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 Omega(0m) and h, DE which evolves with time provides a better fit to the SNe data than LambdaCDM. 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) less than or similar to -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 LambdaCDM based CMB results Omega(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.