Zee model with quasidegenerate neutrino masses and where to find it

TL;DR

This paper introduces a Zee model with a family-dependent $Z_2$ symmetry that predicts quasidegenerate neutrino masses and makes testable predictions for neutrino parameters, lepton flavor violation, and collider signals.

Contribution

The model uniquely combines a $Z_2$ symmetry with radiative neutrino mass generation, constraining parameters and making specific predictions for neutrino masses and experimental signatures.

Findings

Neutrino masses are quasidegenerate with total mass between 100-130 meV.

Lepton flavor violation processes exclude certain parameter regions.

Collider searches for scalar decays into muons can surpass LFV constraints.

Abstract

We present a Zee model with a family dependent $Z_2$ symmetry for radiative neutrino masses. Our motivation is to get a model that correctly describes neutrino oscillation phenomena, while at the same time offers definite predictions. The imposed $Z_2$ symmetry greatly reduces the number of free parameters in the model. These parameters are then determined from the neutrino data, from which one can study its outcomes. Our setup only admits quasidegenerate neutrino masses with the sum of neutrino masses between 100 and 130 meV, the effective Majorana mass between 20 and 40 meV, and the effective electron neutrino mass between 48 and 53 meV. The ratio of the vacuum expectation values of the Higgs doublets, $\tbeta$, is found to be $\tbeta\lesssim 0.5$ and $\tbeta\gtrsim 10$. The former is ruled out by lepton flavor violation (LFV) processes, such as $\mu\to e\gamma$ and $\mu\to e$ conversion, which are determined up to two loops. For the latter, these LFV processes are within reach of the next generation of experiments. Moreover, for $\tbeta\gtrsim10$, the couplings of heavy neutral scalars to dimuon are significant. If they are sufficiently light, i.e., $\lesssim200$ GeV, collider search for their decays into muon pair provides a stronger constraint on most parts of the model parameter space than the LFV ones.