S-shell ΛΛ hypernuclei based on chiral interactions

We generalize the Jacobi no-core shell model (J-NCSM) to study double-strangeness hypernuclei. All particle conversions in the strangeness S = -1,-2 sectors are explicitly taken into account. In two-body space, such transitions may lead to the coupling between states of identical particles and of non-identical ones. Therefore, a careful consideration is required when determining the combinatorial factors that connect themany-body potentialmatrix elements and the free-space two-body potentials. Using second quantization, we systematically derive the combinatorial factors in question for S = 0,-1,-2 sectors. As a first application, we use the J-NCSM to investigate Lambda Lambda s-shell hypernuclei based on hyperon-hyperon (YY) potentials derived within chiral effective field theory at leading order (LO) and up to next-to-leading order (NLO). We find that the LO potential overbinds He-6(Lambda Lambda) while the prediction of the NLO interaction is close to experiment. Both interactions also yield a bound state for He-5(Lambda Lambda). The H-4(Lambda Lambda) system is predicted to be unbound.