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  • 1607.06958v2

    Rights statement: © 2016 American Physical Society

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Nonthermal axion dark radiation and constraints

Research output: Contribution to journalJournal article

Article number065030
<mark>Journal publication date</mark>22/09/2016
<mark>Journal</mark>Physical Review D
Issue number6
Number of pages13
Publication statusPublished
Original languageEnglish


The Peccei-Quinn mechanism presents a neat solution to the strong CPproblem. As a by-product, it provides an ideal dark matter candidate, “the axion”, albeit with a tiny mass. Axions therefore can act as dark radiation if excited with large momenta after the end of inflation. Nevertheless, the recent measurement of relativistic degrees of freedom from cosmic microwave background radiation strictly constrains the abundance of such extra relativistic species. We show that ultrarelativistic axions can be abundantly produced if the Peccei-Quinn field was initially displaced from the minimum of the potential. This in lieu places an interesting constraint on the axion dark matter window with large decay constant which is expected to be probed by future experiments. Moreover, an upper bound on the reheating temperature can be placed, which further constrains the thermal history of our Universe.

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© 2016 American Physical Society