2005ApJ...627...26A

The existence of a dark energy component has usually been invoked as the most plausible way to explain the recent observational results. However, it is also well known that effects arising from new physics (e.g., extra dimensions) can mimic the gravitational effects of a dark energy through a modification of the Friedmann equation. In this paper we investigate some observational consequences of a flat, matter-dominated, and accelerating/decelerating scenario in which this modification is given by H²=g(ρ_m,n,q), where g(ρ_m,n,q) is a new function of the energy density ρ_m, the so-called generalized Cardassian models. We mainly focus our attention on the constraints from the recent Cosmic All-Sky Survey (CLASS) lensing sample on the parameters n and q that fully characterize the models. We show that, for a large interval of the q-n parametric space, these models are in agreement with the current gravitational lenses data. The influence of these parameters on the acceleration redshift, i.e., the redshift at which the universe begins to accelerate, and on the age of the universe at high-redshift is also discussed.