Combined constraints on Cardassian models from supernovae, cosmic microwavebackground and large scale structure observations

Abstract

We confront Cardassian models with recent observational data. These models can be viewedeither as purely phenomenological modifications of the Friedmann equation, or as arising fromcosmic fluids with non-standard properties. In the first case, we find that the models areconsistent with the data for a wide range of parameters but no significant preference over theΛ CDM model is found. In the latter case we find that the fact that the sound speed is non-zero inthese models makes them inconsistent with the galaxy power spectrum from the SloanDigital Sky Survey.