Comment on fermion propagator in real-time quantum-field theory at   finite temperature and density
  Two forms are available for the fermion propagator at finite temperature and density. It is shown that, when one deals with a diquark-condensation-operator inserted Green function in hot and dense QCD, the standard form of the quark propagator does not work. On the other hand, another form of the quark propagator does work. 
A. Ni\'egawa