Electromagnetic and weak current operators for interacting systems within the front-form dynamics

Electromagnetic and weak current operators for interacting systems should properly commute with the Poincare generators and satisfy hermiticity. The electromagnetic current should also satisfy P and T covariance 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 system are directed along the z-axis. Poincare covariance constraints reduce for auxiliary operators to those imposed only by kinematical rotations around the z-axis, while hermiticity requires suitable behaviour of the auxiliary operators under rotations by π around the x- or y-axes. Applications to deep inelastic structure functions and electromagnetic form factors are discussed. Elastic and transition form factors can be extracted without any ambiguity and in the elastic case the continuity equation is automatically satisfied once Poincare, P and T covariance, together with hermiticity, are imposed.