Photon-nucleus scattering and coherent π0 photoproduction in the Δ-hole model

The microscopic Δ-isobar-hole model is applied to the study of photon-nucleus scattering and coherent photoproduction. The role of π and rho exchange together with additional correlations in the Δ-hole interaction are investigated and compared with the situation in π-nucleus scattering. Because of the transverse photon coupling, the coherent forward propagation of pions, and therefore the strong elastic broadening observed in pion-nuclear scattering, is largely suppressed. The photonuclear processes prove to be sensitive to the medium corrections incorporated through the Δ-self-energies, which are responsible for a strong damping of the reaction cross section. Results are shown for 4He and 16O and compared to the available experimental data. (orig.)