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Physicists continue to wrestle with the mystery of dark matter, the elusive substance that makes up about 80% of the matter in the universe but is impossible to detect. Now, a team of researchers has proposed an innovative model that suggests dark matter could have originated before the Big Bang, during the inflationary phase when the universe underwent rapid exponential expansion.
The role of inflation and the formation of dark matter
Inflation, a concept developed about 45 years ago, describes a brief period in the early universe when its size increased exponentially by a factor of about 1026 times in 10-36 seconds. This rapid expansion, which is theorized to have occurred before the regular Big Bang, provides an explanation for several cosmological mysteries, including the flatness and uniformity of the universe and the origin of its structure.
Despite widespread acceptance among cosmologists, the mechanism driving inflation remains unknown. It is attributed to a hypothetical field called the inflaton that spans all of spacetime. During inflation, the universe exists in a state of supercooled expansion, where the temperature drops dramatically. When inflation ends, a process called reheating occurs, which restores the temperature of the universe to its pre-inflation temperature and initiates the production of standard particles, including photons.
Traditional theories of the formation of dark matter
Existing theories suggest that dark matter arises due to interaction with a heat bath of particles, and its amount is determined by the "freezing" or "freezing" mechanism. In the freeze-out model, dark matter remains in equilibrium with the thermal bath during the earliest moments, whereas in the freeze-out model, dark matter never reaches equilibrium due to suppressed interactions.
For example, in ultraviolet (UV) freezing, the temperature of the thermal bath is always lower than the mass of the particles connecting dark matter to the Standard Model of particle physics. This scenario is based on the interaction of quantum fields when dark matter is formed under certain energetic conditions.
A new mechanism: dark matter during inflation
A new model called WIFI (Warm Inflation via ultraviolet Freeze-In) presents an alternative perspective. He suggests that dark matter was created during the inflationary phase through rare interactions in a hot energetic environment. Unlike traditional models, which assume that everything formed during inflation was diluted by the rapid expansion of the universe, the WIFI model suggests that the dark matter that formed during this period could have survived and explained the dark matter observed today.
"What is unique about our model is that dark matter is successfully produced during inflation," explained lead author Kathryn Freese and director of the Weinberg Institute for Theoretical Physics at the University of Texas at Austin. "In most other models, whatever is created during inflation is then 'blown up' by the exponential expansion of the universe to the point where essentially nothing remains."
In this scenario, the inflaton field causing inflation loses some of its energy to radiation, which then forms dark matter particles through the freezing mechanism.
Beyond the Big Bang Singularity
This model is consistent with the idea that inflation predates the Big Bang, challenging the notion of a singularity with infinite density and curvature. Instead, the universe is thought to have had a small but finite size after inflation, about 10-26 meters in diameter. From there, the standard processes of radiation and particle production began, leading to the universe as we know it.
Future Validation and Implications
The WIFI model has not yet been confirmed by observations, but could be tested over the next decade by experiments studying the cosmic microwave background (CMB). Warm inflation, a key component of the WIFI model, will be the focus of these studies. If warm inflation is confirmed, it will increase the credibility of the model and open avenues for understanding other particles and processes in the early universe.
"In our study, we focused on the production of dark matter, but WIFI offers broader applications, such as the production of other particles that may play a crucial role in the evolution of the early universe," said co-author Barmak Shams Es Haghi. "This opens up new avenues for exploration in future studies."
A new chapter in the study of dark matter
Although the origin of dark matter remains a mystery, the WIFI model offers a fascinating framework that links its formation to one of the earliest and most dramatic phases of the universe. By exploring this unconventional path, researchers hope to discover not only the nature of dark matter, but also a new understanding of the origin and evolution of the universe.
