K→ππγ and chiral perturbation theory

Hai Yang Cheng, S. C. Lee, Hoi Lai Yu

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8 Scopus citations


Weak radiative decays KL,S→π+π-γ and K+→π+π0γ are reexamined. The electromagnetic form factors and long-distance contributions to the direct photon emission are evaluated using the higher order effective chiral Lagrangian. We find that (1) the naive soft-pion theorem cannot be applied to the magnetic-type transition amplitude, (2) the shortdistance contribution to KL→π+π-γ is comparable to or even bigger than the long-distance one, (3) the ΔI=1/2 enhancement persists in the decay K+→π+π0γ, (4) to the order of 1/Λχ2χ being the chiral-symmetry breaking scale) the direct photon emission amplitude does not receive a contribution from penguin operators, and (5) the 1/Nc expansion improves the discrepancy between theory and experiment.

Original languageEnglish
Pages (from-to)223-231
Number of pages9
JournalZeitschrift für Physik C Particles and Fields
Issue number2
StatePublished - Jun 1988


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