Minimal Multi-Majoron Model

TL;DR

This paper proposes a minimal multi-Majoron model with two right-handed neutrinos, analyzing its implications for neutrino physics, topological defect formation, and gravitational wave signals from early universe phase transitions.

Contribution

It introduces a UV-complete minimal multi-Majoron model with two Majoron fields, linking neutrino masses, flavor mixing, and cosmological gravitational wave signatures.

Findings

Distinctive gravitational wave spectrum from cosmic strings and phase transitions

Determination of right-handed neutrino mass scales from gravitational wave data

Analysis of topological defect formation and decay in the model

Abstract

In order to provide a natural framework for hierarchical right-handed neutrinos, we propose a realistic ultraviolet complete minimal multi-Majoron model (MMMM). We consider two right-handed neutrinos for simplicity, although the model is readily extendable to more. The minimal model introduces two complex scalar Majoron fields $\phi_1$ and $\phi_2$, whose couplings to the two respective right-handed neutrinos are controlled by an extra global $U(1)_N$ symmetry. We show that a flavon field is required to facilitate the effective Yukawa couplings, in order to implement the type I seesaw mechanism. We analyse the resulting phenomenology related to neutrino masses, flavour mixing and cosmological predictions concerning the formation and decay of topological defects like the global cosmic strings and the domain walls when the $U(1)_N\times U(1)_{B-L}$ symmetry is broken. The resulting gravitational wave spectrum is a distinctive combination of the spectrum from the global cosmic string and strong first-order phase transitions when the symmetries are broken, the strength of the latter being enhanced by the second Majoron field. The resulting characteristic spectrum determines the two right-handed neutrino mass scales within the considered framework.