The Local Structure of Anomaly Inflow

TL;DR

This paper explores the physical origin of the bump-form used in anomaly cancellation for M-theory fivebranes, relating it to fermion zero modes in axion strings, and clarifies the role of covariant anomalies in anomaly inflow.

Contribution

It introduces a detailed construction of the bump-form via fermion zero modes and clarifies the distinction between covariant and consistent anomalies in anomaly inflow.

Findings

Bump-form can be constructed from fermion zero modes.

Covariant anomalies play a key role in anomaly inflow.

Results suggest a clearer understanding of fivebrane anomaly cancellation.

Abstract

Anomaly cancellation for M-theory fivebranes requires the introduction of a "bump-form" which smoothes out the five-brane source. We discuss the physical origin of this bump-form in the simpler case of axion strings in 3+1 dimensions and construct it in terms of the radial profile of the fermion zero modes. Our treatment allows for a clearer understanding of the role played by covariant rather than consistent anomalies when anomalies are canceled by inflow from the bulk. We briefly discuss the generalization of these results to fivebrane anomalies in M theory.