The few-atom problem

These lectures contain a theoretical introduction to the few-body problem with short-range resonant binary interactions. In the first part we discuss the effective range expansion for the two-body scattering amplitude emphasizing the role of the resonance width. In the second part we review the Efimov effect for three atoms, describe the difference in between the Efimovian and non-Efimovian regimes, and discuss the dependence of three-body observables on quantum symmetry, mass imbalance, and resonance width. In the third part we derive the Skorniakov and Ter-Martirosian equation and give several illustrative examples of its solution.