Radiative Neutron-Proton Capture in Effective Chiral Lagrangians

We calculate the cross section for the thermal n+p→d+γ process in chiral perturbation theory to next-to-next-to-leading order using heavy-fermion formalism. The exchange current correction is found to be (4.5±0.3)% in amplitude, and the chiral perturbation at one-loop order gives the cross section σₜₕ0ex0ex=0ex0ex334±2 mb, which is in agreement with the experimental value 334.2±0.5mb. Together with the axial-charge transitions, this provides a strong support for the power of chiral Lagrangians for nuclear physics.