Four-quark condensates and chiral symmetry restoration in a resonance   gas model
  As an alternative to the two-quark condensate we propose a specific four-quark condensate as an order parameter of chiral symmetry restoration. We show that this four-quark condensate is closer connected to observable quantities. Within a resonance gas model we calculate the in-medium changes of two- and four-quark condensate as functions of temperature and baryo-chemical potential. In this way we estimate the line of chiral symmetry restoration in the temperature-potential plane and also as a function of energy and baryon density. It turns out that the line determined from the vanishing of the four-quark condensate is extremely constant as a function of the energy density. 
Stefan Leupold (Giessen Univ.)