UPPER HUBBARD BAND OF THE 2-D HUBBARD-MODEL

We calculate the one-electron Green's function of the Hubbard model on the square lattice using a spin-rotation invariant six-slave boson re presentation. In the strong coupling regime its spectrum splits off in to a quasi particle peak, and a lower and an upper incoherent branch, which we focus on, using a functional integral formulation. By includi ng Gaussian fluctuations around a paramagnetic saddle-point, we obtain the main contributions to G as the graphs which are of lowest order i n tile fluctuations, in the strong coupling regime. The k-dependence o f the weight of the upper band shows tile physically expected behavior . We also find that its total weight quickly decreases away from half- filling under an increase of the hole doping.