A Forgotten 'Ghost Particle' May Explain Why the Universe Exists
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Physicists propose that a long-overlooked type of sterile neutrino, decaying slowly after the Big Bang, tipped the cosmic balance toward matter over antimatter — potentially explaining why anything exists at all.
Physicists Rishav Roshan of the University of Southampton and Sudipta Show of the Indian Institute of Technology Kanpur have published a paper in Physical Review Letters proposing that a specific variety of sterile neutrino — a hypothetical particle that barely interacts with ordinary matter, feeling only gravity and an extraordinarily weak Higgs pull — could resolve one of science's deepest puzzles. The Big Bang should have produced equal quantities of matter and antimatter, which would have annihilated each other, leaving a universe of pure energy. Yet matter survived. The researchers' model describes a 'decoupled' heavy sterile neutrino that, unlike its two sibling sterile neutrinos, stayed alive long enough after the Big Bang to temporarily dominate the universe's total energy density. This temporary dominance shifted the cosmic temperature at the precise moment when matter and antimatter particles were interacting, creating an infinitesimal imbalance that allowed a fraction of matter to survive. A subsequent process then converted part of the excess leptons into quarks, which formed protons and neutrons. Because the study calculates a lightest neutrino mass, it is falsifiable through particle physics experiments. The ghost particle itself is long extinct, but its influence would have left detectable imprints on primordial gravitational waves — ripples in spacetime from the early universe that future observatories such as LISA, a trio of spacecraft 2.5 million kilometres apart, could potentially pick up.
