Berlin 2005 – scientific programme
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HK: Physik der Hadronen und Kerne
HK 24: Elektromagnetische und Hadronische Proben
HK 24.6: Talk
Tuesday, March 8, 2005, 15:30–15:45, TU MA001
The Fubini-Furlan-Rosetti Sum Rule — •Barbara Pasquini1, Dieter Drechsel2, and Lothar Tiator2 — 1Dipartimento di Fisica Nucleare e Teorica, Universita degli Studi di Pavia and INFN, Sezione di Pavia, Pavia, Italy — 2Institut für Kernphysik, Universität Mainz
The Fubini-Furlan-Rossetti sum rule for pion photoproduction on the nucleon is evaluated by dispersion relations at constant t, and the corrections to the sum rule due to the finite pion mass are calculated. Near threshold these corrections turn out to be large due to pion-loop effects, whereas the sum rule value is closely approached if the dispersion integrals are evaluated for sub-threshold kinematics. This extension to the unphysical region provides a unique framework to determine the low-energy constants of relativistic chiral perturbation theory by global properties of the excitation spectrum. In a further extension of this work the unitary isobar model MAID will be constrained by fixed-t dispersion relations. This will considerably improve the description of the non-resonant background contribution and will directly satisfy the requirements of crossing symmetry.