  Flavor oscillation of traveling neutrinos is treated by solving the
one-dimensional Dirac equation for massive fermions. The solutions are given in
terms of squeezed coherent state as mutual eigenfunctions of parity operator
and the corresponding Hamiltonian, both represented in bosonic creation and
annihilation operators. It was shown that a mono-energetic state is
non-normalizable, and a normalizable Gaussian wave packet, when of pure parity,
cannot propagate. A physical state for a traveling neutrino beam would be
represented as a normalizable Gaussian wave packet of equally-weighted mixing
of two parities, which has the largest energy-dependent velocity. Based on this
wave-packet representation, flavor oscillation of traveling neutrinos can be
treated in a strict sense. These results allow the accurate interpretation of
experimental data for neutrino oscillation, which is critical in judging
whether neutrino oscillation violates CP symmetry.
