The atom and atom scattering model to control ultracold collisions
  A modified static exchange model is introduced, it could be useful to control the elastic s-wave scattering length in studying cold-atomic interaction. The theory includes the long-range van der Waals interaction in addition to short-range exchange force. The model is applied on Ps-H system to study the Feshbach resonances e.g. the s-wave elastic phase shifts and the corresponding cross sections at ultracold energies. These are compared with the data obtained using the static exchange model. A very interesting features are observed when we vary the interatomic separation i.e. the strength of dipole-dipole interaction. 
Hasi Ray
physics.atom-ph