Supernova constraints on alternative models to dark energy

The recent observations of Type Ia supernovae suggest that the Universe is accelerating now and decelerated in the recent past. This may be the evidence of the breakdown of the standard Friedmann equation. The Friedmann equation H2∼ρ is modified to be a general form H2=g(ρ). Three models with particular form of g(ρ) are considered in detail. The supernova data published by Tonry et al., Daly & Djorgovski and Knop et al. are used to analyse the models. After the best-fitting parameters are obtained, we then find out the transition redshift zT when the Universe switched from the deceleration phase to the acceleration phase.