# Vector-like Leptons: Muon g-2 Anomaly, Lepton Flavor Violation, Higgs Decays, and Lepton Non-Universality

## TL;DR

This study explores a Standard Model extension with vector-like leptons, analyzing constraints from various experimental data, and finds significant limitations on coupling ratios and an inability to explain certain lepton non-universality observations.

## Contribution

The paper investigates the impact of vector-like leptons on multiple observables, providing new constraints and insights into their couplings and effects on lepton flavor phenomena.

## Key findings

- Muon g-2 anomaly can be addressed within the model.
- Coupling ratio λ_e/λ_μ is constrained to be less than 10^{-4}.
- Model cannot explain the observed R_{K^{*0}} lepton non-universality.

## Abstract

In this paper, we consider the Standard Model (SM) with one family of vector-like (VL) leptons, which couple to all three families of the SM leptons. We study the constraints on this model coming from the heavy charged lepton mass bound, electroweak precision data, the muon anomalous magnetic moment, lepton flavor violation, Higgs decay constraints and a recently measured lepton non-universality observable, $R_{K^{*0}}$. We find that the strongest constraints are coming from the muon $g-2, \ R_{\mu\mu}=\Gamma(h\to\mu\mu)/\Gamma(h\to\mu\mu)_\text{SM}, \ R_{\gamma\gamma}$ and $\text{BR}(\mu\to e\gamma)$. Although VL leptons couple to all three families of the SM leptons, the ratio of electron-VL to muon-VL coupling is constrained to be $\langle\lambda_e/\lambda_\mu\rangle\lesssim10^{-4}$. We also find that our model cannot fit the observed value of $R_{K^{*0}}$.