http://arxiv.org/abs/1401.5615
In this paper we investigate the index of the dark energy equation of state $w$ by using the latest observational data. To explore possible non-linear evolutions in $w$, we adopt a second order $parabolic$ parametrization $w(z)=w_0+w_a(a_0-a)^2$, which has the advantage of describing the possible $inflection$ point in $w$. We use a combined dataset of the SNLS3 supernovae sample, the cosmic microwave background measurements from WMAP9 and Planck, the Hubble parameter measurement from HST, and the baryon acoustic oscillations measurements which includes the most recent results from BOSS DR11 and “improved” WiggleZ. We find that a crossing of $w=-1$ at $z\sim 0.9-1.5$ is favored at about $1\ \sigma$ confidence level (CL), with $w>-1$ at high redshift and $w<-1$ at lower redshift. More interestingly, we find an inflection of $w$ at $z\sim 0.25-0.4$ is mildly favored at $1\ \sigma$ CL, with a phantom behavior at the extreme point $w(z\sim0.25)<-1$ favored at about $2\ \sigma$ CL. Our reconstructed $w$ is in good agreement with the result of Zhao et al (2012). For comparison, the fitting result of linear CPL model $w(z)=w_0+w_a(1-a)$ shows a similar crossing but does not contain an inflection. Compared with the $\Lambda$CDM and the CPL models, the parabolic model provides a better fit with $\Delta \chi^2=-2.9$ and $\Delta \chi^2=-6.4$, respectively. Our result shows the advantage and necessity of considering high order parametrization when investigating the dark energy.
Thu, 23 Jan 14
42/70
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