Reactions A(\gamma, pi^+p) are considered to proceed through the formation of pion-proton pairs on delta constituents in nuclei. We develop the nonrelativistic operator for \Delta^{++}(\gamma, pi^+)p process in an arbitrary frame. The calculated cross section for C12(\gamma, \pi^+p) reaction is compared to the existing experimental data.
@article{arxiv.nucl-th/9808028,
title = {Photopion reactions on deltas preexisting in nuclei},
author = {A. Fix and I. Glavanakov and Yu. Krechetov},
journal= {arXiv preprint arXiv:nucl-th/9808028},
year = {2009}
}