A new model of agegraphic dark energy

In this note, we propose a new model of agegraphic dark energy based on the Károlyházy relation, where the time scale is chosen to be the conformal time η of the Friedmann–Robertson–Walker (FRW) universe. We find that in the radiation-dominated epoch, the equation-of-state parameter of the new agegraphic dark energy wq=−1/3 whereas Ωq=n2a2; in the matter-dominated epoch, wq=−2/3 whereas Ωq=n2a2/4; eventually, the new agegraphic dark energy dominates; in the late time wq→−1 when a→∞, and the new agegraphic dark energy mimics a cosmological constant. In every stage, all things are consistent. The confusion in the original agegraphic dark energy model proposed in R.G. Cai, Phys. Lett. B 657 (2007) 228, arXiv: 0707.4049 [hep-th] disappears in this new model. Furthermore, Ωq≪1 is naturally satisfied in both radiation-dominated and matter-dominated epochs where a≪1. In addition, we further extend the new agegraphic dark energy model by including the interaction between the new agegraphic dark energy and background matter. In this case, we find that wq can cross the phantom divide.