In this paper , we propose a new phenomenological two parameter parameterization of q ( z ) to constrain barotropic dark energy models by considering a spatially flat Universe , neglecting the radiation component , and reconstructing the effective equation of state ( EoS ) .
This two free-parameter EoS reconstruction shows a non-monotonic behavior , pointing to a more general fitting for the scalar field models , like thawing and freezing models .
We constrain the q ( z ) free parameters using the observational data of the Hubble parameter obtained from cosmic chronometers , the joint-light-analysis ( JLA ) Type Ia Supernovae ( SNIa ) sample , the Pantheon ( SNIa ) sample , and a joint analysis from these data .
We obtain , for the joint analysis with the Pantheon ( SNIa ) sample a value of q ( z ) today , q _ { 0 } = -0.51 \substack { +0.09 \ -0.10 } , and a transition redshift , z _ { t } = 0.65 \substack { +0.19 \ -0.17 } ( when the Universe change from an decelerated phase to an accelerated one ) .
The effective EoS reconstruction and the \omega ^ { \prime } - \omega plane analysis point towards a transition over the phantom divide , i.e . \omega = -1 , which is consistent with a non parametric EoS reconstruction reported by other authors .