Can observational growth rate data favour the clustering dark energy models?

TL;DR

This paper investigates how clustering dark energy models influence the cosmic growth index and finds they fit observational growth data better than the standard Lambda-CDM model, with significant redshift variations.

Contribution

It introduces a detailed analysis of the growth index evolution in clustering dark energy scenarios and compares their fit to observational data against Lambda-CDM.

Findings

CDE models fit growth rate data better than Lambda-CDM.

The growth index varies significantly with redshift in CDE models.

The growth index differs from Lambda-CDM's value, especially at recent times.

Abstract

Under the commonly used assumption that clumped objects can be well described by a spherical top-hat matter density profile, we investigate the evolution of the cosmic growth index in clustering dark energy (CDE) scenarios on sub-horizon scales. We show that the evolution of the growth index $\gamma(z)$ strongly depends on the equation-of-state (EoS) parameter and on the clustering properties of the dark energy (DE) component. Performing a $\chi^2$ analysis, we show that CDE models have a better fit to observational growth rate data points with respect to the concordance $\Lambda$CDM model. We finally determine $\gamma(z)$ using an exponential parametrization and demonstrate that the growth index in CDE models presents large variations with cosmic redshift. In particular it is smaller (larger) than the theoretical value for the $\Lambda$CDM model, $\gamma_{\Lambda}\simeq0.55$, in the recent past (at the present time).