On the implications of the `cosmic calibration tension' beyond $H_0$ and the synergy between early- and late-time new physics

TL;DR

The paper explores the implications of the cosmic calibration tension beyond H0, suggesting it indicates the need for new physics in the early universe or combined modifications across cosmic epochs to resolve discrepancies in cosmological measurements.

Contribution

It analyzes how the cosmic calibration tension impacts our understanding of matter density and suggests that early- and late-time new physics could jointly address these issues.

Findings

A larger matter density mma_m is implied by the tension.

Models modifying pre-recombination expansion can accommodate increased mma_m.

Late-time modifications alone cannot resolve the calibration tension.

Abstract

The `cosmic calibration tension' is a $> 5\sigma$ discrepancy between the cosmological distance ladder built from baryonic acoustic oscillations (BAO) calibrated by the Planck/$\Lambda$CDM sound horizon ($r_s$) and Type Ia supernovae (SN1a) calibrated instead with the S$H_0$ES absolute magnitude, assuming the distance-duality relationship (DDR) holds. In this work, we emphasize the consequences of this tension beyond the value of the Hubble constant $H_0$, and the implications for physics beyond $\Lambda$CDM. Of utmost importance, it implies a larger physical matter density $\omega_m\equiv \Omega_m h^2$, as both the fractional matter density $\Omega_m$ and $h\equiv H_0/100$ km/s/Mpc are well constrained from late-time data. New physics in the pre-recombination era must thus be able to decrease $r_s$ while either reducing the value of $\Omega_m$, or increasing the value of $\omega_m$. Assuming a $\Lambda$CDM-like primordial power spectrum, this necessarily results in an increase in the clustering amplitude $\sigma_8$. Deviations from $\Lambda$CDM in the late-time expansion history cannot resolve the calibrator tension but can help relax the required shifts to the matter density and $\sigma_8$: it is in that sense that a combination of early and late-time new physics may help alleviate the tension. More precisely, models that modify the pre-recombination expansion history can accommodate the increase in $\omega_m$ without the need for additional modifications. It is those models which only affect recombination that require additional deviations at late-times to be successful. Hence, the `cosmic calibration tension' points either to a targeted modification of the pre-recombination expansion history, or to a broader change affecting multiple cosmic epochs.