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

TL;DR

This paper investigates how the Standard Model's partial unification scale can guide the construction of new physics models, exploring various scenarios including supersymmetry and string-inspired corrections, with potential unification at around 100 TeV.

Contribution

It introduces a simple parametrization for new physics corrections that achieve full gauge coupling unification near the partial unification scale, applicable to diverse models.

Findings

Unification at about 100 TeV is phenomenologically possible with string-inspired corrections.

Models with equal non-Abelian coupling corrections have unification scales close to the partial unification scale.

Power-law running models relate the unification scale to the number of fermion families in the bulk.

Abstract

In the Standard Model, partial unification of the non-Abelian running gauge couplings is achieved at the scale $\mu^{SM}_{32} \approx 2.8 \times 10^{16}$ 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 $\mu^{SM}_{32}$; 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 $\mu^{SM}_{32}$; for models with power-low running/threshold corrections, we also outline an interesting connection with the number of fermion families propagating in the bulk.