We calculate the pole shift of the pion up to second order in the density, considering the low-temperature expansion of the axial two-point function. To this order both absorptive and dispersive properties of pions are completely determined by two- and three-particle S-matrix elements. In particular, we show how the pole shift can be expressed in terms of these scattering amplitudes and discuss the size of corrections from three-particle collisions.

• Received 11 December 1992

DOI:https://doi.org/10.1103/PhysRevD.47.5138