Article 93302 describes a way to construct 't Hooft operators localized on (d-3)-dimensional submanifolds of d-dimensional spacetime in models with a quantum gauge field, where the gauged group G can be any compact connected Lie group. That construction uses a GNO configuration – a specially chosen Yang-Mills connection on a principal G-bundle. (A Yang-Mills connection is a connection that satisfies the Yang-Mills equations.) This article defines GNO configurations using a connection on a principal U(1)-bundle and a homomorphism from U(1) into G. Specifying such a homomorphism is equivalent (modulo conjugation) to specifying an irreducible representation of the Langlands dual of the group G.
When d=3, these are the same configurations that were historically used to define the asymptotic (far from the centerpoint) structure of GNO monopoles, a generalization the idea of a U(1) magnetic monopole to any compact connected G.
