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Virtual photons to fourth order CHPT with nucleons

Guido Mueller
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Abstract

I discuss the whole mechanism to calculate isospin violation effects in the framework of CHPT. In order to get the correct size of isospin violation one has to include all non-isospin symmetric sources like the electromagnetic interaction, the quark mass difference ($π_0 - η$ mixing), explicit photon loops. As examples I discuss the electromagnetic contributions to the pion nucleon sigma term and to the S-wave pion nucleon scattering length.

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Guido Mueller. 1999-08-26. Virtual photons to fourth order CHPT with nucleons. https://arxiv.org/abs/hep-ph/9908470

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