We introduce a coupled-channel method for elastic three-body scattering in systems of identical bosonic alkali-metal atoms. The approach relies on the numerically exact two-body off-the-energy-shell transition matrix, constructed from realistic multichannel molecular interaction potentials that support many bound states. By rigorously accounting for this off-shell structure, the method captures both the short-range physics as well as multichannel couplings characteristic of alkali-metal potentials without resorting to model pseudopotentials. The central output is the complex three-body scattering hypervolume—the three-body analog of the two-body scattering length—which we obtain with controlled and verifiable numerical accuracy. As a realistic benchmark, we apply our framework to spin-polarized potassium-39, performing full coupled-channel three-body scattering calculations and extracting the hypervolume over experimentally relevant conditions. The method is general and transferable to other atomic species and interaction models featuring deep molecular potentials with an arbitrarily large number of bound states.
The elastic scattering properties of three bosons at low energy enter the many-body description of ultracold Bose gases via the three-body scattering hypervolume
D. We study this quantity for identical bosons that interact via a pairwise finite-range potential. Our calculations cover the regime from strongly repulsive potentials towards attractive potentials supporting multiple two-body bound states and are consistent with the few existing predictions for
D. We present a numerical confirmation of the universal predictions for
D in the strongly interacting regime, where Efimov physics dominates, for a local nonzero-range potential. Our findings highlight how
D is influenced by three-body quasibound states with strong
d-wave or
g-wave characteristics in the weakly interacting regime.