Determining the Hubble Constant without the Sound Horizon: Perspectives with future galaxy surveys

H₀ constraints from galaxy surveys are sourced by two standardisable rulers: the sound horizon scale, r_s, and the equality scale, k_eq. Historically analyses have focused on the former scale, but recent work has shown that the latter can also be measured precisely and provides an independent source of information about the expansion rate of the universe. I will discuss how r_s-based information can be avoided by removing the typically used prior on the baryon density, and thus the sound-horizon calibration; this comes at the cost of significantly degraded constraints. I will present a new method for marginalisation over r_s which allows baryon information to be retained. I will show forecasts with our new method for a Euclid-like spectroscopic survey, contrasting different analysis choices that derive information from the sound horizon scale, the equality scale or a combination thereof. I will also show constraints obtained by applying our approach to the BOSS power spectrum. Consistency of r_s- and k_eq-based H₀ measurements provides a valuable generic consistency test of the cosmological model; any inconsistency hints at beyond-ΛCDM physics. I will illustrate this by means of analysing mock data generated within an Early Dark Energy (EDE) cosmology.