Study of Two-Loop Neutrino Mass Generation Models

TL;DR

This paper investigates two-loop radiative models for Majorana neutrino mass generation involving scalar triplets and doubly charged scalars, predicting a normal hierarchy and specific CP phases, with implications for neutrinoless double beta decay.

Contribution

It provides a detailed analysis of a specific two-loop neutrino mass model, predicting the neutrino mass hierarchy, CP phases, and examining experimental constraints and decay processes.

Findings

Neutrino mass spectrum must be a normal hierarchy.

Predicted CP phases are approximately 1.40π, 1.11π, and 1.47π.

Neutrinoless double beta decay rate can reach current experimental bounds.

Abstract

We study the models with the Majorana neutrino masses generated radiatively by two-loop diagrams due to the Yukawa $\rho \bar \ell_R^c \ell_R$ and effective $\rho^{\pm\pm} W^\mp W^\mp$ couplings along with a scalar triplet $\Delta$, where $\rho$ is a doubly charged singlet scalar, $\ell_R$ the charged lepton and $W$ the charged gauge boson. A generic feature in these types of models is that the neutrino mass spectrum has to be a normal hierarchy. Furthermore, by using the neutrino oscillation data and comparing with the global fitting result in the literature, we find a unique neutrino mass matrix and predict the Dirac and two Majorana CP phases to be $1.40\pi$, $1.11\pi$ and $1.47\pi$, respectively. We also discuss the model parameters constrained by the lepton flavor violating processes and electroweak oblique parameters. In addition, we show that the rate of the neutrinoless double beta decay $(0\nu\beta\beta)$ can be as large as the current experimental bound as it is dominated by the short-range contribution at tree level, whereas the traditional long-range one is negligible.