The BAO scale -- how standard is the standard ruler?

TL;DR

This paper investigates potential biases in BAO measurements caused by mismatches in the sound-horizon scale, especially for future high-precision surveys, and proposes correction strategies to improve cosmological inferences.

Contribution

It extends previous analyses to broader cosmological models, quantifies the bias in BAO measurements, and offers correction methods for future surveys like DESI.

Findings

Bias becomes significant for deviations in cosmological parameters.

Proposed correction strategies can mitigate the bias.

Recommendations for including systematic errors in analyses.

Abstract

Analyses of baryon acoustic oscillations (BAO) commonly employ template-based methods to extract compressed parameters from the clustering of dark-matter tracers, which are then interpreted in terms of ratios of the sound-horizon scale and cosmological distances relative to a fiducial cosmology. A small mismatch between the sound-horizon scale derived from the standard analytic formulation (integral over the sound speed) and the effective scale imprinted in clustered matter can, however, introduce a systematic bias in cosmological inference. We extend previous work to a broader class of cosmological models, quantify this bias for surveys with DESI-like precision, and propose strategies to correct for the effect. We find that the induced bias becomes a significant fraction of the statistical uncertainty for deviations from the fiducial cosmology, at the level of $|\Delta \Omega_m| = 0.03$ and $|\Delta N_\mathrm{eff}| = 0.3$, and for very precise data corresponding to a forecasted Year-5 DESI survey (or other stage IV dark energy galaxy surveys). We present several ways to correct for this effect, suitable for a variety of applications. We therefore recommend that analyses exploring such parameter regimes either apply the proposed corrections or include an appropriate systematic error budget.