QUASI-PARTICLE INSTABILITIES IN MULTICOMPONENT ATOMIC CONDENSATES

We extend the Hartree-Bogoliubov theory to the case of a multicomponen t Bose condensate and determine the resulting quasiparticle frequency spectrum. We show that interferences resulting from cross coupling bet ween the condensate components can lead to a reversal of the sign of t he effective two-body interaction and to the onset of spatial instabil ities.