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The axiverse induced dark radiation problem

Research output: Contribution to journalArticle

Original languageEnglish
Article number9
JournalJournal of High Energy Physics
Issue number4
Early online date1 Apr 2016
Publication statusE-pub ahead of print - 1 Apr 2016


King's Authors


Abstract: The string/M theory Axiverse — a plethora of very light Axion Like Particles (ALPs) with a vast range of masses — is arguably a generic prediction of string/M theory. String/M theory also tends to predict that the early Universe is dominated by moduli fields. When the heavy moduli decay, before nucleosynthesis, they produce dark radiation in the form of relativistic ALPs. Generically one estimates that the number of relativistic species grows with the number of axions in the Axiverse, in contradiction to the observations that Neff ≤ 4. We explain this problem in detail and suggest some possible solutions to it. The simplest solution requires that the lightest modulus decays only into its own axion superpartner plus Standard Model particles and this severely constrains the moduli Kahler potential and mass matrix.

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