The theory can be ruled out – researchers are getting closer to the secret behind dark matter

What has happened?

The Organ Experiment (Oscillating resonant group axion) in Australia has, by using a so-called haloscope, been able to dismiss axion like particle cogenesis-model, one of the many theories that attempt to explain dark matter.

By ruling out a theory, research can now be directed at the remaining candidates. The study was published recently in the journal Science Advances.

What is an axion?

Dark matter makes up around 85 percent of all matter in the universe and got its name because it – apparently – does not interact with electromagnetic fields. It neither reflects, absorbs nor emits electromagnetic radiation.

The reason dark matter is believed to exist is partly because of how it interacts through gravity. For example, many galaxies would behave differently if there were not large proportions of invisible matter.

One of the candidates for dark matter is the axion. It is a hypothetical particle that has never been detected. The weakly interacting particle was first proposed as a solution to a problem that arose in quantum chromodynamics. Quantum chromodynamics is the theoretical description of strong interaction within particle physics, i.e. the description of the force that, among other things, holds atomic nuclei together.

The properties of the axion also mean that it could form part of the dark matter. The particle, if it exists, is electrically neutral, has spin 0 but has an as yet undetermined mass.

How have the researchers ruled out the theory?

There are several ways that scientists try to prove that axions exist. Organs in Australia use a haloscope. There, a strong magnetic field is created in a metal cylinder with the goal of making the hypothetical particles interact with the field.

Since axions are weakly interacting particles, it is difficult to observe them. But if a magnetic field resonates at just the right frequency, interactions can occur. In theory, an axion then creates two photons that we can then measure. The frequency of the measured photons will then be linked to the mass of the hypothetical axion.

A model called Standard model axion seesaw higgs portal inflation (Smash) predicts that the mass of an axion should be between 50 and 200 microelectron volts (μeV). The researchers at Organ aim to scan the majority of the range by changing the frequency of the magnetic field.

According to the theory now ruled out by the researchers, axion-like particle cogenesis-model, the mass of the particle should be between 63 and 67 μeV. In this area, however, no axions have been detected at Organ, and the results have a confidence interval of 95 percent. Because of this, the researchers can thus rule out this specific mass range for the axion.

What comes next?

The scientists at Organ will continue to investigate the possible masses for the particle predicted by the Smash model. Even if the haloscope in Australia doesn’t find axions, they can help other experiments decide where to look.

– Although we have not found anything, it is very exciting because it is Australia’s first large-scale and long-term direct experiment to detect dark matter. It has also given us useful information about what dark matter of axions is not. It tells future axion surveys around the world where not to look, says Aaron Quiskamp, ​​one of the physicists behind the study, in a press release.

More results to come soon

Research is ongoing in several places in the world. Researchers at the Gran Sasso Laboratory in Italy hope within a few months to present physical evidence that dark matter actually exists, Vetenskapsradion reports. The underground detector is one of the world’s largest.