The renormalized superperturbation theory (SPT) approach to the Anderson   model in and out of equilibrium
  The properties of current-carrying steady states of strongly correlated systems away from the linear-response regime are of topical interest. In this article, we review the renormalized perturbation theory, or renormalized SPT of reference [1] for the Anderson model. We present an extension to higher orders and compare the higher-order results with NRG calculations. Finally, we elucidate the role of Ward identities in calculating out-of-equilibrium properties and address claims made in the literature. 
Enrique Mu\~noz, Farzaneh Zamani, Lukas Merker, Theo Costi and Stefan   Kirchner
cond-mat.str-el