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Feshbach Resonance due to Coherent Lambda-Sigma Coupling in Lambda_He^7

Coherent Lambda-Sigma coupling effect in Lambda_He^7 is analyzed within three-body framework of two coupled channels, Lambda-t-t and Sigma-tau-t, where tau represents trinucleon which is either H^3 or He^3. The hyperon-trinucleon (Y tau) and trinucleon-trinucleon (tau tau) interactions are derived by folding G-matrices of YN and NN interactions with trinucleon density distributions. It is found that the binding energy of Lambda_He^7 is 4.04 MeV below the Lambda+t+t threshold without Lambda-Sigma coupling and the binding energy is increased to 4.46 MeV when the coupling effect is included. This state is 7.85 MeV above the He^6+Lambda threshold and it may have a chance to be observed as a Feshbach resonance in Li^7 (e,e'K^+)Lambda_He^7 experiment done at Jefferson Lab.