Three fermions in a box at the unitary limit: universality in a lattice model

Abstract

We consider three fermions with two spin components interacting on a lattice model with an infinite scattering length. Low-lying eigenenergies in a cubic box with periodic boundary conditions, and for a zero total momentum, are calculated numerically for decreasing values of the lattice period. The results are compared to the predictions of the zero-range Bethe–Peierls model in continuous space, where the interaction is replaced by contact conditions. The numerical computation, combined with analytical arguments, shows the absence of negative energy solution, and a rapid convergence of the lattice model towards the Bethe–Peierls model for a vanishing lattice period. This establishes for this system the universality of the zero-interaction range limit.