Remarks on Dynamical Dark Energy Measured by the Conformal Age of the Universe

Ishwaree P. Neupane

doi:10.1103/PhysRevD.76.123006

paper

Remarks on Dynamical Dark Energy Measured by the Conformal Age of the Universe

arXiv:0709.3096 · doi:10.1103/PhysRevD.76.123006

Abstract

We elaborate on a model of conformal dark energy (dynamical dark energy measured by the conformal age of the universe) recently proposed in [H. Wei and R.G. Cai, arXiv:0708.0884] where the present-day dark energy density was taken to be $ρ_{q} \equiv 3 α^{2} m_{P}^{2} / η^{2}$ , where $η$ is the conformal time and $α$ is a numerical constant. In the absence of an interaction between the ordinary matter and dark energy field $q$ , the model may be adjusted to the present values of the dark energy density fraction $Ω Z q ≃ 0.73$ and the equation of state parameter $w Z q < - 0.78$ , if the numerical constant $α$ takes a reasonably large value, $α ≳ 2.6$ . However, in the presence of a nontrivial gravitational coupling of $q$ -field to matter, say $Q$ , the model may be adjusted to the values $Ω Z q ≃ 0.73$ and $w Z q ≃ - 1$ , even if $α \sim O (1)$ , given that the present value of $Q$ is large. Unlike for the model in [R.G. Cai, arXiv:0707.4049], the bound $Ω Z q < 0.1$ during big bang nucleosynthesis (BBN) may be satisfied for almost any value of $α$ . Here we discuss some other limitations of this proposal as a viable dark energy model. The model draws some parallels with the holographic dark energy; we also briefly comment on the latter model.

arXiv comment16 pages, 10 figures, a reference added, the version to appear in Phys. Rev. D

Remarks on Dynamical Dark Energy Measured by the Conformal Age of the Universe

Abstract

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