Paper detail

Improved cosmological constraints on the curvature and equation of state of dark energy

We apply the Constitution compilation of 397 supernova Ia, the baryon acoustic oscillation measurements including the $A$ parameter, the distance ratio and the radial data, the five-year Wilkinson microwave anisotropy probe and the Hubble parameter data to study the geometry of the universe and the property of dark energy by using the popular Chevallier-Polarski-Linder and Jassal-Bagla-Padmanabhan parameterizations. We compare the simple $χ^2$ method of joined contour estimation and the Monte Carlo Markov chain method, and find that it is necessary to make the marginalized analysis on the error estimation. The probabilities of $Ω_k$ and $w_a$ in the Chevallier-Polarski-Linder model are skew distributions, and the marginalized $1σ$ errors are $Ω_m=0.279^{+0.015}_{-0.008}$, $Ω_k=0.005^{+0.006}_{-0.011}$, $w_0=-1.05^{+0.23}_{-0.06}$, and $w_a=0.5^{+0.3}_{-1.5}$. For the Jassal-Bagla-Padmanabhan model, the marginalized $1σ$ errors are $Ω_m=0.281^{+0.015}_{-0.01}$, $Ω_k=0.000^{+0.007}_{-0.006}$, $w_0=-0.96^{+0.25}_{-0.18}$, and $w_a=-0.6^{+1.9}_{-1.6}$. The equation of state parameter $w(z)$ of dark energy is negative in the redshift range $0\le z\le 2$ at more than $3σ$ level. The flat $Λ$CDM model is consistent with the current observational data at the $1σ$ level.