Application of renormalized RPA to polarized Fermi gases

International audienceWe consider a spin-imbalanced Fermi gas at zero temperature in the normal phase on the BCS side of the BCS-BEC crossover and around unitarity. We compute the critical polarization for pairing, the correlated occupation numbers, and the contact in an extension of particle-particle random-phase approximation (RPA) (also called non-self-consistent T-matrix approach or ladder approximation). The so-called renormalized RPA consists in computing the T matrix with self-consistently determined occupation numbers. The occupation numbers are determined either by keeping the self-energy only to first order or by resumming the Dyson equation. In this way, the result for the critical polarization, strongly overestimated in standard RPA, is clearly improved. We also discuss some problems of this approach