2-loop quantum Yang-Mills condensate as dark energy

In seeking a model solving the coincidence problem, the effective Yang-Mills condensate (YMC) is an alternative candidate for dark energy. A study is made for the model up to the 2-loop order of quantum corrections. It is found that, like in the 1-loop model, for generic initial conditions during the radiation era, there is always a desired tracking solution, yielding the current status Omega(Lambda) similar or equal to 0.73 and Omega(m) similar or equal to 0.27. As the time t -> infinity the dynamics is a stable attractor. Thus the model naturally solves the coincidence problem of dark energy. Moreover, if YMC decays into matter, its equation of state (EoS) crosses -1 and takes w similar to -1.1, as indicated by the recent observations. (c) 2007 Elsevier B.V. All rights reserved.