Elucidating ΛCDM: Impact of Baryon Acoustic Oscillation Measurements on the Hubble Constant Discrepancy

Abstract

We examine the impact of baryon acoustic oscillation (BAO) scale measurements on the discrepancy between the value of the Hubble constant (H 0 ) inferred from the local distance ladder and from Planck cosmic microwave background (CMB) data. While the BAO data alone cannot constrain H 0 , we show that combining the latest BAO results with WMAP, Atacama Cosmology Telescope (ACT), or South Pole Telescope (SPT) CMB data produces values of H 0 that are 2.4 − 3.1σ lower than the distance ladder, independent of Planck, and that this downward pull was less apparent in some earlier analyses that used only angle-averaged BAO scale constraints rather than full anisotropic information. At the same time, the combination of BAO and CMB data also disfavors the lower values of H 0 preferred by the Planck high-multipole temperature power spectrum. Combining galaxy and Lyman-α forest (Lyα) BAO with a precise estimate of the primordial deuterium abundance produces H 0 = 66.98 ± 1.18 km s −1 Mpc −1 for the flat ΛCDM model. This value is completely independent of CMB anisotropy constraints and is 3.0σ lower than the latest distance ladder constraint, although 2.4σ tension also exists between the galaxy BAO and Lyα BAO. These results show that it is not possible to explain the H 0 disagreement solely with a systematic error specific to the Planck data. The fact that tensions remain even after the removal of any single data set makes this intriguing puzzle all the more challenging to resolve.

Status of Neutrino Properties and Future Prospects—Cosmological and Astrophysical Constraints

“…For the sake of completeness, we shall also mention that independent estimates of H 0 from BAO measurements conducted by the SDSS III-BOSS DR12 collaboration [23] are in agreement with CMB estimates (see also [62] for a recent discussion). See also Abbott et al [127] for an additional independent estimate of H 0 with a combination of clustering and weak lensing measurements from DES-Y1 with BAO and BBN data.…”

“…Given that the value of the sound horizon is well constrained by CMB observations, measuring the BAO features, possibly at different redshifts, allows to directly constrain the expansion history, as probed by the evolution of the angular diameter distance d A (z) and of the Hubble function H(z), or of their average d V (z). In particular, it is straightforward to see that BAO measurements put tight constraints on the m − H 0 r d plane, along a different degeneracy direction that it is instead probed by CMB [62,63]. Therefore, when estimating neutrino masses, the addition of BAO constraints to CMB data helps breaking the parameter degeneracies discussed in the previous section, yielding in general tighter constraints on this quantity.…”

“…A discussion about the possible reasons behind this discrepancy and ways to alleviate it invoking non-standard cosmological scenarios are beyond the scope of this work. We refer the reader to the dedicated works [62,125,126] for further reading.…”

Baryon Acoustic Oscillations and the Hubble constant: past, present and future

“…Therefore, a constraint on H 0 requires extra data to calibrate the size of the sound horizon; usually CMB anisotropy measurements are used. Recently, [23] used an alternative method, introduced by [24], that uses deuterium abundance measurements and the Big Bang Nucleosysnthesis (BBN) theory. This BAO + BBN method gives a value of H 0 consistent with the Planck value, further decreasing the chances of systematic errors in the CMB measurements.…”

“…This BAO + BBN method gives a value of H 0 consistent with the Planck value, further decreasing the chances of systematic errors in the CMB measurements. [23] emphasized the importance of this method in providing a constraint on H 0 independent of CMB anisotropy measurements and the distance ladder. The focus of this work is to discuss past results of this data combination, compute the latest constraints, and investigate future implications.…”