Comparing instanton contributions with exact results in N=2 supersymmetric scale invariant theories

We discuss the general issues and ambiguities involved in matching the exact results for the low energy effective action of scale invariant N = 2 supersymmetric QCD to those obtained by instanton methods. We resolve the reported disagreements and verify agreement between an infinite series of coefficients in the low energy effective actions calculated in the two approaches. In particular, we show that the exact low-energy effective couplings for SU(N) for all N with 2N fundamental hypermultiplets agree at a special vacuum on the Coulomb branch where a large unbroken discrete global symmetry makes the matching of parameters relatively straightforward.