Vacuum stability in the Standard Model with vector-like fermions

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.

27 pages, 12 figures

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• The Two Scales of New Physics in Higgs Couplings
• Stability of the Standard Model Vacuum with Vector-Like Leptons: A Critical Examination
• The Two Scales of New Physics in Loop-Induced Higgs Couplings
• Neutrino Mass, Vacuum Stability and Higgs Inflation with Vector-Like Quarks and a Single Right-Handed Neutrino
• From Higgs physics to lepton flavour violation: current bounds and future prospects for vector-like lepton models