QUARK CONFINEMENT IN A CONSTITUENT QUACK MODEL

On the level of an effective quark theory, we define confinement by th e absence of quark-antiquark thresholds in correlation functions. We t hen propose a confining Nambu-Jona-Lasinio-type model. We study the mo del's phase structure as well as its behavior under extreme conditions , i.e. high temperature and/or high density.