A Three-Family $SU(4{)}_c\otimes SU(2{)}_w\otimes U(1)$ Type I Vacuum

Abstract

We construct a four dimensional chiral N=1 space-time supersymmetric perturbative Type I vacuum corresponding to a compactification on a toroidal Z_2 X Z_2 X Z_3 orbifold with a discrete Wilson line. This model is non-perturbative from the heterotic viewpoint. It has three chiral families in the SU(4)_c X SU(2)_w X U(1) subgroup of the total gauge group. We compute the tree-level superpotential in this model. There appears to be no obvious obstruction to Higgs the gauge group down to SU(3)_c X SU(2)_w X U(1)_Y and obtain the Standard Model gauge group with three chiral families.

Comments: 8 pages, revtex, minor misprints corrected, some notations and discussions simplified