Constraining cosmic deceleration-acceleration transition with type Ia
  supernova, BAO/CMB and H(z) data
  We revisit the kink-like parametrization of the deceleration parameter q(z),
which considers a transition, at $z_t$, from cosmic deceleration to
acceleration. In this parametrization the initial, at $z \gg z_t$, value of the
q-parameter is $q_i$, its final, z=-1, value is $q_f$ and the duration of the
transition is parametrized by $\tau$. By assuming a flat space geometry we
obtain constraints on the free parameters of the model using recent data from
type Ia supernovae, BAO, CMB and the Hubble parameter H(z). The use of H(z)
data introduces an explicit dependence of the combined likelihood on the
present value of the Hubble parameter $H_0$, allowing us to explore the
influence of different priors when marginalizing over this parameter. We also
study the importance of the CMB information in the results by considering data
from WMAP7, WMAP9 and Planck. We show that the contours and best fit do not
depend much on the different CMB data used and that the considered new BAO data
is responsible for most of the improvement in the results. Assuming a flat
space geometry, $q_i=1/2$ and expressing the present value of the deceleration
parameter $q_0$ as a function of the other three free parameters, we obtain
$z_t=0.67^{+0.10}_{-0.08}$, $\tau=0.26^{+0.14}_{-0.10}$ and
$q_0=-0.48^{+0.11}_{-0.13}$, at 68\% of confidence level, with an uniform prior
over $H_0$. If in addition we fix $q_f=-1$, as in flat $\Lambda$CDM, DGP and
Chaplygin quartessence that are special models described by our
parametrization, we get $z_t=0.66^{+0.03}_{-0.04}$, $\tau=0.33^{+0.04}_{-0.04}$
and $q_0=-0.54^{+0.05}_{-0.07}$, in excellent agreement with flat $\Lambda$CDM
for which $\tau=1/3$. We also obtain for flat wCDM, another dark energy model
described by our parametrization, the constraint on the equation of state
parameter -1.22 < w < -0.78 at more than 99% confidence level.
