2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/204880Within the context of mass-varying neutrinos, we construct a cosmological model that has a phase transition in the electromagnetic fine structure constant αat a redshift of 0.5. The model accommodates hints of a time variable αin quasar spectra and the nonobservance of such an effect at very low redshifts. It is consistent with limits from the recombination and primordial nucleosynthesis eras and is free of instabilities.6 pages, 1 figure. Version to appear in PLBHigh Energy Physics - PhenomenologyAstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext