Table of Links

Abstract and 1 Introduction

2 Some open questions

2.1 What is the abundance of PBHs?

2.2 What is the effect of PBH clustering?

2.3 What fraction of the currently observed GW events can be ascribed to PBHs?

2.4 Are PBHs the Dark Matter?

3 The PBH Roadmap

3.1 High redshift mergers

3.2 Sub-solar PBHs

3.3 Plugging the pair instability gap with PBH?

3.4 PBH eccentricity, 3.5 PBH spin and 3.6 Future gamma-ray telescopes

4 Conclusions and References

4 Conclusions

Support for the existence of PBHs hypothesis comes from a range of arguments spanning dark matter physics, inflationary models, astrophysics, gravitational microlensing and quantum cosmology. None are yet conclusive but the cumulative support for the existence of PBHs seems reasonably compelling. More to the point however is that there is a rich astrophysical agenda of open questions that contribute to a future road map for a plethora of research projects.

Two of the most fundamental PBH probes that distinguish them from astrophysical counterparts are their redshift and mass distributions. This combination provides an armoury of smoking guns that will inevitably enrich the next generation of gravitational wave and gravitational microlensing experiments. Confirmation will require improved statistics as single events may not be conclusive. it is only too easy to come up with rare events that can masquerade as PBH candidates, for example by appealing to higher order generations of merging events or to non-Gaussianity. We have laid out a possible future road map for definitively assessing whether PBHs can present a viable candidate for dark matter, or possibly contribute to other astrophysical or even quantum cosmology anomalies.

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