Abstract:
When nonrelativistic particles interact through short-range forces near the unitarity limit, the two-body system is approximately scale invariant. Renormalization for more-body systems requires a three-body force, which lies on a limit cycle and breaks the symmetry to a discrete subgroup. The remaining, approximate discrete scale invariance gives rise to nearly geometric towers of excited states, including the famous Efimov three-body spectrum. In leading order, all energies are related through the one dimensionful parameter of the three-body force, an example being the Tjon correlation between three- and four-body ground-state energies. I discuss the implications for larger systems, in particular saturation for bosons (such as certain atoms near Feshbach resonances) and clustering for (multi-component) fermions (such as nucleons).
Zoom link will be available via announcement email, or by contacting: stroberg[at]uw.edu.