Multidimensionality of the Hubble tension: the roles of $\Omega_m$ and $\omega_c$

Abstract

The Hubble tension is inherently multidimensional, and bears important implications for parameters beyond $H_0$. We discuss the key role of the matter density parameter $\Omega_m$ and the physical cold dark matter density $\omega_c$. We argue that once $\Omega_m$ and the physical baryon density $\omega_b$ are calibrated, through Baryon Acoustic Oscillations (BAO) and/or Type Ia Supernovae (SNeIa) for $\Omega_m$, and via Big Bang Nucleosynthesis for $\omega_b$, any model raising $H_0$ requires raising $\omega_c$ and, under minimal assumptions, also the clustering parameter $S_8$. We explicitly verify that this behaviour holds when analyzing recent BAO and SNeIa data. We argue that a calibration of $\Omega_m$ as reliable and model-independent as possible should be a priority in the Hubble tension discussion, and an interesting possibility in this sense could be represented by galaxy cluster gas mass fraction measurements.