Stability of the Standard Model Vacuum with Vector-Like Leptons: A Critical Examination

TL;DR

This paper explores how adding vector-like leptons to the Standard Model can stabilize the Higgs vacuum, ensuring its stability up to the Planck scale without extra scalars, while remaining consistent with electroweak precision data.

Contribution

It identifies specific vector-like lepton spectra that stabilize the SM vacuum and analyzes their compatibility with electroweak precision constraints.

Findings

Certain VLL spectra stabilize the Higgs potential.

VLLs can fit within electroweak precision constraints.

Stability conditions narrow the allowed VLL parameter space.

Abstract

The stability of the Standard Model (SM) Higgs vacuum is a long-standing issue in particle physics. The SM Higgs quartic coupling parameter is expected to become negative at high scales, potentially generating an unstable vacuum well before reaching the Planck scale. We investigate whether the introduction of vector-like leptons (VLLs) in six distinct gauge anomaly-independent representations can stabilize the SM vacuum without introducing additional scalar fields. By analyzing the mass spectrum and mixing angles of these VLLs with the SM leptons, we identify conditions under which the Higgs potential remains stable. We demonstrate that there exists a set of allowed but narrowed VLL spectra that can indeed stabilize the SM vacuum. We also study the effect of these VLLs on electroweak precision observables, particularly the oblique parameters S and T to ensure fit within global experimental constraints. Finally, we perform a comprehensive analysis of the parameter space allowed by electroweak precision data and the parameter space required for stability, highlighting cases that accommodate both. This study opens up new avenues for understanding the role of vector-like leptons in extending the validity of the Standard Model up to the Planck scale.