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Chiral O(Q^4) two-body operators for s-wave pion photoproduction on the NN system

A. Gardestig
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Abstract

The two-body currents for s-wave pion photoproduction on the NN system are derived to O(Q^4) in chiral perturbation theory. For the interesting case of 3S1 <-> 1S0 transitions, we show that an axial isovector two-nucleon contact term connects the short-distance physics of pion photoproduction to pion production and several important electroweak reactions. We also find that the standard chiral Lagrangian gives a gamma pi pi N N vertex that have not been explicitly mentioned in previous literature. The corresponding Feynman rule is presented here and some processes where it should be important are briefly discussed.

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A. Gardestig. 2006-04-16. Chiral O(Q^4) two-body operators for s-wave pion photoproduction on the NN system. https://doi.org/10.1103/physrevc.74.017001

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