Influence of Primordial Black Holes on Cosmic Reionization through Semi-Analytical Modelling

This research addresses the influence of Primordial Black Holes (PBHs) on cosmic reionization, using a robust semi-analytical model. This model encapsulates cosmological theory, PBH physics, and radiative transfer, with a lognormal PBH mass function as the fulcrum, with the mean PBH mass set at 30 solar masses and the fraction of dark matter in PBHs ($f_{PBH}$) varied from 1.26 to 10. We also adopt a standard thin-disk accretion model and a one-dimensional radiative transfer code for a comprehensive depiction of cosmic reionization under the influence of PBHs. Our major findings reveal an inverse relationship between PBH mass and ionizing efficiency. For instance, when the mean PBH mass is 10 solar masses, and $f_{PBH}$ is 0.1, the resulting ionizing efficiency is approximately 0.25, which drops to 0.15 with a mean PBH mass of 50 solar masses. However, with $f_{PBH}$ nearing unity, even large PBHs (mean mass of 100 solar masses) can achieve an ionizing efficiency close to 0.2. The ionization history indicates that for a mean PBH mass of 10 solar masses and $f_{PBH}$ at 0.01, rapid ionization commences at z=12.5+0.5/z=12.5-0.5 and concludes at z=9+0.5/z=9-0.5. Conversely, with a larger PBH mass of 100 solar masses and $f_{PBH}$ at 0.01, reionization initiates later, at z=10.8+0.4/z=10.8-0.4. Our two-point correlation function analysis unveils the formation of ionized bubbles with an initial size of approximately 10 Mpc at z=7.5+0.5/z=7.5-0.5 for an $f_{PBH}$ of 0.01, expanding to 20 Mpc by the end of reionization. With $f_{PBH}$ of 0.1, larger bubbles form, starting at approximately 15 Mpc and reaching 30 Mpc by reionization's end. In conclusion, PBHs significantly influence cosmic reionization, with PBH mass and their contribution to dark matter modulating this impact.