  Recent experimental research progress of solar neutrino and neutrino
oscillation reveals that neutrinos do have nonzero mass, which poses a serious
challenge to theoretical physics. Two symmetries, the common invariance under
the space-time inversion and the invariance or violation to maximum under the
space inversion are analyzed for Dirac equation or the equation for
superluminal neutrino respectively. Then a simple three-flavor model containing
only one parameter is proposed and the relations among neutrino oscillation,
parity violation and superluminal property are emphasized.
