Determining the Hubble Constant without the Sound Horizon: Measurements from Galaxy Surveys.- [PDF] - [Article]

Oliver H. E. Philcox, Blake D. Sherwin, Gerrit S. Farren, Eric J. Baxter

Two scales are encoded in the galaxy power spectrum: the sound horizon at recombination and the horizon at matter-radiation equality. By combining BOSS DR12 galaxy power spectra with $\Omega_m$ priors from Pantheon supernovae, we obtain robust $H_0$ measurements via this second, generally unexploited, scale, finding $H_0 = 65.1^{+3.0}_{-5.4}\,\mathrm{km}\,\mathrm{s}^{-1}\mathrm{Mpc}^{-1}$; this differs from the best-fit of SH0ES at 95 percent confidence. Similar results are obtained if $\Omega_m$ is instead constrained from uncalibrated BAO: $H_0 = 65.6^{+3.4}_{-5.5}\,\mathrm{km}\,\mathrm{s}^{-1}\mathrm{Mpc}^{-1}$. Adding the analogous Planck lensing results from Baxter and Sherwin 2020, the posterior shifts to $70.6^{+3.7}_{-5.0}\,\mathrm{km}\,\mathrm{s}^{-1}\mathrm{Mpc}^{-1}$. Using mock data, Fisher analyses, and scale-cuts, we demonstrate that our constraints do not receive significant information from the sound horizon scale. Since many models resolve the $H_0$ controversy by adding new physics to alter the sound horizon, our measurements are a consistency test for standard cosmology before recombination. A simple forecast indicates that such sound-horizon independent constraints could reach $\sigma_{H_0} \simeq 1.6\,\mathrm{km}\,\mathrm{s}^{-1}\mathrm{Mpc}^{-1}$ in the era of Euclid.