Primordial black holes in braneworld cosmologies: astrophysical constraints

In two recent papers we explored the modifications to primordial black hole physics when one moves to the simplest braneworld model, Randall--Sundrum type II. Both the evaporation law and the cosmological evolution of the population can be modified, and additionally accretion of energy from the background can be dominant over evaporation at high energies. In this paper we present a detailed study of how this impacts upon various astrophysical constraints, analyzing constraints from the present density, from the present high-energy photon background radiation, from distortion of the microwave background spectrum, and from processes affecting light element abundances both during and after nucleosynthesis. Typically, the constraints on the formation rate of primordial black holes weaken as compared to the standard cosmology if black hole accretion is unimportant at high energies, but can be strengthened in the case of efficient accretion.