Gravitational waves may cause dark matter in the universe

Dark matter is thought to be ubiquitous, surrounding galaxies and helping to create the largest objects in the universe. But no one knows what it is made of. Now, a new theoretical study presents a unique and surprising scenario that may provide some of the missing pieces of the puzzle. Some of the dark matter may have originated from ancient gravitational waves. These waves traveled through the early universe before stars or constellations appeared.

This hypothesis is the product of a collaboration between Professor Joachim Kopp of the Johannes Gutenberg University Mainz and the PRISMA++ Cluster of Excellence. This work also collaborated with Dr. Azadeh Maleknejad of Swansea University. Additionally, this work was published in Physical Review Letters.

Matter makes up about 4% of our universe. It contains all the planets, stars and living things that we can see. Dark matter is estimated to represent about 23% of the universe. Although astronomers know about its existence because of its influence on the formation of galaxies and the structure of the universe in general, the identity of the particle or particles that contain dark matter is still one of the great unsolved mysteries of physics.

Gravitational waves are waves caused by disturbances in time. Often, they are associated with cataclysmic events such as the merger of two black holes or neutron stars. However, this latest study examines a completely different type of gravitational wave known as stochastic gravitational waves. These are a collection of many non-active signs from the early days of the universe.

In addition to these observable magnetic waves, there are many other types of magnetic waves. Many of these other types of waves were created in the early universe when matter was still gaseous. These earlier waves combined to produce an overall signal that is now spread over a large area. Kopp and Maleknejad investigated the possibility that the existence of gravitational waves in the early universe could have played a role in creating new types of particles.

“We investigated whether the nature of the gravitational waves may turn into Weyl fermion particles, which may act as dark matter. The proposed mechanism for generating dark matter through gravitational waves has not been analyzed by other researchers,” Kopp said.

Based on the results of the survey, it seems that the answer is yes.

According to the current study, stochastic gravitational waves would have produced a massless or nearly massless particle known as a Weyl fermion. After that, this particle will gain mass and exist as dark matter. This would occur after the early universe underwent changes in temperature and density.

This is important because previous dark matter models based on gravity often required very large fields, around 10^14 GeV. They also required very high heating temperatures above 10^13 GeV. Findings from this study provide another way to present the dark matter.

Studies of the role of gravitational waves in the early universe show that gravitational waves can produce new types of particles.

The main goal of this research is to examine whether the background of gravitational waves can change the symmetry of the Weyl fermions created in the expanding universe.

Typically, massless Weyl fermions exhibit a symmetry called conformal symmetry due to the decrease in their energy due to spatial expansion. Therefore, expansion alone cannot produce massless Weyl fermion particles.

However, this study provides evidence that the existence of a gravitational wave background could change the existing picture of Weyl fermions in the expanding universe. It suggests new ways to create Weyl fermions and provides other ways to produce dark matter. By introducing newly formed physical scales into the system, these waves cause an imbalance in the normal system that prevents fermions from being observed.

Breaking that balance is the most important part.

Using a single-loop calculation method, the team estimated how it would be possible to generate fermions with a stochastic gravitational wave background. The researchers used the structure of the broken power law to model the gravitational wave. This is a simplification based on the structure expected in many ancient universe models. It includes the change of phases and the first gravity that arose during that time.

As a result, the team found that the produced fermions behave like radiation shortly after they are created. However, if they gain mass, they may represent all or part of the dark matter we see today.

This mechanism can operate across a wide range of early universe temperatures and dark matter abundances. Most conditions tend to produce them at temperatures much higher than the electroweak mass index. But the temperature is still well below the Planck mass and below what is required by the standard production processes of the universe.

That said, not every event will provide the same amount of dark matter. The final amount of dark matter produced depends on the nature of the gravitational waves, especially at high frequencies. It also depends on whether the source producing the waves is coherent or not coherent over time.

In their study, the researchers also found some potential limitations. They used analytical approximations for estimating the gravity wave conditions rather than exact mathematical calculations. They also neglected the response of fermion production to gravitational waves. However, they confirm that this neglect is reasonable because the energy of fermions is much smaller than that of the magnetic field of gravity.

The study suggests another reason why this work might be more exciting than providing a new way to find dark matter.

The authors say that the same process could also enable the production of other less efficient particles, such as right-handed neutrinos.

The frequencies associated with this condition are likely to be in the kilohertz to gigahertz range today. The lower part of that frequency range may be accessible in the future with technologies such as the Einstein Telescope and the Cosmic Explorer. However, high-frequency models may remain elusive until new detection methods are further developed.

The next step, according to Kopp, is to go beyond the analytical predictions and conduct statistical calculations to refine and improve the predictions from this study. He also explores the additional effects of gravitational waves interacting with the early systems of the universe. He is thinking about the results of the difference between particles and antiparticles.

This research study could help change the way we think about how dark matter is created. It links dark matter to early gravitational waves and paves the way for future experiments to explore.

If confirmed, signals from gravitational waves could provide an indirect way to reveal the origin of the invisible matter that makes up so much of the known universe.