## Revisiting Wess-Zumino-Witten terms

Yasunori Lee, Kantaro Ohmori, Yuji Tachikawa

SciPost Phys. 10, 061 (2021) · published 10 March 2021

### Abstract

We revisit various topological issues concerning four-dimensional ungauged and gauged Wess-Zumino-Witten (WZW) terms for $SU$ and $SO$ quantum chromodynamics (QCD), from the modern bordism point of view. We explain, for example, why the definition of the $4d$ WZW terms requires the spin structure. We also discuss how the mixed anomaly involving the 1-form symmetry of $SO$ QCD is reproduced in the low-energy sigma model.

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