2 8 Ju l 1 99 6 Hydrodynamics of a Bose condensate : beyond the mean field approximation

Self-consistent hydrodynamic one-loop quantum corrections to the Gross-Pitaev-skii equation due to the interaction of the condensate with collective excitations are calculated. It is done by making use a formalism of effective action and ζ-function regularization for a contribution from Bogoliubov particles in hydrodynamic approximation. It turns out to be possible to reduce the problem to the investigation of a determinant of Laplace operator on curved space where a metric is defined by density and velocity of the condensate. Standard methods of quantum gravity let us get the leading logarithmic contribution of the determinant and corresponding quantum corrections. They describe an additional quantum pressure in the condensate, local heating-cooling and evaporation-condensation effects of the Bose-condensed fraction. The effects of these corrections are studied for the correction from excited states in equilibrium situation. Response functions and form factors are discussed in the same approximation.