Kyoung Yee Kim

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 ( 2.513775 ) 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.

On the Ricci dark energy model

We study the Ricci dark energy model (RDE) which was introduced as an alternative to the holographic dark energy model. We point out that an accelerating phase of the RDE is that of a constant dark energy model. This implies that the RDE is not a new model of explaining the present accelerating universe.

HOLOGRAPHIC INTERACTING DARK ENERGY IN THE BRANEWORLD COSMOLOGY

We investigate a model of brane cosmology to find a unified description of the radiation-matter-dark energy universe. It is of the interacting holographic dark energy with a bulk-holographic matter

Equations of state in the Brans–Dicke cosmology

\chi

DENSITY PERTURBATIONS IN DECAYING HOLOGRAPHIC DARK ENERGY MODELS

. This is a five-dimensional cold dark matter, which plays a role of radiation on the brane. Using the effective equations of state

Modified relativistic dynamics

\omega^{\rm eff}_{\rm \Lambda}

Future cosmological evolution in f(R) gravity using two equations of state parameters

instead of the native equations of state

Late-time acceleration in the coupled Cubic Galileon models

\omega_{\rm \Lambda}

MASSIVE GRAVITONS DARK MATTER SCENARIO REVISITED

, we show that this model cannot accommodate any transition from the dark energy with

EVOLUTION OF DISTRIBUTION FUNCTION FOR COSMOLOGICAL NEUTRINO

\omega^{\rm eff}_{\rm \Lambda}\ge-1