Imperfect fluid cosmological model in modified gravity

TL;DR

This paper explores a cosmological model with bulk viscous fluid in modified gravity, deriving exact solutions and analyzing accelerated expansion scenarios, including the occurrence of a big-rip singularity.

Contribution

It introduces a specific bulk viscous fluid model within $f(R,T)$ gravity and provides exact solutions for different equations of state, highlighting the impact on universe expansion.

Findings

Model predicts accelerated expansion for certain parameters.

Exact solutions are derived for specific $f(R,T)$ forms.

Big-rip singularity is observed in the model.

Abstract

In this article, we considered the bulk viscous fluid in the formalism of modified gravity in which the general form of a gravitational action is $f(R, T)$ function, where $R$ is the curvature scalar and $T$ is the trace of the energy momentum tensor within the frame of flat FRW space time. The cosmological model dominated by bulk viscous matter with total bulk viscous coefficient expressed as a linear combination of the velocity and acceleration of the expansion of the universe in such a way that $\xi=\xi_0+\xi_1\frac{\dot{a}}{a}+\xi_2\frac{\ddot{a}}{\dot{a}}$, where $\xi_0$, $\xi_1$ and $\xi_2$ are constants. We take $p=(\gamma-1)\rho$, where $0\le\gamma\le2$ as an equation of state for perfect fluid. The exact solutions to the corresponding field equations are obtained by assuming a particular model of the form of $f(R, T)=R+2f(T)$, where $f(T)=\lambda T$, $\lambda$ is constant. We studied the four possible scenarios for different values of $\gamma$, such as $\gamma=0$, $\gamma=\frac{2}{3}$, $\gamma=1$ and $\gamma=\frac{4}{3}$ with the possible positive and negative ranges of $\lambda$ to observe the accelerated expansion history of the universe. Finally, a big-rip singularity is observed.