The existence of a hidden mass in the universe — dark matter — is beyond doubt today. It manifests itself only through gravity, keeping galaxies from disintegrating and influencing the propagation of light. Everything we observe — stars, planets, gas-makes up only about five percent of the universe, the rest is invisible. Most scientists believe that dark matter consists of unknown particles that barely interact with ordinary matter.

Possible candidates for the role of dark matter particles are the so—called WIMPS, weakly interacting massive particles. Despite years of searching in accelerators and underground laboratories around the world, they have not been found. However, the DAMA/LIBRA installation has been operating for almost three decades, which shows a stable and reproducible effect: scintillation flares in sodium iodide crystals with an energy of 2-6 keV, the number of which increases in June and decreases in December, cyclically repeating from year to year.

The physical nature of these paradoxical results is being studied by scientists from the Research Institute of Physics of the Southern Federal University. The Scientific School operates under the guidance of such world-renowned scientists as Vladimir Korchagin, Doctor of Physico-Mathematical Sciences, Chief Researcher at the Space Research Laboratory, and Professor Maxim Khlopov, Doctor of Physico-Mathematical Sciences, Chief Researcher at the Space Research Laboratory.

Based on the hypothesis of "dark atoms" proposed by Professor Khlopov back in 2010, scientists conclude that dark matter does not consist of single elementary particles, but of neutral composite objects — dark atoms, inside which there are heavy multiply charged particles. The simplest "dark atom" is formed when a doubly negatively charged particle binds to the nucleus of ordinary helium during its formation in the early universe.

"When such dark atoms fly through the Earth, they collide with rock, slow down and lose energy. They are not moving fast enough to knock the core out of the crystal lattice of the detector — this is the effect based on the search for WIMPS in other experiments. However, dark atoms can be captured by sodium nuclei, which are part of the DAMA/LIBRA detector, and form a weakly bound state with them. At the same time, energy is released in the form of a gamma quantum, and its energy just falls into the sensitive range of the installation," said Maxim Khlopov.

For heavy iodine nuclei, such a process turns out to be energetically unprofitable, and this fact explains why other experiments, for example, on xenon, do not see a similar signal.: They simply don't have light nuclei capable of capturing dark atoms.

"The high statistical significance of this result — 13.5 standard deviations — would seem to contradict the negative results of direct WIMP search in other experiments," said Vladimir Korchagin.

A program article published by Rostov astrophysicists in the journal of the first quartile Universe together with the head of the experiment, Dr. Rita Bernabei, and the staff of the laboratory in Italy provides a detailed explanation of the observed annual fluctuations of events and offers an interpretation of the results of other experimental groups in terms of dark atoms.

The key test for this hypothesis will be the Australian installation SABRE South, the first laboratory in the Southern Hemisphere to search for dark matter, similar to DAMA/LIBRA. If it also registers annual fluctuations in the signal, it will be almost definitive proof that the nature of the hidden mass has been revealed.

"If the presence of annual fluctuations of events is confirmed at this facility, then the nature of the hidden mass can be considered established, opening up the unique possibilities of dark atoms for their practical development," Maxim Khlopov emphasizes.

In the meantime, SFedU scientists continue to improve their model by calculating the electrical and nuclear interactions of dark atoms with ordinary matter, as well as taking into account the charge distribution inside the nuclei and their possible deformation. In addition, they are developing a methodology for its comprehensive verification in the search for stable multicharged particles at colliders in combination with an astrophysical search for the effects of the presence of dark atoms in celestial bodies.