WMAP five-year data constraints on the unified model of dark energy and dark matter

We derive constraints on the parameter space of the unified model of dark energy and dark matter, the generalized Chaplygin gas, from the amplitudes and positions of the first few peaks and first trough of the cosmic microwave background radiation power spectrum, using the latest WMAP five-year data.

Figure 1

Contour plots of the first two Doppler peaks and first trough locations, as well as for the baryon acoustic peak, in the (${\Omega }_m$, $h$) plane for the GCG model, with $n_S=0.963$ for $\alpha =0$ (left graphic) and $\alpha =0.2$ (right figure). Full, dashed, dot-dashed, and dotted contours correspond to observational bounds on $l_{p1}$, $l_{p2}$, $l_{d1}$ [Eq. (15)] and the baryon acoustic peak [Eq. (17)], respectively. The box indicates the bounds on $h$ and ${\Omega }_m{h}^2$ from the WMAP five-year data. Darker and lighter shaded areas correspond to the allowed regions with and without BAO, respectively.

Figure 2

Contour plots of the first two Doppler peaks and first trough locations, as well as for the baryon acoustic peak, in the ($A_S$, $\alpha$) plane for the GCG model, with $n_S=0.963$ and $h=0.719$. Full, dashed, dot-dashed, and dotted contours correspond to observational bounds on, respectively, $l_{p1}$, $l_{p2}$, $l_{d1}$ [Eq. (15)] and the baryon acoustic peak [Eq. (17)]. Darker and lighter shaded areas correspond to the allowed regions with and without BAO, respectively.

Figure 3

The spectrum for the GCG model, compared with a $\Lambda \mathrm{CDM}$ model (dashed curve), for $\alpha =0.5$, $n_S=0.963$, $\tau =0.087$ and $h=0.719$, for $A_S=0.7$, 0.8, 0.9, 0.99, 0.999, from top to bottom, respectively (at the plateau).

Figure 4

The spectrum for the GCG model, compared with a $\Lambda \mathrm{CDM}$ model (dashed curve), for $A_S=0.99$, $n_S=0.963$, $\tau =0.087$, and $h=0.719$, for $\alpha =1$, 0.5, 0.2, 0.1, 0, from top to bottom, respectively (at the plateau).

Figure 5

Marginalized posterior probability densities for the model parameters. Dotted lines are the likelihood functions. The vertical dashed lines mark the $1\sigma$ and $2\sigma$ confidence levels.