Physicists have proposed a new theory according to which dark matter emerged during an extremely short inflationary phase when the Universe rapidly expanded exponentially. The article about the new model was published in Physical Review Letters by three scientists from the US state of Texas.

The theory is that dark matter was produced through its interaction with a thermal bath of some species, and its abundance is created by "freeze-out" or "freeze-in." In the freeze-out scenario, dark matter is in chemical equilibrium with the bath at the earliest times—the concentration of each does not change with time.

In the freeze-in picture, dark matter never comes into equilibrium with the bath. Such a suppressed interaction between dark matter and the thermal bath could be due to interactions in quantum field theories, either infrared freeze-in or ultraviolet (UV) freeze-in.

In UV freeze-in, the temperature of the thermal bath is always lower than the masses of the particles that connect dark matter to the Standard Model of particle physics. (Mass and temperature are both proportional to energy and can be related via fundamental constants.)

The theory of cosmic inflation was first proposed in 1981 by the American physicist Alan Guth, proposing a period of exponentially fast expansion in the very early universe where the universe expanded by a factor of about 10x26 in 10x36 seconds. After that inflation ceased, the universe continued to expand, though not exponentially.

Although inflation is mostly accepted by cosmologists as part of the Big Bang picture based on some evidence—though there is meaningful dissent—the driver of inflation is still unknown.

In the paper's WIFI model—Warm Inflation via ultraviolet Freeze-In—dark matter is created through small and rare interactions with particles in a hot, energetic environment.

The WIFI model cannot yet be confirmed by observations. But a key part of the scenario, warm inflation, will be tested over the next decade by the so-called cosmic microwave background experiments.