Standard model partial unification scale as a guide to new physics model building

In the Standard Model, partial unification of the non-Abelian running gauge couplings is achieved at the scale μ 32 SM ≈ 2.8 × 10 16 GeV . Elaborating on this fact, we discuss a simple general parametrization for the new physics corrections leading to full unification at some scale M X . We show that for any new physics model such that the corrections to the non-Abelian couplings are equal (or nearly so), M X is equal (or close to) the partial unification scale μ 32 SM ; the latter scales could be disentangled only if the corrections to the non-Abelian couplings are significantly different. We explore how the parametrization works for some relevant models with new physics below M X , as low-energy supersymmetry, split supersymmetry, etc. As for models with a desert up to M X , we explore, in particular, how the parametrization works for string-inspired corrections; we find a phenomenologically remarkable possibility for unification at about 100 TeV, suggesting a low string scale, in addition to the more conservative possibility for unification at μ 32 SM ; for models with power-law running/threshold corrections, we also outline an interesting connection with the number of fermion families propagating in the bulk.