On the implications of the `cosmic calibration tension' beyond H₀ and the synergy between early- and late-time new physics

The `cosmic calibration tension' is a > 5σ discrepancy between the cosmological distance ladder built from baryonic acoustic oscillations (BAO) calibrated by the Planck/ΛCDM sound horizon (rₛ) and Type Ia supernovae (SN1a) calibrated instead with the SH₀ES 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 H₀, and the implications for physics beyond ΛCDM. Of utmost importance, it implies a larger physical matter density ωₘ≡ Ωₘ h², as both the fractional matter density Ωₘ and h≡ H₀/100 km/s/Mpc are well constrained from late-time data. New physics in the pre-recombination era must thus be able to decrease rₛ while either reducing the value of Ωₘ, or increasing the value of ωₘ. Assuming a ΛCDM-like primordial power spectrum, this necessarily results in an increase in the clustering amplitude σ₈. Deviations from ΛCDM in the late-time expansion history cannot resolve the calibrator tension but can help relax the required shifts to the matter density and σ₈: 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 ωₘ 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.