2024 was yet another exhausting year keeping track of updates on our quest to find the axions. I have been trying my best to collect the exponentially growing literature on my GitHub AxionLimits:

Finally, my GitHub repo is not all about axions! Many new results for dark photons, vector and scalar bosons also came out this year. I’ll leave you to go through my webpage to learn more…

An experiment from Gavilan-Martin et al ( went one step further and looked for axion waves acting across a 1000 km baseline by comparing two K-Rb-3He comagnetometers located in Poland and Germany.

It's also possible to search for axions if they couple to other particles. For example: axions can act on nucleon spins in a similar way to magnetic fields, and so comagnetometers can be repurposed as dark matter detectors. Here are the constraints on the coupling to the neutron:

The cavity approach is the traditional one for looking for axions in the lab. But there are new groups exploring novel approaches who released first results this year. One is ADBC which uses lasers to search for the axion-induced birefringence effect

Some 2024 highlights: there were new results from ADMX, HAYSTAC, CAPP, RADES & ORGAN, using the resonant cavity approach. These are like radios where one has to tune them to just the right frequency to tap into the oscillations in the axion field we would be swimming through.

Of course what everyone would love to see is an experimental detection of axions here on Earth. While this has not happened yet, the global community interested in trying to do this has grown astonishingly fast in recent years. Look at all the experiments now on my map!

Various collaborations searched for axion dark matter in galaxy using this birefringence effect this year. Including CMB experiments like @POLARBEAR as well as pulsar timing arrays like @EPTAGW and PPTA @CSIRO_ATNF

If axions are extremely light then their decays to photons do not happen within the age of the Universe. However, the nature of the axion’s coupling to the photon means that dark matter halos act like a birefringent medium, causing the polarisation of passing photons to rotate.

If axions are heavy, then they could simply decay into two photons with an energy equal to 1/2 the axion mass. Spectra from JWST, WINERED, HST, eROSITA and more (e.g. were used this year to look for this new spectral line in and around our galaxy

Axions are also excellent dark matter candidates. If galaxies are indeed enveloped by halos of axions, then there are many more ways their existence might be revealed to us.

There has been a lot of debate in the literature about how to draw these constraints robustly. Many of these issues were settled in this thorough theoretical treatment of the axion cloud formation by Witte & Mummery

A fascinating technique to exclude axions is to use the fact we see black holes spinning. If axions have a Compton wavelength similar to the Schwarzchild radius of a BH, then a cloud of them can be excited from the vacuum at the cost of the BH’s spin. This is "superradiance"

As an aside, it continues to amaze me how much a single event from almost 40 yrs ago is still one of the best laboratories for testing new physics. Needless to say, the next galactic supernova will be a major event and will generate a lot of papers (and maybe even a discovery?)

Manzari et al improved constraints from the 1987 Supernova. Axions produced in the explosion converting into photons would have been seen in a gamma-ray spectrometer on NASA’s Solar Maximum Mission which happened to be looking in that direction at the time

It’s not all about high-energy astrophysics. This study by Goldstein et al explored how CMB photons could convert into axions as they traverse the Universe, leading to a “patchy screening” effect observable by cross-correlating the CMB with galaxy maps

@NuSTAR_Science continues to prove itself to be one of the most useful instruments to search for axions. Another study by Ruz et al used data from the Sun to look for axions produced in the core, which its magnetic field would then convert into photons