Resonant Fermi gases with a large effective range

Abstract

We calculate the equation of state of a Fermi gas with resonant interactions when the effective range is appreciable. Using an effective field theory for large scattering length and large effective range, we show how calculations in this regime become tractable. Our results are model-independent, and as an application, we study the neutron matter equation of state at low densities of astrophysical interest 0.002 fm^{-3} < rho < 0.02 fm^{-3}, for which the interparticle separation is comparable to the effective range. We compare our simple results with those of conventional many-body calculations.