Fourth Generation Leptons and Muon $g-2$

TL;DR

This paper investigates how hypothetical fourth-generation leptons could influence the muon g-2 anomaly through one-loop quantum corrections, considering constraints from flavor-changing processes and implications for new physics models.

Contribution

It analyzes the one-loop contributions of fourth-generation leptons to muon g-2, including effects of flavor-changing neutral currents and their impact on existing new physics models.

Findings

Fourth-generation leptons can significantly contribute to muon g-2.

Flavor-changing neutral couplings are tightly constrained by $\, o e\,\, ext{gamma}$ decay.

Implications for new physics models are discussed in light of these contributions.

Abstract

We consider the contributions to $g_\mu-2$ from fourth generation heavy neutral and charged leptons, $N$ and $E$, at the one-loop level. Diagrammatically, 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 lepton mixing matrix elements. For $E$, we consider flavor changing neutral couplings arising from various New Physics models, which are stringently constrained by $\mu\to e\gamma$. We assess how the existence of a fourth generation would affect these New Physics models.