Right-Handed Neutrino Masses from the Electroweak Scale

TL;DR

This paper proposes a model where right-handed neutrino masses originate from electroweak symmetry breaking, leading to potentially observable phenomena at colliders and in rare decay experiments, with implications for neutrino mass generation.

Contribution

It introduces a novel scenario where right-handed neutrino Majorana masses are generated at the electroweak scale within a two-Higgs-doublet effective theory, linking neutrino masses to electroweak symmetry breaking.

Findings

Right-handed neutrinos can have masses below the electroweak scale.

The model predicts new Higgs sector phenomenology accessible at colliders.

Potential signals in neutrinoless double beta decay and lepton flavor violation.

Abstract

Heavy right-handed neutrinos are highly motivated due to their connection with the origin of neutrino masses via the seesaw mechanism. If the right-handed neutrino Majorana mass is at or below the weak scale, direct experimental discovery of these states is possible in laboratory experiments. However, there is no a priori basis to expect right-handed neutrinos to be so light since the Majorana mass is a technically natural parameter and could comfortably reside at any scale, including at scales far above the weak scale. Here we explore the possibility that the right-handed neutrino Majorana mass originates from electroweak symmetry breaking. Working within an effective theory with two Higgs doublets, nonzero lepton number is assigned to the bilinear operator built from the two Higgs fields, which is then coupled to the right-handed neutrino mass operator. In tandem with the neutrino Yukawa coupling, following electroweak symmetry breaking a seesaw mechanism operates, generating the light SM neutrino masses along with right-handed neutrinos with masses below the electroweak scale. This scenario leads to novel phenomenology in the Higgs sector, which may be probed at the LHC and at future colliders. There are also interesting prospects for neutrinoless double beta decay and lepton flavor violation. We also explore some theoretical aspects of the scenario, including the technical naturalness of the effective field theory and ultraviolet completions of the right-handed neutrino Majorana mass.