Photoassociation of universal Efimov trimers

In view of recent experiments in ultracold atomic systems, the photoassociation of Efimov trimers, composed of three identical bosons, is studied utilizing the multipole expansion. We study both the normal hierarchy case, where one-body current is dominant, and the strong hierarchy case, relevant for photoassociation in ultracold atoms, where two-body current is dominant. For identical particles in the normal hierarchy case, the leading contribution comes from the r² s-mode operator and from the quadrupole d-mode operator. The s-mode reaction is found to be dominant at low temperature, while as the temperature increases the d-mode becomes as significant. For the strong hierarchy case, the leading contribution comes from a 2-body s-wave δ operator. In both cases log periodic oscillations are found in the cross section. For large but finite scattering length the amplitude of the oscillations becomes larger in comparison to infinite scattering length case. We apply our theory to photoassociation of ⁷Li ultracold atoms and show a good fit to the available experimental results.