HOT AND DENSE PION GAS WITH FINITE CHEMICAL-POTENTIAL

A dense and hot pion system with a dynamically fixed particle number a nd an arbitrary charge is investigated with respect to ultra-relativis tic heavy-ion collisions. The Lagrangian for describing such a system is derived from Weinberg's chiral Lagrangian for the pion-pion interac tion. Pion polarization operators are calculated within the Hartree ap proximation. The pion spectrum in the isospin symmetrical gas is prese nted. The effective in-medium pion gap depends sensitively on the dens ity and the temperature, and it is found to exceed both the free pion mass and the corresponding value for the pion gas in chemical equilibr ium. The possibility of a Bose-Einstein condensation is also discussed .