Pion-pion cross section in a dense and hot pionic gas

We examine the in-medium scattering cross section in a dense and hot pionic gas. We show that the increase of the scattering rate associated with the Bose occupancy factors is largely compensated by a drop in the cross section, when medium effects on the pionic cross section are consistently taken into account. Implications for calculating the pion spectrum at low transverse momentum, in ultrarelativistic heavy ion collisions, are discussed. (orig.)