A quantitative criteria for the coincidence problem
  The cosmic coincidence problem is a serious challenge to dark energy model.
We suggest a quantitative criteria for judging the severity of the coincidence
problem. Applying this criteria to three different interacting models,
including the interacting quintessence, interacting phantom, and interacting
Chaplygin gas models, we find that the interacting Chaplygin gas model has a
better chance to solve the coincidence problem. Quantitatively, we find that
the coincidence index C for the interacting Chaplygin gas model is smaller than
that for the interacting quintessence and phantom models by six orders of
magnitude.
