Virialization of cosmological structures in models with time varying   equation of state
  We study the virialization of the cosmic structures in the framework of flat cosmological models where the dark energy component plays an important role in the global dynamics of the universe. In particular, our analysis focuses on the study of the spherical matter perturbations, as the latter decouple from the background expansion and start to ``turn around'' and finally collapse. We generalize this procedure taking into account models with an equation of state which vary with time, and provide a complete formulation of the cluster virialization attempting to address the nonlinear regime of structure formation. In particular, assuming that clusters have collapsed prior to the epoch of $z_{\rm f}\simeq 1.4$, in which the most distant cluster has been found, we show that the behavior of the spherical collapse model depends on the functional form of the equation of state. 
Spyros Basilakos (Academy of Athens) & Nikos Voglis (Academy of   Athens)