A note on the gamma gamma->pi(0)pi(0) reaction in the 1/N expansion of chi PT

Abstract

In this work we present the results of a complete calculation of the gamma gamma --> pi(0) pi(0) amplitude to leading order in the large N approximation (N being the number of Goldstone bosons) up to order m(pi)(2)/F-2, The amplitude turns to be proportional a to that of pi(+)pi(-) --> pi(0) pi(0). In spite of the fact that this factorization property cannot hold in general (as it was recently pointed our by Morgan and Penington), it appears here since in the large N limit only the I = J = 0 channel contributes to the gamma gamma --> pi(0) pi(0) reaction. Moreover it seems to be a reasonable approximation in this case since it is possible to reproduce, as a prediction, the experimental data starting from a one-parameter fit of the pi pi scattering data.