Baryon Acoustic Oscillations and the Hubble Constant: Past, Present and Future

TL;DR

The paper tackles the $H_0$ tension by combining Baryon Acoustic Oscillations with Big Bang Nucleosynthesis priors to calibrate the sound horizon, thereby obtaining an $H_0$ estimate independent of CMB and distance ladders. It employs a Bayesian suspiciousness statistic to test consistency between Galaxy BAO and Ly$\alpha$ BAO and updates $H_0$ using the latest eBOSS DR14 data, finding $H_0$ consistent with Planck at about $67.6$–$68.1$ km s$^{-1}$ Mpc$^{-1}$ and in strong tension with SH0ES. The work also forecasts DESI's impact, showing that future BAO+$BBN constraints on $H_0$ will be highly sensitive to the adopted BBN priors, highlighting the need for improved nuclear reaction rate measurements. Overall, the results reinforce a Planck-like $H_0$ from BAO+$BBN analyses and emphasize BBN systematics as a key limiting factor for next-generation, model-independent $H_0$ measurements.

Abstract

We investigate constraints on the Hubble constant ($H_0$) using Baryon Acoustic Oscillations (BAO) and baryon density measurements from Big Bang Nucleosynthesis (BBN). We start by investigating the tension between galaxy BAO measurements and those using the Lyman-$α$ forest, within a Bayesian framework. Using the latest results from eBOSS DR14 we find that the probability of this tension being statistical is $\simeq6.3\%$ assuming flat $Λ$CDM. We measure $H_0 = 67.6\pm1.1$ km s$^{-1}$ Mpc$^{-1}$, with a weak dependence on the BBN prior used, in agreement with results from Planck Cosmic Microwave Background (CMB) results and in strong tension with distance ladder results. Finally, we forecast the future of BAO $+$ BBN measurements of $H_0$, using the Dark Energy Spectroscopic Instrument (DESI). We find that the choice of BBN prior will have a significant impact when considering future BAO measurements from DESI.

Figures (3)

• Figure 1: (Left) Parameter constraints in a flat $\Lambda$CDM cosmology from each BAO dataset individually. The different contour orientations are due to the different redshifts of separate datasets. The box represents the boundaries of the plot on the right with the combined BAO measurements. (Right) Comparison of BAO constraints from galaxy clustering and different Ly$\alpha$ forest measurements. The recently released eBOSS DR14 Ly$\alpha$ BAO measurements are visibly more consistent with galaxy BAO than previous results from DR11 and DR12. This is quantified in Table \ref{['tab:tension']}.
• Figure 2: (Left) Current state of the art results for $H_0$ versus $\Omega_m$, independent of CMB anisotropy data. BAO data was combined with a prior on $\Omega_b h^2$ from BBN deuterium measurements (using the theoretical reaction rate). (Right) Our main results using all the BAO samples in Table \ref{['tab:data']}, combined with BBN using both reaction rates.
• Figure 3: (left) Forecast for future BAO results within flat $\Lambda$CDM using different components of DESI. (right) Forecast for Hubble constant results using the full DESI results combined with the two $\Omega_b h^2$ priors from BBN, and the Planck 2018 results PlanckCollaboration:2018 for comparison. The tension in the baryon density between the BBN theoretical constraint (in blue) and the CMB (in red) can clearly be seen in this plot. This shows the importance of solving the BBN tension for the future of BAO + BBN $H_0$ measurements.