Summing the instanton series in Script N = 2 superconformal large-N QCD

We consider the multi-instanton collective coordinate integration measure in Script N = 2 supersymmetric SU(N) gauge theory with N_F fundamental hypermultiplets. In the large-N limit, at the superconformal point where N_F = 2N and all VEVs are turned off, the k-instanton moduli space collapses to a single copy of AdS₅ × S¹. The resulting k-instanton effective measure is proportional to N^1/2g⁴hat Z_k⁽⁶⁾, where hat Z_k⁽⁶⁾ is the partition function of Script N = (1,0) SYM theory in six dimensions reduced to zero dimensions. The multi-instanton can in fact be summed in closed form. As a hint of an AdS/CFT duality, with the usual relation between the gauge theory and string theory parameters, this precisely matches the normalization of the charge-k D-instanton measure in type IIB string theory compactified to six dimensions on K3 with a vanishing two-cycle.