Phenomenology of a four generation superstring model

We discuss the quark-lepton phenomenology of a superstring model compactified on aCP ⁴-based Calabi-Yau manifold defined by? _i Z _i ⁵ = 5 _c Z ₁ Z ₂ Z ₃ Z ₄ Z ₅ leading to four fermion generations using the Yukawa couplings calculated by us in a previous paper. We note that maintaining supersymmetry implies that forc?1, one of theU(1)-subgroup ofE ₆ must break at the Planck scale; on the other hand forc?10⁺⁴, an intermediate scale of about 10¹¹ GeV or 10¹⁴ GeV may be generated without destabilizing the gauge hierarchy. The model may have problems with fast proton decay for some choice ofc; however, understanding small neutrino masses remains a problem.