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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, avoiding assumptions about early-Universe physics. 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 a conservative prior on the amplitude of primordial fluctuations, $A_s$, we find $H_0 = 70.03 \pm 0.97$ km/s/Mpc and $r_d = 144.8 \pm 1.6$ Mpc. Allowing $\Sigma m_\nu$ to vary yields $H_0 = 75.3^{+3.3}_{-4.0}$ km/s/Mpc and $\Sigma m_\nu = 0.55^{+0.23}_{-0.37}$ ($<1.11$ eV) at 68% (95%) CL, and $H_0 = 73.9 \pm 2.2$ km/s/Mpc with $\Sigma m_\nu = 0.46^{+0.21}_{-0.25}$ ($=0.46^{+0.40}_{-0.45}$ eV) at 68% (95%) CL when a prior on $A_s$ is applied. 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 the neutrino mass is varied. As the precision of BAO, CMB lensing, and galaxy lensing/clustering improve, this $r_d$-agnostic framework will provide an independent test of the need for new physics at recombination.