Investigation of the nucleon-resonance structure in exclusive reactions ofpion-pair production on a proton by real and virtual photons

A phenomenological approach to describing the photo- and electroproduction of pion pairs on a proton has been discussed. Basic quasi-two-particle reac tions, gamma(r,v)p --> pi(-)Delta(++) and gamma(r,v)p --> rho p, have been considered. Relevant calculations have been performed with allowance for al l known nucleon resonance states with masses less than 2 GeV. A strong pi p Delta form factor have been introduced to compute the contribution of nonr esonance mechanisms. The effects of absorption in the initial and final sta tes have been analyzed. The results of the present calculations have been c ompared with available experimental data.