A new method for helicity calculations

We propose a new helicity formalism based on the insertion in spinor lines of a complete set of states built up with appropriate unphysical spinors, which are eigenstates of , where p is the momentum flowing in a fermion propagator. The corresponding eigenvalues can be real (p2 > 0) or imaginary (p2 < 0). The method is developed both for massless and massive fermions for which it turns out to be particularly fast. All relevant formulae are given.