A generating functional approach to the Hubbard model Yu. A. Izyumov, N. I. Chaschin, D. S. Alexeev and F. Mancini Eur. Phys. J. B, 45 1 (2005) 69-86 Published online: 16 June 2005 DOI: 10.1140/epjb/e2005-00166-7