Light-front projection of spin-1 electromagnetic current and zero-modes

Abstract

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 ρ-meson case. We found that among the four independent matrix elements of the plus component in the light-front helicity basis only the 0→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.