Nonperturbative model for the halfoffshell \gamma N N vertex
Abstract
Form factors in the nucleonphoton vertex with one offshell nucleon are calculated by dressing the vertex with pion loops up to infinite order. Cutting rules and dispersion relations are implemented in the model. Using the prescription of minimal substitution we construct a \gamma \pi N N vertex and show that it has to be included in the model in order that the WardTakahashi identity for the \gamma N N vertex be fulfilled. The vertex is to be applied in a coupledchannel Kmatrix formalism for Compton scattering, pion photoproduction and pion scattering. The form factors show a pronounced cusp structure at the pion threshold. As an illustration of a consistent application of the model, we calculate the cross section of Compton scattering. To provide gauge invariance in Compton scattering, a fourpoint \gamma \gamma N N contact term is constructed using minimal substitution.
 Publication:

arXiv eprints
 Pub Date:
 June 1999
 arXiv:
 arXiv:nuclth/9906044
 Bibcode:
 1999nucl.th...6044K
 Keywords:

 Nuclear Theory
 EPrint:
 51 pages, 12 Postscript figures, using REVTeX. Submitted to Phys. Rev. C, added references