Observational Constraints on Dynamical Dark Energy with Pivoting Redshift

We investigate the generalized Chevallier-Polarski-Linder (CPL) parametrization, which contains the pivoting redshift zp as an extra free parameter, in order to examine whether the evolution of the dark energy equation of state can be better described by a different parametrization. We use various data combinations from cosmic microwave background (CMB), baryon acoustic oscillations (BAO), redshift space distortion (RSD), weak lensing (WL), joint light curve analysis (JLA), and cosmic chronometers (CC), and we include a Gaussian prior on the Hubble constant value, in order to extract the observational constraints on various quantities. For the case of free zp we find that for all data combinations it always remains unconstrained, and there is a degeneracy with the value of the dark energy equation of state w0p at zp. For the case where zp is fixed to specific values, and for the full data combination, we find that with increasing zp the mean value of w0p slowly moves into the phantom regime, however the cosmological constant is always allowed within 1 sigma confidence-level. In fact, the significant effect is that with increasing zp, the correlations between w0p and wa (the free parameter of the dark energy equation of state quantifying its evolution with redshift), change from negative to positive, with the case zp=0.35 corresponding to no correlation. The fact that the two parameters describing the dark energy equation of state are uncorrelated for zp=0.35 justifies why a non-zero pivoting redshift needs to be taken into account.