Transition Redshift: New constraints from parametric and nonparametric
  methods
  In this paper, we use the Cosmokinematics approach to study the accelerated
expansion of the Universe. This is a model independent approach and depends
only on the assumption that the Universe is homogeneous and isotropic and is
described by the FRW metric. We parametrize the deceleration parameter, $q(z)$,
to constrain the transition redshift ($z_t$) at which the expansion of the
Universe goes from a decelerating to an accelerating phase. We use three
different parametrizations of $q(z)$ namely,
$q_\I(z)=q_{\textnormal{\tiny\textsc{1}}}+q_{\textnormal{\tiny\textsc{2}}}z$,
$q_\II (z) = q_\3 + q_\4 \ln (1 + z)$ and
$q_\III(z)=\frac{1}{2}+\frac{q_{\textnormal{\tiny\textsc{5}}}}{(1+z)^2}$. A
joint analysis of the age of galaxies, strong lensing and supernovae Ia data
indicates that the transition redshift is less than unity i.e. $z_t<1$. We also
use a nonparametric approach (LOESS+SIMEX) to constrain $z_t$. This too gives
$z_t<1$ which is consistent with the value obtained by the parametric approach.
