On the scaling spectrum of the Anderson impurity model

We consider the universal scaling behaviour of the Kondo resonance in the s trong-coupling limit of the symmetric Anderson impurity model, using a rece ntly developed local moment approach. The resultant scaling spectrum is obt ained in closed form, and is dominated by long tails that in contrast to pr evious work are found to exhibit a slow logarithmic decay rather than a pow er-law form, crossing over to characteristic Fermi liquid behaviour on the lowest energy scales. The resultant theory, while naturally approximate, is found to give very good agreement for essentially all frequencies with num erical renormalization group calculations of both the single-particle scali ng spectrum and the self-energy.