Is Neutrino a Superluminal Particle?

Based on the experimental discovery that the mass-square of neutrino is negative, a quantum theory for superluminal neutrino is proposed. Two Weyl equations coupled together via a mass term respecting the maximum parity violation lead to a new equation which describes the superluminal motion of neutrino with permanent helicity. Various strange features of subluminal and superluminal particles can be ascribed to the relative variation of two contradictory fields superposing coherently inside the particle with the change of its speed u in the whole range ($0<u<\infty$). Being compatible with the theory of special relativity, this theory may have various applications.