A study of the Kondo model by means of the Asymptotic Field Approach (AFA) is reported in Ref. . In particular the following properties have been computed:
The AFA results have been compared with the ones obtained by:
By use of a fully self-consistent calculation for composite operators we have shown how to resolve coherent low-energy features embedded in a broad high-energy background. We have illustrated this with the Kondo model in the limit of large spin symmetry group which has often been shown to retain many crucial aspects of low-energy physics. Our numerical estimate for the Kondo temperature agrees very well with the exact solution. At this temperature the Kondo amplitude has a change in the concavity of its slope when plotted as a function of the temperature. At high temperatures the spectral density shows only a high-energy incoherent background. The well-defined singlet excitation mode present at low temperature no longer exists, even if some residual spin-spin interaction persists being energetically favored by a finite bandwidth.