Shallow Efimov tetramer as inelastic virtual state and resonant   enhancement of the atom-trimer relaxation
  We use exact four-boson scattering equations in the momentum-space framework to study the universal properties of shallow Efimov tetramers and their dependence on the two-boson scattering length. We demonstrate that, in contrast to previous predictions, the shallow tetramer in a particular experimentally unexplored regime is not an unstable bound state but an inelastic virtual state. This leads to a resonant behaviour of the atom-trimer scattering length and thereby to a resonant enhancement of the trimer relaxation in ultracold atom-trimer mixtures. 
A. Deltuva
physics.atom-ph cond-mat.quant-gas nucl-th