Ghostly neutrino particles can spontaneously pair up and flip their identities in ways that defy our understanding of the early universe.
Neutrinos are famous for passing through solid lead as if it were air and rarely interacting with anything. Momentum modes within these particle streams can spontaneously swap identities with their antimatter counterparts through collective oscillations. Previous simulations assumed these interactions were negligible because neutrinos are so elusive. This behavior could change how energy moves during a supernova or how the universe cooled down after the Big Bang. Identifying these instabilities means our maps of the cosmos's first moments might be missing a massive amount of hidden particle traffic.
Collective neutrino-antineutrino pair oscillations
arXiv · 2604.25687
In dense neutrino gas, pairing correlations between neutrinos and antineutrinos with opposite momenta can be nonzero in generalized neutrino quantum kinetic equations at the mean-field level. In this Letter, we investigate for the first time the condition under which collective neutrino-antineutrino ($\nu\bar\nu$) pairing instabilities can occur, using simplified toy models consisting of discretized $\nu\bar\nu$ pairs in a homogeneous neutrino gas. We find that, in ansiotropic systems, $\nu\bar\