The Pauli exclusion principle from the optical theorem

Abstract: We analyze a specific class of forward-scattering diagrams with imaginary kinematics, which, via the optical theorem, describe processes involving two identical fermions occupying the same state. What initially seems to be a contradiction turns out to be a key element in how the Pauli exclusion principle manifests itself in scattering theory. The discussion is entirely basic and could easily fit into any quantum field theory textbook. To the best of our knowledge, however, this point has not been addressed in the literature, and we aim to fill this gap.