  Based on the dual principle in super-luminous Lorentz transformation this
work shows that pseudo-spin of a time-like bradyon appears to space-like
observers as iso-spin of a corresponding tachyon. Due to the weak interaction,
lepton-tachyon appears as neutrino with hidden imaginary transcendent mass,
suppressed by a factor of $\rho\sim G_F m^2_0$ compared to the rest mass $m_0$
of a corresponding space-like lepton. Assuming a coexistance of tachyon dark
matter in the solar system, we show that the solar neutrino deficit might be
explained by depolarisation of time-like electrons due to elastic scattering in
time-like plasma and the maximal deficit would reach 0.5. Neither day-night nor
seasonal effects are expected due to dynamic balance of fluxes with opposite
pseudo-spin polarisation.
