Observational constraints on dynamical dark energy with pivoting
  redshift
  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.
