Coherent<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Λ</mml:mi><mml:mi>−</mml:mi><mml:mi>Σ</mml:mi></mml:math>Coupling in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">s</mml:mi></mml:math>-Shell Hypernuclei

It is found that the suppression due to two-body LambdaN-SigmaN coupling solves the overbinding problem in (5)(Lambda)He but it, in turn, causes a severe underbinding in the four-body systems. The shortage of this binding is overcome by introducing explicitly the Lambda-Sigma coupling which is equivalent to the LambdaNN three-body force. This three-body force becomes strong in the 0(+) states of (4)(Lambda)H and (4)(Lambda)He according to the coherently added enhancement. The 0(+)-1(+) splitting in (4)(Lambda)H and (4)(Lambda)He is found partly due to the LambdaN spin-spin interaction and partly due to the Lambda-Sigma coupling in the recent Nijmegen soft-core potential.