Universality of three-body systems in 2D: parametrization of the bound   states energies
  Universal properties of mass-imbalanced three-body systems in 2D are studied using zero-range interactions in momentum space. The dependence of the three-particle binding energy on the parameters (masses and two-body energies) is highly non-trivial even in the simplest case of two identical particles and a distinct one. This dependence is parametrized for ground and excited states in terms of {\itshape supercircles} functions in the most general case of three distinguishable particles. 
F. F. Bellotti, T. Frederico, M. T. Yamashita, D. V. Fedorov, A. S.   Jensen, N. T. Zinner
cond-mat.quant-gas math-ph math.MP