Dark matter accounts for 85% of the universe, so why can't we find it?

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Scientists use cavity heliostats and low-noise Josephson parametric amplifiers to conduct a search for invisible axion dark matter. Cavity telescopes are sensitive instruments designed to detect and study the halos around luminous bodies or other physical phenomena. On the other hand, Josephson parametric amplifiers are technical tools that can be used to manipulate the quantum states of microwave light fields. In the latest study published in the journal Physical Review Letters, the researchers searched for dark matter axions with masses between 2.81-3.31 eV in the Milky Way halo.

The results of this search may help rule out previous theoretical predictions and provide information for future searches for invisible axion dark matter. Nick Du, a co-author of the study and a researcher at the University of Washington, said: "Our research is driven by two different physics mysteries, both of which will be solved by detecting axion dark matter. The first is the mystery of dark matter. Past physics research evidence shows that ordinary matter, which is generally considered, only accounts for about 15% of the total mass of the universe.

The remaining approximately 85% is thought to be made up of particles that do not absorb, emit or reflect light, and therefore cannot be detected using traditional techniques for studying matter. This non-luminous substance, known as dark matter, remains one of the greatest mysteries in contemporary physics, as researchers are still unsure whether it exists and what it is made of. While countless searches for dark matter have been conducted using a variety of instruments, the mysterious substance has not yet been observed or detected.

One possible solution to what dark matter might be comes from another field of physics, nuclear physics, in the form of another mystery known as the strong CP problem. A popular solution to the strong CP problem predicts the existence of a new particle called the axion, which has properties that make it a compelling candidate for dark matter. In the search for axion dark matter, the ADMX collaboration hopes to solve both the strong CP problem and the mystery of the nature of dark matter. The cavity telescope used by the researchers consists of a resonant cavity placed inside a large magnetic field.

According to theoretical predictions, dark matter axions in the galactic halo should couple with the magnetic field in the cavity and produce photons. The number of photons produced is likely to be very small, making the generated signal difficult to detect. However, by tuning the resonant cavity inside the axion halo mirror to the same frequency as the photons, the number of photons produced by the galactic halo can be increased. In a way, the search for axion dark matter is very similar to the way radio operates. As the frequency of the radio is tuned, one can tune in to different radio stations. In this respect the experiment is similar, except that the frequency of our radio station is unknown and the signal is much weaker.

The search for dark matter axions has been going on for decades, and researchers have now conducted several such searches using the CAVITY telescope. While the invisible axions could not be detected so far, the results rule out a range of axion masses that were previously predicted by benchmark theoretical models of axion dark matter. This is actually the second time the experiment has achieved this sensitivity for axion dark matter, but this time, it has tripled the coverage of the previous study. By achieving and expanding this sensitivity, the research has shown that ADMX represents one of the best hopes for finding axion dark matter in the continuing search for it.

The observations gathered by the researchers could inform future searches for dark matter axions, while also paving the way for new theoretical predictions. The researchers are now conducting a new study to search for axion dark matter at higher frequencies. If this search is also unsuccessful, the researchers plan to continue searching for invisible axions at higher frequencies. At higher frequencies, axion dark matter becomes more difficult to detect because the traditional cavities that would be used are no longer as sensitive to axions. However, scientists already have some interesting prototypes to get around this problem, such as experiments that use multi-cavity arrays to search for axion dark matter.

Science X Network | Copyright Science X Network/Ingrid Fadelli/Phys

Reference journal: Physical Review Letters

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