Linear Magnetic Response of Disordered Metallic Rings: Large Contribution from Forward Scattering Interactions

We calculate the effect of electron-electron interactions involving vanishing momentum transfer (forward scattering) on the orbital linear magnetic response of disordered metal rings pierced by a magnetic flux phi. Using the bulk value of the Landau parameter F_0 for copper, we find that in the experiment by L'{e}vy {\it{et al.}} [Phys. Rev. Lett. {\bf{64}}, 2074 (1990)] the forward scattering contribution to the linear magnetic response is larger than the corresponding contribution from large momentum transfers considered by Ambegaokar and Eckern [Phys. Rev. Lett. {\bf{65}}, 381 (1990)]. However, outside the regime of validity of linear response and to first order in the effective screened interaction the persistent current is dominated by scattering processes involving large momentum transfers.