Cosmological perturbations in an effective and genuinely phantom dark energy Universe

TL;DR

This paper analyzes cosmological perturbations in three phantom dark energy models that deviate from ΛCDM, exploring their future singularities and effects on matter distribution, constrained by observational growth rate data.

Contribution

It provides a detailed analysis of perturbations and matter power spectra in three phantom dark energy models with future singularities, constrained by observational data.

Findings

Different models induce distinct future singularities or abrupt events.

The matter power spectrum varies significantly among models.

Models are constrained by growth rate measurements, aligning with observations.

Abstract

We carry out an analysis of the cosmological perturbations in general relativity for three different models which are good candidates to describe the current acceleration of the Universe. These three set-ups are described classically by perfect fluids with a phantom nature and represent deviations from the most widely accepted $\Lambda$CDM model. In addition, each of the models under study induce different future singularities or abrupt events known as (i) Big Rip, (ii) Little Rip and (iii) Little Sibling of the Big Rip. Only the first one is regarded as a true singularity since it occurs at a finite cosmic time. For this reason, we refer to the others as abrupt events. With the aim to find possible footprints of this scenario in the Universe matter distribution, we not only obtain the evolution of the cosmological scalar perturbations but also calculate the matter power spectrum for each model. We have carried the perturbations in the absence of any anisotropic stress and within a phenomenological approach for the speed of sound. We constrain observationally these models using several measurements of the growth rate function, more precisely $f\sigma_8$, and compare our results with the observational ones.