$(g-2)_\mu$ in the 2HDM and slightly beyond -- an updated view

TL;DR

This paper updates the analysis of the muon g-2 anomaly within two Higgs doublet models, showing that adding vector-like leptons improves the fit and extends viable parameter space, despite potential perturbativity issues.

Contribution

It demonstrates how vector-like leptons enhance the fit of muon g-2 in 2HDMs and updates previous constraints with comprehensive theoretical and experimental considerations.

Findings

Vector-like leptons extend the parameter space for muon g-2 explanation.

Lepton-specific and muon-specific 2HDMs perform better with vector-like fermions.

Large Yukawa couplings may challenge perturbativity and unitarity.

Abstract

The recent measurement of the muon $g - 2$ anomaly continues to defy a Standard Model explanation, but can be accommodated within the framework of two Higgs doublet models. If one further includes extra fermion content in the form of a generation of vector like leptons, the allowed parameter range that explains the anomaly is even further extended, and thorny issues of perturbativity and clashes with $B$-decay constraints avoided. We will show how the muon magnetic moment anomaly can be fit within these models, under the assumption that the vector-like leptons do not mix with the muon. We update previous analyses and include all theoretical and experimental constraints, including searches for extra scalars. It is shown that the inclusion of vector-like fermions allows the lepton-specific and muon-specific models to perform much better in fitting the muon's $g - 2$. These fits do require the Yukawa coupling between the Higgs and the vector-like leptons to be large, causing potential problems with perturbativity and unitarity, and thus models in which the vector-like leptons mix with the muon may be preferred.