Ab initio approach to s-shell hypernuclei 3lambdaH, 4lambdaH, 4lambdaHe, and 5lambdaHe with a lambdaN-sigmaN interaction.
Variational calculations for s-shell hypernuclei are performed by explicitly including Sigma degrees of freedom. Four sets of YN interactions [SC97d(S), SC97e(S), SC97f(S), and SC89(S)] are used. The bound-state solution of 5lambdaHe is obtained and a large energy expectation value of the tensor lambdaN-sigmaN transition part is found. The internal energy of the 4He subsystem is strongly affected by the presence of a Lambda particle with the strong tensor lambdaN-sigmaN transition potential.