Exchange currents and the internal structure of the nucleon in quark models

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Abstract
The influence of internal nucleon structure on meson exchange currents has been investigated, in the framework of the nonrelativistic constituent quark model and the MIT bag model with massless quarks. In comparison with the conventional theory of exchange currents, one finds different strengths for the model-dependent higher-order terms and no ambiguity between pseudoscalar and pseudovector pion couplings. Furthermore, the retardation and excitation effects in the many-body system have to be treated consistently, in order to preserve gauge invariance. In this way one obtains 'damping' factors, which differ in structure from the phenomenological form factors.