Top-Hat Spherical Collapse with Clustering Dark Energy. I. Radius
  Evolution and Critical Contrast Density
  Understanding the influence of dark energy on the formation of structures is
currently a major challenge in Cosmology, since it can distinguish otherwise
degenerated viable models. In this work we consider the Top-Hat
Spherical-Collapse (SC) model with dark energy, which can partially (or
totally) cluster, according to a free parameter $\gamma$. The {\it lack of}
energy conservation has to be taken into account accordingly, as we will show.
We determine characteristic quantities for the SC model, such as the critical
contrast density and radius evolution, with particular emphasis on their
dependence on the clustering parameter $\gamma$.
