Article 1 - Abstract
D. Kekez, D. Klabucar, K. Kumericki and I. Picek, Quark off-shell
contributions to K_L -> gamma gamma in a bound-state
approach,
Phys. Lett. B348(1995)239.
(Bielefeld preprint BI-TP 94/21 and Zagreb preprint ZTF-94/05,
also hep-ph/9501350.)
Abstract
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-changing operators for K_L -> gamma gamma
comply with the general behaviour of the matrix elements expected
in the pairing bound-state model used here.
The present calculation in essence agrees
with previous chiral-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).
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