PION PROPERTIES IN A HOT PI-N-DELTA GAS

Based on a recent meson-exchange model for the vacuum pipi interaction we compute self-consistently the in-medium pipi scattering amplitude and pion self-energy in a hot piNDELTA gas. The contributions to the p ion self-energy are calculated from the pipi T-matrix as well as from p-wave interaction with nucleons and thermally abundant DELTA's. Resul ts are presented for two scenarios believed to be realized in the rela tivistic heavy-ion collisions performed at the GSI-SIS and the CERN-Sp S. Possible implications for the observed soft-pion enhancement at bot h SIS and SpS are indicated.