High H 0 Values from CMB E-mode Data: A Clue for Resolving the Hubble Tension?

The E-mode (EE) CMB power spectra measured by Planck, ACTPol, and SPTpol constrain the Hubble constant to be 70.0 ± 2.7, ${72.4}_{-4.8}^{+3.9}$, and ${73.1}_{-3.9}^{+3.3}$ km s−1 Mpc−1 within the standard ΛCDM model (posterior mean and central 68% interval bounds). These values are higher than the constraints from the Planck temperature (TT) power spectrum, and consistent with the Cepheid-supernova distance ladder measurement H0 = 73.2 ± 1.3 km s−1 Mpc−1. If this preference for a higher value was strengthened in a joint analysis it could provide an intriguing hint at the resolution of the Hubble disagreement. We show, however, that combining the Planck, ACTPol, and SPTpol EE likelihoods yields H0 = 68.7 ± 1.3 km s−1 Mpc−1, 2.4σ lower than the distance ladder measurement. This is due to different degeneracy directions across the full parameter space, particularly involving the baryon density, Ωbh2, and scalar tilt, ns, arising from sensitivity to different multipole ranges. We show that the E-mode ΛCDM constraints are consistent across the different experiments within 1.4σ, and with the Planck TT results at 0.8σ. Combining the Planck, ACTPol, and SPTpol EE data constrains the phenomenological lensing amplitude, AL = 0.89 ± 0.10, consistent with the expected value of unity.