We calculate the spin and charge dynamical susceptibilities of a strongly correlated impurity model in a renormalized perturbation theory. The irreducible vertices for the quasiparticle scattering are deduced from the renormalized parameters, which have been calculated by fitting the low-lying levels of a numerical renormalization group (NRG) calculation to those of an effective Anderson model. The susceptibilities are asymptotically exact in the low frequency limit and satisfy the Korringa-Shiba relation. By comparing the results with those calculated from a direct NRG calculation, we show that the renormalized perturbation theory (RPT) description gives a very good description of the spin dynamics for all values of the local interaction U, not only at low frequencies but over the whole relevant frequency range.
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