We present the results of a self-consistent weak-coupling calculation for the renormalized singleparticle properties in an itinerant antiferromagnet.Multiple spin-wave excitations accompany the carrier motion and lead to incoherent contributions to the electronic spectrum. We evaluate the quasiparticle spectral weight and energy dispersion. In agreement with strong-coupling theories we find the minimum of the dispersion of the quasihole energy to have momentum (+vr/2, +sr/2) and the dispersion to be Hat around the corners of the Brillouin zone. Very good agreement is achieved with available exact diagonalization data.

We use a functional-integral representation for the Hubbard model to describe the formation of local moments and their magnetic correlations. In the absence of long-range magnetic order, the presence of well-established local moments alone is sufficient to produce a gap in the electronic spectrum. The local moments are treated within a coherent-potential approximation, and we apply an embedded-cluster method to incorporate their interactions.

We investigate the role of anharmonic local-moment Auctuations in the two-dimensional Hubbard model for intermediate correlation strength in the regime of local-moment formation. Within a functional-integral scheme we perform a linked-cluster expansion of the eA'ective action up to quartic order in the local-moment amplitudes.The resulting quadratic and quartic expansion coefficients are compared in real space and as a function of frequency, temperature, and chemical potential. We find the quartic contribution to suppress quadratic fluctuations and to be more susceptible to nesting than the quadratic term.