Probing a Steep EoS for Dark Energy with latest observations

Abstract

We present a parametrization for the Dark Energy Equation of State "EoS" which has a rich structure, performing a transition at pivotal redshift $z_T$ between the present day value $w_0$ to an early time $w_i=w_a+w_0\equiv w(z\gg 0)$ with a steepness given in terms of $q$ parameter. The proposed parametrization is $w=w_0+w_a(z/z_T{)}^q/(1+(z/z_T){)}^q$, with $w_0$, $w_i$, $q$ and $z_T$ constant parameters. It reduces to the widely used EoS $w=w_0+w_a(1-a)$ for $z_T=q=1$. This transition is motivated by scalar field dynamics such as for example quintessence models. We study if a late time transition is favored by BAO measurements combined with local determination of $H_0$ and information from the CMB. According to our results, an EoS with a present value of $w_0=-0.92$ and a high redshift value $w_i=-0.99$, featuring a transition at $z_T=0.28$ with an exponent $q=9.97$ was favored by data coming from local dynamics of the Universe (BAO combined with $H_0$ determination). We find that a dynamical DE model allows to simultaneously fit $H_0$ from local determinations and Planck CMB measurements, alleviating the tension obtained in a $\Lambda$CDM model. Additionally to this analysis we solved numerically the evolution of matter over-densities in the presence of dark energy both at background level and when its perturbations were considered. We show that the presence of a steep transition in the DE EoS gets imprinted into the evolution of matter overdensities and that the addition of an effective sound speed term does not erase such feature.

arXiv comment10 pages, 12 figures and 3 tables. This article draws heavily from arXiv:1604.01442

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