Cai, YF (reprint author), Chinese Acad Sci, Inst High Energy Phys, POB 918-4, Beijing 100049, Peoples R China.
We propose in this Letter a quintom model of dark energy with a single scalar field phi given by the Lagrangian L = -V(phi)(1 -alpha'/del(mu)phi del(mu) phi + beta'phi square phi)(1/2). In the limit of beta' -> 0 our model reduces to the effective low energy Lagrangian of tachyon considered in the literature. We study the cosmological evolution of this model, and show explicitly the behaviors of the equation of state crossing the cosmological constant boundary. (C) 2007 Elsevier B.V. All riahts reserved.