LRS Bianchi I model with bulk viscosity in f(R,T) gravity

TL;DR

This paper investigates Bianchi I cosmological models with bulk viscosity in f(R,T) gravity, comparing them to GR models, and finds that f(R,T) gravity reduces the impact of bulk viscosity on the effective matter behavior.

Contribution

It introduces solutions for viscous and non-viscous Bianchi I models in f(R,T) gravity, analyzing their physical viability and comparing their behavior to GR models.

Findings

f(R,T) gravity does not alter the geometrical behavior of models.

Bulk viscosity's effect is diminished in f(R,T) gravity.

Matter exhibits diverse behaviors, including transitions from stiff matter to phantom.

Abstract

Locally-rotationally-symmetric Bianchi type-I viscous and non -viscous cosmological models are explored in general relativity (GR) and in f(R,T) gravity. Solutions are obtained by assuming that the expansion scalar is proportional to the shear scalar which yields a constant value for the deceleration parameter (q=2). Constraints are obtained by requiring the physical viability of the solutions. A comparison is made between the viscous and non-viscous models, and between the models in GR and in f(R,T) gravity. The metric potentials remain the same in GR and in f(R,T) gravity. Consequently, the geometrical behavior of the $f(R,T)$ gravity models remains the same as the models in GR. It is found that f(R,T) gravity or bulk viscosity does not affect the behavior of effective matter which acts as a stiff fluid in all models. The individual fluids have very rich behavior. In one of the viscous models, the matter either follows a semi-realistic EoS or exhibits a transition from stiff matter to phantom, depending on the values of the parameter. In another model, the matter describes radiation, dust, quintessence, phantom, and the cosmological constant for different values of the parameter. In general, f(R,T) gravity diminishes the effect of bulk viscosity.