MULTI-INSTANTON CORRECTIONS TO SUPERPOTENTIALS IN TYPE II COMPACTIFICATIONS

We consider two simple examples of multi-instanton configurations in type II four-dimensional superstring compactifications. The first one involves O(1) and U(1) D2-instantons embedded in [Formula: see text] geometry with SU(4) gauge symmetry coming from D6-branes and the second is related to the quiver gauge theory of orientifolded orbifold of conifold containing fractional D (-1)-instantons and D3-branes. The additional zero modes of instantons which appear at the intersection points are lifted through interactions stemming from dimensionally reduced F- and D-terms. It is shown that multi-instanton configurations effectively generate corrections to the usual nonperturbative superpotential for chiral matter.