Tachyonic thermal excitations and causality

TL;DR

This paper investigates the conditions under which a hypothetical tachyonic Fermi gas maintains causality, finding that high temperatures ensure subluminal sound speeds, but stable tachyon matter only exists above a critical temperature.

Contribution

It provides a theoretical analysis of tachyonic thermal excitations, establishing causality conditions and identifying the temperature range for stable tachyon matter.

Findings

Sound speed remains subluminal at high temperatures.

Stable tachyon matter exists only above a critical temperature T_c<0.23m.

Pressure can exceed energy density, with P=2.36E near T_c.

Abstract

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 $T_c<0.23m$ 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 $T\rightarrow T_c$.