Relativistic transformation of temperature for exotic cosmological fluids

Abstract

We study the relativistic transformation of temperature for effective cosmological fluids with negative pressure within a covariant thermodynamic framework. The Lorentz transformation of temperature is derived for barotropic fluids with $p=wρ$ and for the (generalized) Chaplygin gas with $p=-A/ρ^α$. For barotropic fluids with constant negative equation-of-state parameter, we show that negative pressure suppresses the growth of temperature under relativistic boosts. In contrast, the Chaplygin gas exhibits a qualitatively different behavior due to its density-dependent pressure, leading to a monotonic increase of the transformed temperature with velocity. The dependence of the relativistic temperature on the relative velocity and background energy density is illustrated through representative examples.