We investigate the generalized Chevallier-Polarski-Linder ( CPL ) parametrization , which contains the pivoting redshift z _ { p } as an extra free parameter .
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 ) , 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 z _ { p } we find that for all data combinations it always remains unconstrained , and there is a degeneracy with the current value of the dark energy equation of state w _ { 0 } .
For the case where z _ { p } is fixed to specific values , and for the full data combination , we find that with increasing z _ { p } the mean value of w _ { 0 } slowly moves into the phantom regime , however the cosmological constant is always allowed within 1 \sigma confidence-level .
However , the significant effect is that with increasing z _ { p } the correlations between w _ { 0 } and w _ { a } change from negative to positive , with the case z _ { p } = 0.35 corresponding to no correlation .
This feature indeed justifies why a non-zero pivoting redshift should be taken into account .