MAGNETIC EFFECTS, DYNAMICAL FORM-FACTORS, AND ELECTRONIC INSTABILITIES IN THE HUBBARD CHAIN

We identify and classify the possible divergences of the charge and sp in response functions of the Hubbard chain in a constant external magn etic field H = Hz. When 0 < H < H(c), where H(c) is the critical field for full spin polarization, these divergences occur at the momenta +/ -2k(F down) for all values of U and density n = n(up) + n(down) here k (F) = pin/2 and k(Fsigma) = pin(sigma) so that 2k(F) = k(F up) + k(F d own). Divergences at +/-4k(F) show up in the charge function when H = 0 and U --> infinity. Finally, divergences at +/-2k(F up) appear only for certain regions of these parameters. We discuss the possible conne ction of our results to the physics of the quasi-one-dimensional metal s.