The S-wave ΛΛ and N Ξ interactions are studied on the basis of the (2+1)-flavor lattice QCD simulations close to the physical point (m π 146MeV and m K 525MeV). Lattice QCD potentials in four different spin-isospin channels are extracted by using the coupled-channel HAL QCD method and are parametrized by analytic functions to calculate the scattering phase shifts. The ΛΛ interaction at low energies shows only a weak attraction, which does not provide a bound or resonant dihyperon. The N Ξ interaction in the spin-singlet and isospin-singlet channel is most attractive and lead the N Ξ system near unitarity. Relevance to the strangeness=−2 hypernuclei as well as to two-baryon correlations in proton-proton, proton-nucleus and nucleus-nucleus collisions is also discussed.

The ΩΩ system in the ^{1}S_{0} channel (the most strange dibaryon) is studied on the basis of the (2+1)-flavor lattice QCD simulations with a large volume (8.1  fm)^{3} and nearly physical pion mass m_{π}≃146  MeV at a lattice spacing of a≃0.0846  fm. We show that lattice QCD data analysis by the HAL QCD method leads to the scattering length a_{0}=4.6(6)(_{-0.5}^{+1.2})  fm, the effective range r_{eff}=1.27(3)(_{-0.03}^{+0.06})  fm, and the binding energy B_{ΩΩ}=1.6(6)(_{-0.6}^{+0.7})  MeV. These results indicate that the ΩΩ system has an overall attraction and is located near the unitary regime. Such a system can be best searched experimentally by the pair-momentum correlation in relativistic heavy-ion collisions.

The nucleon(N )-Omega(Ω) system in the S-wave and spin-2 channel ( 5 S 2 ) is studied from the (2+1)-flavor lattice QCD with nearly physical quark masses (m π 146 MeV and m K 525 MeV). The time-dependent HAL QCD method is employed to convert the lattice QCD data of the two-baryon correlation function to the baryon-baryon potential and eventually to the scattering observables. The N Ω( 5 S 2 ) potential, obtained under the assumption that its couplings to the D-wave octet-baryon pairs are small, is found to be attractive in all distances and to produce a quasi-bound state near unitarity: In this channel, the scattering length, the effective range and the binding energy from QCD alone read a 0 = 5.30(0.44)( +0.16 −0.01 ) fm, r eff = 1.26(0.01)( +0.02 −0.01 ) fm, B = 1.54(0.30)( +0.04 −0.10 ) MeV, respectively. Including the extra Coulomb attraction, the binding energy of pΩ − ( 5 S 2 ) becomes B pΩ − = 2.46(0.34)( +0.04 −0.11 ) MeV. Such a spin-2 pΩ − state could be searched through two-particle correlations in p-p, p-nucleus and nucleus-nucleus collisions.

The interaction between Λ c and a nucleon (N) is investigated by employing the HAL QCD method in the (2+1)-flavor lattice QCD on a (2.9 fm) 3 volume at m π ≃ 410, 570, 700MeV. We study the central potential in 1 S 0 channel as well as central and tensor potentials in 3 S 1 − 3 D 1 channel, and find that the tensor potential for Λ c N is negligibly weak and central potentials in both 1 S 0 and 3 S 1 − 3 D 1 channels are almost identical with each other except at short distances. Phase shifts and scattering lengths calculated with these potentials show that the interaction of Λ c N system is attractive and has a similar strength in 1 S 0 and 3 S 1 channels at low energies (i.e. the kinetic energy less than about 40 MeV). While the attractions are not strong enough to form two-body bound states, our results lead to a possibility to form Λ c hypernuclei for sufficiently large atomic numbers (A). To demonstrate this, we derive a single-folding potential for Λ c hypernuclei from the Λ c -nucleon potential obtained in lattice QCD, and find that Λ c hypernuclei can exist for A ≥ 12 with the binding energies of a few MeV. We also estimate the Coulomb effect for the Λ c hypernuclei.