Energy lower bound for the unitary N + 1 fermionic model

We consider the stability problem for a unitary N +1 fermionic model, i.e., a system of N identical fermions interacting via zero-range interactions with a different particle, in the case of infinite two-body scattering length. Starting from the two-body boundary condition, we construct an explicit expression for the expectation value of the energy. Then we investigate its boundedness from below and exhibit a sufficient condition on the mass ratio, which guarantees the stability of the model.