Observational constraints on the equation of state of viscous fluid in $f(R, T)$ gravity

TL;DR

This paper explores a viscous $f(R,T)$ gravity cosmological model with bulk viscosity, fitting it to observational data, and finds it can explain the universe's accelerated expansion and behaves like quintessence dark energy.

Contribution

It introduces an exact solution for viscous $f(R,T)$ gravity with observational constraints, highlighting the role of bulk viscosity in cosmic acceleration.

Findings

Model fits observational data well at high redshifts

Bulk viscosity can generate negative pressure for acceleration

Model behaves like quintessence dark energy

Abstract

In this paper, we investigate a cosmological model based on viscous $f(R,T)$ gravity as a potential alternative to dark energy. This model incorporates bulk viscosity and is analyzed using an effective equation of state. We consider the simplest specific model, $f(R,T)=R+\lambda T$, where $\lambda$ is a constant. The exact solution of our viscous $f(R,T)$ cosmological model is derived, and then we use the combined datasets consisting of 31 $H(z)$ data points and 1701 Pantheon+ SNe data points to determine the best-fit values of the model parameters. We find good agreement with observations, particularly at higher redshifts. Our model's behavior, including energy density, pressure with viscosity, effective equation of state, and deceleration parameter, is analyzed. It indicates a shift from decelerated to accelerated phases of the universe's expansion, suggesting that bulk viscosity in the cosmic fluid could effectively generate the negative pressure necessary for cosmic expansion. Finally, we explore statefinder diagnostics to differentiate between various dark energy models, revealing that our model resides in the quintessence region.