  At a critical temperature QCD in the chiral limit undergoes a chiral
restoration phase transition. Above the phase transition the quark condensate
vanishes. The Banks-Casher relation connects the quark condensate to a density
of the near-zero modes of the Dirac operator. In the Nambu-Goldstone mode the
quasi-zero modes condense around zero, \lambda \rightarrow 0, and provide a
nonvanishing quark condensate. The chiral restoration phase transition implies
that above the critical temperature there is no any longer a condensation of
the Dirac modes around zero. If a U(1)_A symmetry is also restored and a gap
opens in the Dirac spectrum then the Euclidean correlation functions are
SU(2N_f) \supset SU(N_f)_L \times SU(N_f)_R \times U(1)_A- symmetric. This
symmetry implies that a free (deconfined) propagation of quarks in Minkowski
space-time that perturbatively interact with unconfined gluons is impossible.
This means that QCD above the critical temperature is not of a quark-gluon
plasma origin and has a more complicated structure.
