The tension in the absolute magnitude of Type Ia supernovae

TL;DR

This paper investigates the tension in the Hubble constant derived from different measurements, emphasizing the role of supernova magnitude calibration and exploring alternative cosmographic models to understand the discrepancy.

Contribution

It extends the analysis of $H_0$ to arbitrary cosmographic models and highlights the impact of supernova magnitude calibration on cosmological inferences.

Findings

Local $H_0$ determined as 73.14 ± 1.10 km/s/Mpc under flat ΛCDM

Alternative model yields $H_0$ of 74.56 ± 1.61 km/s/Mpc

Discrepancy in supernova magnitude calibration methods

Abstract

This study aims to elucidate the tension in the Hubble constant ($H_0$), a key metric in cosmology representing the universe's expansion rate. Conflicting results from independent measurements such as the Planck satellite mission and the SH0ES collaboration have sparked interest in exploring alternative cosmological models. We extend the analysis by SH0ES to an arbitrary cosmographic model, obtaining a competitive local $H_0$ determination which only assumes the standard flat $\Lambda$CDM model ($73.14 \pm 1.10$ km/s/Mpc), and another which only assumes the FLRW metric ($74.56 \pm 1.61$ km/s/Mpc). The study also stresses the importance of the supernova magnitude calibration ($M_B$) in cosmological inference and highlights the tension in $M_B$ when supernovae are calibrated either by CMB and BAO observations or the first two rungs of the cosmic distance ladder. This discrepancy, independent of the physics involved, suggests that models solely changing the Hubble flow and maintaining a sound horizon distance consistent with CMB, fail to explain the discrepancy between early- and late-time measurements of $H_0$.