  We consider non-perturbative QCD effects on the energy spectrum of either one
of the photons in B -> X_s gamma gamma. These are due to the subprocesses in
which a charm quark loop interacts with a self-consistently produced background
static QCD field. The magnitude is estimated to be a few percents in B -> X_s
gamma gamma, but can be quite substantial in B_s -> gamma gamma. An extension
of the Euler-Heisenberg Lagrangian is given.

High Energy Physics - Phenomenology