Finite-temperature excitations of Bose gases in anisotropic traps

The mode frequencies of a weakly interacting Bose gas in a magnetic trap ar e studied as a function of the anisotropy of the trap. As in earlier works, the generalized Hartree-Fock-Bogoliubov equations within the Popov approxi mation are used for our calculations. A feature of our work is the combined use of a mode expansion in a finite basis and a semiclassical approximatio n of the highly excited states. The results are applied to check the accura cy of the recently suggested equivalent zero temperature condensate approxi mation, which involves a much simpler model. [S1050-2947(99)00105-5].