Direct electromagnetic excitation N→Δ(1232), final-state interactions, and the multipoles M1/sub +//sup() 3/2/ and E1/sub +//sup() 3/2/ of photopion production off nucleons in the range 160< or approx. =E/sub γ/< or approx. =800 MeV

In this paper one of the classics of particle theory in the resonance region is reexamined, namely the prediction of the amplitudes M1/sub +//sup() 3/2/ and E1/sub +//sup() 3/2/ of photopion production on nucleons around the resonance Δ(1232). The tool employed for this purpose is the final-state-interaction theory, and the principal aim of the study is to advocate for the appearance of two distinct dynamical mechanisms of photoexcitation in such an approach. Special emphasis is put then on the naturally emerging links between the present treatment and the isobaric approach and calculations based on the static quark model. It is argued that the dynamical meaning of the troublesome arbitrary constants (known to appear in most studies of the type presented in this paper) can be very convincingly explained when the resonances formed in the reaction [Δ(1232) in this specific case] are treated as ''elementary'' objects represented in the T-matrix elements by singularities of the Castillejo-Dalitz-Dyson kind. In the case discussed here, ''direct'' magnetic-dipole excitation N→Δ(1232) seems to emerge very clearly as an independent dynamical mechanism of photoproduction in the p33 state, parallel to the usual electromagnetic excitation of nonresonant πN systems, both followed by resonant pion-nucleon rescattering. It turns out that the magnitude of such direct γNΔ coupling is completely determined by the related strong interactions. The necessity of allowing for both specified mechanisms in this and other similar calculations is emphasized