Parity-nonconserving observables in thermal neutron capture on a proton

We calculate parity-nonconserving observables in the processes where a neutron is captured on a proton at the threshold energy radiating a photon. Various potential models such as Paris, Bonn and Argonne nu 18 are used for the strong interactions, and the meson exchange description is employed for the weak interactions between hadrons. The photon polarization P-gamma in the unpolarized-neutron capture process and photon asymmetry A(gamma) in the polarized-neutron capture process are obtained in terms of the weak meson-nucleon coupling constants. A(gamma) turns out to be basically insensitive to the employed strong interaction models and thus can be uniquely determined in terms of the weak coupling constants, but P-gamma depends significantly on the strong interaction models.