Viscous generalized Chaplygin gas

摘要

Viscous generalized Chaplygin gas (GCG) cosmology is discussed, assuming that there is bulk viscosity in the linear barotropic fluid and GCG. w(gamma) = gamma - 1 and w(g) represent the state equation parameters for barotropic fluid and GCG, respectively, in which gamma = 1 or 4/3 corresponds to ordinary matter or radiation. The dynamical analysis indicates that the phase w(g) = -1 + root 3 gamma kappa tau(g)/(gamma - root 3 kappa tau(gamma)) is a dynamical attractor and the equation of state of GCG approaches it from either wg > -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 tau(g) and tau(gamma) 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.