Scientists have proposed a new theory about the birth of the cosmos, suggesting that the early Universe was shaped by an ancient particle that had been overlooked for decades. Their research addresses one of the greatest mysteries in modern physics: how matter prevailed over antimatter after the Big Bang.
A Slow Decay with Cosmic Consequences
According to current theories, matter and antimatter should have annihilated each other after the enormous explosion, leaving an empty Universe filled only with pure energy. But, as phys.org reports, physicists from the University of Southampton and the Indian Institute of Technology Kanpur say they have found a clue in neutrinos, among the lightest particles in the Universe.
Usually, discussions of neutrinos refer to their three most common types. This year’s Nobel Prize was awarded for developing methods to detect these particles. However, the research team found that another often-overlooked “relative,” known as a “decoupled” heavy neutrino, could have helped matter dominate its opposite.
Study author Dr. Rishav Roshan of Southampton said: “This decoupled heavy neutrino has long been regarded as an unimportant background element in particle physics. Yet it decays incredibly slowly. As the cosmos cooled after the Big Bang, the particle survived long enough to temporarily dominate the Universe’s energy density and trigger a period of matter domination.”
Asymmetry Between Matter and Antimatter in the Early Universe
Most theories explaining why matter prevailed over antimatter ignored the decoupled heavy particle because experts considered its interactions too weak to influence other particles, Roshan added.
However, the researchers from Southampton and Kanpur found that the overlooked particle could affect the asymmetry between particles and antiparticles that is essential to our existence. “The very fact that we are here proves that an asymmetry arose between matter and antimatter,” Roshan added.
The physicists say the decoupled neutrino changed the temperature in the early Universe at which fundamental particles, such as electrons and other leptons, interacted with their antiparticles through the Standard Model’s Higgs boson. This temperature acted as a switch, shaping how the imbalance between matter and antimatter emerged.
Traces in Primordial Gravitational Waves
Study co-author Dr. Sudip Jyoti Show of Kanpur said the findings change our understanding of how the early Universe expanded so rapidly after the Big Bang.
He added: “This gives us a new explanation for how matter prevailed. A dramatic shift in the early expansion of the cosmos leaves distinct, detectable imprints of change, for example, on primordial gravitational waves.”
These gravitational-wave signatures open up new opportunities to unravel the evolution of the early Universe after the Big Bang.
