2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/175378The covariant gauge invariant perturbation theory of scalar cosmological perturbations is developed for a general Scalar-Tensor Friedmann-Lemaitre-Robertson-Walker cosmology in a vacuum. The perturbation equations are then solved exactly in the long wavelength limit for a specific coupling, potential and background. Differences with the minimally coupled case are briefly discussed.19 pages, 3 figures, accepted for publication on PRDGeneral Relativity and Quantum CosmologyAstrophysicstext