Reaction mechanisms in two-body photodisintegration and electrodisintegration of 4He

One- and two-body mechanisms alone cannot reproduce the experimental values of the 4He(γ,p)T reaction cross-section in the Δ region. Meson double scattering is shown to account for the major part of these discrepancies. All together these mechanisms account for the near equality of the cross-section of the 4He(γ,p)T and 4He(γ,n)3He channels. Consequences on the 4He(e,eprimep)T and the 4He(e,eprimen)3He channels are investigated, with a special emphasis on the determination of the 4He wave function and the study of the behavior of bound nucleon form factors. The sensitivity of spin observables, to various interaction effects, is investigated. ((orig.))