Their answer is that a hypothetical particle, called the axion, was not as heavy as previously thought. Lighter axions would act as less catalyst, allowing more matter to survive the early universe. "The reason we have matter in the universe has to do with some exotic decay of this axion-like particle," said Peter Graham, assistant professor of physics at The University of Texas at Austin. "Our calculation was that the axion was just light enough to produce a little bit of this decay and allow enough matter to survive."
Axions are hypothetical elementary particles that were predicted to exist as a solution to the strong CP problem, which is a theoretical puzzle about why there is no electric dipole moment in neutrons. The Peccei-Quinn theory offers an answer, suggesting that axions exist and were very heavy in the early universe, acting as catalysts to turn matter into energy.
After the universe cooled down, some axions would decay and release the matter that would eventually form stars and galaxies. If axions were very heavy, though, there would not have been enough of this matter released, meaning there probably wouldn't be enough matter left today to form stars and galaxies.
The work done by the team at the University of Texas showed that axions probably had a just-right mass to act as catalysts, but not so much to destroy matter. They used data from the Large Hadron Collider, which has collected information on the universe since 2009, as well as data from astrophysical observations of axions.
Graham and his colleagues showed that the axion that solves the strong CP problem does not violate current experimental bounds. They also proposed a new way of detecting the axion particle.
"The next frontier of discovery will likely involve the search for these axions," Graham said. "We would be hunting for the source of matter."
The paper was published in the journal Physical Review Letters.
