Constraining the ΛΛ interaction with terrestrial and astronomical data

Terrestrial double-Λ hypernuclear data and astronomical observations of neutron stars provide complementary constraints on the ΛΛ interaction. In this work, we investigate the ΛΛ interaction within a Skyrme energy density functional framework based on the KIDS (Korea-IBS-Daegu-SKKU) models. We employ a Skyrme-type ΛΛ interaction that includes the standard s- and p-wave terms, as well as a density-dependent term that effectively represents an NΛΛ three-body force. The s-wave terms are constrained using data on double-Λ hypernuclei supplemented by pseudodata obtained from core + 2Λ three-body model calculations including heavier hypernuclei. We show that the data on heavier systems are essential to simultaneously constrain the two s-wave parameters. We further explore the impact of the p-wave and NΛΛ components on the neutron-star properties and find that appropriate repulsive contributions of these terms yield consistency with current neutron-star mass-radius observations. These results indicate that the present framework provides phenomenologically acceptable equations of state for dense (N, Λ) matter over a wide range of densities and highlight the importance of future experimental data on heavier double-Λ hypernuclei.