THE SYMMETRY OF THE MOMENTUM DISTRIBUTION-FUNCTIONS IN THE HUBBARD-MODEL AT HALF-FILLING

In this article, by exploiting the unitary partial particle-hole transformations between the positive-U and negative-U Hubbard models at half-filling, we shall rigorously show that the momentum distribution functions of these models possess some symmetry, which was originally realized only for the ideal tight-binding electron models on a d-dimensional simple cubic lattice.