  This paper proposes that the elusive neutrino is a space-like unitary
irreducible representation of the Poincare Group. Although its imaginary mass
is not a physical observable, its square is. This amount is found
experimentally to be negative. Therefore, the neutrino is a tachyon with a
measurable property; the square of its mass. This paper does not resolve the
problem of how the neutrino propagates in the space. Further studies are
necessary to address this question.
