The Ly$\alpha$ forest flux correlation function: a perturbation theory perspective

Understand

The Ly$\alpha$ forest provides one of the best means of mapping large-scale structure at high redshift, including our tightest constraint on the distance-redshift relation before cosmic noon.

• We describe how the large-scale correlations in the Ly$\alpha$ forest can be understood as an expansion in cumulants of the optical depth field, which itself can be related to the density field by a bias expansion.
• This provides a direct connection between the observable and the statistics of the matter fluctuations which can be computed in a systematic manner.
• We discuss the way in which complex, small-scale physics enters the predictions, the origin of the much-discussed velocity bias and the `renormalization' of the large-scale bias coefficients.