SS-HORSE extension of the no-core shell model: Application to resonances in 7He

Theoretical ab initio studies of resonances in the unbound 7He nucleus are presented. We perform no-core shell-model calculations with NN interactions Daejeon16 and JISP16 and utilize the SS-HORSE method to calculate the S matrix for two-body channels n + 6He and n + 6He??? with 6He respectively in the ground and excited 2+ states as well as for the four-body democratic decay channel 4He + n + n + n. The resonant energies and widths are obtained by numerical location of the S-matrix poles. We describe all experimentally known 7He resonances and suggest an interpretation of an observed wide resonance of unknown spin-parity.