  Quantum field theory of space-like particles is investigated in the framework
of absolute causality scheme preserving Lorentz symmetry. It is shown that
tachyons are associated with unitary orbits of Poincar\'e mappings induced from
SO(2) little group instead of SO(2,1) one. Therefore the corresponding
elementary states are labelled by helicity. A particular case of the helicity
$\lambda=\pm{1/2}$ is investigated in detail and a corresponding consistent
field theory is proposed. In particular, it is shown that the Dirac-like
equation proposed by Chodos {\it et al}., inconsistent in the standard
formulation of QFT, can be consistently quantized in the presented framework.
This allows us to treat more seriously possibility that neutrinos can be
fermionic tachyons as it is suggested by the present experimental data about
neutrino masses.
