Reducing the Quadratic Divergence in the Higgs Mass Squared Without Top Partners

TL;DR

This paper explores extended Higgs sector models that reduce the quadratic divergence in the Higgs mass without low-scale top partners, aiming to lower fine-tuning while remaining consistent with experimental constraints.

Contribution

It generalizes the Veltman condition to extended Higgs sectors and analyzes a minimal model with two extra scalars to reduce Higgs mass divergence.

Findings

Fine-tuning is significantly lowered in the minimal model at a 5 TeV cutoff.

The model avoids low-scale Landau poles despite strong coupling at the cutoff.

Reduced top Yukawa couplings make the model testable at upcoming LHC runs.

Abstract

We examine a model with multiple scalar fields to see whether it is possible to reduce the fine- tuning of the SM Higgs mass without introducing low scale top partners. Our approach may be regarded as a generalization of the condition proposed by Veltman, who attempted to predict the Higgs mass using the criterion that the various low energy contributions to the quadratic divergence of the Higgs mass cancel. Although the Veltman condition predicts the wrong Higgs mass in the Standard Model, it can still be adapted to extended Higgs sectors. Furthermore, theories with additional Higgs bosons can lead to suppressed Yukawa couplings of the top quark to the 125 GeV Higgs, making the associated one-loop divergence smaller. Here, we review possible extensions of the Standard Model where the Veltman condition could be realized, and study in detail one minimal model with two extra scalar fields. For this model and for a cutoff of 5 TeV, we show that the overall fine-tuning can be considerably lowered without introducing low-scale Landau poles, albeit the Higgs sector will be strongly coupled at the cutoff. Models where the top Yukawa coupling is reduced, in particular, will be within the reach of the upcoming LHC searches.