$ is zero. 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 constant in first case whereas in other case it is taken 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 supernovae Ia observations. Some physical and geometric properties of the models are also discussed.