Precision Unification in \lambda SUSY with a 125 GeV Higgs

TL;DR

This paper explores how strong coupling effects in mbda SUSY models with a 125 GeV Higgs can preserve gauge coupling unification despite non-perturbative physics, offering a potential solution to fine-tuning issues.

Contribution

It demonstrates that classes of UV completions can naturally correct gauge coupling unification discrepancies in mbda SUSY models with strong coupling effects.

Findings

Strong coupling can correct the mbda SUSY unification discrepancy.

Certain scenarios allow strong coupling to benefit t-b unification.

Unification can be maintained despite non-perturbative physics.

Abstract

It is challenging to explain the tentative 125 GeV Higgs signal in the Minimal Supersymmetric Standard Model (MSSM) without introducing excessive fine-tuning, and this motivates the study of non-minimal implementations of low energy supersymmetry (SUSY). A term \lambda SH_uH_d involving a Standard Model (SM) singlet state S leads to an additional source for the quartic interaction raising the mass of the lightest SM-like Higgs. However, in order to achieve m_h \approx 125 GeV with light stops and small stop mixing, it is necessary for \lambda \gtrsim 0.7 and consequently \lambda may become non-perturbative before the unification scale. Moreover, as argued by Barbieri, Hall, et al. low fine-tuning prefers the region \lambda~1-2, leading to new or non-perturbative physics involving S below the GUT scale (`\lambda SUSY' models). This raises the concern that precision gauge coupling unification, the prime piece of indirect experimental evidence for low energy SUSY, may be upset. Using the NSVZ exact \beta-function along with well motivated assumptions on the strong coupling dynamics we show that this is not necessarily the case, but rather there exist classes of UV completions where the strong-coupling effects can naturally correct for the present ~3% discrepancy in the two-loop MSSM unification prediction for \alpha_s. Moreover, we argue that in certain scenarios a period of strong coupling can also be beneficial for t-b unification, while maintaining the small to moderate values of tan\beta preferred by the Higgs mass.