Effects of shear and rotation on the spherical collapse model for   clustering dark energy
  In the framework of the spherical collapse model we study the influence of shear and rotation terms for dark matter fluid in clustering dark energy models. We evaluate, for different equations of state, the effects of these terms on the linear overdensity threshold parameter, $\delta_{\rm c}$, and on the virial overdensity, $\Delta_{\rm V}$. The evaluation of their effects on $\delta_{\rm c}$ allows us to infer the modifications occurring on the mass function. Due to ambiguities in the definition of the halo mass in the case of clustering dark energy, we consider two different situations: the first is the classical one where the mass is of the dark matter halo only, while the second one is given by the sum of the mass of dark matter and dark energy. As previously found, the spherical collapse model becomes mass dependant and the two additional terms oppose to the collapse of the perturbations, especially on galactic scales, with respect to the spherical non-rotating model, while on clusters scales the effects of shear and rotation become negligible. The values for $\delta_{\rm c}$ and $\Delta_{\rm V}$ are higher than the standard spherical model. Regarding the effects of the additional non-linear terms on the mass function, we evaluate the number density of halos. As expected, major differences appear at high masses and redshifts. In particular, quintessence (phantom) models predict more (less) objects with respect to the $\Lambda$CDM model and the mass correction due to the contribution of the dark energy component has negligible effects on the overall number of structures. 
F. Pace, R. C. Batista, A. Del Popolo
astro-ph.CO