ELECTROMAGNETIC AND WEAK CURRENT OPERATORS FOR INTERACTING SYSTEMS WITHIN THE FRONT-FORM DYNAMICS

Electromagnetic and weak current operators for interacting systems sho uld properly commute with the Poincare generators and satisfy hermitic ity. The electromagnetic current should also satisfy P and T covarianc e and the continuity equation, We show that in front-form dynamics the current operator can be constructed from auxiliary operators, defined in a Breit frame where the initial and final three-momenta of the sys tem are directed along the z-axis, Poincare covariance constraints red uce for auxiliary operators to those imposed only by kinematical rotat ions around the z-axis, while hermiticity requires suitable behaviour of the auxiliary operators under rotations by pi around the x- or y-ax es. Applications to deep inelastic structure functions and electromagn etic form factors are discussed. Elastic and transition form factors c an be extracted without any ambiguity and in the elastic case the cont inuity equation is automatically satisfied once Poincare, P and T cova riance, together with hermiticity, are imposed. (C) 1998 Elsevier Scie nce B.V.