Strong coupling resistivity in the Kondo model

By applying methods of integrable quantum field theory to the Kondo problem, we develop a systematic perturbation expansion near the IR (strong coupling) fixed point. This requires the knowledge of an infinity of irrelevant operators and their couplings, which we all determine exactly. A low temperature expansion (ie all the corrections to Fermi liquid theory) of the resistivity then follows, extending for instance the well known Nozieres $T^2$ result in the exactly screened case to arbitrary order. The example of the ordinary Kondo model is worked out in details: we determine $\rho$ up to order $T^6$, and compare the result with available numerical data.