Heavy neutrino could explain matter-antimatter asymmetry

Physicists at the University of Southampton and IIT Kanpur propose that a long-lived "decoupled" heavy neutrino reshaped the early universe's expansion and tipped the balance toward matter. The particle's slow decay could have triggered a temporary matter-dominated period and shifted the temperature at which leptons interacted with their antiparticles. The theory predicts detectable imprints in primordial gravitational waves.

• Study published in Physical Review Letters on September 8, 2026
• The heavy neutrino decays so slowly it briefly dominated the universe's energy density
• A shift in lepton-antilepton interaction temperature set the matter-antimatter imbalance
• Primordial gravitational waves could carry detectable traces of the process