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 α and ζ₀ on the spherical collapse by varying their values and compare with the ΛCDM model. The results show that for the VGCG model, smaller ζ₀ and larger α make the structure formation earlier and faster, and the collapse curves of the VGCG model are almost coincident with those of the ΛCDM model when the model parameter α is less than 10⁻²