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Isospin breaking in pion-nucleon scattering at threshold by radiative processes

T. E. O. Ericson·A. N. Ivanov
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Abstract

We investigate the dispersive contribution by radiative processes such as (pi- proton to neutron gamma) and (pi- proton to Delta gamma) to the pion-nucleon scattering lengths of charged pions in the heavy baryon limit. They give a large isospin violating contribution in the corresponding isoscalar scattering length, but only a small violation in the isovector one. These terms contribute 6.3(3)% to the 1s level shift of pionic hydrogen and give a chiral constant F_pi^2f_1=-25.8(8) MeV.

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T. E. O. Ericson, A. N. Ivanov. 2005-03-29. Isospin breaking in pion-nucleon scattering at threshold by radiative processes. https://arxiv.org/abs/hep-ph/0503277

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