Instability of holographic dark energy models

TL;DR

This paper compares the stability of holographic dark energy with Chaplygin gas and tachyon models, revealing that holographic dark energy is classically unstable due to negative squared sound speed, unlike the other models.

Contribution

It provides a detailed analysis of the squared speeds of sound in different dark energy models, highlighting the classical instability of holographic dark energy.

Findings

Holographic dark energy has negative squared sound speed with future event horizon cutoff.

Chaplygin gas and tachyon models have non-negative squared sound speeds.

Holographic dark energy's classical instability challenges its physical viability.

Abstract

We investigate the difference between holographic dark energy, Chaplygin gas, and tachyon model with constant potential. For this purpose, we examine their squared speeds of sound which are evaluated to zeroth order in perturbation theory and hence depends only on time. We find that the squared speed for holographic dark energy is always negative when choosing the future event horizon as the IR cutoff, while those for Chaplygin gas and tachyon are non-negative. This means that the perfect fluid for holographic dark energy is classically unstable. Hence the holographic interpretation for Chaplygin gas and tachyon is problematic.