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 A even has the global anomaly associated to π 4(USp) = ℤ2. We discuss manifestations of this fact in the context of the superconformal field theory R 2,2N 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