Charge symmetry breaking two-pion exchange

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Abstract
Two-pion exchange (TPE) contribution to the charge symmetry breaking class IV neutron-proton interaction is examined in a potential and coupled channels approach. Based on nonrelativistic πNN and πNΔ vertices, a TPE interaction is treated in two ways, as a potential or as a part calculable by the coupled channels method plus a residual potential interaction. A practical parametrization of the TPE potentials is given, which can also be used in the case of class III charge symmetry breaking (CSB) forces as well as for charge symmetric interactions. The results show that below 300 MeV the TPE contribution to CSB in elastic np scattering is insignificant, whereas at higher energies it should not be neglected.