Backgound Gluon Effects on B -> X_s gamma gamma
  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. 
S. Rai Choudhury and York-Peng Yao (Randall Laboratory of Physics)