Consistency between pion exchange currents andN−Npotential in doubly radiativen−pcapture

Abstract

The consistency between the exchange currents in the pionic range and the Reid soft-core potential, which has an asymptotic beahvior like ${V}_{\mathrm{OPE}}$, is studied in the doubly radiative $n\ensuremath{-}p$ capture process. The cross section is evaluated using the interaction Hamiltonian expressed by means of the nuclear current, that includes the two-body terms deriving from one-pion exchange. The gauge invariance is preserved by the generalized contact term. This cross section is compared to that obtained with the Siegert form of the interaction Hamiltonian. The difference between the values of the cross section, which is of the order of 24%, constitutes a quantitative estimate of the lack of consistency between pion exchange currents and the nuclear potential considered. The use of purely phenomenological wave functions leads to a great disagreement. Finally, the existence of an exchange effect of the order of 30% is pointed out in the process under examination, which occurs via the emission of two $E1$ photons.