Four nucleon systems : a zoom to the open problems in nuclear interaction

Faddeev-Yakubovski equations in configuration space are used to solve four nucleon problem for bound and scattering states. Different realistic interaction models are tested, elucidating open problems in nuclear interaction description. On one hand, by example of nonlocal Doleschall potential, we reveal possibility of reducing three-nucleon force. On the other hand we disclose discrepancies in describing n+$^3$H resonance, which seems to be hardly related with off-shell structure of nucleon-nucleon interaction.