Global symmetries: locality, unitarity, and regularity

We study the apparent tension between locality and unitarity for symmetries in quantum field theory. This emerges in the context of categorical symmetries where symmetry operators are generically non-invertible. We argue that locality imposes particular regularities in the action of symmetries on the Hilbert space. This allows us to introduce an observable that can measure the properties of the non-locality for symmetry operators. We study it for a class of examples and demonstrate that this observable can encode data associated to the fusion algebra of symmetries.