String probes, simple currents, and the no global symmetries conjecture

TL;DR

This paper explores how string probes and chiral currents relate to the global structure of gauge groups in quantum gravity, providing new insights into center one-form symmetries and their obstructions.

Contribution

It introduces a string-theoretic perspective on center one-form symmetries, linking chiral simple currents to gauging obstructions and applying this to various string compactifications.

Findings

Gauged center one-form symmetries correspond to chiral simple current extensions.

Obstructions to gauging these symmetries match known field theoretic and geometric constraints.

Identifies worldsheet simple currents as sources of BPS particles in 6d supergravity.

Abstract

Center one-form symmetries in consistent quantum gravity theories are expected to be either broken or gauged, thereby determining the global form of the gauge group. We shed light on this expectation from the perspective of distinguished extended objects, which we denote by faithful string probes, for which the gauge symmetry is realized as a holomorphic current algebra. We argue that the worldsheet counterpart of gauged center one-form symmetries is the existence of chiral simple currents extending the current algebra. Accordingly, we show that the consistency condition for such extensions reproduce and generalize known field theoretic and geometric obstructions to the gauging of center one-form symmetries in six and eight dimensions. We verify this picture in a number of examples arising from heterotic string compactifications, and apply it to infer the gauge group topology of a recently identified class of six-dimensional models with no known F-theoretic realization. In 6d supergavity, our results also clarify an observation of Kim and Vafa on the existence of BPS particles required for consistency upon circle reduction: these particles arise from worldsheet simple currents whose existence is dictated by the presence of a gauged center one-form symmetry. Intriguingly, in several models across different dimensions we find composite higher-spin chiral currents beyond the current algebra, hinting at a stringy generalization of center one-form symmetries in the bulk.