Covariance of Light-Front Models: Pair Current

Abstract

We compute the "+" component 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.

Comments: 17 pages,include 5 figures (lfcxx.eps, lfczx.eps,lfczz.eps, lfcagg.eps and lfcaqq.eps), use latex,epsf,elsart, e-mail: pacheco@lpnp66.in2p3.fr, tobias@fis.ita.cta.br, naus1@fel.tno.nl, sauer@itp.uni-hannover.de, Accepted in Nucl.Phys. A (1999)