Shell-Model Calculations for_(Λ)¹⁶O and_(Λ)¹⁷O Using Microscopic Effective Interactions with Sigma Degrees of Freedom

Shell-model calculations in a large model space are performed for _{\Lambda}^{16}O and_{\Lambda}^{17}O. Effective interactions with degrees of freedom of \Sigma in addition to \Lambda and nucleons are derived from hyperon-nucleon and nucleon-nucleon interactions within the framework of the unitary-model-operator approach. Effects of the \Sigma degrees of freedom and the parity-mixing intershell coupling on the \Lambda hypernuclear structure are investigated, employing the Nijmegen NSC97a-f and NSC89 hyperon-nucleon potentials.