Accuracy of cosmological parameters using the baryon acoustic scale

TL;DR

This paper evaluates the accuracy of using the baryon acoustic scale as a standard ruler for cosmological parameter estimation, comparing simple approximations to full numerical calculations.

Contribution

It demonstrates that the approximation of the acoustic scale is highly reliable (within 0.15%) for standard cosmological models and common extensions.

Findings

Approximation accuracy is better than 0.15% for most parameters.

Full correlation function analysis confirms the reliability of the simple approximation.

Useful for efficient cosmological parameter constraints in BAO studies.

Abstract

Percent-level measurements of the comoving baryon acoustic scale standard ruler can be used to break degeneracies in parameter constraints from the CMB alone. The sound horizon at the epoch of baryon drag is often used as a proxy for the scale of the peak in the matter density correlation function, and can conveniently be calculated quickly for different cosmological models. However, the measurements are not directly constraining this scale, but rather a measurement of the full correlation function, which depends on the detailed evolution through decoupling. We assess the level of reliability of parameter constraints based on a simple approximation of the acoustic scale compared to a more direct determination from the full numerical two-point correlation function. Using a five-parameter fitting technique similar to recent BAO data analyses, we find that for standard {\Lambda}CDM models and extensions with massive neutrinos and additional relativistic degrees of freedom, the approximation is at better than 0.15% for most parameter combinations varying over reasonable ranges.