Unitarity and Discrete Scale Invariance

While the complexity of some many-body systems may stem from a profusion of distinct scales, as we approach two-body unitarity (through experimental control or as a theoretical limit) rich structures exist even though there is no more than one essential scale. I comment, from the point of view of effective field theory, on some current problems in the transition from few to many bodies in bosonic and multi-state fermion systems, where order emerges from the discrete scale invariance associated with a single, contact three-body force.