Electric dipole moments of charged leptons with sterile fermions

TL;DR

This paper investigates how sterile fermions influence charged lepton electric dipole moments, showing that at least two sterile states are needed for non-zero contributions, with potential significance near future experimental sensitivities.

Contribution

It demonstrates the minimal conditions for sterile fermions to affect lepton EDMs and applies this to the Inverse Seesaw model, highlighting potential observable effects.

Findings

Sterile fermions can significantly contribute to lepton EDMs if non-degenerate and above electroweak scale.

The minimal realisation of the Inverse Seesaw can produce electron EDMs near experimental detection.

Heavy pseudo-Dirac states in the model are key to potential EDM signals.

Abstract

We address the impact of sterile fermions on charged lepton electric dipole moments. We show that in order to have a non-vanishing contribution to electric dipole moments, the minimal extension necessitates the addition of at least two sterile fermion states. Sterile neutrinos can give significant contributions to the charged lepton electric dipole moments if the masses of the non-degenerate sterile states are both above the electroweak scale. In addition, the Majorana nature of neutrinos is also important. Furthermore, we apply the computations of the electric dipole moments for the most minimal realisation of the Inverse Seesaw mechanism, in which the Standard Model is extended by two right-handed neutrinos and two sterile fermion states. We show that the two pairs of (heavy) pseudo-Dirac mass eigenstates can give significant contributions to the electron electric dipole moment, lying close to future experimental sensitivity. We further discuss the possibility of beyond the minimal Inverse Seesaw models and of having a successful leptogenesis in this framework.