  We recently proposed a nonlocal form for the 3-body induced interaction that
is consistent with the Fock space representation of interaction operators but
leads to a fractional power dependence on the density. Here we examine the
implications of the nonlocality for the excitation spectrum. In the
two-component weakly interacting Fermi gas, we find that it gives an effective
mass that is comparable to the one in many-body perturbation theory. Applying
the interaction to nuclear matter, it predicts a large enhancement to the
effective mass. Since the saturation of nuclear matter is partly due to the
induced 3-body interaction, fitted functionals should treat the effective mass
as a free parameter, unless the two- and three-body contributions are
determined from basic theory.
