Soft modes associated with chiral transition in hot QCD

摘要

Fluctuations of the chiral order parameter in a hot and/or dense QCD plasma is discussed. If the transition is of second order or weak first order, the fluctuation gets large strength with small width and behaves as a bosonic quasi-particle in the plasma. This was first pointed out by Kunihiro and the present author on 1985 and was called ''soft mode''. General properties of the soft mode and its relation to the recent measurement of the hadronic screening length on the lattice are discussed in this report.