The role of boson-fermion correlations in the resonance theory of   superfluids
  Correlations between a composite boson and a fermion pair are considered in the context of the crossover theory of fermionic to bosonic superfluidity. It is shown that such correlations are the minimal ingredients needed in a many-body theory to generate the right boson-boson scattering length in the Bose-Einstein limit of the crossover. 
M. J. Holland, C. Menotti, L. Viverit