Axion thermalization in the early universe -: art. no. 023004

We reanalyze the conditions under which we have a primordial thermal population of axions. We extend a previous study and take into account processes involving gluons and quarks. We conclude that if the Peccei-Quinn scale satisfies F-a<1.2x10(12) GeV there is thermal axion production. In this case, a period in the early universe exists where axions would interact with the QCD plasma and we point out that nonthermal axions produced before the end of this period would thermalize.