Efimov Physics Beyond Three Particles

Abstract

Efimov physics originally refers to a system of three particles. Here we review recent theoretical progress seeking for manifestations of Efimov physics in systems composed of more than three particles. Clusters of more than three bosons are tied to each Efimov trimer, but no independent Efimov physics exists there beyond three bosons. The case of a few heavy fermions interacting with a lighter atom is also considered, where the mass ratio of the constituent particles plays a significant role. Following Efimov’s study of the (formula presented) system, the (formula presented) system was shown to have its own critical mass ratio to become Efimovian. We show that the (formula presented) system becomes Efimovian at a mass ratio which is smaller than its sub-systems thresholds, giving a pure five-body Efimov effect. The (formula presented) and (formula presented) systems are also discussed, and we show the absence of 6— and 7—body Efimov physics there.