Comment on "Acoustics of tachyon Fermi gas" [E. Trojan and G.V. Vlasov,   arXiv:1103.2276 (hep-ph)]
  In contrast to Trojan and Vlasov [arXiv:1103.2276 (hep-ph)], it is found that an ideal Fermi gas of tachyons has a subluminous velocity of sound for any particle density and, therefore, the causality condition for a tachyon gas holds always true. Also, an ideal Fermi gas of tachyons never possesses an exotic equation of state with the pressure exceeding the energy density. 
S. N. Burmistrov
hep-ph astro-ph.CO