A three-family SU(6) type I compactification

We construct a four dimensional chiral N=1 space-time supersymmetric Type I vacuum corresponding to a compactification on a toroidal Z(2)xZ(2)xZ(3) orbifold. Using recent results in four dimensional orientifolds, we argue that this model has a well defined world-sheet description. An interesting feature of this model is that the gauge group contains an SU(6) subgroup with three chiral generations. Moreover, this model contains D5-branes and therefore corresponds to a non-perturbative heterotic vacuum. This is the first example of a consistent chiral N=1 supersymmetric string vacuum which is non-perturbative from the heterotic viewpoint, has a perturbative description in a dual theory, and possesses some phenomenologically interesting characteristics. We also compute the tree-level superpotential in this theory. (C) 1998 Elsevier Science B.V. All rights reserved.