30th CEMS Colloquium

Title

Limit Cycle and Universal Three-Body Parameter in Efimov Physics

Abstract

The Efimov effect is among the few experimentally realized phenomena that exhibit renormalization-group limit cycle. Here the low-energy spectrum of three particles is determined by the three-body parameter.

In ultracold atom experiments, it has recently been discovered that the three-body parameter takes on a near-constant universal value when measured in units of the effective range of the interaction. We have recently demonstrated that the physical origin of the universality of the three-body parameter is the deformation of the relative configuration of the three atoms as they come close. Then the following question arises: What is the relationship between the universality of the three-body parameter and the onset of the limit cycle at which the Efimov state emerges. By using the functional renormalization-group method for various finite-range interaction potentials, we show that the onset of the renormalization-group flow into the limit cycle is universal, regardless of short-range details. We have thus connected a missing link between the two universalities of the Efimov physics.