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

Wednesday Jun 25, 2025, 3:00 PM → 4:00 PM Asia/Seoul

CTPU Seminar Room (IBS)

Abstract:
For over 40 years, scattering of charged fermions off of a magnetic
monopole has puzzled us. For some initial states, the final state seems to
possess fractional particle numbers (aka "semitons"), but there are no such
states in the Fock space of a 4d QFT (hence "unitarity" problem). By a
concrete calculation in Polchinski's "fermion-rotor system," an accurate
effective theory of monopole-fermion scattering, I will show how this
puzzle is resolved. The calculation reveals that the processes
traditionally thought of as involving semitons do not undergo any
scattering at all, while the traditional results without semitons are
correct as they are. This finding can impact the experimental bounds on
monopole abundance as the most stringent bounds have been based on the
traditional analyses.