  Manifestly Lorentz covariant Feynman rules are given in terms of a "scalar"
field for each helicity, dramatically simplifying the calculation of amplitudes
with massless particles. The spinor helicity formalism is properly identified
as a null complex spacelike (not lightlike) gauge, where two massless external
momenta define the reference frame. Usually this gauge is applied only to
external line factors; we extend this method to vertices and propagators by
modifying the action itself using lightcone methods.
