Cosmological tests with the joint lightcurve analysis

Abstract

We examine whether a comparison between wCDM and $R_{\textrm{h}}=ct$ using merged Type-Ia SN catalogs produces results consistent with those based on a single homogeneous sample. Using the Betoule et al. (Astron. Astrophys., 568 (2014) 22). Joint Lightcurve Analysis (JLA) of a combined sample of 613 events from SNLS and SDSS-II, we estimate the parameters of the two models and compare them. We find that the improved statistics can alter the model selection in some cases, but not others. In addition, based on the model fits, we find that there appears to be a lingering systematic offset of ~0.04–0.08 mag between the SNLS and SDSS-II sources, in spite of the cross-calibration in the JLA. Treating wCDM, ΛCDM and $R_{\textrm{h}}=ct$ as separate models, we find in an unbiased pairwise statistical comparison that the Bayes Information Criterion (BIC) favors the $R_{\textrm{h}}=ct$ Universe with a likelihood of $82.8\%$ vs. $17.2\%$ for wCDM, but the ratio of likelihoods is reversed ($16.2\%$ vs. $83.8\%$ ) when $w_{\textrm{de}}=-1$ (i.e., ΛCDM) and strongly reversed ($1.0\%$ vs. $99.0\%$ ) if in addition k = 0 (i.e., flat ΛCDM). We point out, however, that the value of k is a measure of the net energy (kinetic plus gravitational) in the Universe and is not constrained theoretically, though some models of inflation would drive $k\rightarrow 0$ due to an expansion-enforced dilution. Since we here consider only the basic ΛCDM model, the value of k needs to be measured and, therefore, the pre-assumption of flatness introduces a significant bias into the BIC.