  The Faddeev-Yakubovsky equations have been solved in configuration space for
the four nucleon system. The n+t elastic cross section has been calculated
using several realistic interactions and a phenomenological three-nucleon
force. Special attention is devoted to the description of the observed resonant
structure at $T_{lab}\approx 4$ MeV. In the present state of the calculations,
the realistic NN interactions are unable to describe the energy region
considered, i.e. n+t S- and P- waves. Whereas the inclusion of a three-nucleon
force improves the zero energy region, the disagreement in the resonant peak
remains. This failure contrasts with the results of a pure phenomenological
model. The origin of this disagreement as well as the possible issues are
discussed.
