Strong coupling unification and extra dimensions Original Research Article

We analyze the implications of electroweak and strong coupling unification in a very general class of models extending the minimal supersymmetric standard model in 4 + p dimensions (p ⩾ 0). In general, electroweak precision data require the presence of large extra dimensions (low compactification scales, Mc) and/or low unification scale, MU. In particular, the actual experimental value of the strong coupling at MZ imposes an upper bound on the compactification and unification scales. In four-dimensional theories (Mc ≅ MU) with canonical hypercharge assignment we find MU ≲ 109 GeV. In theories with extra dimensions (Mc < MU) we find Mc ≲ 107 GeV, for a supersymmetric spectrum at the TeV scale.