This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists have unveiled a new theory on the birth of the cosmos, suggesting the early universe was shaped by an ancient particle that has been overlooked for decades. Their research tackles one of the greatest conundrums in modern physics—how matter triumphed over antimatter in the aftermath of the Big Bang.
According to current theories, both should have annihilated each other after a colossal explosion, leaving nothing but an empty universe of pure energy. But physicists at the University of Southampton and the Indian Institute of Technology Kanpur say they found a clue in a neutrino, one of the lightest particles in the universe. The team discovered that an often-ignored relative of these particles, known as a 'decoupled' heavy neutrino, could have helped matter dominate over its counterpart.
Rishav Roshan from Southampton said, "This decoupled heavy neutrino has long been dismissed as an irrelevant background detail in particle physics. "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." The new paper has been published in Physical Review Letters.
Most theories on why matter won over antimatter ignored the decoupled heavy particle because experts deemed it too weak to have any impact on others, added Roshan. However, the Southampton and Kanpur researchers found that the forgotten particle could affect the particle–antiparticle asymmetry essential for our existence. "The fact that we are here at all proves that an asymmetry between matter and antimatter occurred," added Roshan.
"The decoupled neutrino shifted the temperature in the early universe at which fundamental particles—like electrons and other leptons—interacted with their antiparticles with the help of the Standard Model Higgs boson. "This temperature acts like a switch that shapes how the matter-antimatter imbalance was built up." Paper co-author Dr. Sudipta Show from Kanpur said the findings change our understanding of how the early universe expanded so quickly after the Big Bang.
He added, "It offers us a new explanation for how matter won. "The dramatic shift in the early expansion of the cosmos leaves distinct but detectable imprints of changes, for example on primordial gravitational waves. "These gravitational wave signatures open up new avenues for us to unravel the evolution of the early universe after the Big Bang." Rishav Roshan et al., Delayed Charged Lepton Yukawa Equilibration in Minimal Seesaw, Physical Review Letters (2026).
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