Evolution of primordial black holes in Jordan-Brans-Dicke cosmology

We consider the evolution of primordial black holes in a generalized Jordan-BransDicke cosmological model where both the Brans-Dicke scalar field and its coupling to gravity are dynamical functions determined from the evolution equations. The evaporation rate for the black holes is different from the case in standard cosmology. We show that the accretion of radiation can proceed effectively in the radiation dominated era. It follows that the black hole lifetime shortens for low initial mass, but increases considerably for larger initial mass, thus providing a mechanism for the survival of primordial black holes as candidates of dark matter. We derive a cut-off value for the initial black hole mass, below which primordial black holes evaporate out in the radiation dominated era, and above which they survive beyond the present era.