  Atom loss resonances in ultracold trapped atoms have been observed at
scattering lengths near atom-dimer resonances, at which Efimov trimers cross
the atom-dimer threshold, and near two-dimer resonances, at which universal
tetramers cross the dimer-dimer threshold. We propose a new mechanism for these
loss resonances in a Bose-Einstein condensate of atoms. As the scattering
length is ramped to the large final value at which the atom loss rate is
measured, the time-dependent scattering length generates a small condensate of
shallow dimers coherently from the atom condensate. The coexisting atom and
dimer condensates can be described by a low-energy effective field theory with
universal coefficients that are determined by matching exact results from
few-body physics. The classical field equations for the atom and dimer
condensates predict narrow enhancements in the atom loss rate near atom-dimer
resonances and near two-dimer resonances due to inelastic dimer collisions.

Quantum Gases