Using modern nucleon-nucleon interactions in the description of the A=3,4
nuclei, it is not possible to reproduce both the three- and four-nucleon
binding energies simultaneously. This is one manifestation of the necessity of
including a three-nucleon force in the nuclear Hamiltonian. In this paper we
will perform a comparative study of some, widely used, three-nucleon force
models. We will analyze their capability to describe the aforementioned binding
energies as well as the n−d doublet scattering length. A correct description
of these quantities can be considered a stringent requirement for a nuclear
Hamiltonian containing two- and three-nucleon interaction terms. As we will
show, this requirement is not fulfilled by several of the models available in
the literature. To satisfy it, we propose modifications in the parametrization
of the three-nucleon forces and we study their effects on few selected N−d
low energy scattering observables.Comment: 30 pages, 10 figure
