Origin of the Universal Three-body Parameter in Atomic Efimov Physic

Several experiments [1] with different kinds of ultra-cold atoms have revealed that the three-body parameter that fixes the Efimov spectrum of few-atom systems near broad Feshbach resonances is universally determined by the atoms' van der Waals length. Using model potential calculations we find that the three-body parameter originates from a deformation of the three-atom system due to universal two-body correlations at separations on the order of the van der Waals length scale [3]. This simple physical picture is consistent with the universality of the three-body parameter observed in the experiments [1], as well as previous numerical calculations [2]. It explains why the low-energy physics of three bosonic atoms near a broad resonance is solely determined by their two-body parameters.\\[4pt] [1] F. Ferlaino, A. Zenesini, M. Berninger, B. Huang, H.-C. N\"agerl, R. Grimm, Few-Body Syst 51: 113-133 (2011).\\[0pt] [2] J.Wang, J.P.D'Incao, B.D.Esry, and C.H.Greene, Phys. Rev. Lett. 108, 263001 (2012).\\[0pt] [3] P. Naidon, S. Endo, M. Ueda, arXiv:1208.3912 (2012).