Continuum coupling and spectroscopic properties of nuclei

The nucleus is a correlated open quantum many-body system. The presence of states that are unbound to particle emission may have significant impact on spectroscopic properties of nuclei, especially those close to the particle drip lines. In the framework of the continuum shell model in the complex momentum-plane, we discuss salient effects of the continuum coupling on the spectroscopic factors, one-neutron overlap integrals, and energies of excited states in $^{6}$He and $^{18}$O. We demonstrate the presence of non-perturbative threshold effects in many-body wave functions of weakly-bound and unbound states.