2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/180168We present a model based on the idea that Planck-scale effects may produce a small explicit breaking of global symmetries. The model contains a new complex scalar field $Ψ$, charged under a certain global U(1) symmetry, interacting with a new real scalar field $χ$, neutral under U(1). For exponentially small breaking, the model accounts for both {\em early} and {\em late} periods of acceleration of the universe.To appear in the proceedings of 2nd International Conference on Quantum Theories and Renormalization Group in Gravity and Cosmology (IRGAC 2006), Barcelona, Spain, 11-15 Jul 2006; 6 pagesAstrophysicstext