Scientists from the Institute for Nuclear Research of the Russian Academy of Sciences have formulated a new physical model that allows you to create the amount of dark matter necessary for research from neutrinos. The work was carried out within the framework of a project supported by a grant from the Russian Science Foundation, and its results were published in the Journal of Cosmology and Astroparticle Physics (JCAP) and presented at the 6th International Conference on New Frontiers in Physics.
Dark matter makes up 25% of the total matter in the Universe, does not emit electromagnetic radiation and does not directly interact with it. Nothing is known for certain about the nature of dark matter, except that it can cluster - gather into condensations. To describe dark matter, astrophysicists extend the Standard Model of Particle Physics, an established theory in theoretical physics that describes the electromagnetic, weak, and strong interactions. Today, scientists have come to the conclusion that this model does not fully describe reality, because it does not take into account neutrino oscillations - the transformation of different types of neutrinos into each other.
Neutrinos are fundamental particles that have no electrical charge (neutral). Neutrinos participate only in weak and gravitational interactions, because the intensity of their interaction with anything is very low. Neutrinos are "left" and "right". Sterile neutrinos are called "right", they, unlike others, are not contained in the Standard Model and do not interact with particles - carriers of fundamental interactions of nature (gauge bosons). In this case, sterile neutrinos are mixed with active neutrinos, which are "left-handed" particles and are present in the Standard Model. Active neutrinos include all types of neutrinos, except for sterile ones.
Neutrino detector, inside view / Roy Kaltschmidt, Lawrence Berkeley National Laboratory
Scientists have studied the X-ray spectral line, recently discovered in radiation from a number of galaxy clusters. This line corresponds to photons with an energy of 3.55 keV. Usually this would mean that these atoms emit these photons due to the transition of an electron from one level to another, however, substances with a difference between the levels of 3.55 keV do not exist in nature. Scientists have suggested that this X-ray line could appear due to the decay of a sterile neutrino into a photon and an active neutrino. So the authors determined that the mass of the sterile neutrino was approximately 7.1 keV. For comparison, the mass of a proton is 938 272 keV.
Installation & quot; Troitsk Nu-Mass & quot; / Institute for Nuclear Research RAS
Sterile neutrinos can be detected in ground-based laboratories such as Troitsk Nu-Mass and KATRIN. These installations are aimed at searching for sterile neutrinos using the radioactive decay of tritium (the "heavy" isotope of hydrogen 3H). At the Troitsk Nu-Mass plant, located in the city of Troitsk, Moscow Region, the strongest restrictions on the squared mixing angle were obtained. The mixing angle is a dimensionless quantity that characterizes the amplitude of the neutrino transition from one state to another. The measured quantity is the square of this angle, since it determines the probability of transition in a single act of interaction.
“This paper proposes a model in which oscillations, that is, the birth of sterile neutrinos, begin not at the early stages of the evolution of the Universe, but much later. This leads to the fact that fewer sterile neutrinos are produced, which means that the mixing angle can be larger. This is achieved through changes in the hidden sector. The hidden sector of the model consists of sterile neutrinos and a scalar field. The scalar field is responsible for the qualitative change (phase transition) of the sector structure. Sterile neutrino production is possible only after this phase transition. Therefore, less sterile neutrinos are born in our model, which allows us to produce the required amount of dark matter from sterile neutrinos with a mass of the order of kiloelectronvolts with a large square of the mixing angle up to 10-3, said one of the authors of the article, Anton Chudaykin. Research Assistant at the Institute for Nuclear Research, Russian Academy of Sciences.
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As scientists note, the very possibility of producing the required amount of dark matter from neutrinos of a certain mass is of interest from the point of view of cosmology.
The constellation of Cancer from the Subaru telescope. Contour lines indicate the distribution of dark matter / National Astronomical Observatory of Japan and Hyper Suprime-Cam Project
The fact is that previously cold dark matter, completely consisting of heavy and inactive particles that do not prevent the formation of dwarf galaxies in any way, well described the entire set of experimental data. With the improvement of the experiment, it turned out that in fact there are fewer such galaxies than expected. This means that dark matter, most likely, is not all cold, it contains admixtures of warm dark matter, which consists of faster and lighter particles. It turns out that the theory and research results diverged, and scientists needed to explain why this happened. They concluded that dark matter contains a small fraction of light sterile neutrinos, which explains the shortage of dwarf satellite galaxies.
Blend Angle Squared Parameter Space Constraints - “ mass of sterile neutrino ” in the proposed model (the color represents the proportion of sterile neutrinos in the total energy density of dark matter) and from direct searches (green lines). / Anton Chudaykin
Light sterile neutrinos, however, cannot make up all dark matter. The latest research in this area says that the share of the light component in the total density of dark matter today should not exceed 35%.
“The positive signal received in the future from any of these installations may be an argument in favor of the proposed model, which will lead to a qualitatively new understanding of the nature of dark matter particles in the Universe,” the scientist concluded.
The work was carried out in collaboration with scientists from the Moscow Institute of Physics and Technology and the University of Manchester (Great Britain).