Renormalization for a model of photon scattering off a charged harmonic oscillator

In the electric dipole approximation the model of a charged harmonic oscillator interacting with the radiation field becomes quadratic and soluble, but it needs a UV cutoff for the photon frequency. The model’s renormalizability is only apparent; physics requires that the cutoff be kept finite. The cutoff plays the role of a parameter that characterizes the high frequency behavior of the photon cross section.