Systematic 1/S study of the 2D Hubbard model at half-filling
  The 2D Hubbard model is extended by placing 2S orbitals at each lattice site and studied in a systematic 1/S expansion. The 1/S results for the magnetic susceptibility and the spectra of spin-wave excitations at half-filling are consistent with the large S calculations for the Heisenberg antiferromagnet. The 1/S corrections to the fermionic spectrum lift the degeneracy along the edge of the magnetic Brillouin zone yielding minima at (+- pi/2, +- pi/2). Relation to previous papers on the subject is discussed. 
A.V.Chubukov and K.A.Musaelian