On the γNΔ coupling constants and on the ratio of quadrupole to magnetic dipole transitions

Abstract

It is recalled that the standard mechanism of on-shell rescattering in the (3, 3) channel off the Born terms of pion photoproduction, necessary to provide a unitary theory, substantially accounts for E₁₊ (3/2) multipole. Explicit consideration of dispersive effects allows the authors to estimate the bare gamma N Delta quadrupole coupling constants and to conclude that the Delta is essentially a bare deformed baryon, brought to a rather symmetric situation by the pion cloud. Existing literature is surveyed.