Fourth Generation Leptons and Muon $g-2$

TL;DR

This paper investigates how hypothetical fourth-generation leptons could influence the muon anomalous magnetic moment, analyzing one-loop contributions within various models, including effects from neutral and charged leptons.

Contribution

It provides a detailed calculation of fourth-generation lepton contributions to muon g-2, considering both neutral and charged leptons, and explores flavor-changing effects in extended Higgs models.

Findings

Neutral lepton contribution is suppressed by off-diagonal PMNS matrix elements.

Charged lepton contribution can be significant with flavor-changing neutral couplings.

Results suggest potential explanations for muon g-2 anomaly within extended lepton models.

Abstract

We consider the contributions to $g_\mu-2$ from fourth generation neutral and charged leptons, $N$ and $E$, at the one-loop level. Diagramatically, there are two types of contributions: boson-boson-$N$, and $E$-$E$-boson in the loop diagram. In general, the effect from $N$ is suppressed by off-diagonal PMNS matrix element $V_{N\mu}$, from the Standard Model to the Two-Higgs Doublet Models. With contribution from $E$, we consider flavor changing neutral couplings.