Cosmology has made fundamental progress thanks to the role of standard rulers. The acoustic peak in the Large Scale Structure clustering correlation function is one of them. However, in the era of precision cosmology, its power has been highly challenged by how late time non-linearities distort the correlation function. To overcome this problem currently the distance measurements based on Baryon Acoustic Oscillations rely on fixed-model-templates and reconstruction methods. However this is realized at the price of highly increasing the difficult-to-quantify theoretical priors that may overestimate the precision and accuracy of the distance estimates.
Fortunately this is not the end of the story! I will explain how we can evade non-linearities identifying a scale in the correlation function, called the “linear point”, that is an excellent cosmological standard ruler: it is constant in redshift and it is not affected by non-linear effects to within 0.5% percent precision. Hence we measure the location of the linear point in the galaxy correlation function in the Twelfth Data Release (DR12) of the Baryon Oscillation Spectroscopic Survey (BOSS) collaboration. Combining our linear point measurements with the Cosmic Microwave Background constraints from the Planck satellite we estimate the isotropic-volume distance without relying on a model-template or reconstruction method. Our remarkable result suggests that all the distance information contained in the Baryon Acoustic Oscillations can be conveniently compressed into the single length associated with the linear point.