Slave-boson mean-field theory of the Anderson lattice with finite U and orbital degeneracy

We consider a stoichiometric metallic Anderson lattice with orbital degeneracy and finite U. The correlations in the f shell are formulated in terms of a complete set of ''auxiliary bosons,'' generalizing in this way Kotliar and Ruckenstein's approach for the Hubbard model to arbitrary electronic configurations. A Gutzwiller type of mean-field approximation is introduced for the case where the occupancy of the fn configurations for n>2 is excluded. The occupation probabilities are discussed as a function of U and the f-level position. For sufficiently large U the paramagnetic solution becomes unstable towards ferromagnetism. This instability is suppressed with increasing orbital degeneracy. The case of a Kondo insulator with electron-hole symmetry is also discussed in mean-field theory