  The chiral phase transition in QCD can be supercooled in the thermal history
of the universe to be instantaneously out-of equilibrium, if QCD is coupled to
a dark QCD sector exhibiting the dark chiral phase transition of the first
order. In that case the QCD sigma meson field (as the chiral order parameter,
or the light quark condensate) starts to roll in a nonadiabatic way down to the
true QCD vacuum. Meanwhile a dynamic baryonic chemical potential can be
generated solely within QCD, which is governed by the dynamic motion of the QCD
sigma meson field, analogously to the spontaneous baryogenesis or the
leptogenesis via the Higgs or axionlike relaxation scenario. When QCD is
further allowed to communicate with a dark fermion with mass of order of 1 GeV
and the baryon number violating coupling to neutron, the nonadiabatic QCD sigma
motion along with the nonadiabatic baryon chemical potential can trigger the
preheating and produce the baryon number asymmetry. We discuss this scenario in
details to find that the QCD-induced dynamic baryon chemical potential plays a
significant role for the QCD preheating and the baryogenesis, which yields the
desired amount of the asymmetry today consistently with current astrophysical,
cosmological, and terrestrial experimental constraints. Cosmological and
phenomenological consequences characteristic to the present scenario are also
addressed.
