Abstract:

We re-analyze the Cepheid data used to infer the value of H0 by calibrating SnIa. We do not enforce a universal value of the empirical Cepheid calibration parameters RW (Cepheid Wesenheit color-luminosity parameter) and MWH (Cepheid Wesenheit H-band absolute magnitude). Instead, we allow for variation of either of these parameters for each individual galaxy. We also consider the case where these parameters have two universal values: one for low galactic distances D<Dc and one for high galactic distances D>Dc where Dc is a critical transition distance. We find hints for a 3σ level mismatch between the low and high galactic distance parameter values. We then use AIC and BIC criteria to compare and rank the following types of models: Base models: Universal values for RW and MWH (no parameter variation), I Individual fitted galactic RW with a universal fitted MWH, II Universal fixed RW with individual fitted galactic MWH, III Universal fitted RW with individual fitted galactic MWH, IV Two universal fitted RW (near and far) with one universal fitted MWH, V Universal fitted RW with two universal fitted MWH (near and far), VI Two universal fitted RW with two universal fitted MWH (near and far). We find that the AIC and BIC criteria consistently favor model IV instead of the commonly used Base model where no variation is allowed for the Cepheid empirical parameters. The best fit value of the SnIa absolute magnitude MB and of H0 implied by the favored model IV is consistent with the inverse distance ladder calibration based on the CMB sound horizon H0=67.4±0.5kms−1Mpc−1. Thus in the context of the favored model IV the Hubble crisis is not present. This model may imply the presence of a fundamental physics transition taking place at a time more recent than 100Myrs ago.