Gross-Pitaevskii Model for Nonzero Temperature Bose-Einstein Condensates

Momentum distributions and temporal power spectra of nonzero temperature Bose-Einstein condensates are calculated using a Gross-Pitaevskii model. The distributions are obtained for micro-canonical ensembles (conservative Gross-Pitaevskii equation) and for grand-canonical ensembles (Gross-Pitaevskii equation with fluctuations and dissipation terms). Use is made of an equivalence between statistics of the solutions of conservative Gross-Pitaevskii and dissipative complex Ginzburg-Landau equations. In all cases the occupation numbers of modes follow a k^(-2) dependence, which corresponds in the long wavelength limit (k->0) to Bose-Einstein distributions. The temporal power spectra are of f^(-a) form, where: a=2-D/2 with D the dimension of space.