Constraints on a Cardassian model from SNIa data - revisited

Abstract

We discuss some observational constraints resulting only from SNIa observations, imposed on the behavior of the original flat Cardassian model, and its extension with the curvature term included. We test the models using the Perlmutter SN Ia data as well as the new Knop and Tonry samples. We estimate the Cardassian model parameters using the best-fitting procedure and the likelihood method. In the fitting procedure we use the density variables for matter, Cardassian fluid and curvature, and include the errors in redshift measurements. For the Perlmutter sample in the non-flat Cardassian model we obtain the high or normal matter density universe ($Ω_{m,0} \ge 0.3$), while for the flat Cardassian model we have the high density universe. For sample A in the high density universe we also find the negative values of estimates of $n$ which can be interpreted as the phantom fluid effect. For the likelihood method we get that a nearly flat universe is preferred. We show that, if we assume that the matter density is 0.3, then $n \approx 0$ in the flat Cardassian model, which corresponds to the Perlmutter model with the cosmological constant. Testing with the Knop and Tonry SN Ia samples show no significant differences.