Energy dependence of the S-wave nucleon-nucleon separable potentials

We have constructed the energy dependence of the separable potentials for the¹S₀ and³S₁ nucleon-nucleon channels which reproduce exactly the experimental phase shifts up to 460 MeV. We point out that by means of the Yamaguchi form factors, the potentials become energy independent at threshold and can therefore be analytically continued into the unphysical region E<0 where they are required in the three-body problem.