Calculation of the nucleon magnetic moments by dispersion-theory methods

The magnetic moments of the neutron and proton are calculated within the framework of the S-matrix perturbation theory recently developed by Dashen and Frautschi. In the present context, this method expresses the magnetic moments in terms of a dispersion integral involving photopion production. Evaluation of this integral in terms of contributions from appropriate low-mass intermediate states yields results for the individual magnetic moments which are larger than the experimental values by about a factor of two. The calculation does, however, give an approximately correct value for the ratio of the isovector moment to the isoscalar moment, and a value for the isoscalar moment that agrees with the experimental value to within about a factor of two.