Leading-order 2πγ exchange NN interaction: Central potentials proportional to gA 0 and gA 2

Abstract

We calculate at two-loop order in chiral perturbation theory the electromagnetic corrections to the leading-order 2π exchange NN interaction proportional to gA0 and gA2. The resulting 2πγ exchange potential contains isospin-breaking components which reach up to about -2% of the corresponding isovector 2π exchange potential. With a value of only -17keV at r = mπ-1 = 1.4fm the charge-independence breaking central potential obtained here is negligibly small in comparison to the one generated by the isoscalar c3 contact vertex. Our calculation confirms that the largest long-range isospin-violating NN potentials arise from the 2πγ exchange diagrams involving the large low-energy constants c4 ≃ - c3 ≃ 3.3GeV^-1 representing the important Δ(1232) dynamics.