Viscous Generalized Chaplygin Gas

Viscous generalized Chaplygin gas (GCG) cosmology is discussed, assuming that there is bulk viscosity in the linear barotropic fluid and GCG. w γ = γ - 1 and w g represent the state equation parameters for barotropic fluid and GCG, respectively, in which γ = 1 or [Formula: see text] corresponds to ordinary matter or radiation. The dynamical analysis indicates that the phase [Formula: see text] is a dynamical attractor and the equation of state of GCG approaches it from either w g > -1 or w g < -1 depending on the choice of its initial cosmic density parameter and the ratio of pressure to critical energy density, where τ g and τ γ are viscosity parameters. Therefore, the equation of state w g will cross the boundary w g = -1 if we choose initial value w g < -1. Furthermore, we show that bulk viscosity coefficients should satisfy inequalities from the point of view of dynamics.