2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/197321We present simple, concrete, two-fermion models that exhibit thermodynamically stable isotropic translationally-invariant gapless superfluid states (breached pair superfluidity). The mass ratio between the components and the momentum structure of the interaction are crucial for determining the stability of such states: Idealized, momentum-independent (``contact'') interactions are insufficient.5 pages, REVTeX4. Minor updates in response to comments. References addedHigh Energy Physics - PhenomenologySuperconductivitytext