We study dilute gases with short-range interactions and large two-body scattering lengths. At temperatures between the condensation temperature and the scale set by the range of the potential there is a high degree of universality. The first two terms in the expansion of thermodynamic functions in powers of the fugacity z, which measures the diluteness of the system, are determined by the scattering length only. The term proportional to $z^3$ depends only on one new parameter describing the three-body physics. We compute the third term of the expansion and show that, for many values of this new parameter, the $z^3$ term may be the dominant one.

• Received 3 September 2002

DOI:https://doi.org/10.1103/PhysRevB.67.174513