Confronting Dark Energy Models with Astrophysical Data

We discuss fits of cosmological dark energy models to the available data on high-redshift supernovae and baryon oscillations. We consider a conventional model with Cold Dark Matter and a cosmological constant (LambdaCDM), a model invoking super-horizon perturbations (SHDM) and models based on Liouville strings in which dark energy is provided by a rolling dilaton field (Q-cosmology). The two main high-redshift supernova data sets give compatible constraints on these models. We find that LambdaCDM fits very well the combined supernova data sets. These are also compatible with the data on baryon acoustic oscillations, yielding together a determination of the matter density in the LambdaCDM (assuming a flat Universe) which is comparable with that provided by the three-year WMAP data. The supernova data are also fit quite well by the super-horizon model. A naive version of the Q-cosmology model does not fit the supernova data, but a simple parametrization of the full version of the model that includes off-shell effects fits the data very well. A detailed discussion of the model-dependent off-shell corrections to the Q-cosmology model is given in the Appendix.