Comments on the twisted punctures of A even class S theory

Abstract

We point out that the USp symmetry associated to a full twisted puncture of a class S theory of type Aeven has the global anomaly associated to π4(USp) = ℤ2. We discuss manifestations of this fact in the context of the superconformal field theory R2,2N introduced by Chacaltana, Distler and Trimm. For example, we find that this theory can be thought of as a natural ultraviolet completion of an infrared-free SO(2N + 1) gauge theory with 2N flavors, whose USp(4N) symmetry clearly has the global anomaly.