We review the γγ->ππ data and conclude that the experiments should be redone and that an increase of 10² in the rates is expected at DAPHNE. The status of the data on the pion polarizability? _? is also considered briefly. We compare the data with the prediction of chiral perturbation theory. In the case of neutral pions, by including the exchange of vector resonances in the t-channel, we prove that the O (p⁶) contribution cannot be neglected and gives (20 -30) % of the cross-section at (460 - 490) meV.
D et al. (Wed,) studied this question.