Conserved electromagnetic currents in a relativistic optical model
  A simple model of a relativistic optical model is constructed by reducing the three-body Bethe-Salpeter equation to an effective two-body optical model. A corresponding effective current is derived for use with the optical-model wave functions. It is shown that this current satisfies a Ward-Takahashi identity involving the optical potential which results in conserved current matrix elements. 
J. W. Van~Orden