Instability of agegraphic dark energy models

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.Comment: 15 pages 4 figure

Instability of QCD Ghost Dark Energy Model

“…However, the perfect fluid of holographic DE with future event horizon is classically unstable because its squared speed is always negative [31] . Also in [32], it is shown that the agegraphic model of DE have a negative sound speed squared in flat, non-flat and also in the presence of interaction indicating the instability of this model against perturbations.…”

“…In this paper, we would like to generalize the approach presented in [28,31,32] to GDE model in a universe with spacial curvature in the presence of interaction between the dark matter and DE. Various aspects of GDE have recently investigated.…”

Dark Energy

“…In these two models, the IR cutoff length scale is given by the conformal time η and the average radius of the Ricci scalar curvature |R| −1/2 , respectively. There have been some numerical studies on these two models [574,586,587,588,589,590]. In general, these studies showed that the ADE and RDE models are not favored by current observations.…”

New Agegraphic Dark Energy Model With Generalized Uncertainty Principle

“…Hence we expect that for the present and future dark energy-dominated universe, the EOS is reduced to that of new agegarphic dark energy model as [30,31,32,52] …”