Light-Front projection of spin-1 electromagnetic current and zero-modes
  The issue of the contribution of zero-modes to the light-front projection of the electromagnetic current of phenomenological models of vector particles vertices is addressed in the Drell-Yan frame. Our analytical model of the Bethe-Salpeter amplitude of a spin-1 fermion-antifermion composite state gives a physically motivated light-front wave function symmetric by the exchange of the fermion and antifermion, as in the $\rho$-meson case. We found that among the four independent matrix elements of the plus component in the light-front helicity basis only the $0\to 0$ one carries zero mode contributions. Our derivation generalizes to symmetric models, important for applications, the above conclusion found for a simplified non-symmetrical form of the spin-1 Bethe-Salpeter amplitude with photon-fermion point-like coupling and also for a smeared fermion-photon vertex model. 
J. P. B. C. de Melo (Laborat\'orio de Fisica Te\'orica e   Computa\c{c}\~ao Cient\'ifica - LFTC, Universidade Cruzeiro do Su...
hep-ph nucl-th