Dilute Bose-Einstein condensate with large scattering length
A dilute Bose gas of atoms with large scattering length as compared to their range of interaction was studied. The energy density of a homogenous Bose-Einstein condensate (BEC) was calculated up to the second order in the low-density expansion. The instability due to three-body recombination was reflected by the imaginary part of a second order correction to energy density. The coefficient of the three body mean-field term in energy density was calculated which was found to be very large for Efimov state near threshold.