Revisiting wess-zumino-witten terms

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.