Neutrino Anomalies in an Extended Zee Model

TL;DR

This paper presents an extended Zee model that explains solar and atmospheric neutrino anomalies through loop-induced neutrino masses without right-handed neutrinos, using a softly broken symmetry.

Contribution

It introduces a novel extended Zee model with a specific symmetry breaking pattern that naturally accounts for neutrino mass scales and mixing angles relevant to neutrino anomalies.

Findings

The model explains atmospheric neutrino anomalies via one-loop neutrino masses.

It generates a two-loop mass splitting for the solar neutrino problem.

A variant accommodates the large-angle MSW solution.

Abstract

We discuss an extended $SU(2)\times U(1)$ model which naturally leads to mass scales and mixing angles relevant for understanding both the solar and atmospheric neutrino anomalies. No right-handed neutrinos are introduced in the model.The model uses a softly broken $L_e-L_{\mu}-L_{\tau}$ symmetry. Neutrino masses arise only at the loop level. The one-loop neutrino masses which arise as in the Zee model solve the atmospheric neutrino anomaly while breaking of $L_e-L_{\mu}-L_{\tau}$ generates at two-loop order a mass splitting needed for the vacuum solution of the solar neutrino problem. A somewhat different model is possible which accommodates the large-angle MSW resolution of the solar neutrino problem.