Holographic dark energy: quantum correlations against thermodynamical description

TL;DR

This paper investigates the quantum entanglement and thermodynamic properties of holographic dark energy, revealing that quantum correlations may influence its entropy and the validity of the generalized second law in cosmological models.

Contribution

It analyzes the entanglement entropy of holographic dark energy and tests the generalized second law under different models and parameter choices.

Findings

Original Li's model passes the GSL for specific parameters.

Saturated model with Hubble IR cutoff violates the GSL.

Quantum correlations affect the thermodynamic behavior of HDE.

Abstract

Classical and quantum entropic properties of holographic dark energy (HDE) are considered in view of the fact that its entropy is far more restrictive than the entropy of a black hole of the same size. In cosmological settings (in which HDE is promoted to a plausible candidate for being the dark energy of the universe), HDE should be viewed as a combined state composed of the event horizon and the stuff inside the horizon. By any interaction of the subsystems, the horizon and the interior become entangled, raising thereby a possibility that their quantum correlations be responsible for the almost purity of the combined state. Under this circumstances, the entanglement entropy is almost the same for both subsystems, being also of the same order as the thermal (coarse grained) entropy of the interior or the horizon. In the context of thermodynamics, however, only additive coarse grained entropies matter, so we use these entropies to test the generalized second law (GSL) of gravitational thermodynamics in this framework. While we find that the original Li's model passes the GSL test for a special choice of parameters, in a saturated model with the choice for the IR cutoff in the form of the Hubble parameter, the GSL always breaks down.