paper

On the use of the local prior on the absolute magnitude of Type Ia supernovae in cosmological inference

arXiv:2101.08641 · doi:10.1093/mnras/stab1200

Abstract

A dark-energy which behaves as the cosmological constant until a sudden phantom transition at very-low redshift () seems to solve the >4 disagreement between the local and high-redshift determinations of the Hubble constant, while maintaining the phenomenological success of the CDM model with respect to the other observables. Here, we show that such a hockey-stick dark energy cannot solve the crisis. The basic reason is that the supernova absolute magnitude that is used to derive the local constraint is not compatible with the that is necessary to fit supernova, BAO and CMB data, and this disagreement is not solved by a sudden phantom transition at very-low redshift. We make use of this example to show why it is preferable to adopt in the statistical analyses the prior on as an alternative to the prior on . The three reasons are: i) one avoids potential double counting of low-redshift supernovae, ii) one avoids assuming the validity of cosmography, in particular fixing the deceleration parameter to the standard model value , iii) one includes in the analysis the fact that is constrained by local calibration, an information which would otherwise be neglected in the analysis, biasing both model selection and parameter constraints. We provide the priors on relative to the recent Pantheon and DES-SN3YR supernova catalogs. We also provide a Gaussian joint prior on and that generalizes the prior on by SH0ES.

9 pages, 6 figures, 3 tables. Title changed to better describe the scope, expanded analysis and discussion, v3 reflects version accepted for publication in MNRAS; code and up-to-date values of the prior on the absolute magnitude of Type Ia supernovae are available at https://github.com/valerio-marra/CalPriorSNIa

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