Comment on "Normal phase of an imbalanced Fermi gas".

Recently Mora and Chevy [1], in studying the energy of an atomic Fermi gas consisting of a majority species, 1, and a minority species, 2, showed that, due to interatomic interactions, the energy density E of the gas has a contribution of the form E = 12fn 2 2, where ni is the density of species i. They attribute this term to a “modification of the single polaron properties due to Pauli blocking’. In this Comment, we demonstrate that E may equivalently be understood in terms of the familiar interaction between minority atoms induced by the majority component. Our treatment is inspired by the theory of dilute solutions of He in superfluid He [2]. We consider the interaction between two minority atoms in momentum states p and p, since f is the Landau quasiparticle interaction between minority atoms. Since the momenta are small compared with other relevant momentum scales, we neglect the momentum dependence of the interaction. For the moment, we regard the two atoms as being distinguishable, and the effects of quantum statistics will be taken into account later. The effective interaction, Tpp′, between the atoms is the change in the energy of a quasiparticle in the momentum state p when the distribution function for quasiparticles in the state p is varied, and it may be written in the form [2]