Spin-dependent effective interactions for halo nuclei

We discuss the spin dependence of the effective two-body interactions appropriate for three-body computations. The only reasonable choice seems to be the fine and hyperfine interactions known for atomic electrons interacting with the nucleus. One exception is the nucleon-nucleon interaction imposing a different type of symmetry. We use the two-neutron halo nucleus ${}^{11}\mathrm{Li}$ as an illustration. We demonstrate that models with the wrong spin dependence are basically without predictive power. The Pauli forbidden core and valence states must be consistently treated.