Hubble tension or a transition of the Cepheid SnIa calibrator parameters?

We reanalyze the Cepheid data used to infer the value of the Hubble constant H-0 by calibrating type Ia supernovae. We do not enforce a universal value of the empirical Cepheid calibration parameters R-W (Cepheid Wesenheit color-luminosity parameter) and M-H(W) (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 < D-c and one for high galactic distances D > D-c, where D-c is a critical transition distance. We find hints for a 3 sigma level mismatch between the low and high galactic distance parameter values. We then use model selection criteria [Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC)], which penalize models with large numbers of parameters, to compare and rank the following types of R-W and M-H(W) parameter variations: Base models: Universal values for R-W and M-H(W); (no parameter variation), I: Individual fitted galactic R-W with one universal fitted M-H(W), II: One universal fixed R-W with individual fitted galactic M-H(W), III: One universal fitted R-W with individual fitted galactic M-H(W), IV: Two universal fitted R-W (near and far) with one universal fitted M-H(W), V: One universal fitted R-W with two universal fitted M-H( )W(near and far), and VI: Two universal fitted R-W (near and far) with two universal fitted M-H(W) (near and far). We find that the AIC and BIC model selection 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 M-B and of H-0 implied by the favored model IV is consistent with the inverse distance ladder calibration based on the cosmic microwave background sound horizon H-0 = 67.4 +/- 0.5 km s(-1) Mpc(-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 100 Myr ago.

Automated summary

The reanalysis of Cepheid data revealed hints of mismatch between low and high galactic distance parameters. Utilizing model selection criteria favored model IV, with best-fit values consistent with cosmic background calibration, indicating absence of the Hubble crisis under this model.