Double Compton scattering
= Double Compton scattering
<Double Compton scattering> is $e^-+\gamma\to e^-+\gamma+\gamma$, together with its inverse. The forward reaction has one incoming and two outgoing <photons>, so it changes their number and can source the <divergence> of the <photon number current>. Ordinary <Compton scattering> has one incoming and one outgoing <photon> and conserves <photon> number. Forward and inverse rates can balance without either reaction individually conserving it.