Tachyonic approach to neutrino dark matter

We apply a new approach based on three relativistic groups (bradyon, tachyon and instanton) forming the `Lorentz groupoid' which allows, in particular, to consider tachyons without introducing imaginary masses and negative energies (related, as known, to violation of causality and unitarity). This leads to effectively scalar conglomerate composed of tachyonic neutrino and antineutrino spinor wave functions as a viable model for stationary dark matter. We also briefly discuss a relevant early non-stationary high-energy stage of the universe evolution.