https://doi.org/10.1140/epjc/s10052-015-3357-1
Regular Article - Theoretical Physics
A dispersive treatment of 
decays
1
Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, University of Bern, Sidlerstrasse 5, 3012, Bern, Switzerland
2
Department of Physics, Indiana University, Bloomington, IN, 47405, USA
3
Center for Exploration of Energy and Matter, Indiana University, Bloomington, IN, 47403, USA
4
Theory Center, Thomas Jefferson National Accelerator Facility, Newport News, VA, 23606, USA
5
Helmholtz-Institut für Strahlen- und Kernphysik (Theory) and Bethe Center for Theoretical Physics, University of Bonn, 53115, Bonn, Germany
* e-mail: stoffer@itp.unibe.ch
Received:
23
January
2015
Accepted:
10
March
2015
Published online:
28
April
2015
decays have several features of interest: they allow an accurate measurement of 
-scattering lengths; they provide the best source for the determination of some low-energy constants of 
PT; one form factor is directly related to the chiral anomaly, which can be measured here. We present a dispersive treatment of decays that provides a resummation of - and 
-rescattering effects. The free parameters of the dispersion relation are fitted to the data of the high-statistics experiments E865 and NA48/2. The matching to PT at NLO and NNLO enables us to determine the LECs 
, 
and 
. With recently published data from NA48/2, the LEC 
can be determined as well. In contrast to a pure chiral treatment, the dispersion relation describes the observed curvature of one of the form factors, which we understand as a rescattering effect beyond NNLO.
© SIF and Springer-Verlag Berlin Heidelberg, 2015
