Left-Handed Physics is not right for EDMs

TL;DR

This paper investigates how complex couplings in heavy new physics models with lepton flavor-changing interactions affect electric dipole moments (edms), revealing that edms vanish at one loop in various bases despite complex amplitudes for flavor-changing decays.

Contribution

It demonstrates that in certain models, edms are suppressed at one loop and vanish in different flavor bases, clarifying the impact of flavor basis rotations on edm calculations.

Findings

One-loop edms vanish in mass and Yukawa bases.

Two-loop contributions are necessary for edm generation.

Flavor basis rotations do not induce edms at one loop.

Abstract

Heavy New Physics models with lepton flavour-changing interactions are motivated by neutrino masses, and generically induce dipole interactions for leptons, which can be flavour-changing ($l_j\to l_i \gamma$) or flavour-diagonal (magnetic and electric dipole moments(edms)). We focus on models with complex couplings, and where the singlet Standard Model leptons ($\{e_R^i\}$) do not interact with the New Physics. In such models, edms are calculated to arise at two loops, despite that complex amplitudes for $l_j\to l_i \gamma$ appear at one loop. We explore whether the extra loop suppression of edms survives flavour basis rotations that could be induced by flavour-changing NP contributions to the charged lepton mass matrix. We show that one-loop edms vanish in both the mass and Yukawa eigenstate bases.