Gauge unification in nonminimal models with extra dimensions

We consider gauge unification in nonminimal models with extra spacetime dimensions above the TeV scale. We study the possibility that only a a subset of the supersymmetric standard model gauge and Higgs fields live in the higher dimensional 'bulk'. In two of the models we present, a choice for bulk MSSM matter fields can be found that preserves approximate gauge unification. This is true without the addition of any exotic matter multiplets, beyond the chiral conjugate mirror fields required to make the Kaluza-Klein excitations of the matter fields vector-like. In a third model, only a small sector of additional matter fields is introduced. In each of these examples we show that gauge unification can be obtained without the necessity of large string scale threshold corrections. We comment briefly on the phenomenology of these models in the case where the compactification scale is as low as possible. (C) 1999 Elsevier Science B.V. All rights reserved.