Sound-Horizon-Agnostic Inference of the Hubble Constant and Neutrino Mass from BAO, CMB Lensing, and Galaxy Weak Lensing and Clustering

Abstract

We present a sound-horizon-agnostic determination of the Hubble constant, $H_0$, by combining DESI DR2 baryon acoustic oscillation (BAO) data with the latest cosmic microwave background (CMB) lensing measurements from Planck, ACT, and SPT-3G, the angular size of the CMB acoustic scale, Dark Energy Survey Year-3 ($3\times2$-pt) galaxy weak lensing and clustering correlations, and the Pantheon+ supernova sample. In this analysis, The sound horizon at the drag epoch, $r_d$, is treated as a free parameter. By combining uncalibrated comoving distances from BAO and supernovae with constraints on the matter density $\Omega_m h^2$ from CMB and galaxy lensing/clustering, we break the $r_d$-$H_0$ degeneracy and obtain $H_0 = 70.0 \pm 1.7$ km/s/Mpc when the sum of the neutrino masses is fixed at $\Sigma m_\nu = 0.06$ eV. With an informative prior on the amplitude of primordial fluctuations, $A_s$, we find $H_0 = 70.03 \pm 0.97$ km/s/Mpc. Allowing $\Sigma m_\nu$ to vary, we find that the neutrino mass is weakly constrained and strongly prior-dependent. Consequently, the inferred $H_0$ is sensitive to the choice of the $\Sigma m_\nu$ prior, with a uniform prior biasing results toward larger neutrino masses and higher $H_0$, while a logarithmic prior reduces this bias significantly. Forecasts for the completed DESI BAO program, combined with Simons-Observatory-like CMB lensing, next-generation $3\times2$-pt data, and expanded supernova samples predict $\sigma(H_0) \simeq 0.67$ km/s/Mpc with fixed $\Sigma m_\nu$, and $\sigma(H_0) \simeq 1.1$ km/s/Mpc with $\Sigma m_\nu < 0.133$ ($<0.263$) eV at 68% (95%) CL when $\Sigma m_\nu$ is varied.