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. 
Ernst Trojan
astro-ph.CO cond-mat.stat-mech