in terms of these six Dirac neutrino masses and the CP-violating Dirac phase, which are used to find constraints to induce maximal CP violation. To obtain simple and useful relations in the minimal seesaw model, we choose one combination of Dirac neutrino masses to vanish, which includes texture one zero. The detailed discussions to reach various constraints on Dirac neutrino masses are presented in Appendix \[sec:Appendix\]. In Sec.\[sec:3\], we derive necessary constraints on the Dirac neutrino masses to induce maximal CP violation. Finally, further assuming maximal atmospheric neutrino mixing, we determine six Dirac neutrino masses to be real or imaginary. The final section Sec.\[sec:4\] is devoted to summary and discussions, which include a preliminary argument on the creation of the baryon number of the universe via the leptogenesis based on our constraints on the Dirac neutrino masses.

\[sec:2\]Dirac masses and Dirac CP violation
============================================

The minimal seesaw model contains two extra right-handed neutrinos. We understand that a $2 \times 2$ heavy neutrino mass matrix $M_R$ and a charged lepton mass matrix are transformed into diagonal and real ones. After the heavy right-handed neutrinos are decoupled, the minimal seesaw mechanism generates a symmetric $3 \times 3$ light neutrino mass matrix $M_\nu$ 