A renormalization approach to many-atom radiation processes

We present a second-order many-body perturbation approach to coherent radiation processes. The theory gives a unified view of several many-atom effects as eigenmodes of the interacting atom-field system. Two renormalization procedures are essential to perform our program; (complex) energy renormalization using a noncanonical transformation and light-velocity renormalization using Bogoliubov transformation for field operators.