Spectroscopic factors of resonance states with the Gamow shell model

We provide an investigation of the spectroscopic factors of resonance states in $A =5-8$ nuclei using two distinct nuclear models, the Gamow shell model (GSM) and the no-core shell model (NCSM). Configuration mixing is treated exactly in both GSM and NCSM. GSM employs the complex-energy Berggren ensemble, which treats bound, unbound resonance, and non-resonant continuum single-particle states on an equal footing. As a result, continuum coupling is taken into account in GSM, whereas it is absent in NCSM, where the harmonic oscillator basis is used. We first calculate low-lying states of helium isotopes and isotones. The results indicate that GSM can more accurately reproduce the low-lying resonance states than NCSM.  The spectroscopic factors of the resonance states are also computed. Results from the GSM and NCSM are compared and show that continuum coupling plays an important role in the calculations of spectroscopic factors of resonance states. Overlap functions related to the resonance states are also systematically calculated by the GSM and NCSM. It is then demonstrated that wave function asymptotes can only be reproduced in GSM, where continuum coupling is taken into account.