title: Final state interactions in [Formula: see text] decays: [Formula: see text] rule vs. [Formula: see text].
abstract: Dispersive effects from strong [Formula: see text] rescattering in the final state interaction (FSI) of weak [Formula: see text] decays are revisited with the goal to have a global view on theirrelativeimportance for the [Formula: see text] rule and the ratio [Formula: see text] in the standard model (SM). We point out that this goal cannot be reached within a pure effective (meson) field approach like chiral perturbation theory in which the dominant current-current operators governing the [Formula: see text] rule and the dominant density-density (four-quark) operators governing [Formula: see text] cannot be disentangled from each other. But in the context of a dual QCD approach, which includes both long-distance dynamics and the UV completion, that is, QCD at short-distance scales, such a distinction is possible. We find then that beyond the strict largeNlimit,Nbeing the number of colours, FSIs are likely to be important for the [Formula: see text] rule but much less relevant for [Formula: see text]. The latter finding diminishes significantly hopes that improved calculations of [Formula: see text] would bring its SM prediction to agree with the experimental data, opening thereby an arena for important new physics contributions to this ratio.
authors.affiliation: TUM Institute for Advanced Study, Lichtenbergstr. 2a, 85748 Garching, Germany.|Physik Department, TU München, James-Franck-Straße, 85748 Garching, Germany.
authors.forename: Andrzej J
authors.initials: AJ
authors.lastname: Buras
authors.affiliation: Centre for Cosmology, Particle Physics and Phenomenology (CP3), Université catholique de Louvain, Chemin du Cyclotron 2, 1348 Louvain-la-Neuve, Belgium.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Gérard