% miko:type: atomic
% miko:title: Baryon Acoustic Oscillations
% miko:summary: A standard ruler imprinted by sound waves in the early photon-baryon plasma.
% miko:tags: cosmology
% miko:difficulty: undergrad
% miko:related: complete-cosmology, cosmic-microwave-background, matter-radiation-equality
% miko:keywords: BAO, sound horizon, large-scale structure

\documentclass{article}
\usepackage{amsmath}
\title{Baryon Acoustic Oscillations}
\begin{document}
\maketitle

\section{Origin}

Before recombination, photons and baryons behaved as a coupled plasma.
Pressure-supported sound waves propagated through this medium.

\section{Standard Ruler}

The maximum distance such waves could travel before decoupling defines the
sound horizon. This leaves a preferred scale in the distribution of galaxies.

\section{Cosmological Use}

BAO measurements constrain the expansion history by comparing the observed
scale to the predicted sound horizon.

\end{document}
