General Property of Neutrino Mass Matrix and CP Violation
  It is found that the atmospheric neutrino mixing angle of \theta_{atm} is determined to be \tan\theta_{atm}=Im(B)/Im(C) for B=M_{\nu_e\nu_\mu} and C=M_{\nu_e\nu_\tau}, where M_{ij} is the ij element of M^\dagger_\nu M_\nu with M_\nu as a complex symmetric neutrino mass matrix in the (\nu_e, \nu_\mu, \nu_\tau)-basis. Another mixing angle, \theta_{13}, defined as U_{e3} = \sin\theta_{13}e^{-i\delta} is subject to the condition: \tan 2\theta_{13} \propto |\sin\theta_{atm}B+\cos\theta_{atm}C| and the CP-violating Dirac phase of \delta is identical to the phase of \sin\theta_{atm}B^\ast+\cos\theta_{atm}C^\ast. The smallest value of |\sin \theta_{13}| is achieved at \tan\theta_{atm}=-Re(C)/Re(B) that yields the maximal CP-violation and that implies C=-\kappa B^\ast for the maximal atmospheric neutrino mixing of \tan\theta_{atm}=\kappa=\pm 1. The generic smallness of |\sin \theta_{13}| can be ascribed to the tiny violation of the electron number conservation. 
Ichiro Aizawa, Masaki Yasue