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The structure of A = 3 Σ-hypernuclei is investigated on the basis of a central two-body ΣN interaction. We perform a three-body coupled-channel calculation by using the coupled-rearrangement-channel variational method. The results suggest that there exist unstable bound states of S = 1 2 , i.e. Σ3H, Σ3He and Σ3n, due to the channel coupling through the ΣN potential which strongly admixes 3S1, TNN = 0 and 1S0, TNN = 1 states in the NN pair. The total isospin T = 1 is approximately a very good quantum number (≳ 96%). In Σ3He and Σ3n, energies are largely affected by the Coulomb potential and dependent on the model of the ΣN potential. The characteristic features of the nucleus-Σ potential are also discussed.

Σ-hypernuclear continuum spectra in the 4He(stopped K−,π+) reaction at KEK are analyzed within the framework of DWIA to elucidate a qualitative validity of the Σ-N interaction. It is found that considering coupled-channels between Σ−+3H and n+(ΣNN)0, an intermediate (ΣNN)0 state induces a ΣN→ΛN conversion decay while the Σ−−3H channel has a weak conversion. This result implies that the decay occurs mainly in the Σ-N I = 1 2 , 3S1 state.