Vacuum stability in the Standard Model with vector-like fermions

TL;DR

This paper investigates how adding scalar fields and vector-like fermions to the Standard Model can stabilize the Higgs potential up to high energies, with potential observable effects at the LHC.

Contribution

It introduces a model-independent analysis of vacuum stability with vector-like fermions and an additional scalar, identifying parameter regions compatible with stability.

Findings

Allowed fermion masses around 1 TeV.

Scalar and fermion mixing angles constrained by stability.

Vector-like fermions could be detected at the LHC.

Abstract

The discovery of Standard-Model like Higgs at 125 GeV may raise more questions than the answers it provides. In particular, the hierarchy problem remains unsolved, and the Standard Model Higgs quartic self-coupling becomes negative below the Planck scale, necessitating new physics beyond the Standard Model. In this work we investigate a popular scenario, extensions of the Standard Model with vector-like fermion fields, such as the ones present in models with extra dimensions or in Higgs composite models, using a model independent approach. Since fermions decrease the Higgs quartic coupling at high energies, only exacerbating the self-coupling problem, we introduce first an additional scalar, which by itself is enough to overcome the vacuum stability limit, and then explore the effects of vector-like fermions in singlet, doublet and triplet representations. For each model, we identify the allowed fermion masses and mixing angles with the third family fermions required to satisfy the vacuum stability condition, and compare different representations. Allowed fermion masses emerge at around 1 TeV, raising hope that these will be found at the LHC. We also examine corrections to oblique parameters S and T from additional scalar and vector-like quarks which also impose constraints on mixing and mass splitting of both sectors., but these restrictions are relatively weak compared to the vacuum stability.