Overlooked heavy neutrino may help explain why matter survived the Big Bang, study proposes
Researchers in Southampton and Kanpur say a long-lived, weakly interacting particle could have shaped the early imbalance between matter and antimatter.
Physicists from the University of Southampton and the Indian Institute of Technology Kanpur have proposed that a little-studied relative of the neutrino may have helped matter outlast antimatter in the early universe, according to ScienceDaily. The site's report is based on materials provided by the University of Southampton, and it says the study was published in Physical Review Letters.
The research focuses on a hypothetical particle called a "decoupled" heavy neutrino. It has generally been seen as too weakly connected to other particles to have much effect on the universe. The team's calculations suggest that because it decays so slowly, it may have lived long enough to briefly dominate the universe's energy density as the cosmos cooled after the Big Bang.
“This decoupled heavy neutrino has long been dismissed as an irrelevant background detail in particle physics.”Dr. Rishav Roshan, University of Southampton, study author
The question matters because, as ScienceDaily explains, scientists believe matter and antimatter were made in nearly equal amounts in the early universe. When the two meet, they annihilate. If the amounts had been exactly equal, almost all matter could have vanished, leaving nothing to form stars, planets or life.
In the proposed scenario, the heavy neutrino shifted the temperature at which particles such as electrons interacted with their antiparticles with the help of the Higgs boson. Dr. Roshan described that temperature as acting "like a switch that shapes how the matter-antimatter imbalance was built up."
ScienceDaily reports that earlier attempts to explain the imbalance generally left this particle out, on the assumption that its weak interactions made it unimportant. The new work challenges that assumption.
Co-author Dr. Sudipta Show of IIT Kanpur said the particle's effect on the early expansion of the universe could leave "distinct but detectable imprints" on primordial gravitational waves, the ripples in space and time that scientists believe early processes may have produced. Finding those patterns could eventually offer a way to test the idea.
Much is still unknown. The particle is hypothetical, and ScienceDaily states that the explanation "remains theoretical." The report does not say when or how the predicted gravitational wave signatures might be searched for, or what instruments could detect them. It also does not include any response from other physicists, and this account rests on that single report.
