Unification with enlarged Kaluza-Klein dimensions

In minimal theories with extra spatial dimensions at scales μ0 much lower than the conventional GUT scale, unification can give too-large predictions for α3(MZ) given α1(MZ) and α2(MZ) as empirical input. We systematically study the effects of adding extra states above the compactification scale on running of the gauge couplings and find several simple examples that give unification where all αi(MZ) are consistent with low-energy data. We study both the supersymmetric and nonsupersymmetric unification.