Small Neutrino Masses from a Decoupled Singlet Scalar Field

TL;DR

This paper presents a model extending the Standard Model with additional scalars and right-handed neutrinos under a $Z_4$ symmetry, explaining small neutrino masses, dark matter stability, and leptogenesis through symmetry breaking and loop processes.

Contribution

It introduces a novel $Z_4$ symmetry framework that links neutrino mass generation, dark matter stability, and leptogenesis in a unified model.

Findings

Small neutrino masses achieved at one-loop level.

Dark matter stability ensured by $Z_4$ symmetry.

Leptogenesis compatible with the model's scalar sector.

Abstract

We propose a unified solution with $Z_4$ discrete symmetry for small neutrino masses and stability of dark matter. The Standard Model is extended with an inert doublet scalar, a dark singlet scalar, a spurion scalar and right-handed neutrinos, which all transform nontrivially under $Z_4$. After the $Z_4$ symmetry is broken to $Z_2$ by the VEV of the spurion, much below the mass scale of the dark singlet scalar, a small lepton number violating coupling for the inert doublet is generated at tree level, so small neutrino masses are obtained at one-loops for relatively light new fields. We discuss the important roles of the $Z_4$ symmetry for neutrino masses, dark matter physics and thermal leptogenesis.