Evolution and thermodynamics of new holographic dark energy with bulk viscosity in modified $f(R, T)$ gravity

TL;DR

This paper introduces a bulk viscous new holographic dark energy model within modified $f(R,T)$ gravity, analyzing its cosmic evolution, phase transitions, and thermodynamic consistency, with results close to observational data.

Contribution

It develops a viscous holographic dark energy model in $f(R,T)$ gravity, deriving solutions for universe evolution and analyzing phase transitions and thermodynamics.

Findings

Transition from deceleration to acceleration depends on viscous parameters.

Large viscous effects lead to perpetual acceleration.

Model's effective EoS parameter is close to -1, matching observations.

Abstract

In this paper, bulk viscosity is introduced in new holographic dark energy (HDE) to describe the effects of cosmic non-perfect fluid on the evolution of the universe in modified $f(R,T)$ gravity. Assuming $f(R,T)=R+\lambda T$, where $R$ is the Ricci scalar, $T$, the trace of energy-momentum tensor and $\lambda$ is a constant, we derive a general function of Hubble parameter with bulk viscous form to provide a procedure for the viscous new HDE model building. Especially, we assume the total bulk viscosity coefficient proportional to the velocity of the expansion of the universe in such a way that $\zeta=\zeta_0+\zeta_1 H$. We obtain the solutions of the scale factor and deceleration parameter and classify all the possible scenarios (deceleration, acceleration and their transition) with different parameter regions chosen properly for positive and negative ranges of $\lambda$, and $\zeta_0$ and $\zeta_1$ to analyze the evolution of the universe. It is observed that there is a transition from decelerated phase to accelerated phase at early or late time depending on the values of viscous terms. For large values of viscous terms it always accelerates through out the evolution. Furthermore, we also investigate the statefinder pair $\{r, s\}$ and $\textit{Om}$ diagnostics for the viscous new HDE model to discriminate with other existing DE models. Our viscous model is also different from other existing dark energy models. The evolution of effective equation of state parameter is -0.9745 which is very close to the observation. The entropy and generalized second law of thermodynamics are valid for this model under some constraints of bulk viscous coefficient. The analysis shows that the dark energy phenomena may be explained as the effect of bulk viscosity in the cosmic medium.