1201.5446 (Yun-He Li et al.)

On initial condition of the new agegraphic dark energy model    [PDF]

Yun-He Li, Jing-Fei Zhang, Xin Zhang

The initial condition $\Omega_{\rm de}(z_{\rm ini})=n^2(1+z_{\rm
ini})^{-2}/4$ at $z_{\rm ini}=2000$ widely used to solve the differential
equation of $\Omega_{\rm de}$, the density of the new agegraphic dark energy
(NADE), makes the NADE model be a single-parameter dark-energy cosmological
model. However, this initial condition, we find, is only applicable in a flat
universe with only dark energy and pressureless matter. In fact, in order to
obtain more information from current observational data, such as cosmic
microwave background (CMB) and baryon acoustic oscillations (BAO), it often
needs us to consider the contribution of radiation. For this situation, the
initial condition mentioned above becomes invalid. To overcome this shortage,
we deeply investigate the evolution of NADE in the matter-dominated and
radiation-dominated epochs, and obtain a new initial condition $\Omega_{\rm
de}(z_{\rm ini}) = \frac{n^2(1+z_{\rm ini})^{-2}}{4} (1+\sqrt{F(z_{\rm
ini})})^2$ at $z_{\rm ini}=2000$. Here
$F(z)\equiv\frac{\Omega_{r0}(1+z)}{\Omega_{m0}+\Omega_{r0}(1+z)}$ with
$\Omega_{r0}$ and $\Omega_{m0}$ the current density parameters of radiation and
pressureless matter, respectively. This revised initial condition is applicable
for the differential equation of $\Omega_{\rm de}$ obtained in the standard FRW
universe with dark energy, pressureless matter, radiation and even spatial
curvature, and can still keep the NADE model being a single-parameter model.
With the revised initial condition and the observational data of type Ia
supernova (SNIa), CMB and BAO, we finally constrain the NADE model. The results
show that the single free parameter $n$ of the NADE model can be constrained
tightly.

View original: http://arxiv.org/abs/1201.5446