Viscous Fluid Cosmology in Symmetric Teleparallel Gravity

In this article, the viscous fluid cosmological model is analyzed in the framework of recently proposed f(Q) gravity by assuming three different forms of bulk viscosity coefficients, specifically, (i)zeta=zeta(0)+zeta(1)(a+a)+zeta(2)(a/'a) (i)zeta =zeta(0)+zeta(1)(a/a), (ii) = zeta(0)+zeta(1)(a/a) (ii)zeta = zeta(0)/zeta(1) (a/a), and (iii)zeta=zeta 0 and a linear f(Q) model, particularly, f(Q)=alpha Q where alpha not equal 0 is free model parameter. The bulk viscosity coefficients and the model parameter values using the combined H(z)+Pantheon+BAO data set are estimated. The asymptotic behavior of our cosmological bulk viscous model is studied by utilizing the phase space method. It is found that corresponding to all three cases, our model depicts the evolution of the universe from matter dominated decelerated epoch (a past attractor) to a stable de-sitter accelerated epoch (a future attractor). Furthermore, the physical behavior of effective pressure, effective equation of state (EoS), and the statefinder parameters are studied. It is also found that the pressure component in the presence of bulk viscosity shows negative behavior and the effective EoS parameter predicts the accelerated expansion phase of the universe for all three cases. Moreover, the trajectories of the model lie in the quintessence region and it converges to the CDM fixed point in the far future. It is found that the accelerated de-Sitter like phase comes purely from the zeta over bar case without any geometrical modification to GR. Moreover, the late-time behavior of all three cases of viscosity coefficients are identical. Furthermore, a non-linear f(Q) model is considered, specifically, f(Q)= -Q+beta Q(2), and then analyzed the behavior of model using dynamical approach. It is also found that the late-time behavior of the considered non-linear model f(Q)= -Q+beta Q(2) with beta <= 0 is similar to the linear case, whereas for the case beta>0 results are quite different.