2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/27417We investigate quantitatively the effects of strong electron-electron coupling onto the dynamics of lattice electrons. To that purpose the self-consistent version of the bubble-chain approximation at zero temperature and half filling of the Anderson (Hubbard) model is used. Special attention is paid to a critical region of an electron-hole correlation function shaping the transition from weak to strong interaction. We find an analytic solution with Fermi-liquid properties on the weak-coupling side of the critical region around the two-particle pole. It is shown that Fermi-liquid theory does not lead to a consistent behavior of the self-consistent solution on the strong-coupling side of the critical region.10 pages, using RevTeX, no figuresCondensed Mattertext