Dissecting the Hubble tension: Insights from a diverse set of Sound Horizon-free H0 measurements

Abstract

The Hubble tension is commonly framed as a discrepancy between local, late-time measurements favoring $H_0\approx 73$ km s${}^{-1}$ Mpc${}^{-1}$ and early-time, Sound-Horizon-based measurements favoring $H_0\approx 67$ km s${}^{-1}$ Mpc${}^{-1}$. We challenge this viewpoint by analyzing 88 Sound Horizon Free $H_0$ measurements, categorized into four classes: Distance Ladder measurements using local calibrators; Local $\hat{I}›$CDM measurements assuming the standard expansion history; Pure Local measurements independent of $H(z)$ shape; and CMB Sound--Horizon--Free measurements using CMB data without the Sound Horizon scale. Our analysis reveals that the 30 Distance Ladder measurements yield $H_0=72.73\pm 0.39$ km s${}^{-1}$ Mpc${}^{-1}$ ($\ddot{I}{‡}_{\hat{I}}^2½=0.72$), while the 58 Distance Ladder-Independent/Sound Horizon Free measurements collectively yield $H_0=69.37\pm 0.34$ km s${}^{-1}$ Mpc${}^{-1}$ ($\ddot{I}{‡}_{\hat{I}}^2½=0.95$), a $6.5\ddot{I}ƒ$ tension exceeding the Planck--SH0ES discrepancy. This tension remains significant at a minimum value of $3.9\ddot{I}ƒ$ after accounting for correlations. Among categories, Local $\hat{I}›$CDM measurements favor the lowest value ($H_0=67.61\pm 0.96$ km s${}^{-1}$ Mpc${}^{-1}$), Pure Local yield an intermediate value ($H_0=71.03\pm 0.69$ km s${}^{-1}$ Mpc${}^{-1}$), and CMB Sound Horizon Free measurements give $H_0=69.07\pm 0.44$ km s${}^{-1}$ Mpc${}^{-1}$. We conclude that the Hubble tension is better characterized as a discrepancy between the Distance Ladder and all other methodologies, rather than an early-vs-late-time split. We also identify a $2.9\ddot{I}ƒ$ internal tension among Distance Ladder Independent/Sound Horizon Free measurements: analyses assuming $\hat{I}›$CDM systematically recover lower $H_0$ values compared to cosmological-model-independent methods. This suggests either unrecognized systematics in the Distance Ladder or deviations from $\hat{I}›$CDM or both.

31 pages 4 figures. Added 5 new measurents. Added comments and references. Main conclusions unchanged. The numerical analysis files used for the construction of the figures may be found at https://github.com/ipantos/Dissecting-the-Hubble-Tension