Raising the Higgs Mass in Supersymmetry with t-t' Mixing

TL;DR

This paper proposes adding a vector-like fourth generation to the MSSM to increase the Higgs mass via mixing with the top sector, addressing the Little Hierarchy problem.

Contribution

It introduces a novel mechanism where t-t' mixing raises the Higgs mass in supersymmetry, allowing for lighter superpartners and compatibility with experimental constraints.

Findings

Higgs mass of 125 GeV achievable with soft masses around 900 GeV

Model predicts new quarks and squarks with masses above 750 GeV

Landau pole can be pushed above GUT scale with additional fields

Abstract

In this article we propose a new strategy to address the Little Hierarchy problem. We show that the addition of a fourth generation with vector-like quarks to the minimal supersymmetric standard model (MSSM) can raise the predicted value of the physical Higgs mass by mixing with the top sector. The mixing requires a larger top quark Yukawa coupling (by up to $\sim 6 %$) to produce the same top mass. Since loop corrections to $m_h$ go as $y_{top}^4$, this will in turn increase the predicted value of the physical Higgs mass, a point not previously emphasized in the literature. In the presence of mixing, for A-terms and soft masses around 900 GeV, a Higgs mass of 125 GeV can be generated while retaining perturbativity of the gauge couplings, evading constraints from electroweak precision measurements (EWPM) and recent LHC searches, and pushing the Landau pole for the top Yukawa above the GUT scale. Soft masses can be as low as 800 GeV in parts of parameter space with a Landau pole at $\sim 10^{10}$ GeV. However, the Landau pole can still be pushed above the GUT scale if one sacrifices perturbative unification by adding fields in a $\mathbf{5}$+$\mathbf{\bar{5}}$ representation. With a ratio of weak-scale vector masses $\neq 1$, soft masses may be slightly below $800$ GeV. The model predicts new quarks and squarks with masses $\gtrapprox 750$ GeV. We briefly discuss potential paths for discovery or exclusion at the LHC.