Effects of vectorlike leptons on $h\to 4\ell$ and the connection to the muon g-2 anomaly

TL;DR

This paper investigates how vectorlike leptons can influence Higgs decays to four leptons and explores their potential role in explaining the muon g-2 anomaly by analyzing decay processes, interference effects, and experimental constraints.

Contribution

It provides a detailed calculation of Higgs decay channels involving vectorlike leptons, including off-shell effects and interference, and connects these to muon g-2 anomaly explanations.

Findings

Constraints on heavy lepton masses and couplings from Higgs decay measurements.

Potential impact of vectorlike leptons on Higgs to four lepton decay rates.

Parameter regions where vectorlike leptons could explain muon g-2 anomaly.

Abstract

The mixing of new vectorlike leptons with leptons in the standard model can generate flavor violating couplings of $h$, $W$ and $Z$ between heavy and light leptons. Focusing on the couplings of the muon, the partial decay width of $h\to e_4^\pm \mu^\mp$, where $e_4$ is the new lepton, can be significant when this process is kinematically allowed. Subsequent decays $e_4^\pm \to Z\mu^\pm$ and $e_4^\pm \to W^\pm \nu$ lead to the same final states as $h \to ZZ^* \to Z \mu^+\mu^-$ and $h \to WW^* \to W \mu\nu$, thus possibly affecting measurements of these processes. We calculate $h\to e_4 \ell_i \to Z\ell_i\ell_j$, where $\ell_{i,j}$ are standard model leptons, including the possibility of off-shell decays, interference with $h\to ZZ^* \to Z \ell_i \ell_i$, and the mass effect of $\ell_{i,j}$ which are important when the mass of $e_4$ is close to the mass of the Higgs boson. We derive constraints on masses and couplings of the heavy lepton from the measurement of $h\to 4\ell$. We focus on the couplings of the muon and discuss possible effects on $h\to ZZ^*$ from the region of parameters that can explain the anomaly in the measurement of the muon g-2.