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