The case for dynamical dark energy revisited

We investigate the behaviour of dark energy using the recently released supernova data of Riess et al 2004 and a model independent parametrization for dark energy (DE). We find that, if no priors are imposed on Ω 0m and h , DE which evolves with time provides a better fit to the SNe data than ΛCDM. This is also true if we include results from the WMAP CMB data. From a joint analysis of SNe + CMB, the best fit DE model has w 0 ≲ −1 at the present epoch and the transition from deceleration to acceleration occurs at z T = 0.39 ± 0.03. However, DE evolution becomes weaker if the ΛCDM based CMB results Ω 0m = 0.27 ± 0.04, h = 0.71 ± 0.06 are incorporated in the analysis. In this case, z T = 0.57 ± 0.07. Our results also show that the extent of DE evolution is sensitive to the manner in which the supernova data is sampled.