Pion cloud and the Q(2) dependence of gamma*N <->Delta transition form factors

Recent experiments indicate that the behavior exhibited by the ratios E1+/M 1+ and S1+/M1+ of the gamma*N <-> Delta transition remains small and negati ve for Q(2) less than or equal to 4.0 GeV2. It implies that perturbative QC D is still not applicable at these momentum transfers. We show that these d ata can be explained in a dynamical model for electromagnetic production of pions, together with a simple scaling assumption for the bare gamma*N Delt a form factors. Within our model we find that the bare Delta is almost sphe rical and the electric E2 and Coulomb C2 quadrupole excitations of the phys ical Delta are nearly saturated by the pion cloud contribution in Q(2) less than or equal to 4.0 GeV2.