  The conventional derivation of neutrino oscillation treats neutrino mass
eigenstate as plane wave with an overall evolution phase. Nevertheless, due to
the intrinsic parity-violating nature of weak interactions, only the
left-chiral neutrino can be produced as initial condition. On the other hand,
the neutrino mass term connects the left-chiral component to the right-chiral
one and unavoidably leads to generation of the later through oscillation. This
chiral oscillation has significant consequences on the detection of the
cosmological relic neutrinos. The event rate is reduced by a factor of 2 than
the conventional prediction.
