Quantum liquids resulted from the models with four-fermion interaction

A (nearly) perfect liquid discovered in the experements with ultrarelativistic heavy ion collisions is investigated by studying the quark ensembles with four-fermion interection as a fundamental theoretical approach. The comparative analysis of several quantum liquid models is performed and it results in the conclusion that the presence of gas---liquid phase transition is their characteristic feature. The problem of instability of the quark droplets of small quark number is discussed and argued to be rooted in the chiral soliton formation. An existence of mixed phase of the vacuum and baryon matter is proposed as a possible reason of the latter stability.