Strong Isospin-Breaking Effects on the Delta I=3/2 Amplitude in K-->pi pi at Next-to-Leading Order in the Chiral Expansion

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  • 6 December 1999
Abstract
The potentially large contribution to the K --> pi pi Delta I=3/2 amplitude, resulting from strong isospin-breaking modifications to the weak Delta I=1/2 amplitude, is evaluated at next-to-leading order (NLO) in the chiral expansion. NLO contributions are shown to significantly reduce the leading order result (from 15% to 8.3\pm 3.2 % of the experimental value). Combined with recent results on the corresponding electromagnetic contributions, one finds that the ratio of the intrinsic strengths of octet and 27-plet effective weak operators can be taken to be that obtained from experimental data, analyzed ignoring isospin breaking, to an accuracy better than ~ 10%. The question of the consequences of the sum of strong and electromagnetic isospin breaking for the extraction of the relative phase, phi, between the I=0 and I=2 contributions to the K_S amplitudes is also investigated. Isospin-breaking effects are shown to unambiguously exacerbate the existing discrepancy between phi and the difference, delta_0-delta_2, of the I=0 and I=2 phase shifts.

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