Comment on "Density and Spin response of a strongly-interacting Fermi gas in the attractive and quasi-repulsive regime"

TL;DR

This paper critiques a previous study on a strongly-interacting Fermi gas, highlighting that their diagrammatic approach violates gauge invariance, leading to unphysical predictions like a Meissner effect in the normal phase.

Contribution

It identifies a fundamental flaw in the prior work's theoretical method, emphasizing the importance of gauge invariance in such calculations.

Findings

Diagrammatic method violates gauge invariance

Predicts Meissner effect in normal phase due to this violation

Collective mode contributions are misrepresented in symmetry-broken phase

Abstract

This is a comment on Phys. Rev. Lett. 108, 080401 (2012) by Palestini et al. We pointed out that the diagrammatic method in that article violates gauge invariance. As a consequence, there will a Meissner effect in the normal phase and the contribution from collective modes are not mentioned in the symmetry-broken phase.