Leandros Perivolaropoulos

Leandros Perivolaropoulos

I review the current status of the Hubble tension emphasizing the following:

1. Current measurements of H_0 indicate a tension not between early and late time measurements of H_0 but between distance ladder based measurements which favor a high value of H0 and all other measurements which favor a low value of H0. These measurements include sound horizon based measurements and one step measurements that are independent of the sound horizon involving both late and early time physics. The one step sound horizon free measurements (31), are consistent with each other (\chi^2/dof=1) provided that two outliers (TDCOSMO I and MCP-SH0ES) are removed one of which has been shown to be plagued with systematics (TDCOSMO I).

2. Models for the resolution of the Hubble tension using H(z) deformations, are faced with serious challenges. The most important challenge is the inconsistency between BAO and SnIa distances at low redshifts if SnIa are calibrated with distance ladder and BAO with the sound horizon scale. These data can not be simultaneously fit by this class of models. In addition these models can not be consistent with late time one step H_0 measurements that favor low values of H_0.

3.  Models for the resolution of the Hubble tension using pre recombination physics that decreases the sound horizon scale,  are also faced with serious challenges. The most important challenge is that even if they manage to consistently increase the predicted value of H_0, they will still be unable to fit one step measurements of H_0 that are independent of the sound horizon scale and favor a lower value of H_0.

4. Based on the above it becomes highly likely that there is a problem with distance ladder measurements which is the only class of measurements based on local astrophysics (redshifts between 0 and 0.01 or distances between 0 and 40Mpc and times between present and 150Myrs ago). I thus argue that the Hubble tension may indicate a new phenomenon in the above scales which may either manifest as a common unknown systematic effect in diverse distance ladder based measurements or a fundamental physics transition which affects the above local scales or times.