Non-gaussian likelihoods for Type Ia Supernovae Cosmology: Implications for Dark Energy and H0

Abstract

The latest improvements in the scale and calibration of Type Ia supernovae catalogues allow us to constrain the specific nature and evolution of dark energy through its effect on the expansion history of the universe. We present the results of Bayesian model comparison on the SNe Ia catalogue Pantheon+, where Flat ΛCDM is preferred by the data over all other models and we find moderate evidence ($\Delta \log \mathcal {Z} \sim 2.5$) to reject a number of alternate dark energy models. The effect of peculiar velocity corrections on model comparison is analysed, where we find that removing peculiar velocity corrections lessens the $\Delta \log \mathcal {Z}$ of each cosmology against ΛCDM and overall reduces the strength of ΛCDM in the model comparison. As well as comparing cosmological models, the Bayesian methodology is extended to testing for non-gaussianity in the distribution of the Pantheon+ Hubble residuals. We find that adding a scale parameter to the Pantheon+ covariances, or alternately using a multivariate Student’s t-distribution fits the data better than the fiducial analysis, producing a marginalised evidence increase of $\Delta \log \mathcal {Z} = 1.70$ and 2.70 respectively. This improved treatment of the scatter produces a 5 % decrease in the uncertainty of the Hubble constant as compared to SH0ES, finding H0 = 73.67 ± 0.99km.s−1.Mpc−1 in 5.6σ tension with Planck, guided by the evidence when marginalising over both cosmological and scatter models. We also explore MB transition models as a potential solution for the Hubble tension, finding no evidence to support these models among the SN data.