Constraints on exotic lepton doublets with minimal coupling to the standard model

TL;DR

This paper explores the theoretical implications and experimental constraints of introducing exotic lepton doublets that minimally couple to the Standard Model, focusing on flavor-changing processes and magnetic moments.

Contribution

It derives constraints on exotic lepton doublet couplings using current experimental data and analyzes their impact on lepton magnetic moments, showing negligible effects.

Findings

Constraints on exotic lepton couplings from leptonic Z decays and flavor-changing processes

Exotic doublets induce flavor-changing currents at tree level

Negligible contribution of doublets to lepton anomalous magnetic moments

Abstract

We investigate the consequences of introducing a set of exotic doublet leptons which couple to the standard model leptons in a minimal way. Through these additional gauge invariant and renormalizable coupling terms, new sources of tree-level flavor changing currents are induced via mixing. In this work, we derive constraints on the parameters that govern the couplings to the exotic doublets by invoking the current low-energy experimental data on processes such as leptonic Z decays, $\ell \rightarrow 3 \ell'$, $\ell \rightarrow \ell' \gamma$, and $\mu$-$e$ conversion in atomic nuclei. Moreover, we have analyzed the role these doublets play on the lepton anomalous magnetic moments, and found that their contribution is negligible.