2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/192604By demanding that a bounce is nonsingular and that perturbations are well-behaved at all times, we narrow the scope of possible models with one degree of freedom that can describe a bounce in the absence of spatial curvature. We compute the general properties of the transfer matrix of perturbations through the bounce, and show that spectral distortions of the Bardeen potential $Φ$ are generically produced only for the small wavelengths, although the spectrum of long wavelength curvature perturbations produced in a contracting phase gets propagated unaffected through such a bounce.Replaced with version accepted to JCAPAstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext