Unitarity-limited elastic collision rate in a harmonically trapped Fermi gas

We derive the elastic collision rate for a harmonically trapped Fermi gas in the extreme unitarity limit where the s-wave scattering cross section is sigma(k)=4pi/k(2), with (h) over bark the relative momentum. The collision rate is given in the form Gamma=gamma I(T/T-F)-the product of a universal collision rate gamma=k(B)T(F)/(6pi(h) over bar) and a dimensionless function of the ratio of the temperature T to the Fermi temperature T-F. We find that I has a peak value of similar or equal to4.6 at T/T(F)similar or equal to0.4, Isimilar or equal to82 (T/T-F)(2) for T/T(F)less than or equal to0.15, and Isimilar or equal to2(T-F/T)(2) for T/T-F>1.5. We estimate the collision rate for recent experiments on a strongly-interacting degenerate Fermi gas of atoms.