2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/14771Understanding axion cosmology has important experimental consequences since it constrains the range of allowed values for the axion mass. In the standard thermal scenario, which assumes Peccei-Quinn symmetry restoration after inflation, an axion string network forms at the phase transition $T\sim\fa$ and then radiatively decays into a cosmological background of axions. Under standard assumptions for the evolution of this string network and the radiation from it, axions must have a mass of $\ma\sim 100μ{\rm eV}$ with large specified uncertainties. We discuss critically the various suggestions in the literature that the axion mass migh be lighter.8 PagesAstrophysicstext