Thermal properties of a hot pion gas beyond the quasiparticle approximation

Within the Matsubara formalism we derive expressions for the pion selfenergy and the two-pion propagator in a hot pion gas. These quantities are used to selfconsistently calculate the in-medium ππ amplitude beyond the quasiparticle approximation (QPA). The results are shown to differ significantly from QPA-based calculations. We also examine the impact of chiral constraints on the ππ interaction in a chirally improved version of the Jülich ππ model.