Collapse of a Bose condensate with attractive interactions

We examine the Gross-Pitaevskii (GP) model for Bose-Einstein condensates in parabolic traps with attractive interactions. The decay of metastable cond ensates is investigated by applying the instanton formalism to the GP field theory. Employing various dynamical trial states, we derive within a coher ent state path integral approach a collective coordinate description in ter ms of the condensate radius, in agreement with (and extending) earlier resu lts. We then solve numerically for the complete instanton field configurati on and compare with the collective coordinate approach. Adjusting only the effective mass of the collective coordinate, the two schemes are then in go od agreement. [S1050-2947(99)05701-7].