Deviations from tribimaximal mixing due to the vacuum expectation value misalignment in A_4 models

TL;DR

This paper investigates how deviations in vacuum expectation value alignment in A_4 models affect neutrino mixing predictions, emphasizing the importance of neutrino mass observables for model discrimination.

Contribution

It classifies A_4 models based on particle assignments and analyzes the impact of VEV misalignment on neutrino mixing and mass observables, including a generalized seesaw model.

Findings

Deviations influence neutrino mixing angles and mass observables.

Mass-related observables can exclude certain models with future data.

A generalized seesaw model includes additional A_4 scalar representations.

Abstract

The addition of an A_4 family symmetry and extended Higgs sector to the Standard Model can generate the tribimaximal mixing pattern for leptons, assuming the correct vacuum expectation value alignment of the Higgs scalars. Deviating this alignment affects the predictions for the neutrino oscillation and neutrino mass observables. An attempt is made to classify the plethora of models in the literature, with respect to the chosen A_4 particle assignments. Of these models, two particularly popular examples have been analyzed for deviations from tribimaximal mixing by perturbing the vacuum expectation value alignments. The effect of perturbations on the mixing angle observables is studied. However, it is only investigation of the mass-related observables (the effective mass for neutrinoless double beta decay and the sum of masses from cosmology) that can lead to the exclusion of particular models by constraints from future data, which indicates the importance of neutrino mass in disentangling models. The models have also been tested for fine-tuning of the parameters. Furthermore, a well-known seesaw model is generalized to include additional scalars, which transform as representations of A_4 not included in the original model.