Avoiding the Big-Rip Jeopardy in a Quintom Dark Energy Model with Higher   Derivatives
  In the framework of a single scalar field quintom model with higher derivative, we construct in this paper a dark energy model of which the equation of state (EOS) $w$ crosses over the cosmological constant boundary. Interestingly during the evolution of the universe $w<-1$ happens just for a period of time with a distinguished feature that $w$ starts with a value above -1, transits into $w<-1$, then comes back to $w>-1$. This avoids the Big Rip jeopardy induced by $w<-1$. 
Xiao-fei Zhang and Taotao Qiu