QUARK OFF-SHELL CONTRIBUTIONS TO K-L-]GAMMA-GAMMA IN A BOUND-STATE APPROACH

We present a new piece of evidence in favour of the importance of the quark off-shellness in the kaon. The matrix elements of the flavour-ch anging operators for K-L --> gamma gamma comply with the general behav iour of the matrix elements expected in the pairing bound-state model used here. The present calculation in essence agrees with previous chi ral-quark results. The off-shell contribution turns out to be dominant (the model on-shell amplitude being at the 10% level). Compared with the chiral perturbation-theory approach, our off-shell contribution is an entirely new O(p(4)) direct-decay piece, whereas the non-diagonal magnetic-moment term belongs to the order O(p(6)).