https://doi.org/10.1140/epjc/s10052-016-4586-7
Regular Article - Theoretical Physics
Final state interactions in 
decays: 
rule vs. 
1
TUM Institute for Advanced Study, Lichtenbergstr. 2a, 85748, Garching, Germany
2
Physik Department, TU München, James-Franck-Straße, 85748, Garching, Germany
3
Centre for Cosmology, Particle Physics and Phenomenology (CP3), Université catholique de Louvain, Chemin du Cyclotron 2, 1348, Louvain-la-Neuve, Belgium
* e-mail: aburas@ph.tum.de
Received:
9
September
2016
Accepted:
12
December
2016
Published online:
3
January
2017
Dispersive effects from strong 
rescattering in the final state interaction (FSI) of weak decays are revisited with the goal to have a global view on their relative importance for the rule and the ratio 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 rule and the dominant density–density (four-quark) operators governing 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 large N limit, N being the number of colours, FSIs are likely to be important for the rule but much less relevant for . The latter finding diminishes significantly hopes that improved calculations of would bring its SM prediction to agree with the experimental data, opening thereby an arena for important new physics contributions to this ratio.
© The Author(s), 2017
