Journal Article

Revisiting the A4 model for leptons in light of NuFIT 3.2

Kang, Sin Kyu, Takagi, Kenta, Shimizu, Yusuke, Tanimoto, Morimitsu, Takahashi, Shunya

2018

Overview

We revisit the $A_4$ model for leptons in light of the new result of NuFIT 3.2. We introduce a new flavon $\\eta$ transforming as an $A_4$ singlet $1'$ or $1''$, which couples to both charged leptons and neutrinos in next-to-leading-order operators. The model consists of five parameters: the lightest neutrino mass $m_1$, the vacuum expectation value of $\\eta$, and three CP-violating phases after inputting the experimental values of $\\Delta m_{\\rm atm}^2$ and $\\Delta m_{\\rm sol}^2$. The model with the $1''$ singlet flavon gives the prediction of $\\sin^2 \\theta_{12}$ around the best fit of NuFIT 3.2 while staying near the maximal mixing of $\\theta_{23}$. Inputting the experimental mixing angles with the $1\\,\\sigma$ error-bar, the Dirac CP-violating phase is clearly predicted to be $|\\delta_\\text{CP}|=50$–$120^\\circ$, which will be tested by the precise observed value in the future. In order to get the best-fit value $\\sin^2\\theta_{23}=0.538$, the sum of three neutrino masses is predicted to be larger than $90$meV. The cosmological observation for the sum of the neutrino masses will also provide a crucial test of our predictions. It is remarked that the model is consistent with the experimental data only for the normal hierarchy of neutrino masses.

• Publisher: Oxford University Press
• Subject: Neutrinos