Subthreshold resonances in few-neutron systems

Three- and four-neutron systems are studied within the framework of the hyperspherical approach with a local S-wave nn-potential. Possible bound and resonant states of these systems are sought as zeros of three- and four-body Jost functions in the complex momentum plane. It is found that zeros closest to the origin correspond to subthreshold (nnn) 1/2- and (nnnn) 0+ resonant states. The positions of these zeros turned out to be sensitive to the choice of the nn-potential. For the Malfliet-Tjon potential they are E0(3n) = -4.9 - i6.9 (MeV) and E0(4n) = -2.6 - i9.0 (MeV). Movement of the zeros with an artificial increase of the potential strength also shows an extreme sensitivity to the choice of potential. Thus, to generate 3n and 4n bound states, the Yukawa potential needs to be multiplied by 2.67 and 2.32 respectively, while for the Malfliet-Tjon potential the required multiplicative factors are 4.04 and 3.59. (author)