Elucidating $Λ$CDM: Impact of Baryon Acoustic Oscillation Measurements on the Hubble Constant Discrepancy (1707.06547v2)

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 $2.4-3.1\sigma$ 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-$\alpha$ forest (Ly$\alpha$) BAO with a precise estimate of the primordial deuterium abundance produces $H_0=66.98\pm1.18$ km s$^{-1}$ Mpc$^{-1}$ for the flat $\Lambda$CDM model. This value is completely independent of CMB anisotropy constraints and is $3.0\sigma$ lower than the latest distance ladder constraint, although $2.4\sigma$ tension also exists between the galaxy BAO and Ly$\alpha$ 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.

The Influence of Baryon Acoustic Oscillation Measurements on the Hubble Constant Discrepancy

Baryon Acoustic Oscillation (BAO) measurements have become instrumental in exploring the discrepancy in estimates of the Hubble constant, $H_0$, particularly the disparities between the local distance ladder and Cosmic Microwave Background (CMB) data. A rigorous investigation into the BAO's role elucidates its contributions and reveals further complexities in resolving the $H_0$ tensions.

Context and Motivation

There exists significant tension between the $H_0$ value derived from local distance ladder techniques, as provided by Riess et al. (2016) with $H_0 = 73.24 \pm 1.74$ km/s/Mpc, and that deduced from the Planck CMB measurements, which yield lower estimates. The cause of this discrepancy poses a fundamental challenge in cosmology as current data suggests potential inadequacies in our understanding of the $\Lambda$CDM model or systematic errors in measurements.

Key Findings

1. BAO’s Role in Constraining $H_0$:
   • The research indicates that while BAO data alone cannot independently constrain $H_0$, when combined with CMB data from sources like WMAP, ACT, or SPT, it produces $H_0$ estimates that are $2.4 - 3.1\sigma$ lower than the local distance ladder, independent of the Planck dataset. This downward adjustment had not been apparent in earlier studies that used only angle-averaged BAO constraints, highlighting the necessity of incorporating full anisotropic information.
2. Discrepancy Among Different Measurements:
   • The paper discusses the significance of BAO measurements from galaxy surveys and contrasting results of higher-redshift Lyman-$\alpha$ forest BAOs. The combination of galaxy and Lyman-$\alpha$ BAO measurements indicates $H_0 = 66.98 \pm 1.18$ km/s/Mpc in a flat $\Lambda$CDM model, which remains $3.0\sigma$ lower than the local distance ladder's estimate. These findings underscore that systematic errors specific to Planck data cannot solely explain the disagreements.
3. Combined BAO and Primordial Deuterium Estimates:
   • Incorporating precise estimates of primordial deuterium abundance into the BAO analysis offers a robust method for making the $H_0$ determination independent of CMB anisotropy, yielding constraints tighter than direct distance ladder methods.

Implications and Future Directions

The results presented have profound implications for both methodological practices and theoretical paranormal modeling in cosmology:

• Data Integration: The necessity of using full anisotropic BAO data instead of angle-averaged estimates to avoid misleading constraints highlights an important practice for future analyses.
• Model Consideration: These findings urge reconsideration of the standard $\Lambda$CDM model, especially under the assumption of uniformity and homogeneity at large scales.
• Further Observational Efforts: Refining measurements, especially regarding systematics in both CMB and local $H_0$ estimates, remains crucial. Enhanced observational strategies in current and future telescopic missions could play a decisive role in narrowing down these divergences.

The exploration of such measurements remains pivotal in the pursuit of understanding cosmic expansion, and continued advancements in precision cosmology are expected to shed further light on this intricate puzzle.