Recombination of N bosons near threshold

We derive a generalized cross section for scattering events involving an arbitrary number of particles, and apply our result to the recombination of N bosons. We obtain a semi-analytical formula that encapsulates the overall Wigner threshold scaling as well as resonant enhancements due to the presence of N-body states near threshold. For the case N=4, we obtain quantitative results for the event rate that exhibit resonant enhancement due to known universal 4-boson states tied to Efimov physics.