Dynamical dark energy in models with evolution close to $\hat{I}›$CDM

Abstract

In this communication we address whether or not there is an equivalence between the kinematical and dynamical descriptions of the spatially flat $\hat{I}›$CDM model. We address this by investigating whether an almost $\hat{I}›$CDM expansion history ($j(z)\approx 1$) corresponds to an almost $\hat{I}›$CDM model ($w_{\mathrm{DE}}(z)\approx -1$) by considering two particular explicit examples. At least for the cases considered, this turns out not to be the case. Instead, what we find is that an almost $\hat{I}›$CDM cosmic evolution rather corresponds to an \emph{almost unified dark fluid model}. Considering that one never gets the exact condition $j(z)=1$ from any cosmographic data sets, this raises further questions on whether the $\hat{I}›$CDM model is the best candidate for the standard model of the evolution of the universe.

22 pages, 28 figures, 1 table. Some figures ammended. PRD accepted version