We study a two-dimensional Hubbard model with a Fermi surface containing th
e saddle points (pi, 0) and (0, pi). Including Cooper and Peierls channel c
ontributions leads to a one-loop renormalization group flow to strong coupl
ing. Various fixed points are found by varying hopping energies as well as
Coulomb repulsion. Natures of these fixed points are investigated through r
esponse functions. (C) 2000 Elsevier Science B.V.