Dark matter remains one of the biggest mysteries in modern physics. It is clear that 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, there are many proposals for new experiments: they aim to detect dark matter directly through its scattering from the constituents of atomic nuclei of a detection medium, i.e. 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 abruptly, which on the one hand makes it potentially detectable today and at the same time can explain the abundance of dark matter.
The new diversity in the dark matter sector
Since the search for heavy dark matter particles, or so-called WIMPS, has not yet been successful, the research community is looking for alternative dark matter particles, especially lighter ones. At the same time, phase transitions are generally expected in the dark sector; after all, there are several in the visible sector, the researchers say. But previous studies have tended to neglect 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 can 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 it occurs in just 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,” McGehee said.
Constraints in the nucleon-mass coupling plane of the mediator due to cooling of HB stars  and SN 1987A as well as rare kaon decays  (grey shading). Credit: Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.031803
And this is how the researchers envision it: In particle physics, an interaction is usually mediated by a specific particle, a 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 remains constant, and on the other hand, the interaction is driven or strengthened in such a way that the dark matter should be directly detectable,” Pierce said.
The new model covers almost the entire range of parameters of the planned experiments.
“The HYPER model of dark matter can cover almost the entire range that the new experiments make accessible,” Elor said.
Specifically, the research team first considered the maximum cross section of mediator-mediated interaction with the protons and neutrons of an atomic nucleus to be consistent with astrological observations and certain particle physics decays. The next step was to consider whether there was a model for dark matter that would exhibit this interaction.
“And here we came up with the idea of the phase transition,” McGehee said. “We then calculated how much dark matter exists in the universe and then simulated the phase transition using our calculations.”
There are many limitations to take into account, such as a constant amount of dark matter.
“Here, we have to systematically consider and include many scenarios, for example asking the question of whether it is really safe for our mediator not to suddenly lead to the formation of new dark matter, which of course it must not be,” Elor said. . “But in the end, we were convinced that our HYPER model works.”
The research is published in the journal Physical Review Letters.
Gilly Elor et al, Maximizing Direct Detection with Highly Interactive Particle Relic Dark Matter, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.031803
Provided by the University of Michigan
Citation: A New Model for Dark Matter (2023, Jan 23) Retrieved Jan 23, 2023 from https://phys.org/news/2023-01-dark.html
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