Constraints on primordial black holes and primeval density perturbations from the epoch of reionization

Abstract

We investigate the constraint on the abundance of primordial black holes (PBHs) and the spectral index $n$ of primeval density perturbations given by the ionizing photon background at the epoch of reionization. Within the standard inflationary cosmogony, we show that the spectral index $n$ of the power-law power spectrum of primeval density perturbations should be $n<$1.27. Since the universe is still optical thick at the reionization redshift $z\sim 6$ - 8, this constraint is independent of the unknown parameter of reheating temperature of the inflation. The ionizing photon background from the PBHs can be well approximated by a power law spectrum $J(\hat{I}½)\propto \hat{I}{½}^3$, which is greatly different from those given by models of massive stars and quasars.

4 pages, 3 eps figues, to be published in ApJ Letters