The Type-I Seesaw family

TL;DR

This paper analyzes the Type-I Seesaw family of neutrino mass models, including variants with low-scale and spontaneous lepton number violation, highlighting their phenomenological implications and model classifications.

Contribution

It provides a systematic categorization of minimal models with spontaneous lepton number violation and explores their rich majoron phenomenology.

Findings

All models relate to a form of the type-I seesaw with explicit lepton number violation.

Identified models with significant majoron-related phenomenology.

Some models predict sizable decay rates involving the majoron despite heavy mediators.

Abstract

We provide a comprehensive analysis of the Type-I Seesaw family of neutrino mass models, including the conventional type-I seesaw and its low-scale variants, namely the linear and inverse seesaws. We establish that all these models essentially correspond to a particular form of the type-I seesaw in the context of explicit lepton number violation. We then focus into the more interesting scenario of spontaneous lepton number violation, systematically categorizing all inequivalent minimal models. Furthermore, we identify and flesh out specific models that feature a rich majoron phenomenology and discuss some scenarios which, despite having heavy mediators and being invisible in processes such as $\mu \to e \gamma$, predict sizable rates for decays including the majoron in the final state.