A Note on Agegraphic Dark Energy

Ishwaree P. Neupane

doi:10.1016/j.physletb.2009.02.012

paper

A Note on Agegraphic Dark Energy

arXiv:0708.2910 · doi:10.1016/j.physletb.2009.02.012

Abstract

Recently a new model of dynamical dark energy, or time-varying $Λ$ , was proposed by Cai [arXiv:0707.4049] by relating the energy density of quantum fluctuations in a Minkowski space-time, namely $ρ_{q} \equiv 3 n^{2} m_{P}^{2} / t^{2}$ , where $n \sim O (1)$ and t is the cosmic time, to the present day dark energy density. In this note, we show that the model can be adjusted to the present values of dark energy density parameter $Ω_{q}$ ( $≃ 0.73$ ) and the equation of state $w Z q$ ( $≃ - 1$ ) only if the numerical coefficient $n$ takes a reasonably large value ( $n ≳ 3$ ) or the present value of the gravitational coupling of q-field to (dark) matter is also nonzero, namely, $Q ~ ≃ \frac{2}{n} (Ω Z q 0)^{3/2} > 0$ where $Ω Z q 0$ is the present value of dark energy density fraction. We also discuss some of the difficulties of this proposal as a viable dark energy model with a constant $n$ ; especially, the bound imposed on the dark energy density parameter $Ω_{q} < 0.1$ during big bang nucleosynthesis (BBN) requires $n < 1/6$ . To overcome this drawback, we outline a few modifications where such constraints can be weakened or relaxed. Finally, by establishing a correspondence between the agegraphic dark energy scenario and the standard scalar-field model, we also point out some interesting features of an agegraphic quintessence model.

18 pages, several eps figures; significant changes in Secs. 2 & 3, Journal version

A Note on Agegraphic Dark Energy

Abstract

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