Quantum Yang-Mills Condensate Dark Energy Models
  We review the quantum Yang-Mills condensate (YMC) dark energy models. As the
effective Yang-Mills Lagrangian is completely determined by the quantum field
theory, there is no adjustable parameter in the model except the energy scale.
In this model, the equation-of-state (EOS) of the YMC dark energy, $w_y > -1$
and $w_y < -1$, can both be naturally realized. By studying the evolution of
various components in the model, we find that, in the early stage of the
universe, dark energy tracked the evolution of the radiation, i.e. $w_y \to
1/3$. However, in the late stage, $w_y$ naturally runs to the critical state
with $w_y = -1$, and the universe transits from matter-dominated into dark
energy dominated stage only at recently $z \sim 0.3$. These characters are
independent of the choice of the initial condition, and the cosmic coincidence
problem is avoided in the models. We also find that, if the possible
interaction between YMC and dust matter is considered, the late time attractor
solution may exist. In this case, the EOS of YMC must evolve from $w_y>0$ into
$w_y < -1$, which is slightly suggested by the observations. At the same time,
the total EOS in the attractor solution is $w_{tot} = -1$, the universe being
the de Sitter expansion in the late stage, and the cosmic big rip is naturally
avoided. These features are all independent of the interacting forms.
