If matter and antimatter had annihilated each other completely after the Big Bang, the universe would have been left with energy and no matter. Explaining why matter survived, when current theories suggest the two should have wiped each other out, remains one of the biggest puzzles in modern physics.
Physicists at the University of Southampton and the Indian Institute of Technology Kanpur have proposed an explanation involving a particle largely overlooked for decades. Known as a “decoupled” heavy neutrino, it is a heavier relative of the neutrino, one of the lightest particles in the universe. Most theories explaining the matter-antimatter imbalance have ignored this heavy relative because its interactions with other particles were considered too weak to have an impact.
“The fact that we are here at all proves that an asymmetry between matter and antimatter occurred,” said study author Dr. Rishav Roshan of the University of Southampton.
The new research, published in Physical Review Letters, connects that imbalance to the early universe’s expansion. Co-author Dr. Sudipta Show of the Indian Institute of Technology Kanpur said the findings change our understanding of how quickly the cosmos expanded after the Big Bang.
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