Sterile Neutrino Dark Matter, Matter-Antimatter Separation, and the QCD Phase Transition

The Universe may contain sufficiently small size matter-antimatter domains at temperatures of a few hundred MeV, without violating the success of Big Bang Nucleosynthesis. We demonstrate that this possibility enhances the keV scale sterile neutrino production and may lead to its abundance consistent with the observable energy density of dark matter (DM). We suggest that the separation of matter and antimatter, creating temporarily macroscopic domains occupied by hadronic matter and quark-gluon plasma with an excess of baryons over anti-baryons and vice versa largely exceeding the average baryon and lepton asymmetries of the Universe, may appear because of the first-order QCD phase transition. Although the lattice studies provided a piece of evidence in favour of a smooth crossover between the hadronic and quark-gluon phases at high temperatures and zero chemical potential for baryonic number, we argue that these simulations might not rule out relatively weekly first-order phase transition. We discuss several scenarios of matter-antimatter separation at the QCD phase transition and the production of DM sterile neutrinos in each of them. One of the possibilities requires the presence of lepton asymmetry of the Universe, which can be smaller than that needed for the DM correct abundance in the homogeneous case.