On the dispersive two-photon 
amplitude
J.O. Eeg1 - K. Kumericki2 - I. Picek2
1 Department of Physics, University of Oslo, N-0316 Oslo, Norway
(e-mail: j.o.eeg@fys.uio.no)
2 Department of Physics, Faculty of Science, University of Zagreb,
POB 162, HR-10001 Zagreb, Croatia
(e-mail: kkumer@phy.hr,
picek@phy.hr)
Received: 30 April 1997
Abstract
We present a full account of the two-loop electroweak, two-photon mediated
short-distance dispersive KL
decay amplitude.
QCD corrections change the sign of this amplitude and reduce it by
an order of magnitude.
Thus, the QCD-corrected two-loop amplitude represents
only a small fraction (with the central value of 5%) of the
one-loop weak short-distance
contribution, and has the same sign.
In combination with a recent measurement, the
standard-model prediction of the short-distance
amplitude, completed in this paper,
provides a constraint on the otherwise uncertain
long-distance dispersive amplitude.
Copyright Springer-Verlag
