Dark Energy and QCD Ghost
  It has been suggested that the dark energy that explains the observed
accelerating expansion of the universe may arise due to the contribution to the
vacuum energy of the QCD ghost in a time-dependent background. The argument
uses a four-dimensional simplified model. In this paper, we put the discussion
in more realistic model keeping all components of the QCD vector ghost and show
that indeed QCD ghost produces dark energy proportional to the Hubble parameter
$H\Lambda_{QCD}^3$ ($\Lambda_{QCD}$ is the QCD mass scale) which has the right
magnitude $\sim (3\times 10^{-3}$ eV)$^4$.
