We study the phenomenology of heterotic superstring models compactified on Calabi-Yau manifolds with non-abelian fundamental groups which can yield the rank-5 gauge group SU(3) c × SU(2) L × U(1) 2 in four dimensions. We examine one 2-generation model and several 4-generation models. They all have fatal problems with proton decay and/or neutrino masses. The most interesting 4-generation model avoids rapid proton decay at the expense of a neutrino weighing more than the proton and an unrealistic pattern of Cabibbo mixing.
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