Omega vs. pi, and 6d anomaly cancellation


Change log
Authors
Lohitsiri, N 
Abstract

In this note we review the role of homotopy groups in determining non-perturbative (henceforth global') gauge anomalies, in light of recent progress understanding global anomalies using bordism. We explain why non-vanishing of $\pi_d(G)$ is neither a necessary nor a sufficient condition for there being a possible global anomaly in a $d$-dimensional chiral gauge theory with gauge group $G$. To showcase the failure of sufficiency, we revisit global anomalies' that have been previously studied in 6d gauge theories with G=SU(2), SU(3), or G2. Even though π6(G)≠0, the bordism groups Ω7Spin(BG) vanish in all three cases, implying there are no global anomalies. In the case of G=SU(2) we carefully scrutinize the role of homotopy, and explain why any 7-dimensional mapping torus must be trivial from the bordism perspective. In all these 6d examples, the conditions previously thought to be necessary for global anomaly cancellation are in fact necessary conditions for the local anomalies to vanish.

Description
Keywords
Anomalies in Field and String Theories, Gauge Symmetry
Journal Title
Journal of High Energy Physics
Conference Name
Journal ISSN
1029-8479
1029-8479
Volume Title
2021
Publisher
Springer Science and Business Media LLC