2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/175369This paper investigates the late-time behaviour of certain cosmological models where oscillations play an essential role. Rigorous results are proved on the asymptotics of homogeneous and isotropic spacetimes with a linear massive scalar field as source. Various generalizations are obtained for nonlinear massive scalar fields, $k$-essence models and $f(R)$ gravity. The effect of adding ordinary matter is discussed as is the case of nonlinear scalar fields whose potential has a degenerate zero.17 pages, additional referencesGeneral Relativity and Quantum Cosmologytext