Baryon Acoustic Oscillations from a Different Angle

TL;DR

This paper introduces a novel analysis method for BAO measurements using rotations to define new quantities, enabling straightforward consistency tests with Planck LCDM cosmology and providing insights into dark energy properties.

Contribution

It proposes a new rotational analysis approach for BAO data, offering improved consistency checks with Planck LCDM and critiquing existing statistical methodologies.

Findings

Dperp from Planck is precisely determined and aligns well with DESI DR2.

Dpar measurements remain consistent with Planck LCDM despite improved accuracy.

No significant evidence supports evolving dark energy from combined BAO and CMB data.

Abstract

This paper presents an alternative way of analysing Baryon Acoustic Oscillation (BAO) distance measurements via rotations to define new quantities Dperp and Dpar. These quantities allow simple tests of consistency with the Planck LCDM cosmology. The parameter Dperp is determined with negligible uncertainty from Planck under the assumption of LCDM. Comparing with measurements from the Dark Energy Spectroscopic Instrument (DESI), we find that the measurements of Dperp from Data Release 2 (DR2) move into significantly better agreement with the Planck LCDM cosmology compared to DESI Data Release 1 (DR1). The quantity in the orthogonal direction Dpar provides a measure of the physical matter density omega_m in the LCDM cosmology. The DR2 measurements of Dpar remain consistent with Planck LCDM despite the substantial improvement in their accuracy compared to the earlier DR1 results. From the comparison of Planck and DESI BAO measurements, we find no significant evidence in support of evolving dark energy. We also investigate a rotation in the theory space of the w_0 and w_a parameterization of the dark energy equation-of-state w(z). We show that the combination of DESI BAO measurements and the CMB constrain w(z=0.5) = -0.996 pm 0.046, i.e. very close to the value expected for a cosmological constant. We present a critique of the statistical methodology employed by the DESI collaboration and argue that it gives a misleading impression of the evidence in favour of evolving dark energy. An Appendix shows that the cosmological parameters determined from the Dark Energy Survey 5 Year supernova sample are in tension with those from DESI DR2 and parameters determined by Planck.