Theories of meson-exchange currents

Abstract

Different theories of meson-exchange currents are discussed. It is shown that what we call meson-exchange currents is clearly a matter of definition and is strongly related to the corresponding nucleon-nucleon potentials. The exchange current operators are discussed to the order of 1/M³ (M nucleon mass). Special attention has been paid to the electric dipole operator in the long wavelength limit showing the existence of correction terms to the conventional Siegert operator. The generalization of the Bethe-Levinger sum-rule is given. A quantitative discussion of meson-exchange currents is given for some electromagnetic interactions processes with light nuclei.