Two new companion papers on arXiv report a coordinated comparison of proposed solutions to the “Hubble tension,” the discrepancy between the Hubble constant inferred from local distance-ladder measurements (e.g., SH0ES) and early-universe inferences (from CMB and related probes). The authors note that the tension now reaches nominal significance above 7σ and that recent, higher-precision CMB and BAO measurements sharpen the challenge. Using a common analysis framework and up-to-date datasets—cosmic microwave background (CMB), baryon acoustic oscillations (BAO), and Type Ia supernovae—the study evaluates fourteen representative alternatives to the standard ΛCDM model.
The models are grouped by mechanism: late-time changes to the expansion history, modifications of recombination, added pre-recombination radiation, and early energy injection (including non-radiative cases). The “group stage” results indicate that early dark energy and early modified-gravity models perform best, shifting the inferred H0 toward about 70 km s⁻¹ Mpc⁻¹ and reducing the remaining discrepancy with SH0ES to roughly 2.5–3.6σ, depending on the statistical metric. Intermediate improvement comes from varying the electron mass at recombination, while enhanced-radiation and late-time scenarios do not outperform ΛCDM. The companion paper extends the competition with robustness checks across analysis choices and additional model variations (including neutrino masses and curvature/CPL dark energy parametrization).
