Quantum field theory of space-like particles is investigated in the framework of absolute causality scheme preserving Lorentz symmetry. It is related to an appropriate choice of the synchronization procedure (definition of time). In this formulation existence of field excitations (tachyons) distinguishes an inertial frame (privileged frame of reference) via spontaneous breaking of the so called synchronization group. In this scheme relativity principle is broken but Lorentz symmetry is exactly

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... reserved in agreement with local properties of the observed world. It is shown that tachyons are associated with unitary orbits of Poincaré mappings induced from SO(2) little group instead of SO(2,1) one. Therefore the corresponding elementary states are labelled by helicity. The cases of the helicity λ = 0 and λ = ±1/2 are investigated in detail and a corresponding consistent field theory is proposed. In particular, it is shown that the Dirac-like equation proposed by Chodos 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 might be fermionic tachyons as it is suggested by experimental data about neutrino masses.