On Instantons at Large Charge

Abstract: The large R-charge limit of two-point functions of chiral primary operators in rank-one N=2 superconformal field theories exhibits a universal behavior controlled by the effective field theory on their Coulomb branch. In the case of SU(2) SQCD with four flavors, this behavior is expected to be independent of the exactly-marginal gauge coupling. We provide an analytic test of this prediction by computing the correlators directly via supersymmetric localization. Our analysis clarifies the interplay between the weak-coupling expansion and the large-charge expansion, with special emphasis on the precise role played by gauge-theory instantons in the latter regime. We conclude with remarks on the implications of our results for analogous observables in Argyres-Douglas theories.