The structure of hypernuclei and hyperon mixing in neutron-star matter

We review our recent studies of the structure of hypernuclei within the framework of the Gaussian expansion method for s- and p-shell hypernuclei and the mean-field approach for sd-shell hypernuclei. Specifically, we focus on the structures of (i) the energy splittings of the 3/2⁺-5/2⁺ and 3/2^--1/2^- levels in 9 Be and 13 within the framework of 2α +and 3α+ three- and four-body cluster models for the hyperon-nucleon (Y-N) spin-orbit force; (ii) the 3n system for N - σN coupling; (iii) the weakly bound states or resonant states of neutron-rich hypernuclei such as 6H and 7 He within the framework of t + n + n and α ++n + four-body models; and (iv) the tensor correlation effect and super-deformation structure of hypernuclei based on sd-shell nuclei with mass 20 ≤ A ≤ 40 using the deformed Skyrme-Hartree-Fock model and the antisymmetrized molecular dynamics model. As an extreme limit of nuclei including multiple hyperons, we review hyperon effects in neutron-star matter in the high-density region using recent Y-N interactions.