The Ly? forest flux correlation function: a perturbation theory perspective

The Ly$\alpha$ forest provides one of the best means mapping large-scale structure at high redshift, including our tightest constraint on distance-redshift relation before cosmic noon. We describe how correlations in can be understood as an expansion cumulants optical depth field, which itself related to density field by a bias expansion. This direct connection between observable and statistics matter fluctuations computed systematic manner. discuss way complex, small-scale physics enters predictions, origin much-discussed velocity `renormalization' coefficients. Our calculations are within context perturbation theory, but we also make contact with earlier work using peak-background split. Using equations motion demonstrate, all orders that flux power spectrum becomes linear times square quadratic cosine angle line sight. Unlike case galaxies, both isotropic anisotropic pieces receive contributions from physics.