Field dependent quasiparticles in models of strongly correlated   electrons
  In earlier work we showed how the low energy behavior of the symmetric Anderson model in a magnetic field $H$ could be described in terms of field dependent renormalized quasiparticles. Here we extend the approach to the non-symmetric Anderson impurity model and to the infinite dimensional Hubbard model within the DMFT approach. We present NRG results for the local spectral densities and the local longitudinal and transverse dynamic spin susceptibilities for the different parameter regimes and a sequence of values of the magnetic field. We calculate the renormalized parameters for the quasiparticles. Away from half-filling we find quasiparticle weights, $z_\sigma(H)$, which differ according to the spin type $\sigma=\uparrow$ or $\sigma=\downarrow$. Using the renormalized perturbation theory, we show that the low energy features in the NRG results can be well described in the metallic phase in terms of these field dependent parameters. We also check Luttinger's theorem for the Hubbard model and find it to be satisfied in all parameter regimes and for all values of the magnetic field. 
J. Bauer and A.C. Hewson