Applications of the unitary transformation method to the theory of photomeson processes on nuclei

The unitary transformation method is used in the description of single pion photoproduction off nuclei to construct effective operators acting in the nucleon sector of the Fock space of hadronic states. The problem of ensuring the gauge independence of calculations in the sector is considered. In this connection, an extension of the Siegert theorem is proposed to employ. Attention is paid to the off-energy-shell effects in the amplitude of pion photo(electro)production on bound nucleon. The one-body contribution to the amplitude has been calculated with taking into account the structure of hadrons participating in the reaction. 47 refs.; 6 figs