Missing final state puzzle in the monopole-fermion scattering

TL;DR

This paper resolves a scattering puzzle involving monopoles and fermions by identifying new particle excitations with condensates, ensuring consistent final states in monopole-fermion interactions.

Contribution

It introduces novel particle excitations in monopole backgrounds, explaining how fermion number violation and charge conservation are reconciled.

Findings

Discovery of multi-fermion condensates as particle excitations

Resolution of the final state puzzle in monopole-fermion scattering

Description of excitations as closed-string configurations

Abstract

It has been known that when a charged fermion scatters off a monopole, the fermion in the $s$-wave component must flip its chirality, i.e., fermion number violation must happen. This fact has led to a puzzle; if there are two or more flavors of massless fermions, any superposition of the fermion states cannot be the final state of the $s$-wave scattering as it is forbidden by conservation of the electric and flavor charges. The unitary evolution of the state vector, on the other hand, requires some interpretation of the final states. We solve the puzzle by finding new particle excitations in the monopole background, where multi-fermion operators exhibit condensation. The particles are described as excitations of closed-string configurations of the condensates.