Axion Cosmology and Dark Matter Phenomana

Axions, originally proposed to resolve the strong CP problem in quantum chromodynamics, have emerged as leading candidates for the non-luminous matter that dominates cosmic structure formation. In the early Universe, the misalignment mechanism and topological defect decay can generate a relic population of ultralight axions or axion-like particles, which behave as a cold Bose–Einstein condensate on galactic scales. Their feeble couplings to photons, nucleons and electrons allow them to elude direct detection while influencing astrophysical processes, from stellar evolution to the propagation of electromagnetic signals. In cosmology, axions can modify the cosmic microwave background spectrum, affect large-scale structure through wave-like interference patterns and alleviate small-scale crises by suppressing subgalactic clumping. Laboratory and astrophysical searches exploit resonant cavities, precision magnetometry and high-field helioscopes to probe axion-photon conversions, whereas spin-precession experiments and nuclear magnetic resonance techniques target their coupling to nuclear moments. Together, these efforts map the viable parameter space of axion mass and interaction strength, offering hope for a comprehensive understanding of dark matter’s nature and its role in cosmic evolution.

Research from Nature Portfolio

Recent experiments using ultrahigh-sensitivity comagnetometers have extended terrestrial bounds on axion-like dark matter. One study operating in the Spin-Exchange Relaxation-Free regime combined noble-gas and alkali vapour sensors to search for time-varying magnetic fields induced by axion couplings to neutrons and protons. Covering previously unexplored mass ranges around 10⁻¹² to 10⁻¹⁰ eV, it improved proton-coupling limits by orders of magnitude and set world-leading terrestrial constraints on neutron interactions. In parallel, advances in helioscope technology have yielded the most stringent limits to date on axion–photon conversion from solar axions. By repurposing a high-field magnet with low-background X-ray optics, the latest campaign achieved sub-10⁻¹⁰ GeV⁻¹ sensitivity to the axion–photon coupling, rivalling astrophysical bounds and guiding the design of next-generation searches.

Axion Cosmology and Dark Matter Phenomana publication trend

The graph below shows the total number of articles in axion cosmology and dark matter phenomana across all publications each year (not limited to Nature Index journals).

Technical terms

Axion: Hypothetical light pseudoscalar particle arising from solutions to the strong CP problem in quantum chromodynamics, and a leading dark matter candidate.

Axion-like particle (ALP): Generalisation of the QCD axion with similar couplings to standard fields but not necessarily tied to QCD dynamics.

Haloscope: Resonant cavity experiment that detects axion conversions to photons in a strong magnetic field.

Comagnetometer: Precision instrument comparing spin precession rates of different atomic species to detect exotic fields such as those sourced by axions.

Spin-Exchange Relaxation-Free (SERF) regime: Magnetometry regime in alkali vapours where spin-exchange collisions do not limit coherence, yielding ultrahigh magnetic sensitivity.

References

1. Constraints on axion-like dark matter from a SERF comagnetometer. Nature Communications (2023).
2. New CAST limit on the axion–photon interaction. Nature Physics (2017).
3. Laboratory Constraints on the Neutron-Spin Coupling of feV-Scale Axions. Physical Review X (2023).
4. Axion-mediated Transport of Fast Radio Bursts Originating in Inner Magnetospheres of Magnetars. The Astrophysical Journal Letters (2023).
5. Extended Search for the Invisible Axion with the Axion Dark Matter Experiment. Physical Review Letters (2020).