Improved constraints on the dark energy equation of state using Gaussian processes

Abstract

We perform a comprehensive study of the dark energy equation of state (EoS) utilizing the model-independent Gaussian processes (GP). Using a combination of the Union 2.1 data set, the 30 newly added H(z) cosmic chronometer data points and Planck's shift parameter, we modify the usual GaPP code and provide a tighter constraint on the dark energy EoS than the previous literature about GP reconstructions. Subsequently, we take the ``controlling variable method '' to investigate directly the effects of the variable matter density parameter ${\mathrm{\ensuremath{\Omega}}}_{m0}$, variable cosmic curvature ${\mathrm{\ensuremath{\Omega}}}_{k0}$, and variable Hubble constant ${H}_{0}$ on the dark energy EoS. We find that too small or large ${\mathrm{\ensuremath{\Omega}}}_{m0}$, ${\mathrm{\ensuremath{\Omega}}}_{k0}$, and ${H}_{0}$ are all disfavored by our GP reconstructions based on current cosmological observations. Subsequently, we find that variables ${\mathrm{\ensuremath{\Omega}}}_{m0}$ and ${\mathrm{\ensuremath{\Omega}}}_{k0}$ affect the reconstructions of the dark energy EoS but hardly affect the reconstructions of the normalized comoving distance $D(z)$ and its derivatives ${D}^{\ensuremath{'}}(z)$ and ${D}^{\ensuremath{'}\ensuremath{'}}(z)$. However, variable ${H}_{0}$ affects the reconstructions of the dark energy EoS by affecting obviously those of $D(z)$, ${D}^{\ensuremath{'}}(z)$, and ${D}^{\ensuremath{'}\ensuremath{'}}(z)$. Furthermore, we find that the results of our reconstructions support substantially the recent local measurement of ${H}_{0}$ reported by Riess et al.