Cosmic expansion with standard particle physics repertoire
 

New path for warm inflation
 

To the point

• New model of “warm inflation”: Three researchers propose that the early, rapid expansion of the universe (inflation) took place in a warm environment consisting of known elementary particles.
• Role of the strong force and axion-like particles: The strong interaction plays a central role in this process: gluons couple to a field of hypothetical axion-like particles, whose interaction provides the necessary heat energy for inflation. 
• Experimental testability: The model is largely based on known particles and forces of the Standard Model – this means that the first moments of the universe could be measurable on Earth in the future.

How did the universe come into being? There are a multitude of theories on this subject. In a recent paper, three scientists formulate a new model: according to this, inflation, the first, very rapid expansion of the universe, would have taken place in a warm environment consisting of known elementary particles. In addition, the strong force, one of the fundamental interactions in the Standard Model of particle physics, plays a central role. This makes it possible to measure the first fractions of a second of the universe on Earth.

The model developed by the authors is based on the following scenario: Just before the Big Bang, the universe underwent a very brief phase of accelerated cosmic inflation. However, widely accepted hypotheses stipulate that this early universe was cold and empty, requiring a hitherto unknown process to ignite the hot plasma observed afterwards—at the moment of the actual Big Bang. There are also models for warm inflation. The authors now present a new approach for this type of inflation.

“Our study shows a completely new path to warm inflation,” says Sebastian Zell, a scientist in the “Cosmology and Particle Physics” department at the Max Planck Institute for Physics. “Even as the early universe expanded, it could have been immersed in a heat bath of known elementary particles.” This inflation model has an advantage over models we know to date: it can be explained largely using “on-board resources,” i.e., well-studied particles and forces in the Standard Model. This makes the first moments of the universe accessible to measurements on Earth.

Coupling provides heat energy

However, the approach now presented does not work without extending the standard model: Gluons, which mediate the strong force in atomic nuclei, bind to a field of hypothetical, axion-like particles. “The coupling of these particles to the strong force would provide sufficient energy to heat up the expanding universe,” explains Sebastian Zell. “This makes warm inflation feasible.”

The existence of cosmic axions or related particles could solve several open questions in particle physics. One example is the nature of dark matter. Many experiments are therefore working to detect these particles. One of these is MADMAX, in which the MPP is playing a leading role. “In view of these efforts, “In view of these efforts, we see a realistic chance to test warm inflation in a future experiment,” concludes Sebastian Zell.