Unbinding slave spins in the Anderson impurity model

We show that a generic single-orbital Anderson impurity model, lacking, for instance, any kind of particle-hole symmetry, can be exactly mapped without any constraint onto a resonant level model coupled to two Ising variables, which reduce to one if the hybridization is particle-hole symmetric [1]. The mapping can be straightforwardly extended to a multiorbital impurity model where the isolated impurity Hamiltonian does not include Coulomb exchange terms. We also demonstrate how single-particle Green’s functions of the physical fermions can be calculated without constraints, which would, for instance, allow exploiting DMFT to study in the slave-spin representation Hubbard-like models in lattices with infinite coordination. The generality of the mapping allows to study a wide range of problems varying from the Mott-transition in infinite-dimensionality to transport in quantum dots.
[1] D. Guerci and M. Fabrizio Phys. Rev. B 96, 201106(R)