Israel-Stewart approach to viscous dissipative extended holographic Ricci dark energy dominated universe

TL;DR

This study applies the Israel-Stewart formalism to viscous extended holographic Ricci dark energy, analyzing its cosmological evolution, thermodynamics, and statefinder parameters, revealing phantom behavior and thermodynamic law validity.

Contribution

It introduces a viscous EHRDE model using Israel-Stewart theory, exploring its dynamics, thermodynamics, and statefinder diagnostics, which is a novel combination in dark energy research.

Findings

EoS parameter behaves like phantom ($w_{DE} \, \leq \, -1$) under bulk viscosity.

Effective pressure decays over time, indicating universe acceleration.

Thermodynamic second law holds in the viscous EHRDE universe.

Abstract

This paper reports a study on the truncated Israel-Stewart formalism for bulk viscosity using the extended holographic Ricci dark energy (EHRDE), where the density of dark energy is given as a combination of the Hubble parameter and its derivative. The equations of motion are integrated and the resulting model is analysed under many aspects, including the state finder parameters and the generalised thermodynamics second law. Under the consideration that the universe is dominated by EHRDE the evolution equation for the bulk viscous pressure $\Pi$ in the framework of the truncated Israel-Stewart theory has been taken as $\tau \dot{\Pi}+\Pi=-3\xi H$, where $\tau$ is the relaxation time and $\xi$ is the bulk viscosity coefficient. Considering effective pressure as a sum of thermodynamic pressure of EHRDE and bulk viscous pressure it has been observed that under the influence of bulk viscosity the EoS parameter $w_{DE}$ is behaving like phantom i.e. $w_{DE}\leq -1$. It has been observed that the magnitude of the effective pressure $p_{eff}=p+\Pi$ is decaying with time. We also investigated the case for a specific choice of scale factor namely $a(t)=(t-t_0)^{\frac{\beta}{1-\alpha}}$. For this choice we have observed that a transition from quintessence to phantom is possible for the equation of state parameter. However, the $\Lambda$CDM phase is not attainable by the statefinder trajectories for this choice. Finally it has been observed that in both of the cases the generalized second law of thermodynamics is valid for the viscous EHRDE dominated universe enveloped by the apparent horizon.