  Based on experimental evidences supporting the hypothesis that neutrinos
might be tachyonic fermions, a new Dirac-type equation is proposed and a
spin-1/2 tachyonic quantum theory is developed. The new Dirac-type equation
provides a solution for the puzzle of negative mass-square of neutrinos. This
equation can be written in two spinor equations coupled together via nonzero
mass while respecting the maximum parity violation, and it reduces to one Weyl
equation in the massless limit. Some peculiar features of tachyonic neutrino
are discussed in this theoretical framework.
