Effective field theory for few-boson systems

We study universal bosonic few-body systems within the framework of effective field theory at leading order (LO). We calculate binding energies of systems of up to six particles and the atom-dimer scattering length. Convergence to the limit of zero-range two-and three-body interactions is shown, indicating that no additional few-body interactions need to be introduced at LO. Generalizations of the Tjon line are constructed, showing correlations between few-body binding energies and the binding energy of the trimer, for a given dimer energy. As a specific example, we implement our theory for He-4 atomic systems and show that the results are in surprisingly good agreement with those of sophisticated He-4 - He-4 potentials. Potential implications for the convergence of the EFT expansion are discussed.