Split Higgs triplet

TL;DR

This paper proposes a split Higgs triplet model with a special dimension-6 operator that allows for small neutrino masses and potential resolution of Hubble constant tension, without high-dimensional lepton number violation.

Contribution

It introduces a novel split Higgs triplet mechanism involving a specific dimension-6 operator, enabling neutrino mass generation and addressing cosmological tensions.

Findings

The scalar component can have a small quadratic term, enabling a small vacuum expectation value.

The model can generate Majorana neutrino masses without Weinberg operator.

It offers a framework for non-standard neutrino self-interactions.

Abstract

We find if a Higgs triplet with hypercharge has a special dimension-6 operator with the standard model Higgs doublet, i.e. a square of the trilinear triplet-doublet coupling, its scalar(pseudo-scalar) component can obtain a small quadratic term while its pseudo-scalar(scalar) and charged-scalar components can hold their masses heavy enough. Such split Higgs triplet can spontaneously develop a small vacuum expectation value to realize a Majorana neutrino mass generation without causing any high-dimensional lepton number violations including the well-known Weinberg dimension-5 operator. Alternatively it can mediate a non-standard neutrino self-interaction motivated by resolving the tension in Hubble constant measurements. This effective theory with rich observable phenomena can be induced by the Georgi-Machacek Higgs triplets at tree level or some dark matter fields at one-loop order.