Can tetraneutron exist from theoretical point of view?
  A theoretical possibility is shown for the bound state of a tetraneutron to exist in the case of the proposed neutron-neutron potentials in the singlet state with two attractive wells separated by a repulsive barrier. The anomalous behaviours are revealed for the calculated size, density distribution, and pair correlation functions of a hypothetical tetraneutron. 
I.V. Simenog, B.E. Grinyuk, Yu.M. Bidasyuk