Monopole-Fermion Scattering and the Solution to the Semiton/Unitarity Puzzle

We study Polchinski’s “fermion-rotor system” as an accurate description of charged Weyl fermions scattering on a magnetic monopole core in the limit of zero gauge coupling. Traditionally it was thought such scattering could lead to fractional particle numbers (“semitons”). By direct calculations we show those semitonic processes are in fact free propagation, facilitated by composite fermion-rotor operators interpolating the “forbidden” states, effectively “recovering” both ingoing and outgoing states in every lowest partial wave. Non-semitonic Callan-Rubakov processes are unchanged.