Exponential Cardassian Universe
  The expectation of explaining cosmological observations without requiring new energy sources is forsooth worthy of investigation. In this letter, a new kind of Cardassian models, called exponential Cardassian models, for the late-time universe are investigated in the context of the spatially flat FRW universe scenario. We fit the exponential Cardassian models to current type Ia supernovae data and find they are consistent with the observations. Furthermore, we point out that the equation-of-state parameter for the effective dark fluid component in exponential Cardassian models can naturally cross the cosmological constant divide $w=-1$ that observations favor mildly without introducing exotic material that destroy the weak energy condition. 
Dao-jun Liu, Chang-bo Sun, Xin-zhou Li