 If the average spacing between the particles in a gas is greater than the scattering length (that is, in the so-called dilute limit), then one can approximate the true interaction potential that features in this equation by a pseudopotential.At sufficiently low temperature where the de Broglie wavelength is much longer than the range of boson-boson interaction, the scattering process can be well approximated by the s-wave scattering (i.e.formula_7 in the partial wave analysis, a.k.a.