Dark matter challenges our understanding of the universe: what physicists have discovered.

Physicists have concluded that dark matter cannot be too heavy, meaning it cannot be made up of very massive particles, as this could undermine our understanding of the Universe. The study has been published on the preprint server arXiv, reports Space.

Strange Phenomena in the Universe

Physicists already have ample evidence that something unusual is happening in the Universe. Stars are rotating around the centers of galaxies too rapidly. The galaxies themselves are moving within galaxy clusters too quickly. Large-scale structures in the Universe are expanding too rapidly. When considering only ordinary matter, its gravity is insufficient to explain these strange phenomena.

Therefore, most scientists believe that all these anomalies in the Universe can be attributed to the presence of dark matter, which has mass, is electrically neutral, and almost never interacts with ordinary matter. It is thought that dark matter constitutes the majority of the mass in the Universe, being roughly five times more abundant than the matter we observe.

Mass of Dark Matter Particles

Experiments aimed at detecting rare interactions between dark and ordinary matter have yielded no results. However, these experiments were focused on a specific mass range: approximately 10 to 1000 giga-electronvolts (GeV). This mass range includes the heaviest known elementary particles, such as the top quark and W boson.

Physicists have posed the question: could dark matter be lighter or heavier than previously thought? That is, could it be composed of lighter or heavier particles? The authors of the study concluded that dark matter cannot be too heavy, as this would undermine our best model of the Universe.

Dark matter interacts very rarely with ordinary matter. In the very early Universe, when it was hotter and denser, such interactions occurred much more frequently. As the Universe began to cool and expand, these interactions slowed down and then nearly ceased, rendering dark matter invisible.

The Heavy Dark Matter Problem and the Higgs Boson

There are numerous models of potential elementary particles that dark matter could consist of. However, these particles mostly interact with ordinary particles via the Higgs boson. This fundamental particle of the Universe interacts with nearly all other particles and gives them mass. Physicists already know the approximate mass of the Higgs boson — 125 GeV. The authors of the study found that this mass imposes an upper limit on the mass of dark matter particles.

The problem is that the Higgs boson interacts with both dark and ordinary matter, and in many models serves as a connecting link between them. But both types of matter also interact with the Higgs boson. These interactions manifest as slight changes in the mass of the Higgs boson.

Physicists determined that if dark matter particles have a mass greater than a few thousand GeV, their contribution to the change in the mass of the Higgs boson would be exceedingly large. Since the Higgs boson plays a crucial role in determining many fundamental physical phenomena, in such a case, it would completely disable interactions between particles.

Light Dark Matter

At the same time, physicists believe that dark matter might not interact with ordinary matter at all, or such interactions could occur through some exotic mechanism that does not involve the Higgs boson.

On the other hand, dark matter could be lighter than we think, meaning it could consist of very light particles. For example, it is suggested that such particles could be ultra-light axions. In this case, there should be no disruption to the model of the Universe. Scientists believe that if their findings are confirmed, then efforts should focus on searching for dark matter particles with small rather than large mass.