Cosmological perturbations in an effective and genuinely phantom dark energy Universe

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 ΛCDM 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 σ8, and compare our results with the observational ones.

Cosmological constraints of phantom dark energy models

“…This result implies that f σ 8 is larger for phantom DE models as compared with ΛCDM. This result is in agreement with [55,83].…”

“…We have as well computed the evolution of the Bardeen gravitational potential. We have confirmed that indeed in phantom DE models, it is expected that the Bardeen gravitational potential will flip its sign in the future [55,83]. This is in accordance with the fact that all the structures will be destroyed in phantom DE models.…”

“…All matter perturbations are connected through the quantities Ψ and Ψ x . The initial conditions will be fixed as done in [55]; i.e. (i) we will assume adiabatic conditions for densities contrast and velocities (cf Eqs.…”

“…To avoid such instabilities, in [53,54] the authors suggest a decomposition of the pressure in its adiabatic and non adiabatic contributions. In [55] this method is applied and initial conditions are imposed at the radiation dominated epoch. On the other hand, in [56] the authors analyse the effects of non adiabaticity on the growth rate for several DE models and compute the observable f σ 8 .…”

Classical and quantum fate of the little sibling of the big rip in f(R) cosmology

“…It is characterized by the divergence of the observable Universe and the expansion rate, keeping the derivative of this rate a finite value [14]. For observational constraints on this type of models see references [15][16][17]. Nonetheless, the common belief is that these singularities will be cured or avoided in the quantum realm, as it is assumed to happen with the big bang (see [11,[18][19][20] for reviews on the topic).…”