  In this letter I analyze the constraints imposed by unitarity on the flavor
central charges of four-dimensional ${\mathcal N}=2$ SCFTs with general
reductive global symmetry groups. I derive several general and far-reaching
consequences of unitarity by computing the norms of flavor singlet Higgs branch
operators appearing in the squares of "moment map" operators via the associated
vertex operator algebra, and imposing the requirement that they be
non-negative.
