A Poincar\'e Covariant Current Operator for Deep Inelastic Structure   Functions and Deuteron Electromagnetic Properties
  In front-form dynamics the current operator can be constructed from auxiliary operators, defined in a Breit frame where initial and final three-momenta of the system are directed along the $z$ axis. Poincar\'e covariance constraints reduce for auxiliary operators to the ones imposed only by kinematical rotations around the $z$ axis.   Elastic and transition form factors can be extracted without any ambiguity and in the elastic case the continuity equation is automatically satisfied, once Poincar\'e, ${\cal P}$ and ${\cal T}$ covariance, together with hermiticity, are imposed. Applications to deep inelastic structure functions in an exactly solvable model and to the calculation of the deuteron electromagnetic form factors are presented. 
F.M. Lev (JINR-Dubna), E. Pace (Rome University), G. Salme`   (INFN-Rome)