A Twist on Scattering from Defect Anomalies

TL;DR

This paper explores how defect anomalies enable exotic scattering processes involving twist operators across various models, including massless fermions, integrable theories, and lattice spin chains.

Contribution

It introduces the concept that defect anomalies facilitate categorical scattering, provides concrete examples, and solves related scattering problems in new integrable models.

Findings

Defect anomalies trap charges at junctions, enabling new transmission channels.

Emergence of twist operators linked to defect anomalies in massless fermions.

Explicit solutions for scattering in new massive integrable theories.

Abstract

In the presence of extended defects, familiar incoming particles can scatter into exotic outgoing states created by twist operators. We show that one possible mechanism driving these "categorical scattering" processes is the presence of localized 't Hooft anomalies on the defect's worldvolume. Defect anomalies trap non-trivial charges at junctions between the symmetry lines and the interface, opening new transmission channels that would naively appear to violate selection rules. After outlining the general mechanism, we investigate several concrete examples with defects, interfaces, and boundaries. For models of massless chiral fermions already studied in the literature, we show that the emergence of twist operators can be understood as a consequence of defect anomalies. We then introduce new massive integrable theories in which a similar phenomenon occurs, and we explicitly solve the associated scattering problem, obtaining new integrable solutions. Finally, we construct lattice spin chains with defects where similar physics is expected to arise.