A Model of Neutrino Mass Matrix With $\delta =-\pi /2$ and ${\theta }_{23}=\pi /4$

Abstract

Experimental data have provided stringent constraints on neutrino mixing parameters. In the standard parameterization the mixing angle ${\theta }_{23}$ is close to $\pi /4$. There are also evidences show that the CP violating phase is close to $-\pi /2$. We study neutrino mass matrix reconstructed using this information and find several interesting properties. We show that a theoretical model based on the $A_4$ symmetry naturally predicts $\delta =-\pi /2$ and ${\theta }_{23}=\pi /4$ when the Yukawa couplings and scalar vacuum expectation values are real reaching a $\mu -\tau$ exchange and CP conjugate symmetry limit. In this case CP violation solely comes from the complex group theoretical Clebsh-Gordan coefficients. The model also predicts $|V_{e2}|=1/\sqrt{3}$ consistent with data. With complex Yukawa couplings the values for $\delta$ and ${\theta }_{23}$ can be significantly deviate away from the symmetry values $-\pi /2$ and $\pi /4$, respectively. But $|V_{e2}|=1/\sqrt{3}$ is not altered. This matrix is an excellent lowest order approximation for theoretical model buildings of neutrino mass matrix.

Comments: RevTex 9 pages, no figure. Version appeared in CJP