2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/157507The behavior of strongly correlated Fermi systems is investigated beyond the onset of a phase transition where the single-particle spectrum $ξ({\bf p})$ becomes flat. The Landau-Migdal quasiparticle picture is shown to remain applicable on the ordered side of this transition. Nevertheless, low-temperature properties evaluated within this picture show profound changes relative to results of Landau theory, as a direct consequence of the flattening of $ξ({\bf p})$. Stability conditions for this class of systems are examined, and the nature of antiferromagnetic quantum phase transitions is elucidated.5 pages, 5 figuresStrongly Correlated Electronstext