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

TL;DR

This study combines multiple cosmological data sets to refine constraints on the universe's curvature and dark energy properties, emphasizing the importance of marginalized analysis and revealing that dark energy's equation of state is negative up to redshift 2.

Contribution

It provides updated, marginalized constraints on dark energy parameters using combined observational data and compares statistical methods for error estimation.

Findings

Dark energy's equation of state is negative up to redshift 2 at >3σ

Flat ΛCDM model is consistent with data at 1σ

Marginalized errors for key cosmological parameters are provided

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 $\chi^2$ 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 $\Omega_k$ and $w_a$ in the Chevallier-Polarski-Linder model are skew distributions, and the marginalized $1\sigma$ errors are $\Omega_m=0.279^{+0.015}_{-0.008}$, $\Omega_k=0.005^{+0.006}_{-0.011}$, $w_0=-1.05^{+0.23}_{-0.06}$, and $w_a=0.5^{+0.3}_{-1.5}$. For the Jassal-Bagla-Padmanabhan model, the marginalized $1\sigma$ errors are $\Omega_m=0.281^{+0.015}_{-0.01}$, $\Omega_k=0.000^{+0.007}_{-0.006}$, $w_0=-0.96^{+0.25}_{-0.18}$, 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 $3\sigma$ level. The flat $\Lambda$CDM model is consistent with the current observational data at the $1\sigma$ level.