Title: Monopole-Fermion Scattering and the Solution to the Semiton/Unitarity Puzzle
For over 40 years, scattering of charged fermions off of a magnetic monopole has puzzled theorists as it seemed in some cases the final state must possess fractional particle numbers (aka "semitons") but there are no such states in the Fock space of 4d QFT (hence "unitarity" problem). I will describe a concrete calculation that reveals how this puzzle is resolved in Polchinkski's "fermion-rotor system," an accurate effective theory of monopole-fermion scattering. The calculaton shows that the processes traditionally thought of as involving semitons are actually mere free propagation with no scattering at all, while the traditional results without semitons are correct. The free propagation is facilitated by composite rotor-fermion operators that can interpolate essential states missed by traditional methods. This finding can have a drastic impact on the experimental bounds on monopole abundance as the most stringent bounds have been based on the traditional analyses.
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