We consider a Fermi gas of free tachyons as a continuous medium and find whether it satisfies the causality condition. There is no stable tachyon matter with the particle density below critical value n T and the Fermi momentum k F < 3 2 m that depends on the tachyon mass m. The pressure P and energy density E cannot be arbitrary small, but the situation P > E is not forbidden. Existence of shock waves in tachyon gas is also discussed. At low density n T < n < 3.45n T the tachyon matter remains stable but no shock wave survives.

We consider an ideal Fermi gas of tachyonic thermal excitations as a continuous medium and establish when it satisfies the causality condition. At high temperature the sound speed is always subluminal c s < 1, but there is no stable form of tachyon matter below the critical temperature T < T c = 0.23m that depends on the tachyon mass m. The pressure P and energy density E cannot be arbitrary small, but P can exceed E, and P = 2.36E when T → T c .

The original article contains two typographical errors. (A) The normal nuclear density ρ 0 was given in incorrect units. The correct value is ρ 0 = 2.8 × 10 17 kg/m 3 . (B) Formula (9) for the Hartree contribution to the energy density appeared with a misprint. The correct formula isThese misprints do not affect the other equations, and thus, all the remaining calculations, graphs, and conclusions remain correct and unchanged. 049902-1 0556-2813/2011/83(4)/049902 (1)

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