Gauge-Stringy Instantons in N=2 U(N) Gauge Theories

Using D3/D(-1) brane set-up in type IIB string theory we introduce gauge-stringy instantons in N=2 U(N) supersymmetry theories with one matter multiplet in symmetric representation. In addition to the gauge and stringy moduli there exist extra zero modes that we refer to as "gauge-stringy" moduli. We show that the measure of the moduli space in this model becomes dimensionless for arbitary N when the gauge instanton charge k_g is equal to the stringy instanton charge k_s. This property of gauge-stringy instantons leads to having equal contributions from all instanton charges k_s=k_g=k in the effective action. We derive the gauge-stringy instanton partition function and calculate the corrections to the prepotential due to k=1,2 gauge-stringy instanton charges. As a by-product the partition function for gauge k-instanton is obtained which coincides with the result from the standard ADHM construction.