Reevaluation of heavy-fermion-induced electron EDM at three loops

TL;DR

This paper reevaluates the three-loop mechanism transmitting CP violation from heavy to light fermions, finding additional contributions that strengthen bounds on various fermion EDMs and improve existing limits.

Contribution

It introduces previously missing contributions at the order of electron to muon and tau mass ratios, leading to more accurate bounds on fermion electric dipole moments.

Findings

The electron EDM bounds are tightened by 1.4 times.

Updated limits on tau, muon, charm, and bottom quark EDMs.

Enhanced understanding of three-loop CP violation transmission mechanisms.

Abstract

Motivated by improved limits on electric dipole moments (EDMs), we revisit the three-loop light-by-light mechanism that transmits $CP$ violation from a heavy fermion to a light one. Applying it to the electron EDM induced by EDMs of heavier flavors, we find additional contributions at the order $ m_e/m_\mu $ or $m_e/m_\tau$ that were missing before and that make the result 1.4 times larger. Consequently we improve bounds on the tau EDM, and update indirect limits on the muon EDM as well as charm and bottom quark color EDMs.