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

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 Omega(m0), variable cosmic curvature Omega(k0), and variable Hubble constant H-0 on the dark energy EoS. We find that too small or large Omega(m0), Omega(k0), and H-0 are all disfavored by our GP reconstructions based on current cosmological observations. Subsequently, we find that variables Omega(m0) and 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'(z) and D ''(z). However, variable H-0 affects the reconstructions of the dark energy EoS by affecting obviously those of D(z), D'(z), and D ''(z). Furthermore, we find that the results of our reconstructions support substantially the recent local measurement of H-0 reported by Riess et al.