Large CP violation in flavor violating muon decays

TL;DR

This paper explores new possibilities for observing CP violation in muon-to-electron flavor violating decays, highlighting potential signals in upcoming experiments like Mu3e, and analyzing the theoretical framework connecting low-energy observables to high-energy physics.

Contribution

It demonstrates that CP violation can appear in muon flavor violating decays independently of electric dipole moments, and provides a detailed EFT analysis linking low-energy measurements to high-energy theories.

Findings

CP violation can manifest in muon decays without affecting electron EDMs.

Full one-loop analysis connects muon decay observables to high-energy physics.

A simple UV model illustrates how these patterns can arise.

Abstract

We identify new room for CP violation in lepton flavor violating observables not bound by the electric dipole moment of leptons. By focusing on new physics in the muon-electron sector, we show that CP violation can make its first appearance in lepton flavor violating muon decays rather than in the electric dipole moment of the electron, further motivating the experimental program of Mu3e. We tackle this issue by performing the full one-loop running and matching from the low energy observables at the muon scale, including the T-odd asymmetry in $\mu\to3e$ decays, to the Standard Model effective field theory above the electroweak scale. We then sketch a simple UV model that can give rise to these patterns.