Cusps in K --> 3 pi decays
  The pion mass difference generates a pronounced cusp in K --> 3 pi decays. As has recently been pointed out by Cabibbo and Isidori, an accurate measurement of the cusp may allow one to pin down the S-wave pi pi scattering lengths to high precision. Here, we present and illustrate an effective field theory framework that allows one to determine the structure of this cusp in a straightforward manner. The strictures imposed by analyticity and unitarity are respected automatically. 
Gilberto Colangelo (University of Bern), Juerg Gasser (University of   Bern), Bastian Kubis (University of Bonn), Akaki Ruse...