Probing the course of cosmic expansion with a combination of
  observational data
  We study the cosmic expansion history by reconstructing the deceleration
parameter $q(z)$ from the SDSS-II type Ia supernova sample (SNIa) with two
different light curve fits (MLCS2k2 and SALT-II), the baryon acoustic
oscillation (BAO) distance ratio, the cosmic microwave background (CMB) shift
parameter, and the lookback time-redshift (LT) from the age of old passive
galaxies. Three parametrization forms for the equation of state of dark energy
(CPL, JBP, and UIS) are considered. Our results show that, for the CPL and the
UIS forms, MLCS2k2 SDSS-II SNIa+BAO+CMB and MLCS2k2 SDSS-II SNIa+BAO+CMB+LT
favor a currently slowing-down cosmic acceleration, but this does not occur for
all other cases, where an increasing cosmic acceleration is still favored.
Thus, the reconstructed evolutionary behaviors of dark energy and the course of
the cosmic acceleration are highly dependent both on the light curve fitting
method for the SNIa and the parametrization form for the equation of state of
dark energy.
