Instability of agegraphic dark energy models

TL;DR

This paper analyzes the stability and cosmological viability of agegraphic dark energy models, finding they are classically unstable and only suitable for certain parameter ranges, thus questioning their effectiveness.

Contribution

It provides a detailed stability analysis of agegraphic dark energy models and identifies parameter constraints for their applicability in cosmology.

Findings

Squared speed of sound is always negative, indicating classical instability.

The model describes matter/radiation-dominated universe only for specific parameter values.

It is no more effective than holographic dark energy in explaining dark energy.

Abstract

We investigate the agegraphic dark energy models which were recently proposed to explain the dark energy-dominated universe. For this purpose, we calculate their equation of states and squared speeds of sound. We find that the squared speed for agegraphic dark energy is always negative. This means that the perfect fluid for agegraphic dark energy is classically unstable. Furthermore, it is shown that the new agegraphic dark energy model could describe the matter (radiation)-dominated universe in the far past only when the parameter $n$ is chosen to be $n>n_c$, where the critical values are determined to be $n_c=2.6878(2.5137752)$ numerically. It seems that the new agegraphic dark energy model is no better than the holographic dark energy model for the description of the dark energy-dominated universe, even though it resolves the causality problem.