Phase-space analysis of the viscous fluid cosmological models in the coincident $f(Q)$ gravity

Abstract

In this article, we consider a newly proposed parameterization of the viscosity coefficient $ζ$, specifically $ζ=\barζ_0 {Ω^s_m} H $, where $\barζ_0 = \frac{ζ_0}{Ω^s_{m_0}} $ within the coincident $f(Q)$ gravity formalism. We consider a non-linear function $f(Q)= -Q +αQ^n$, where $α$ and $n$ are arbitrary model parameters, which is a power-law correction to the STEGR scenario. We find an autonomous system by invoking the dimensionless density parameters as the governing phase-space variables. We discuss the physical significance of the model corresponding to the parameter choices $n=-1$ and $n=2$ along with the exponent choices $s=0, 0.5$, and $1.05$. We find that model I shows the stable de-Sitter type or stable phantom type (depending on the choice of exponent $s$) behavior with no transition epoch, whereas model II shows the evolutionary phase from the radiation epoch to the accelerated de-Sitter epoch via passing through the matter-dominated epoch. Hence, we conclude that model I provides a good description of the late-time cosmology but fails to describe the transition epoch, whereas model II modifies the description in the context of the early universe and provides a good description of the matter and radiation era along with the transition phase.