1/N expansion of the nonequilibrium infinite-U Anderson Model

Results are presented for the nonequilibrium infinite-U Anderson model using a large-N approach, where $N$ is the degeneracy of the impurity level, and where nonequilibrium is established by coupling the level to two leads at two different chemical potentials so that there is current flow. A slave-boson representation combined with Keldysh functional integral methods is employed. Expressions for the static spin susceptibility $\chi_S$ and the conductance $G$ are presented to ${\cal O}(\frac{1}{N})$ and for an applied voltage difference $V$ less than the Kondo temperature. The correlation function for the slave-boson is found to be significantly modified from its equilibrium form in that it acquires a rapid decay in time with a rate that equals the current induced decoherence rate. Physical observables are found to have a rather complex dependence on the coupling strength to the two leads which can lead to asymmetric behavior $\chi_S(V) \neq \chi_S(-V)$, $G(V)\neq G(-V)$ both in the mixed valence and in the Kondo regime.