Effective field theory and cold Fermi gases near unitary limit

TL;DR

This paper uses Effective Field Theory to analyze ultracold Fermi gases near the unitary limit, highlighting the importance of three-body forces for reparametrisation invariance and estimating associated uncertainties.

Contribution

It demonstrates the necessity of three-body forces in EFT descriptions of Fermi gases near unitarity to ensure reparametrisation invariance and addresses off-shell uncertainties.

Findings

Universal proportionality constant described in both narrow and broad Feshbach resonances

Reparametrisation invariance requires three-body forces

Uncertainties due to off-shell effects are estimated

Abstract

We study a dynamics of ultracold Fermi-gases near the unitary limit in the framework of Effective Field Theory. It is shown that, while one can obtain a reasonable description of the universal proportionality constant both in the narrow and the broad Feshbach resonance limits, the reguirement of the reparametrisation invariance leads to appearance of the three body forces needed to cancel the otherwise arising off-shell uncertainties. The size of the unsertainties is estimated.