Dispersion theory and the low-energy constants for neutral-pion photoproduction

  • B. Pasquini
  • D. Drechsel
  • L. Tiator Email author
Hadron Physics


The relativistic amplitudes of pion photoproduction are evaluated by dispersion relations at t = const. The imaginary parts of the amplitudes are taken from the MAID model covering the absorption spectrum up to center-of-mass energies W = 2.2GeV. For sub-threshold kinematics the amplitudes are expanded in powers of the two independent variables ν and t related to energy and momentum transfer. Subtracting the loop corrections from this power series allows one to determine the counter terms of covariant baryon chiral perturbation theory. The proposed continuation of the amplitudes into the unphysical region provides a unique framework to derive the low-energy constants to any given order as well as an estimate of the higher-order terms by global properties of the absorption spectrum.


13.40.Gp Electromagnetic form factors 13.60.Le Meson production 14.20.Gk Baryon resonances with S = 0 25.20.Lj Photoproduction reactions 25.30.Rw Electroproduction reactions 


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© Società Italiana di Fisica and Springer-Verlag 2006

Authors and Affiliations

  1. 1.Dipartimento di Fisica Nucleare e TeoricaUniversità degli Studi di Pavia; INFN, Sezione di PaviaPaviaItaly
  2. 2.Institut für KernphysikJohannes Gutenberg-UniversitätMainzGermany

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