The role of the pion cloud in electroproduction of the Delta (1232)

We calculate the ratios E2/M1 and C2/M1 of the multipole amplitudes for electroproduction of the Delta(1232) in the range of photon virtuality 0 < -K-2 < 1 GeV2 in a chiral chromodielectric model and a linear sigma-model. We find that relatively large experimental values can be explained in terms of the pion contribution alone; the contribution arising from d-state quark admixture remains below 10%. We describe the pion cloud as a coherent state and use spin and isospin projection to obtain the physical nucleon and the Delta. The A(1/2) and A(3/2) amplitudes are reasonably well reproduced in the sigma-model; in the chromodielectric model, however, they are a factor of two too small.