After a brief review of the challenges of calculating scattering amplitudes for electric and magnetic charges as well as a discussion of Wigner’s “little group” and the helicity amplitude approach, I will discuss how S-matrix calculations can be extended to include magnetic charges. The answer involves an extension of the concept of helicity to a "pairwise helicity" involving two particles. With this in hand, the notorious Rubakov-Callan processes are quite quite simple.

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