  It is shown that it is possible to quantitatively explain quantum Monte Carlo
results for the Green's function of the two-dimensional Hubbard model in the
weak to intermediate coupling regime. The analytic approach includes vertex
corrections in a paramagnon-like self-energy. All parameters are determined
self-consistently. This approach clearly shows that in two dimensions
Fermi-liquid quasiparticles disappear in the paramagnetic state when the
antiferromagnetic correlation length becomes larger than the electronic thermal
de Broglie wavelength.
