Three generations in the fermionic construction Original Research Article

We obtain three generation SU(3)c × SU(2)L × U(1)Y string models in all of the exactly solvable (0, 2) constructions sampled by fermionization. None of these examples, including those that are symmetric abelian orbifolds, rely on the ℤ2 × ℤ2 orbifold underlying the NAHE basis. We present the first known three generation models for which the hypercharge normalization, k1, takes values smaller than that obtained from an SU(5) embedding, thus lowering the effective gauge coupling unification scale. All of the models contain fractional electrically charged and vectorlike exotic matter that could survive in the light spectrum.