BEYOND THE GUTZWILLER APPROXIMATION IN THE SLAVE-BOSON APPROACH - INCLUSION OF FLUCTUATIONS WITH THE CORRECT CONTINUUM-LIMIT OF THE FUNCTIONAL INTEGRAL

We study the single-band Hubbard model via the functional-integral fou r-slave-boson formulation introduced by Kotliar and Ruckenstein, and s how that a proper treatment of the continuum limit of the functional i ntegral removes the inconsistencies due to an incorrect handling of th is limit so far performed in the literature. It follows from our analy sis that the Kotliar and Ruckenstein mean-field solution has to be aba ndoned in order to include fluctuation corrections in a systematic way . We show explicitly how to construct a suitable alternative solution which admits the inclusion of fluctuations.