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Physicists Further Narrow Down Range of Search for Dark Matter

In the 21st century, the search for dark matter is one of the most fascinating challenges in fundamental physics. For a long time, scientists have been aware that it does exist, as it would have otherwise been hard to explain numerous astrophysical observations.

Experimental setup for atomic spectroscopy using cesium atom vapor. (Image credit: Dionysis Antypas)

For instance, stars rotate at a greater speed in galaxies when compared to their speed if only “normal” matter occurred. Generally, the matter that can be seen only accounts for, at the very most, 20% of the entire matter in the universe. This means that a significant 80% is dark matter.

There’s an elephant in the room but we just can’t see it,” stated Professor Dmitry Budker, a researcher at the PRISMA+ Cluster of Excellence of Johannes Gutenberg University Mainz (JGU) and the Helmholtz Institute Mainz (HIM), explaining the issue he and several of his colleagues from all over the world are struggling with.

Dark Matter Could Consist of Extremely Light Particles

To date, no one is aware of what dark matter is made of. Scientists in the field are taking into account and studying a wide variety of possible particles that could theoretically qualify as candidates. Extremely lightweight bosonic particles, presently believed to be one of the most promising prospects, are one among these.

These can also be regarded as a classical field oscillating at a specific frequency. But we can’t yet put a figure on this—and therefore the mass of the particles. Our basic assumption is that this dark matter field is coupled to visible matter and has an extremely subtle influence on certain atomic properties that would normally be constant.

Dmitry Budker, Professor and Researcher, PRISMA+ Cluster of Excellence, JGU and HIM

Budker and his colleagues in Mainz have now come up with a new technique that has been described in the recent issue of the pioneering specialist journal Physical Reviews Letters. This method involves the use of atomic spectroscopy and also cesium atom vapor.

These atoms become excited only on exposure to laser light of a highly specific wavelength. The assumption is that small changes in the corresponding observed wavelength would specify coupling of the cesium vapor to a dark matter particle field.

In principle, our work is based on a particular theoretical model, the hypotheses of which we are experimentally testing. In this case, the concept underlying our work is the relaxion model developed by our colleagues and co-authors at the Weizmann Institute in Israel.

Dr Dionysis Antypas, Study Principal Author, JGU

As stated by the relaxion theory, there are possibilities of the existence of a region in the vicinity of huge masses such as the Earth where the density of dark matter is higher, thus allowing the coupling effects to be easily observed and detected.

Previously Inaccessible Frequency Range Searched

The scientists have used their new technique to access a previously unexplored frequency range where, as proposed in relaxion theory, the effects of specific forms of dark matter on the atomic properties of cesium will have to be relatively easy to identify.

Furthermore, the study outcomes permit the researchers to create new restrictions as to what the nature of dark matter is expected to be. Dmitry Budker relates this meticulous search to the quest for a tiger in a desert.

In the frequency range that we’ve explored in our current work, we still have not pinpointed dark matter. But at least, now that we’ve searched in this range, we know we don’t have to do it again.

Dmitry Budker, Professor and Researcher, PRISMA+ Cluster of Excellence, JGU and HIM

The researchers are yet to know where dark matter—the tiger in the metaphor—is hiding; however, they now know where it is not.

We just keep on targeting in more closely on the part of the desert where the tiger is most likely to be. And, at some point, we will catch him,” reiterated Budker.


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