Enhanced Electromagnetic Transition Dipole Moments and Radiative Decays of Massive Neutrinos due to the Seesaw-induced Non-unitary Effects

TL;DR

This paper demonstrates that non-unitary effects from the seesaw mechanism can significantly enhance the electromagnetic transition dipole moments and radiative decay rates of massive neutrinos, linking their electromagnetic properties to their mass origin.

Contribution

It introduces how non-unitary effects from the seesaw mechanism can lift GIM suppression, leading to substantial enhancements in neutrino electromagnetic properties.

Findings

Electromagnetic transition dipole moments can be enhanced by O(10^2).

Radiative decay rates can be increased by O(10^4).

Significant correlation between neutrino electromagnetic properties and their mass origin.

Abstract

In a simple extension of the standard electroweak theory where the phenomenon of lepton flavor mixing is described by a 3x3 unitary matrix V, the electric and magnetic dipole moments of three active neutrinos are suppressed not only by their tiny masses but also by the Glashow-Iliopoulos-Maiani (GIM) mechanism. We show that it is possible to lift the GIM suppression if the canonical seesaw mechanism of neutrino mass generation, which allows V to be slightly non-unitary, is taken into account. In view of current experimental constraints on the non-unitarity of V, we find that the effective electromagnetic transition dipole moments of three light Majorana neutrinos and the rates of their radiative decays can be maximally enhanced by a factor of O(10^2) and a factor of O(10^4), respectively. This important observation reveals an intrinsic and presumably significant correlation between the electromagnetic properties of massive neutrinos and the origin of their small masses.