The Coincidence Problem in YM Field Dark Energy Models

The coincidence problem is one of the most troubles for the dark energy models, which has been gracefully answered in the quintessence and k-essence models with tracking solutions. In this letter, we study this problem in the Yang-Mills (YM) field dark energy models, and find that it is also naturally avoided in this kind of models: no matter what kind of initial condition the YM fields have, at present, they get the similar state. We also constrain the present equation-of-state (EoS) of the YM field by the observation result of the Big Bang nucleosynthesis (BBN), and find $\omega_{y_0}<-0.94$