Phenomenology of a four generation superstring model

We discuss the quark-lepton phenomenology of a superstring model compactified on a CP4-based Calabi-Yau manifold defined by ΣiZi5 = 5cZ1Z2Z3Z4Z5 leading to four fermion generations using the Yukawa couplings calculated by us in a previous paper. We note that maintaining supersymmetry implies that for c ≅ 1, one of the U(1)-subgroup of E6 must break at the Planck scale; on the other hand for c ≅ 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 of c; however, understanding small neutrino masses remains a problem. (orig.)