Left-handed physics is not right for leptonic EDMs

Heavy New Physics models with lepton flavour-changing interactions are motivated by neutrino masses, and generically induce dipole interactions for charged leptons – which can be flavour-changing ( lⱼ→ lᵢ γ l j → l i γ ), or flavour-diagonal (magnetic and electric dipole moments(edms)). We focus on models with complex couplings, and where the singlet Standard Model leptons ( ⁱ\ { 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 lⱼ→ lᵢ γ l j → l i γ 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.