Chiral Symmetry Restoration and the sigma-meson
  The sigma-meson, which is at best a broad resonance in the vacuum, may suffer a substantial red-shift and appear as a soft and narrow collective mode at finite temperature and baryon densities. The physics behind this softening phenomena and its relation to the partial restoration of chiral symmetry are discussed. Possible experiments in laboratory to test the idea are also summarized. 
Tetsuo Hatsuda (Univ. of Tokyo) and Teiji Kunihiro (Yukawa Institute   for Theoretical Physics, Kyoto Univ.)