Four-body calculation of ΛH and ΛHe with realistic YN and NN interactions

We carried out four-body calculations of _Λ⁴H and _Λ⁴He taking both the 3N + Λ and 3N + Σ channels explicity with the use of realistic NN and YN interactions. The Σ-channel component plays an important role in binding energies of the A = 4 hypernuclei though the admixture is approximately 1%. The ΛN - ΣN coupling is found to be of central-force type in the Nijmegen model D and of tensor-force type in the model F.