Dispersive representation of K -> 3 pi amplitudes and cusps

Abstract

The NA48/2 collaboration has shown clear experimental evidence for a cusp in the data for K -> pi pi^0 pi^0. This effect can be used to extract information on the pi-pi scattering lengths. We address this issue using a two-loop dispersive construction of pi pi -> pi pi and K -> pi pi pi amplitudes in the presence of isospin breaking.

Comments: 4 pages, 1 figure, to appear in Proceedings of the conference QCD 08, Montpellier, 7-12 July 2008