HYPER (HighlY Interactive Picle Relics)

A team of researchers recently proposed a new candidate for dark matter: HYPER, or “Highly Interactive Particle Relics”.

A phase transition in the early universe alters the strength of the interaction between dark matter and ordinary matter.

Dark matter remains one of the great mysteries of modern physics. Obviously, it must exist, because without dark matter, for example, the motion of galaxies cannot be explained. But dark matter has never been possible to detect in an experiment.

Currently, proposals for new experiments are numerous: they aim to detect dark matter directly through its diffusion from the components of the atomic nuclei of the detection medium, namely protons and neutrons.

A team of researchers — Robert McGee and Aaron Pearce of the University of Michigan and Jelli Ellor of Johannes Gutenberg University Mainz in Germany — has proposed a new dark matter candidate: HYPER, or “Highly Interactive Particulate Relics.”

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

This image from NASA’s Hubble Space Telescope shows the distribution of dark matter at the center of the giant galaxy cluster Abell 1689, which contains about 1,000 galaxies and trillions of stars.
Dark matter is a form of invisible matter that accounts for most of the mass in the universe. Hubble cannot see dark matter directly. Astronomers inferred its location by analyzing the effect of gravitational lensing, in which the light from galaxies behind Abell 1689 is distorted by the interference of matter in the cluster.
The researchers used the observed positions of 135 lens images of 42 background galaxies to calculate the location and amount of dark matter in the cluster. They mapped inferred dark matter concentrations, stained blue, on an image of the cluster taken by Hubble’s Advanced Camera for Surveys. If the mass’s gravity came only from visible galaxies, the lensing distortions would be much weaker. The map reveals that the densest concentration of dark matter is in the core of the cluster.
Abell 1689 is located 2.2 billion light-years from Earth. Photo taken in June 2002.
Image credit: NASA, ESA, D. Coe (NASA Jet Propulsion Laboratory / California Institute of Technology, Space Telescope Science Institute), N. Benitez (Astrophysical Institute of Andalusia, Spain), T. Broadhurst (University of the Basque Country, Spain) and H Ford (Johns Hopkins University)

The new diversity in the dark matter sector

Because the search for heavy dark matter particles, or WIMPS, has yet to bear fruit, the research community is searching 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 of them in the visible sector, according to the researchers. But previous studies tend to overlook it.

“There hasn’t been a consistent model of dark matter for the mass scale that some of the planned experiments hope to reach,” said Ellor, the postdoctoral researcher. in theoretical physics at JGU.

The challenge for an adequate model: If dark matter interacts strongly with ordinary matter, the (accurately known) amount of it formed in the early universe would be very small, which contradicts 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 underpins the HYPER model, is that the interaction suddenly changes at once, so we can get the best of both worlds: the right amount of dark matter and too much interaction for us to detect.” , He said. McGee.

Here’s how researchers think about it: In particle physics, the interaction is usually mediated by a specific particle, the so-called medium, just like dark matter interacts with ordinary matter. Both the formation of dark matter and its detection operate through this medium, and the strength of the interaction depends on its mass: the greater the mass, the weaker the interaction.

The medium must first be heavy enough to form the right amount of dark matter and then light enough for the dark matter to be detected. The fix: There was a phase transition after the formation of dark matter, in which the mass of the medium suddenly decreased.

“So, on the one hand, the amount of dark matter remains constant, and on the other hand, the interaction is stimulated or enhanced in such a way that the dark matter is directly detectable,” Pearce said.

The new model covers almost the entire parameter range of the planned experiments

“The HYPER model of dark matter is able to cover almost the full range that the new experiments make possible,” Ellor said.

Specifically, the research team first considered that the maximum interaction cross-section of the medium with the protons and neutrons of the atomic nucleus was consistent with astronomical observations and some decomposition in particle physics. The next step was to determine if there was a model of dark matter that showed this interaction.

“This is where the idea of ​​transition came from,” McGee said. “We then calculated the amount of dark matter in the universe and then simulated the phase transition using our calculations.”

Several limitations must be taken into account, such as a fixed amount of dark matter.

“Here we have to systematically consider and include several scenarios, for example by asking ourselves whether it is really certain that our medium does not suddenly lead to the formation of new dark matter, which of course it should not be,” Elor He said. . “But in the end, we were convinced that our HYPER model worked.”

Publication of the research in the journal Physical examination letters.

Reference: “Maximizing Direct Detection Using Highly Interacting Particle Dark Matter” By Jelly Ellor, Robert McGee, and Aaron Pierce, Jan. 20, 2023, Available Here. Physical examination letters.
DOI: 10.1103 / PhysRevLett.130.031803

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