Stability of hot tachyon gas
  We consider a tachyon gas that obeys Maxwell-Boltzmann statistics. The sound
speed is always subluminal and it tends to the limiting minimum value
$c_s=1/\sqrt{2}$ in non-relativistic gas (at low temperature), decreasing
monotonously with the growth of temperature and attaining ultra-relativistic
limit $c_s=1/% \sqrt{3}$ at high temperature. The hot tachyon gas always
satisfies the causality.
