Covariance of light-front models: pair current

We compute the + component, i.e., j(+) = j(0) + j(3), of the electromagnetic current of a composite spin-one two-fermion system for vanishing momentum transfer component q(+) = q(0) + q(3). In particular, we extract the nonvanishing pair production amplitude on the light-front. It is a consequence of the longitudinal zero momentum mode, contributing to the Light-front current in the Breit-frame. The covariance of the current is violated, if such pair terms are not included in its matrix elements. We illustrate our discussion with some numerical examples. (C) 1999 Elsevier Science B.V. All rights reserved.