We derive exact general relations between various observables for N bosons with zero-range interactions, in two or three dimensions, in an arbitrary external potential. Some of our results are analogous to relations derived previously for two-component fermions and involve derivatives of the energy with respect to the two-body s-wave scattering length a. Moreover, in the three-dimensional case, where the Efimov effect takes place, the interactions are characterized not only by a, but also by a three-body parameter Rt. We then find additional relations which involve the derivative of the energy with respect to Rt. In short, this derivative gives the probability of finding three particles close to each other. Although it is evaluated for a totally lossless model, it also gives the three-body loss rate always present in experiments (due to three-body recombination to deeply bound diatomic molecules), at least in the limit where the so-called inelasticity parameter η is small enough. As an application, we obtain, within the zero-range model and to first order in η, an analytic expression for the three-body loss rate constant for a nondegenerate Bose gas at thermal equilibrium with infinite scattering length. We also discuss the generalization to arbitrary mixtures of bosons and/or fermions.
Physical Review A
- Pub Date:
- November 2012
- Ultracold gases trapped gases;
- Condensed Matter - Quantum Gases
- Published version, augmented by (i) a note in section III on the universal correction to the ground state energy of the 2D weakly interacting Bose gas due to a nonzero interaction range and (ii) a note in section IV.C on the decay rate due to three-body losses of an Efimov trimer close to the atom-dimer dissociation threshold