Spherical Collapse for Viscous Generalized Chaplygin Gas Model
  The nonlinear collapse for viscous generalized Chaplygin gas Model (VGCG) was analyzed in the framework of spherical top-hat collapse. As the VGCG and baryons are essential to form the large scale structure, we focused on their nonlinear collapse in this paper. We discussed the influence of model parameters $\alpha$ and $\zeta_{0}$ on the spherical collapse by varying their values and compare with $\Lambda CDM$. 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 VGCG model is almost distinguished with the $\Lambda CDM$ model when the model parameter $\alpha$ is less than $10^{-2}$. 
Wei Li and Lixin Xu
astro-ph.CO