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 .