Tachyons as gauge fields and the dark matters in the Universe -- Tachyons compatible with causality

A tachyon field having a negative squared-masses $-m_t^2$ can be described in terms of infinitely degenerate massless fields. The degeneracy can be described as a gauge freedom. This picture for tachyons does not contradict causality. It is seen that the tachyons can be quenched in the Lorentz gauge, and the effects can be represented by the gauge factor. The accelerated expansion of the Universe and the dark energies are interpreted in terms of the gauge factor