Transition from quintessence to the phantom phase in the quintom model

Abstract

Assuming the Hubble parameter is a continuous and differentiable function of comoving time, we investigate necessary conditions for the quintessence to phantom phase transition in the quintom model. For power-law and exponential potential examples, we study the behavior of dynamical dark energy fields and the Hubble parameter near the transition time, and show that the phantom-divide line $\ensuremath{\omega}=\ensuremath{-}1$ is crossed in these models.