A model for the gamma N->pi pi N reaction

We have studied the gamma N --> pi pi N reaction using a model which includes N, Delta(1232), N*(1440) and N*(1520) intermediate baryonic states and the rho-meson as intermediate pi pi resonance. The model reproduces fairly well experimental cross sections below E(gamma) = 800 MeV and invariant-mass distributions even at higher energies. One of the interesting findings of the study is that the gamma N --> N*(1520) --> Delta pi process is very important and interferes strongly with the dominant Delta-Kroll-Ruderman term to produce the experimental peak of the cross section.