Instanton effects in the quark plasma

In superdense matter it is generally believed that hadrons will lose their individuality and, instead, a plasma of quarks will emerge. Such a plasma would be described by the dynamics of QCD, constrained to account for the finite quark density which characterizes the system. The author discusses non-perturbative effects caused by instantons. Before discussing the more technically involved QCD problem, he treats the Abelian-Higgs model in two dimensions in the presence of massless fermions. The general physical picture which will emerge in this simplified model is probably not too distant from the one in QCD, however, the latter is far from being well understood. After a brief account of the path integral formalism the Higgs model is discussed and then goes on to describe what has been accomplished in QCD. (4 refs)