Flow equation analysis of the anisotropic Kondo model - art. no. 140402

We use the method of infinitesimal unitary transformations to calculate zer o-temperature correlation functions in the strong-coupling phase of the ani sotropic Kondo model. We find the dynamics on all energy scales including t he crossover behavior from weak to strong coupling. The integrable structur e of the Hamiltonian is not used in our approach. Our method should also be useful in other strong-coupling models since few other analytical methods allow the evaluation of their correlation functions on all energy scales.