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Dispersion Relations and Sum Rules for the pi ->gamma gamma* and gamma* ->gamma pi form factor

Tran N. Truong
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Abstract

Sum rules for the off-shell isovector form factor pi -> gamma gamma* are given in terms of the pion form factor and the gamma pi ->pi pi experimental data. Similarly the corresponding sum rules for the isoscalar form factor are given in terms of the experimental photon-3 pi form factor and the gamma pi -> 3 pi amplitude. For some set of parameters, e.g. rho -> pi gamma width = 90 KeV, the pi -> gamma gamma rate and the slope parameter of the decay pi -> gamma e plus e minus are in good agreement with the experimental data.

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Tran N. Truong. 2001-02-24. Dispersion Relations and Sum Rules for the pi ->gamma gamma* and gamma* ->gamma pi form factor. https://arxiv.org/abs/hep-ph/0102300

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