The state equation of Yang-Mills field dark energy models

In this paper, we study the possibility of building Yang-Mills (YM) field dark energy models with equation of state (EoS) crossing -1, and find that it cannot be realized by the single YM field models, no matter what kind of Lagrangian or initial condition. But the states of -1 < ω < 0 and ω < -1 all can be naturally got in this kind of model. The former is like a quintessence field, and the latter is like a phantom field. This states that one can build a model with two YM fields, one with the initial state of -1 < ω < 0, and the other with ω < -1. We give an example model of this kind, and find that its EoS is larger than -1 in the past and less than -1 at the present time. We also find that this change must be from ω > -1 to <-1, and it will go to the critical state of ω = -1 with the expansion of the universe, which character is the same as the single YM field models, and the big rip is naturally avoided