On the use of the local prior on the absolute magnitude of Type Ia supernovae in cosmological inference · arXivDesk
2101.08641Jan 21, 20219 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
On the use of the local prior on the absolute magnitude of Type Ia supernovae in cosmological inference
A dark-energy which behaves as the cosmological constant until a sudden phantom transition at very-low redshift (z<0.1) seems to solve the >4σ disagreement between the local and high-redshift determinations of the Hubble constant, while maintaining the phenomenological success of the ΛCDM model with respect to the other observables. Here, we show that such a hockey-stick dark energy cannot solve the H0
Nearby in the stack
crisis. The basic reason is that the supernova absolute magnitude
MB
that is used to derive the local
H0
constraint is not compatible with the
MB
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
MB
as an alternative to the prior on
H0
. 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
q0=−0.55
, iii) one includes in the analysis the fact that
MB
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
MB
relative to the recent Pantheon and DES-SN3YR supernova catalogs. We also provide a Gaussian joint prior on