Discrete Hubbard-Stratonovich transformations for systems with orbital degeneracy

Abstract A discrete Hubbard-Stratonovich transformation is presented for systerns with an orbital degeneracy N and a Hubbard Coulomb interaction. An exact transformation is obtained by introducing an external field which takes N + 1 values. Alternative approximate transformations are presented, where the field takes fewer values, for instance two values corresponding to an Ising spin.