Refreshments in the Hbar at 3:30 pm
The Efimov effect, which was predicted in the early seventies, was originally presented as a universal effect where short-range details of the scattering potential are irrelevant. After the experimental discovery some thirty years later, several experiments revealed that the three-body parameter, which was thought to be non-universal, is also universal when compared to the typical range of the potential. The experimental tool for exploring Efimov physics is a Feshbach resonance, and it is expected that far away from resonance the details of the finite range interaction potentials will matter again. The problem is therefore intriguing, as finite range parameters both give rise to universal and non-universal effects.
Feshbach resonances including finite range effects can be described very accurately by a few range parameters only. Our goal is to build-in these parameters as accurate as we can into few-body physics models. Therefore we developed an off-the-energy-shell two-body T-matrix for a finite range square-well potential, which is directly linked to the three-body Efimov effect. We use this square-well model to generalize the Feshbach formalism to an off-shell theory, including the additional range parameters. From this, we are able to study the influence of these range parameters on the Efimov spectrum.