Living Near Unitarity

Coordinators: Olivier Dulieu, Chris Greene, Alejandro Kievsky, and Daniel Phillips

In the limit that a quantum-mechanical two-body interaction generates a bound state directly at threshold (“the unitary limit”) the low-energy two-body scattering amplitude has continuous scale invariance. The corresponding three-body system has a discrete scale invariance that leads to the “Efimov effect”: a geometrical tower of states related by a discrete scale transformation. Efimov’s prediction has been confirmed and the properties of a gas of fermions with interactions tuned to the unitarity limit investigated extensively. Astonishingly, the unitarity limit is almost realized for nucleon-nucleon interaction at energy scales that are 19 orders of magnitude larger. This situation occurs in several nuclei near the limits of nuclear stability. The ability of rare-isotope facilities to produce neutron-rich nuclei in which the last few neutrons are weakly bound makes unitarity a topic of significant current interest in nuclear physics. This program will bring together scientists who are interested in the implications of these theoretical concepts and experimental findings for both nuclei and atomic-molecular systems. Our goal is to facilitate synergy between explorations in these apparently disparate subdisciplines. With the general picture of universality and physics near the unitarity limit now established we want to refine details of that picture, explore its implications for atomic and nuclear reactions, and discuss novel AMO contexts in which the unitarity limit may be manifest.