Higher-form symmetries as higher automorphism bundles

Abstract

The notion of global higher-form symmetries has received much attention, but leaves room for a more systematic mathematical formulation. In this article, we highlight the concept of higher automorphism bundles from the field of higher categorical differential geometry and higher gauge theory, and we demonstrate that this neatly reproduces and clarifies many examples and phenomena discussed in the literature. We rigorously construct the higher-form symmetries of pure gauge theory of a general strict Lie $2$-group, featuring center higher-form symmetries. We then apply this explicitly to several physically-relevant examples, such as $U(1)$ bundles, bundle gerbes, and certain string $2$-groups related to $SU(n)$ instanton restriction, and $5d$ supergravity. We elaborate on the nontrivial interplay between global higher-form symmetries, connection data, and symmetry gauging.