Search for lepton flavor violation at future lepton colliders

TL;DR

This paper investigates the potential of future lepton colliders, specifically the ILC, to improve constraints on lepton flavor violation processes through four-Fermi contact interactions, surpassing current experimental limits.

Contribution

It introduces a comprehensive analysis of LFV processes at the ILC, demonstrating significant potential to tighten existing bounds on LFV parameters, especially for tau lepton processes.

Findings

ILC can improve upper limits on LFV parameters for tau by over an order of magnitude.

Polarized electron beams enhance sensitivity to LFV effects.

Current experimental bounds can be significantly surpassed at future colliders.

Abstract

Lepton flavor violating (LFV) processes via four-Fermi contact interactions at future International Linear Collider (ILC) are studied. The effective Lagrangian is composed of six-operators, and the LFV effects on both $e^+ e^- \to e^+ \ell^-$ and $e^- e^- \to e^- \ell^-$ ($\ell=\mu$ or $\tau$) processes can be parametrized by three parameters. Taking account of previous experimental results of LFV processes $\mu\to 3e$ and $\tau \to 3e$, we find that the upper limits on the LFV parameters for $\ell=\tau$ could be improved at the ILC experiment using the polarized electron beam. The improvement of the upper limits is more than an order of magnitude smaller than previous ones.