Gravitational ABJ Anomaly, Stochastic Matter Production, and Leptogenesis

Partially chiral stochastic gravitational wave backgrounds can arise from various processes in the early Universe. The gravitational ABJ anomaly links the chirality of the gravitational field to the chiral fermions, resulting in the stochastic generation of fermionic matter in the radiation era. We show that this mechanism can account for the entire dark matter relic density and discuss its potential as a leptogenesis scenario to explain the observed matter-antimatter asymmetry in the Universe. Remarkably, this letter reveals that even if gravitational waves become unpolarized later, their temporary chirality during their generation process leaves a lasting imprint on the fermionic matter, preserved as a quantum remnant.