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

Abstract

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.