Radii and neutron correlations of (6,8)He within the Gamow Shell Model

We study the spatial correlations between halo neutrons in 6,8He within the complex-energy Gamow Shell Model (GSM). To this end, we calculate the neutron and proton radii, and two-neutron correlations in a large shell model space consisting of the 0p3/2 resonance and non-resonant p-sd scattering continuum. We use schematic forces and the finite-range Modified Minnesota interaction.The calculated charge radii, corrected for the core polarization and spin-orbit effects, are compared to the values extracted from measured atomic isotope shifts.We find that the charge radius of 6He primarily depends on the two-neutron separation energy and the shell-model occupation of the 0p3/2 orbit.We confirm that the ground-state GSM wave function of 6Heis dominated by the S=0 component representing a di-neutron structure. On the other hand, the correlation density of the 2+ resonance in 6He indicates a very weak di-neutron correlations in this state. We study the effect of pairing correlations on the neutron and charge radii of 6He and we confirm the presence of the Pairing-Anti-Halo effect in this light system.Finally, we calculate the charge radius of 8He in the full GSM space with the help of the Density Matrix Renormalization Group (DMRG) technique. The results of our realistic GSM+DMRG studies presented in this work show promise for extending the reach of the realistic complex-energy shell model to heavier halo systems