CONSERVING APPROXIMATIONS FOR FINITE N AND U = INFINITY HUBBARD-MODEL

It is shown that in the conserving RPA approximation for the N = 2 and U = infinity Hubbard model the self-energy contains terms which are a bsent in the N = infinity version of the RPA (RPA(infinity)) and in th e slave-boson(SB) method. For the nearly half-filled (n almost-equal-t o 1) case the ferro- and antiferro-magnetic susceptibilities chi(s)(k over arrow pointing right) - at k over arrow pointing right = 0 and k over arrow pointing right = (pi, pi, pi) - are strongly enhanced and p roportional to (1 - n)-1. Due to the enhanced chi(s) the self-energy i s strongly frequency dependent and the effective mass(m) is strongly enhanced, i.e. m approximately (1 - n)-1. These results are obtained in the limit of D = infinity dimensions. The difference between N = 2 and N = infinity theories is briefly analyzed.