Relativistic description of the np→ηd reaction near threshold

Relativistic effects in a three-body calculation of the np→ηd process are considered. Parametrizations for the ηN interaction obtained from phenomenological meson-nucleon models are probed. Relativistic effects on the range and strength of the pion exchange contribution to the reaction mechanism are seen to be large, while boost effects of the two-body interactions are negligible. The relativistic calculation confirms previous nonrelativistic results, showing that the shape of the cross section near threshold is essentially determined by the ηd final-state interaction alone. As for the region away from threshold, the relativistic pion exchange contribution is seen to dominate the other mechanisms of the reaction. It turns out that, within the relativistic reaction model, the np→ηd experimental data call for a comprehensive study to find parameters of the meson-nucleon interactions which are consistent with η production, both on the nucleon as well as on the deuteron.