A new paper suggests that a weak background of stochastic gravitational waves from the early universe created low-mass particles that may have later become the dark matter that shapes galaxies and large cosmic structures.
Gravitational waves may have played a role in the creation of dark matter in the earliest moments of the universe, according to new research. The study presents new calculations that describe a previously unexplored new way in which dark matter could have formed, involving stochastic gravitational waves.
This research addresses a central question in particle physics: what the universe is made of. Everyday objects like planets, stars, and living organisms are made of visible matter, but it only makes up about four percent of the universe. The rest is mostly invisible, and includes dark matter and dark energy.
Dark matter alone makes up about 23 percent of the universe. Observations show that it is scattered throughout space, shaping galaxies and the largest cosmic structures. Despite its widespread influence, the elementary particles that make up dark matter are still unknown. Scientists continue to explore this mystery through both theoretical models and experiments.
A new method for particle formation
Gravitational waves are ripples in space-time that are typically produced by highly energetic events, such as collisions between black holes or neutron stars. Stochastic gravitational waves, on the other hand, arise from a variety of processes that do not involve massive astronomical bodies.
These weaker waves contribute to a background signal that fills the universe. Many of them were created very early in the universe's history. They may have been created in events such as phase transitions of matter as the universe cooled after the hot Big Bang, or from Joule magnetic fields.
"In this paper, we explore the possibility that gravitational waves – thought to be ubiquitous in the early universe – were partially converted into dark matter particles," explained Professor Joachim Kopp. "This leads to a new mechanism of dark matter formation that has not been explored before."
Discovering particles
The researchers suggest that gravitational waves could create massless or nearly massless fermions. Fermions include familiar particles such as electrons, protons, and neutrons.
According to their model, these early particles later gained mass and evolved into the dark matter that still exists today.
"The next step in developing this research direction is to move beyond our analytical estimates and perform numerical calculations to improve the accuracy of our predictions. Another direction for future research is to investigate additional possible effects of gravitational waves in the early universe. One example of this would be a mechanism that could explain the known difference between the particles and antiparticles that were created," said Cope.
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