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Limit data and plots for constraints on axions and axion-like particles

MIT Licence DOI

This page showcases my python scripts for reproducing plots of axion constraints. Various plots are available, see the jupyter notebooks (and the figures below) for different configurations. All the limit data can be found in the limit_data folder, at the very least I hope this can save you some time digitising plots.

Please email me [] or make a pull request if you would like any limits being added.

Disclaimer: the limits listed here have been collected from an extremely wide array of papers (not all of them published) and from several different sub-fields. There may be wildly varying levels of uncertainty, assumption, model dependence, and importantly, differing levels of statistical rigour. There is not necessarily any fixed convention for what even constitutes a bound. This goes especially for experimental projections, which vary considerably in their respective levels of optimism. Therefore, one should exercise some caution when reading these plots: they are not intended to be the definitive word on the status of the axion. I more see them as a way to advertise the many ways one can search, and give a rough picture for what is allowed and what is ruled out. Some may see my inclusion of certain bounds as being overly democratic, however I felt that it was important for this extremely active field to be fully reflected in these plots.


Axion-photon coupling

Click on the plots to see the notebooks

Download: png, pdf

With projected limits

Download: png, pdf

Dimensionless Axion-photon coupling (with projected limits)

Download: png, pdf


Axion-electron coupling

Download: png, pdf
Download (without projections): png, pdf

Underground detectors


Astro bounds:

Axion-neutron coupling

Download: png, pdf
Download (without projections): png, pdf


Note: CASPEr and nEDM limits account for stochastic correction reported in 1905.13650

Astro bounds

Axion CP-violating couplings

For more details see our paper: arXiv:2010.XXXX

Download Scalar Nucleon: png, pdf
Download Electron-Nucleon: png, pdf
Download Nucleon-Nucleon: png, pdf

Download combined limits


Thank you to: Itay Bloch, Raymond Co, Chris Dessert, Maurizio Giannotti, Alexander Gramolin, Alex Millar, Pablo Quílez, Javier Redondo, Jan Schuette-Engel, Philip Sørensen, and Edoardo Vitagliano for comments and corrections that have greatly helped improve these plots.