Medium effects close to s- and p-wave Feshbach resonances in atomic Fermi gases

Abstract

Many-body effects may influence properties, such as scattering parameters, nature of pairing, etc., close to a Feshbach resonance in the fermion BEC-BCS crossover problem. We study effects such as these using a tractable crossing-symmetric approach. This method allow us to include quantum fluctuations, such as, density, current, spin, spin-current and the higher-order fluctuations in a self-consistent fashion. The underlying fermion interaction is reflected in the "driving" term. We perform calculations here on both Bose-Einstein condensate (BEC) and BCS sides, and taking the driving term to be finite range, and of arbitrary strength. These are related to two-body singlet and triplet scattering parameters, and can be connected with experimental s- and p-wave Feshbach resonances. We include the $\ell=0$ density and spin fluctuations, as well as $\ell=1$ current and spin-current fluctuations. We calculate renormalized scattering amplitudes, pairing amplitudes, nature of pairing, etc., on both the BEC and BCS sides. We then compare our results qualitatively with experiments.