[Paper Review] Axion Dark Matter

J. Jaeckel, G. Rybka+153 more|arXiv (Cornell University)|Mar 28, 2022

Dark Matter and Cosmic Phenomena23 citations

TL;DR

Snowmass 2021 white paper that reviews axion dark matter motivation, cosmology, and a comprehensive experimental roadmap for detecting QCD axions and ALPs across a wide mass range.

ABSTRACT

Axions are well-motivated dark matter candidates with simple cosmological production mechanisms. They were originally introduced to solve the strong CP problem, but also arise in a wide range of extensions to the Standard Model. This Snowmass white paper summarizes axion phenomenology and outlines next-generation laboratory experiments proposed to detect axion dark matter. There are vibrant synergies with astrophysical searches and advances in instrumentation including quantum-enabled readout, high-Q resonators and cavities and large high-field magnets. This white paper outlines a clear roadmap to discovery, and shows that the US is well-positioned to be at the forefront of the search for axion dark matter in the coming decade.

Motivation & Objective

• Motivate axions as compelling dark matter candidates and summarize their theoretical status (QCD axion and ALPs).
• Outline axion cosmology, production mechanisms, and local structure implications relevant to DM searches.
• Present a roadmap of next-generation laboratory experiments to detect axion dark matter across mass ranges.
• Highlight enabling technologies and synergies with astrophysical observations to reach the QCD axion parameter space.

Proposed method

• Review the QCD axion solution to the strong CP problem and its mass–decay constant relation (m_a ~ f_a^-1).
• Discuss axion couplings, especially axion–photon interactions, and their model dependence via anomaly coefficients (E/N).
• Summarize non-thermal misalignment production and other cosmological scenarios for axion/ALP DM.
• Catalog current and proposed experiments (e.g., ADMX G2, DMRadio-m, ADMX-EFR, HAYSTAC, MADMAX, etc.) across mass ranges.
• Emphasize required technology development: quantum-enabled readout, high-Q cavities, large high-field magnets, and spin ensembles.
• Provide a phased plan from current projects to a potential “Ultimate Axion Facility” for broader ALP searches.

Experimental results

Research questions

• RQ1 What is the viable parameter space for QCD axions and ALPs as dark matter given cosmological production and astrophysical constraints?
• RQ2 What experimental strategies and technologies are capable of probing the QCD axion parameter space across the full mass range?
• RQ3 How can a coordinated roadmap of experiments, technologies, and theory/astrophysics work together to achieve discovery within the next decade?

Key findings

• Axions remain a well-motivated dark matter candidate with a clear experimental path to discovery in the coming decade.
• The QCD axion mass is tied to the Peccei–Quinn scale f_a, yielding a characteristic relation between m_a and f_a that guides search strategies.
• A broad mass range requires multiple, complementary techniques, including high-field magnet–based searches, resonant cavities, and quantum-enabled readout technologies.
• Current and planned experiments (e.g., ADMX G2, DMRadio-m, ADMX-EFR) aim to scan significant portions of the QCD axion parameter space, with additional small-scale projects to fill gaps.
• Advances in enabling technologies (quantum sensors, high-Q resonators, large magnets) and synergies with astrophysical probes are essential to realize an ultimate axion search facility.
• The paper outlines a four-component roadmap emphasizing execution of current projects, diversification with small-scale experiments, technology development, and theory/astrophysics extensions beyond the QCD axion.