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

TL;DR

This paper clarifies the nature of fermion-monopole scattering, demonstrating that what was thought to be fractional particle number processes are actually free propagations, resolving the semiton/Unitarity puzzle.

Contribution

It provides a detailed calculation showing that semitonic processes are free propagations, challenging previous interpretations of fractional particle numbers in monopole-fermion interactions.

Findings

Semitonic processes are free propagation, not fractionalization.

Composite operators interpolate forbidden states, restoring unitarity.

Non-semitonic processes remain unaffected.

Abstract

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.