The Spectrum of the Axion Dark Sector

Abstract

Axions arise in many theoretical extensions of the Standard Model of particle physics, in particular the "string axiverse". If the axion masses, $m_a$, and (effective) decay constants, $f_a$, 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, $n_{\mathrm{ax}}\sim \mathcal{O}(10-100)$, with the masses and decay constants drawn from statistical distributions. This reduces the number of parameters from $2n_{\mathrm{ax}}$ 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.

39 pages, 28 figures, 2 tables

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Cited by in corpus (16)

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• Constraints on ultralight scalar bosons within black hole spin measurements from LIGO-Virgo's GWTC-2
• Probing the Early Universe with Axion Physics and Gravitational Waves
• No evidence for axions from Chandra observation of magnetic white dwarf
• Observability of the very-high-energy emission from GRB 221009A
• Axion-like Particles Implications for High-Energy Astrophysics
• Gravitational waves and neutrino oscillations in Chern-Simons axion gravity
• Pulsar Timing Residual induced by Wideband Ultralight Dark Matter with Spin 0, 1, 2
• Ultra-light axions and the kinetic Sunyaev-Zel'dovich Effect
• Axion-like particle oscillations
• Phenomenology of the companion-axion model: photon couplings
• Accurate method for ultralight axion CMB and matter power spectra
• ALP Anarchy
• A Prototype Hybrid Mode Cavity for Heterodyne Axion Detection
• Cosmology of the companion-axion model: dark matter, gravitational waves, and primordial black holes
• Axions in Type IIA Superstring Theory and Dark Matter