Effective interaction techniques for the Gamow shell model

We apply a contour deformation technique in momentum space to the newly developed Gamow shell model, using the drip-line nuclei ⁵He, ⁶He, and ⁷He as test cases. A major problem in Gamow shell-model studies of nuclear many-body systems is the increasing number of many-body configurations due to the large number of resonant and complex-continuum single-particle orbits necessary to reproduce multiparticle bound and resonant states. We address this problem using two different effective operator approaches generalized to the complex momentum plane. These are the Lee-Suzuki similarity transformation method for complex interactions and the multireference perturbation theory method. We show that a combination of these two approaches results in a drastic truncation of the number of relevant configurations compared with direct diagonalization. This offers interesting perspectives for studies of weakly bound systems.