  The symmetric heavy-light ansatz is a method for finding the ground state of
any dilute unpolarized system of attractive two-component fermions.
Operationally it can be viewed as a generalization of the Kohn-Sham equations
in density functional theory applied to N-body density correlations. While the
original Hamiltonian has an exact Z_2 symmetry, the heavy-light ansatz breaks
this symmetry by skewing the mass ratio of the two components. In the limit
where one component is infinitely heavy, the many-body problem can be solved in
terms of single-particle orbitals. The original Z_2 symmetry is recovered by
enforcing Z_2 symmetry as a constraint on N-body density correlations for the
two components. For the 1D, 2D, and 3D attractive Hubbard models the method is
in very good agreement with exact Lanczos calculations for few-body systems at
arbitrary coupling. For the 3D attractive Hubbard model there is very good
agreement with lattice Monte Carlo results for many-body systems in the limit
of infinite scattering length.
