Late-Time Viscous Cosmology in $f(R,T)$ Gravity

TL;DR

This paper explores late-time cosmic acceleration within $f(R,T)$ gravity using a bulk viscous fluid, analyzing cosmological parameters and energy conditions, and finds the model aligns with observations and mimics dark energy behaviors.

Contribution

It introduces a novel $f(R,T)$ gravity model with viscous fluid to explain late-time acceleration, analyzing its dynamics and compatibility with observational data.

Findings

Deceleration parameter sensitive to $ ext{alpha}$, flips sign around 10 Gyrs.

EoS parameter close to -1 at current epoch, matching Planck data.

Model mimics Chaplygin gas early and Quintessence later.

Abstract

The article communicates an alternative route to suffice the late-time acceleration considering a bulk viscous fluid with viscosity coefficient $\zeta =\zeta _{0}+ \zeta _{1} H + \zeta _{2} H^{2}$, where $\zeta _{0}, \zeta _{1}, \zeta _{2}$ are constants in the framework of $f(R,T)$ modified gravity. We presume the $f(R,T)$ functional form to be $f=R+2\alpha T$ where $\alpha$ is a constant. We then solve the field equations for the Hubble Parameter and study the cosmological dynamics of kinematic variables such as deceleration, jerk, snap and lerk parameters as a function of cosmic time. We observe the deceleration parameter to be highly sensitive to $\alpha$ and undergoes a signature flipping at around $t\sim 10$ Gyrs for $\alpha=-0.179$ which is favored by observations. The EoS parameter for our model assumes values close to $-1$ at $t_{0}=13.7$Gyrs which is in remarkable agreement with the latest Planck measurements. Next, we study the evolution of energy conditions and find that our model violate the Strong Energy Condition in order to explain the late-time cosmic acceleration. To understand the nature of dark energy mimicked by the bulk viscous baryonic fluid, we perform some geometrical diagnostics like the $\{r,s\}$ and $\{r,q\}$ plane. We found the model to mimic the nature of a Chaplygin gas type dark energy model at early times while a Quintessence type in distant future. Finally, we study the violation of continuity equation for our model and show that in order to explain the cosmic acceleration at the present epoch, energy-momentum must violate.