Approximation to Feynman amplitudes valid for small masses

A simple procedure is given for exploiting the smallness of the electron mass in approximating Feynman amplitudes. Using helicity conservation, the Dirac matrices are factored out leaving amplitudes no more complicated than those for spinless particles. For the case of bremsstrahlung the helicity structure is exhibited and the validity of helicity conservation is studied. To exhibit the simplicity and power of the method an amplitude for trident production is written down by inspection. It is shown to agree with the value obtained by Bjorken and Chen using projection operators and traces