Systems, such as cold atoms and light halo nuclei, share universal features at low energies, for which details of inter-particle interactions are not essential. We study three-body physics in such systems in an effective-field-theory (EFT) framework.
We will discuss universal behavior in three-body systems and higher-order effective-range corrections beyond universality. We study effective-range effects perturbatively up to the next-to-next-to-leading order (N2LO) for the case of three identical bosons. We apply this analysis to recombination features in cold atomic gases and properties of Helium trimers. Effective range corrections also play an important role in the EFT study of few-nucleon systems and halo nuclei.
The ground-state of Helium-6 can be treated as a two-neutron halo with an alpha core. This bound state is generated by the resonant neutron-neutron and neutron-alpha interactions. The latter is dominated by a shallow p-wave resonance. We present a calculation of Helium-6 in an EFT approach appropriate for halo systems.