QUARK OFF-SHELL EFFECTS IN B-]GAMMA-GAMMA-DECAYS

We demonstrate that in the decay of a heavy-light quark system, like the process B(s) --> gammagamma under consideration, there is an important contribution coming from operators that vanish on the free quark mass-shell. Although numerical estimates are model-dependent, the significance of genuine off-shell effects is quite general, and independent of the details of the boundstate dynamics. Such contributions will typically be somewhat smaller, but still significant in magnitude compared with the contribution from the standard off-diagonal, b --> sgamma magnetic-moment operator.