Isovector electromagnetic exchange currents in the chiral approach

TLDR: In this article, the structure of the isovector e.m. field was studied and the Lagrangian approach is consistent with the prediction of the low energy theorem at threshold.

Abstract: The problem studied in the paper concerns the structure of the isovector e.m. MEC operators of the A1−, ϱ- and π ranges in the interval of intermediate energies. The two main dynamic principles which we invoke in our considerations are the current conservation and the gauge chiral invariance. Respecting them consistently allows us to describe correctly the interaction of NA1 ϱπ system with the external e.m. field. Our main results are as follows: (i) We verified that our Lagrangian approach is consistent with the prediction of the low energy theorem at threshold. (ii) We showed explicitly the continuity equation which the longitudinal parts of our currents obey. (iii) We proved the equivalence relation for the MEC operator of the pion range and demonstrated the existence of the seagull current in the MEC operator built up using PS πN coupling. This new term influences strongly the exchange charge density.