  A successful baryogenesis mechanism is proposed in the cosmological framework
of Brans-Dicke modified gravity. Primordial black holes with small mass are
produced at the end of the Brans-Dicke field domination era. The Hawking
radiation reheats a spherical region around every black hole to a high
temperature and the electroweak symmetry is restored there. A domain wall is
formed separating the region with the symmetric vacuum from the asymmetric
region where electroweak baryogenesis takes place. First order phase transition
is not needed. In Brans-Dicke cosmologies black hole accretion can be strong
enough to lead to black holes domination which extends the lifetime of black
holes and therefore baryogenesis. The analysis of the whole scenario, finally,
results in the observed baryon number which can be achieved for a CP-violation
angle that is predicted by observationally accepted Two-Higgs Doublet Models.
The advantage of our proposed scenario is that naturally provides both black
hole domination and more efficient baryogenesis for smaller CP violating angles
compared to the same mechanism applied in a FRW cosmological background.
