Double-pion electro- and photoproduction viewed from mass-dispersion and current-algebra theory

Abstract

We discuss the electro- and photoproduction of two pions off nucleons within the frame work of current algebra and the new mass-dispersion relations developed by De Alfaro, Fubini, Furlan, and Rossetti. The results obtained by a one-pion reduction are compared with those obtained in earlier calculations, and the importance of dispersion corrections, not obtained thus far are pointed out. Also noted is that the proposal, suggested by some authors to obtain indirectly by means of the electroproduction process the t-dependence of the axial vector form factor, appears rather dim. Next both pions are reduced out. In the case in which the pions form an iso-singlet important dispersive corrections could be present due to a low-lying σ-meson (if it exists) and the N 11+(1400), Roper resonance, intermediate states. Dispersive corrections which effect the amplitudes in which the pions form an iso-quintet are also discussed. The dipion production amplitudes are given for the kinematical configuration in which the pions are at rest in the Breit frame of the nucleons.