Feshbach Resonances and Medium Effects in ultracold atomic Gases

TL;DR

This paper develops an effective low energy theory for multi-channel scattering in ultracold atomic gases, incorporating medium effects that influence collective mode properties, with results aligning well with experiments.

Contribution

It introduces a parameter-free theoretical framework for Feshbach resonances that includes many-body medium effects in both open and closed channels.

Findings

Medium effects significantly increase scattering rates.

The theory accurately predicts collective mode frequencies and damping.

Results agree well with experimental observations.

Abstract

We develop an effective low energy theory for multi-channel scattering of cold atomic alkali atoms with particular focus on Feshbach resonances. The scattering matrix is expressed in terms of observables only and the theory allows for the inclusion of many-body effects both in the open and in the closed channels. We then consider the frequency and damping of collective modes for Fermi gases and demonstrate how medium effects significantly increase the scattering rate determining the nature of the modes. Our results obtained with no fitting parameters are shown to compare well with experimental data.