Bayesian Evidence for a cosmological constant using new high-redshift supernova data

We carry out a Bayesian model selection analysis of different dark energy parametrizations using the recent luminosity distance data of high redshift supernovae from Riess et al. 2007 and from the new ESSENCE Supernova Survey. Including complementary cosmological datasets, we found substantial evidence ( (E) 1) against a time-varying dark energy equation of state parameter, and against phantom dark energy models. We find a small preference for a standard cosmological constant over accelerating non-phantom models where w is constant, but allowed to vary in the range -1 to -0. 33.