Physics of the pion liquid

Excited hadronic matter in the temperature interval T=100-200 MeV is not an ideal pion gas, but rather a liquid, in which attractive interaction among particles plays an important role. The pion dispersion curve is in this case essentially modified by a kind of collective momentum-dependent potential, which becomes important as the "quasipion" comes to the boundary of the system. We show that these effects can provide an explanation for a number of recent experimental puzzles, in particular, for the observed copious production of soft pions and soft photons in high-energy hadronic reactions.