Authors: (1) Antonio Riotto, Département de Physique Theorique, Universite de Geneve, 24 quai Ansermet, CH-1211 Geneve 4, Switzerland and Gravitational Wave Science Center (GWSC), Universite de Geneve, CH-1211 Geneva, Switzerland; (2) Joe Silk, Institut d’Astrophysique, UMR 7095 CNRS, Sorbonne Universite, 98bis Bd Arago, 75014 Paris, France, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore MD 21218, USA, and Beecroft Institute of Particle Astrophysics and Cosmology, Department of Physics, University of Oxford, Oxford OX1 3RH, UK. 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 3.1 High redshift mergers The PBH model predicts a binary merger rate density which grows monotonically with redshift [31, 32, 33]. Focusing those binaries generated at early epochs, one has a well-defined time evolution with redshift This paper is available on arxiv under CC BY 4.0 DEED license. Authors: (1) Antonio Riotto, Département de Physique Theorique, Universite de Geneve, 24 quai Ansermet, CH-1211 Geneve 4, Switzerland and Gravitational Wave Science Center (GWSC), Universite de Geneve, CH-1211 Geneva, Switzerland; (2) Joe Silk, Institut d’Astrophysique, UMR 7095 CNRS, Sorbonne Universite, 98bis Bd Arago, 75014 Paris, France, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore MD 21218, USA, and Beecroft Institute of Particle Astrophysics and Cosmology, Department of Physics, University of Oxford, Oxford OX1 3RH, UK. Authors: Authors: (1) Antonio Riotto, Département de Physique Theorique, Universite de Geneve, 24 quai Ansermet, CH-1211 Geneve 4, Switzerland and Gravitational Wave Science Center (GWSC), Universite de Geneve, CH-1211 Geneva, Switzerland; (2) Joe Silk, Institut d’Astrophysique, UMR 7095 CNRS, Sorbonne Universite, 98bis Bd Arago, 75014 Paris, France, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore MD 21218, USA, and Beecroft Institute of Particle Astrophysics and Cosmology, Department of Physics, University of Oxford, Oxford OX1 3RH, UK. Table of Links Abstract and 1 Introduction Abstract and 1 Introduction 2 Some open questions 2 Some open questions 2.1 What is the abundance of PBHs? 2.1 What is the abundance of PBHs? 2.2 What is the effect of PBH clustering? 2.2 What is the effect of PBH clustering? 2.3 What fraction of the currently observed GW events can be ascribed to PBHs? 2.3 What fraction of the currently observed GW events can be ascribed to PBHs? 2.4 Are PBHs the Dark Matter? 2.4 Are PBHs the Dark Matter? 3 The PBH Roadmap 3 The PBH Roadmap 3.1 High redshift mergers 3.1 High redshift mergers 3.2 Sub-solar PBHs 3.2 Sub-solar PBHs 3.3 Plugging the pair instability gap with PBH? 3.3 Plugging the pair instability gap with PBH? 3.4 PBH eccentricity, 3.5 PBH spin and 3.6 Future gamma-ray telescopes 3.4 PBH eccentricity, 3.5 PBH spin and 3.6 Future gamma-ray telescopes 4 Conclusions and References 4 Conclusions and References 3.1 High redshift mergers The PBH model predicts a binary merger rate density which grows monotonically with redshift [31, 32, 33]. Focusing those binaries generated at early epochs, one has a well-defined time evolution with redshift This paper is available on arxiv under CC BY 4.0 DEED license. This paper is available on arxiv under CC BY 4.0 DEED license. available on arxiv