Abstract

The issue of electroweak vacuum stability in the Standard Model remains a significant theoretical challenge. This thesis investigates the role of vector-like fermions in stabilizing the electroweak vacuum. We focus on three scenarios: the Higgs-Scalar Model with Vector-Like Quarks, Two-Higgs Doublet Model with Vector-Like Quarks, and Vector-Like Leptons in the Standard Model, exploring how the introduction of these additional fermions can modify the stability of the vacuum. We examine all gauge-anomaly-free vector-like representations under the SM gauge symmetry, and we analyze each of these models, taking into account all experimental constraints and electroweak precision observables, and considering both direct and indirect constraints from collider and cosmological data. The
work shows that, under certain conditions for the vector-like fermion masses and mixing parameters, the electroweak vacuum can be stabilized in all models studied, providing a viable mechanism for addressing the vacuum stability problem in the Standard Model.