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 O(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) not equal chi(S)(-V), G(V) not equal G(-V) both in the mixed valence and in the Kondo regime.