Open string instantons and superpotentials - art. no. 026001

We study the F terms in N = 1 supersymmetric, d = 4 gauge theories arising from D(p + 3)-branes wrapping supersymmetric p-cycles in a Calabi-Yau three fold. if p is even the spectrum and superpotential for a single brane are d etermined by purely classical (alpha' --> 0) considerations. If p = 3, supe rpotentials for massless modes are forbidden to all orders in alpha' and ma y only be generated by open string instantons. For this latter case we find that such instanton effects are generically present. Mirror symmetry relat es even and odd p and thus perturbative and nonperturbative superpotentials ; we provide a preliminary discussion of a class of examples of such mirror pairs.