A New Model for Dark Matter

A team of researchers has just proposed a new candidate for dark matter: HYPER, or “Highly Interactive Particle Relics.” The phase transition in the early universe changes the strength of the interaction between dark matter and normal matter. Dark matter remains one of the biggest mysteries in modern physics. Clearly it must exist, because without dark matter, for example, the movement of galaxies cannot be explained. But it has never been possible to detect dark matter in an experiment.

Currently, proposals for new experiments are numerous: they aim to detect dark matter directly through its diffusion from the constituents of atomic nuclei of a detection medium, that is, protons and neutrons. A team of researchers, Robert McGehee and Aaron Pierce of the University of Michigan and Gilly Elor of the Johannes Gutenberg University of Mainz in Germany, have now proposed a new candidate for dark matter: HYPER, or “Highly Interactive Particle Relics.”

In the HYPER model, some time after the formation of dark matter in the early universe, the strength of its interaction with normal matter increases considerably, which, on the one hand, makes it potentially detectable today and at the same time can explain the abundance of dark matter. to import. Question.

Since the search for heavy dark matter particles, or WIMPS, has not yet come to fruition, the research community is looking for alternative dark matter particles, especially lighter ones. At the same time, phase transitions are generically expected in the dark sector; after all, there are several of them in the visible sector, according to the researchers. But previous studies have tended to overlook them.

“There has not been a consistent model of dark matter for the range of masses that some planned experiments hope to access.” However, our HYPER model illustrates that a phase transition may actually help make dark matter more easily detectable,” said Elor, a postdoctoral researcher. in theoretical physics at JGU.

The challenge for a proper model: if dark matter interacts too strongly with normal matter, its (precisely known) amount formed in the early universe would be too small, contradicting astrophysical observations. However, if produced in the right amount, the interaction would be too weak to detect dark matter in current experiments.

“Our central idea, which underlies the HYPER model, is that the interaction changes abruptly once, so that we can have the best of both worlds: the right amount of dark matter and a large interaction so that we can detect it,” he said. McGehee. And here’s how the researchers think about it: In particle physics, an interaction is usually mediated by a specific particle, the so-called mediator, just like the interaction of dark matter with normal matter. Both the formation of dark matter and its detection work through this mediator, with the strength of the interaction depending on its mass: the greater the mass, the weaker the interaction. The mediator must first be heavy enough for the correct amount of dark matter to form, and then light enough for the dark matter to be detectable. The solution: There was a phase transition after the formation of dark matter, during which the mass of the mediator suddenly decreased. “So, on the one hand, the amount of dark matter is kept constant, and on the other hand, the interaction is stimulated or enhanced in such a way that the dark matter should be directly detectable,” Pierce said.

Reference: “Maximizing Direct Detection with Highly Interactive Particle Relic Dark Matter” by Gilly Elor, Robert McGehee, and Aaron Pierce, Jan 20, 2023, Physical Exploration Letters. DOI: 10.1103/PhysRevLett.130.031803