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Cosmological Magnetic Fields from Ultralight Dark Matter
Robert Brandenberger1, Jürg Fröhlich2, Hao Jiao1,3
1McGill University, Department of Physics, Montréal, Quebec H3A 2T8, Canada.
Physical Review Letters
|February 6, 2026
Summary
A new mechanism explains the origin of large-scale magnetic fields after the early universe
Area of Science:
- Cosmology
- Astrophysics
- Particle Physics
Background:
- The origin of cosmological magnetic fields remains a significant unsolved problem in astrophysics.
- Existing theories struggle to explain the observed magnetic field strengths on large scales.
Purpose of the Study:
- To propose a novel mechanism for generating magnetic fields on cosmological scales.
- To investigate the role of dark matter interactions in early universe magnetogenesis.
Main Methods:
- Utilizing axion electrodynamics with a pseudoscalar dark matter field (ϕ).
- Analyzing the parametric resonance instability of the electromagnetic field.
- Incorporating the ϕF∧F coupling term in the Lagrangian.
Main Results:
- Demonstrated a mechanism for generating magnetic fields after cosmological recombination.
- Magnetic fields exceeding observational lower bounds can be produced.
- Generation occurs on astrophysically relevant scales (approximately 1 Mpc).
Conclusions:
- The proposed mechanism offers a viable explanation for large-scale magnetic fields.
- Axion-like dark matter provides a potential source for early universe magnetogenesis.
- The model predicts observable magnetic field strengths shortly after recombination.
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