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Spectrum of the axion dark sector

Research output: Contribution to journalArticle

Original languageEnglish
Article number083510
Pages (from-to)083510-1 - 083510-39
Number of pages39
JournalPhysical Review D (Particles, Fields, Gravitation and Cosmology)
Issue number8
Early online date11 Oct 2017
Publication statusPublished - 15 Oct 2017

King's Authors


Axions arise in many theoretical extensions of the Standard Model of particle physics, in particular the "string axiverse." If the axion masses, ma, and (effective) decay constants, fa, lie in specific ranges, then axions contribute to the cosmological dark matter and dark energy densities. We compute the background cosmological (quasi)observables for models with a large number of axion fields, nax∼O(10-100), with the masses and decay constants drawn from statistical distributions. This reduces the number of parameters from 2nax to a small number of "hyperparameters." We consider a number of distributions, from those motivated purely by statistical considerations to those where the structure is specified according to a class of M-theory models. Using Bayesian methods, we are able to constrain the hyperparameters of the distributions. In some cases, the hyperparameters can be related to string theory, e.g., constraining the number ratio of axions to moduli, or the typical decay constant scale needed to provide the correct relic densities. Our methodology incorporates the use of both random matrix theory and Bayesian networks.

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