Spherical collapse for a viscous generalized Chaplygin GaS model

The nonlinear collapse for a viscous generalized Chaplygin gas model (VGCG) is analyzed in the framework of spherical top-hat collapse. Because the VGCG and baryons are essential to form the large-scale structure, we focus on their nonlinear collapse in this paper. We discuss the influence of model parameters alpha and zeta(0) on the spherical collapse by varying their values and compare with the I > CDM model. The results show that for the VGCG model, smaller zeta(0) and larger alpha make the structure formation earlier and faster, and the collapse curves of the VGCG model are almost coincident with those of the I > CDM model when the model parameter alpha is less than 10(-2).