The Hypernuclei _Λ⁴He and _Λ⁴H: Challenges for Modern Hyperon-Nucleon Forces

The hypernuclei _Λ⁴He and _Λ⁴H provide important information on the hyperon-nucleon interaction. We present accurate Faddeev-Yakubovsky calculations for the Λ separation energies of the 0⁺ ground and the 1⁺ excited states based on the Nijmegen SC YN interactions. We explicitly take the Σ admixture into account. Mass differences of the baryons and the charge dependence of the interaction are considered. The results show that the Nijmegen models cannot predict all separation energies simultaneously hinting to failures of the current interaction models. It is pointed out that the differences of the Λ separation energies of _Λ⁴He and _Λ⁴H are interesting observables to probe the YN interaction models.