Scientists say they might have found the reason that we are here.
A neglected, ancient particle could hold the clue to why the universe exists at all.
For years, scientists have been troubled by a central question: how matter was able to win out over antimatter, after the Big Bang. Current theories suggest that they each should have annihilated each other after a huge explosion, leaving a universe made up of pure energy.
AdvertisementAdvertisementAdvertisementAdvertisementThat clearly did not happen, given that we are here. But physicists have never been able to explain exactly why.
Now, researchers say that a clue might have been hiding in a neutrino, one of the universe's lightest particles. A neglected relative of those particles – called a 'decoupled' heavy neutrino – could have helped matter to survive as the universe was coming into existence.
"This decoupled heavy neutrino has long been dismissed as an irrelevant background detail in particle physics," said Rishav Roshan, from the University of Southampton, an author on the new paper.
"However, it decays incredibly slowly. As the cosmos cooled after the Big Bang, the particle lived long enough that it temporarily took over the energy density of the universe and triggered a matter-dominated period."
AdvertisementAdvertisementPreviously, researchers had ignored that particle because they thought it was too weak to have an effect on others, the researchers said. But it was in fact more powerful than they realised, the new paper suggests, and may help us understand why the matter that makes us and everything else up was able to survive.
"The fact that we are here at all proves that an asymmetry between matter and antimatter occurred," said Dr Roshan.
"The decoupled neutrino shifted the temperature in the early universe at which fundamental particles – like electrons and other leptons – interacted with their anti-particles with the help of Standard Model Higgs boson.
"This temperature acts like a switch that shapes how the matter-antimatter imbalance was built up."
AdvertisementAdvertisementThe findings would not only help explain how we were able to exist, but what has happened in the universe since. It could help us better understand the mystery of dark matter, the material that makes up most of the mass of the universe but is so far entirely invisible, for instance.
The researchers suggest that the new work could lead to yet more theoretical research into how the theory would fit with our current understanding of the birth of the universe. But it also suggests ways of checking it concretely, including looking at the gravitational waves that come to us from the early universe and seeing whether they carry any trace of that process.
The work is reported in a new paper, 'Delayed Charged Lepton Yukawa Equilibration in Minimal Seesaw', published in the journal Physical Review Letters.
