Dark energy versus

We explore the possibility of discriminating dark energy models from the study of the growth of matter perturbations. For the sake of simplicity, instead of dealing with a great number of models, we have chosen a simple model of dark energy ($p_x=\omega_0\rho_{x}^{\gamma}$, with $\omega_00$; px, and $\rho_x$ being pressure and energy density), which is able to reproduce a great number of different behaviours. A combination of WMAP data with other results have been used to estimate model parameters. The study has been made for collapsing shells in spherical clusters virialized at redshifts $z=1$, 0.1 and 0.025 with line-of-sight velocity dispersion $\sigma_{\rm los}= 750$ and $1000~\rm km\, s^{-1}$. According to shell velocities, our dark energy models are clearly differentiated from the $\Omega_{\rm m0}=1$ model (the greater the $\sigma_{\rm los}$ is, the more differentiated the models are). However, the differences among dark energy models are not so large. From our results, the nearest clusters with large $\sigma_{\rm los}$ are the idoneous ones to discriminate models. In fact, we think that from observations of caustics in nearby spherical clusters, it would be possible to make an estimation of $\Omega_{\rm m0}$.