A CHIRAL N=1 TYPE-I VACUUM IN 4 DIMENSIONS AND ITS HETEROTIC DUAL

In this paper we consider type I string theory compactified on a Z(7) orbifold. The model has N=1 supersymmetry, a U(4)x U(4) xU(4) xSO(8) g auge group, and chiral matter. There are only D9-branes (for which we discuss tadpole cancellation conditions) in this model corresponding t o a perturbative heterotic description in a certain region of the modu li space. We construct the heterotic dual, match the perturbative type I and heterotic tree-level massless spectra via giving certain scalar s appropriate vacuum expectation values, VEVs, and point out the cruci al role of the perturbative superpotential (on the heterotic side) for this matching. The relevant couplings in this superpotential turn out to be nonrenormalizable (unlike the Z-orbifold case discussed by Kaku shadze, where Yukawa couplings sufficed for duality matching). We also discuss the role of the anomalous U(1) gauge symmetry present in both type I and heterotic models. In the perturbative regime we match the (tree-level) moduli spaces of these models. We point out possible gene ralizations of the Z(3) and Z(7) cases to include D5-branes which woul d help in understanding nonperturbative five-brane dynamics on the het erotic side.