Dirac CP phase in the neutrino mixing matrix and the Froggatt-Nielsen mechanism with ${\rm \bf det} \bf [M_\nu]=0$

Abstract

We discuss the Dirac CP violating phase $\delta_{CP}$ in the Froggatt-Nielsen model for a neutrino mass matrix $M_\nu$ imposing a condition ${\rm det} [M_\nu]=0$. This additional condition restricts the CP violating phase $\delta_{CP}$ drastically. We find that the phase $\delta_{CP}$ is predicted in the region of $\pm (0.4- 2.9)$ radian, which is consistent with the recent T2K and NO$\nu$A data. There is a remarkable correlation between $\delta_{CP}$ and $\sin^2\theta_{23}$. The phase $\delta_{CP}$ converges on $\sim \pm \pi/2$ if $\sin^2\theta_{23}$ is larger than $0.5$. Thus, accurate measurements of $\sin^2\theta_{23}$ are important for a test of our model. The effective mass $m_{ee}$ for the neutrinoless double beta decay is predicted in the rage of $3.3-4.0$ meV.