Anomaly and Superconnection

TL;DR

This paper explores anomalies in fermionic systems with spacetime-dependent mass using superconnections, unifying anomaly descriptions across dimensions and boundary conditions, with applications to index theorems and string theory.

Contribution

It introduces a superconnection framework to describe fermion anomalies in various dimensions, extending traditional anomaly polynomials and connecting to index theorems and string theory interpretations.

Findings

Anomalies are expressed via superconnections and their Chern characters.

Unified treatment of anomalies in systems with interfaces and boundaries.

Application of results to index theorems like Atiyah-Patodi-Singer and Callias-type.

Abstract

We study anomalies of fermions with spacetime dependent mass. Using Fujikawa's method, it is found that the anomalies associated with the $U(N)_+\times U(N)_-$ chiral symmetry and $U(N)$ flavor symmetry for even and odd dimensions, respectively, can be written in terms of superconnections. In particular, the anomaly for a vector-like $U(1)$ symmetry is given by the Chern character of the superconnection in both even and odd dimensional cases. It is also argued that the non-Abelian anomaly for a system in D-dimensional spacetime is characterized by a (D+2)-form part of the Chern character of the superconnection which generalizes the usual anomaly polynomial for the massless case. These results enable us to analyze anomalies in the systems with interfaces and spacetime boundaries in a unified way. Applications to index theorems, including Atiyah-Patodi-Singer index theorem and Callias-type index theorem, are also discussed. In addition, we give a natural string theory interpretation of these results.