Thermodynamical properties of dark energy

TL;DR

This paper explores the thermodynamical behavior of dark energy, deriving its entropy under various models and examining the validity of thermodynamic laws in these contexts.

Contribution

It introduces a model for dark energy entropy based on temperature evolution and analyzes thermodynamic laws for different dark energy equations of state.

Findings

Entropy is positive and within bounds for $w>-1$ and Chaplygin gas.

Total entropy obeys the generalized second law for certain dark energy models.

Phantom energy models violate entropy positivity and the second law.

Abstract

We have investigated the thermodynamical properties of dark energy. Assuming that the dark energy temperature $T\sim a^{-n}$ and considering that the volume of the Universe enveloped by the apparent horizon relates to the temperature, we have derived the dark energy entropy. For dark energy with constant equation of state $w>-1$ and the generalized Chaplygin gas, the derived entropy can be positive and satisfy the entropy bound. The total entropy, including those of dark energy, the thermal radiation and the apparent horizon, satisfies the generalized second law of thermodynamics. However, for the phantom with constant equation of state, the positivity of entropy, the entropy bound, and the generalized second law cannot be satisfied simultaneously.