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 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.