Nuclear-exchange-current operator and nucleon-nucleon interaction

Isovector exchange currents are constructed in a gauge-invariant way from a nucleon-nucleon potential by using an approach applicable to different components of the potential. The method is based on an extension of the use of minimal substitution to the isospin-dependent potential and the continuity equation. A one-pion-exchange potential is used as an example and the results are found to be in agreement with those obtained using field theory. One-pion-exchange effects in the electric dipole moment of a two-nucleon system is discussed and a modification of the Siegert theorem is found. (orig.)