The Singly-Charged Scalar Singlet as the Origin of Neutrino Masses

TL;DR

This paper explores how a singly-charged scalar singlet can generate neutrino masses, deriving constraints on its couplings and analyzing implications for lepton flavor physics, W-boson mass, and anomalies.

Contribution

It introduces a novel framework linking the scalar singlet to neutrino mass generation and derives new constraints on its Yukawa couplings.

Findings

Constraints on antisymmetric Yukawa couplings

Implications for lepton-flavour universality

Potential to address the Cabibbo Angle Anomaly

Abstract

We consider the generation of neutrino masses via a singly-charged scalar singlet. Under general assumptions we identify two distinct structures for the neutrino mass matrix. This yields a constraint for the antisymmetric Yukawa coupling of the singly-charged scalar singlet to two left-handed lepton doublets, irrespective of how the breaking of lepton-number conservation is achieved. The constraint disfavours large hierarchies among the Yukawa couplings. We study the implications for the phenomenology of lepton-flavour universality, measurements of the $W$-boson mass, flavour violation in the charged-lepton sector and decays of the singly-charged scalar singlet. We also discuss the parameter space that can address the Cabibbo Angle Anomaly.