Exploring the evolution of color-luminosity parameter $β$ and its effects on parameter estimation

It has been found in previous studies that, for the Supernova Legacy Survey three-year (SNLS3) data, there is strong evidence for the redshift-evolution of color-luminosity parameter $β$. In this paper, using three simplest dark energy models ($Λ$CDM, $w$CDM, and CPL), we further explore the evolution of $β$ and its effects on parameter estimation. In addition to the SNLS3 data, we also take into account the Planck distance priors data, as well as the latest galaxy clustering (GC) data extracted from SDSS DR7 and BOSS. We find that, for all the models, adding a parameter of $β$ can reduce $χ^2_{min}$ by $\sim$ 36, indicating that $β_1 = 0$ is ruled out at 6$σ$ confidence levels. In other words, $β$ deviates from a constant at 6$σ$ confidence levels. This conclusion is insensitive to the dark energy models considered, showing the importance of considering the evolution of $β$ in the cosmology-fits. Furthermore, it is found that varying $β$ can significantly change the fitting results of various cosmological parameters: using the SNLS3 data alone, varying $β$ yields a larger $Ω_m$ for the $Λ$CDM model; using the SNLS3+CMB+GC data, varying $β$ yields a larger $Ω_m$ and a smaller $h$ for all the models. Moreover, we find that these results are much closer to those given by the CMB+GC data, compared to the cases of treating $β$ as a constant. This indicates that considering the evolution of $β$ is very helpful for reducing the tension between supernova and other cosmological observations.

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