Recombination-independent determination of the sound horizon and the Hubble constant from BAO

Understand

The Hubble tension and attempts to resolve it by modifying the physics of (or at) recombination motivate finding ways to determine $H_0$ and the sound horizon at the epoch of baryon decoupling $r_{\rm d}$ in ways that neither rely on a recombination model nor on late-time Hubble data.

• In this work, we investigate what one can learn from the current and future BAO data when treating $r_{\rm d}$ and $H_0$ as independent free parameters.
• It is well known that BAO gives exquisite constraints on the product $r_{\rm d}H_0$.
• We show here that imposing a moderate prior on $\Omega_{\rm m} h^2$ breaks the degeneracy between $r_{\rm d}$ and $H_0$.