Shift of the molecular bound state threshold in dense ultracold Fermi gases withFeshbach resonance

Abstract

We consider a dense ultracold Fermi gas in the presence of a Feshbach resonance.We investigate how the threshold for bound state formation, which is just at theFeshbach resonance for a dilute gas, is modified due to the presence of the Fermisea. We make use of a preceding framework of handling this many-body problem.We restrict ourselves to the simple case where the chemical potential μ isnegative, which allows us to cover in particular the classical limit where the effectis seen to disappear. We show that, within a simple approach where basically onlythe effect of Pauli exclusion is included, the Fermi sea produces a largeshift of the threshold, which is of the order of the width of the Feshbachresonance. This is in agreement with very recent experimental findings.