When a system is probed at distance scales much longer than the scale of the underlying interaction it can be approximated using a series of contact interactions. For low energies and few nucleons, pionless effective field theory (EFT) is an example of such a theory in which nuclear physics can be described via contact interactions between nucleons and possible external currents. A similar theory can be used to describe halo-nuclei along the neutron drip line. I will describe how recent techniques for strictly perturbative three-body calculations with contact interactions have been used to probe scattering and bound state properties of three-nucleon systems using pionless EFT, and how these techniques can also be used for halo-nuclei along the neutron drip line.
