Photon-photon scattering, pion polarizability, and chiral symmetry.

Recent attempts to detect the pion polarizability via analysis of γγ → ππ measurements are examined. The connection between calculations based on dispersion relations and on chiral perturbation theory is established by matching the low energy chiral amplitude with that given by a full dispersive treatment. Using the values for the polarizability required by chiral symmetry, predicted and experimental cross sections are shown to be in agreement.