The growth index of matter perturbations using the clustering of dark energy

Abstract

We have put forward a new unified framework which provides a consistent and rather complete account of the growth index of matter perturbations in the regime where the dark energy is allowed to have clustering. In particular, we find that the growth index is not only affected by the cosmological parameters but rather it depends on the choice of the considered dark energy (homogeneous or clustered). Using the {\em Planck} priors and performing a standard ${\chi }^2$-minimization between theoretical expectations and growth data, we statistically quantify the ability of the growth index to represent the observations. Finally, based on the growth index analysis we find that the growth data favour the clustered dark energy scenario.

Comments: 6 pages, 2 figures Accepted for publication in MNRAS (minor corrections: a new title, some new references and the Planck2015 priors are included)