  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.
