On phantom thermodynamics with negative temperature

TL;DR

This paper explores the thermodynamic behavior of a universe with dark energy fluids, demonstrating that phantom phases with negative temperatures can be physically consistent under certain conditions.

Contribution

It shows that the phantom phase with $w<-1$ can be thermodynamically consistent even with negative temperatures, expanding understanding of dark energy thermodynamics.

Findings

Phantom phase can be thermodynamically allowed with negative temperature.

Existence of conditions maintaining physical values of pressure and density.

Thermodynamic consistency of dark energy fluids with $w<-1$.

Abstract

We discuss the thermodynamic properties of the Friedmann-Robertson-Walker universe with dark energy fluids labelled by $\omega=p/\rho<-1/3$. Using the integrability condition, we show that the phantom phase of $w<-1$ can still be thermodynamically allowed even when the temperature takes on negative values because in that case, there exists at least a condition of keeping physical values for $p$ and $\rho$