We use type Ia supernovae ( SN Ia ) data in combination with recent baryonic acoustic oscillations ( BAO ) and cosmic microwave background ( CMB ) observations to constrain a kink-like parametrization of the deceleration parameter ( q ) .
This q -parametrization can be written in terms of the initial ( q _ { i } ) and present ( q _ { 0 } ) values of the deceleration parameter , the redshift of the cosmic transition from deceleration to acceleration ( z _ { t } ) and the redshift width of such transition ( \tau ) .
By assuming a flat space geometry , q _ { i } = 1 / 2 and adopting a likelihood approach to deal with the SN Ia data we obtain , at the 68 \% confidence level ( C.L .
) , that : z _ { t } = 0.56 ^ { +0.13 } _ { -0.10 } , \tau = 0.47 ^ { +0.16 } _ { -0.20 } and q _ { 0 } = -0.31 ^ { +0.11 } _ { -0.11 } when we combine BAO/CMB observations with SN Ia data processed with the MLCS2k2 light-curve fitter .
When in this combination we use the SALT2 fitter we get instead , at the same C.L .
: z _ { t } = 0.64 ^ { +0.13 } _ { -0.07 } , \tau = 0.36 ^ { +0.11 } _ { -0.17 } and q _ { 0 } = -0.53 ^ { +0.17 } _ { -0.13 } .
Our results indicate , with a quite general and model independent approach , that MLCS2k2 favors Dvali-Gabadadze-Porrati-like cosmological models , while SALT2 favors \Lambda CDM-like ones .
Progress in determining the transition redshift and/or the present value of the deceleration parameter depends crucially on solving the issue of the difference obtained when using these two light-curve fitters .