BCS-BEC crossover with unequal mass fermions

We investigate the crossover from BCS pairing to molecular BEC in an atomic gas with two fermion species with masses $m_\up \ne m_\dn$ tuned through a Feshbach resonance. We present results for the T=0 equation of state as a function of the scattering length including the effects of Gaussian fluctuations about the mean field ground state. We compute the ground state energy as a function of $m_\up/m_\dn$ at unitarity and find excellent agreement with the quantum Monte Carlo result for $m_\up/m_\dn = 6.67$ for a $^{40}$K-$^6$Li mixture. We show that the dimer scattering length in the BEC limit as a function of $m_\up/m_\dn$ compares well with exact four-body results of Petrov {\it et al}. We also derive the condition for trapping frequencies to obtain an unpolarized gas in a harmonic trap.