  The existence of multi-neutron systems has always been a debatable question.
Indeed, both inter-nucleon correlations and a large continuum coupling occur in
these states. We then employ the ab-initio no-core Gamow shell model to
calculate the resonant energies and widths of the trineutron and tetraneutron
systems with realistic interactions. Our results indicate that trineutron and
tetraneutron are both unbound and bear broad widths. The calculated energy and
width of tetraneutron are also comparable with recent experimental data.
Moreover, our calculations suggest that the energy of trineutron is lower than
that of tetraneutron, while its resonance width is also narrower. This strongly
suggests that trineutron is more likely to be experimentally observed than
tetraneutron. We thus suggest experimentalists to search for trineutron at low
energy.
