Pairs in the light-front and covariance
  The electromagnetic current of bound systems in the light-front is constructed in the Breit-Frame, in the limit of momentum transfer $q^+=(q^0+q^3)$ vanishing. In this limit, the pair creation term survives and it is responsible for the covariance of the current. The pair creation term is computed for the $j^+$ current of a spin one composite particle in the Breit-frame. The rotational symmetry of $j^+$ is violated if the pair term is not considered. 
J. P. B. C de Melo (Instituto de Fisica da Universidade de Sao Paulo),   J.H.O. Sales, T. Frederico (Departamento de Fisica,...