Anomaly matching and a Hopf–Wess–Zumino term in six-dimensional, N=(2,0) field theories Original Research Article

We point out that the low energy theory of 6d N=(2,0) field theories, when away from the origin of the moduli space of vacua, necessarily includes a new kind of Wess–Zumino term. The form of this term is related to the Hopf invariant associated with π7(S4). The coefficient of the Wess–Zumino term is fixed by an anomaly matching relation for a global flavor symmetry. For example, in the context of a single M5 brane probe in the background of N distant M5 branes, the probe must have the Hopf–WZ term with coefficient proportional to N(N+1). Various related checks and observations are made. We also point out that there are skyrmionic strings, and propose that they are the W-boson strings.