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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.
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?
3.3 Plugging the pair instability gap with PBH?
3.4 PBH eccentricity, 3.5 PBH spin and 3.6 Future gamma-ray telescopes
Future experiments abound, ranging from approved projects to imminently enter the detailed design phase, to provide significantly enhanced constraints on PBH scenarios, including terrestrial laser interferometers (Einstein Telescope, Cosmic Explorer)[25], and space laser interferometers (LISA, DECIGO [26], TianQin and Taiji [27]), to atomic interferometers on the ground with demonstrators under construction and extensions planned to km scales (AION MAGIS, MAGIA, MIGA, ELGA, ZAIGA), as well as in space (AEDGE) [28], and designs for lunar interferometer/seismometer arrays (LGWA, GLOC)[29].
The science goals focus on bridging frequency gaps in the LIGO/VIRGO/KAGRA frequency range that has so far led to hundreds of detections of BH mergers in the (10 − 100)M⊙ range by going both to higher and lower frequencies. The new science that can be explored ranges from the masses and equation of state of neutron stars as well as multimessage signals from core collapse supernovae to kpc distances (kHz to Hz range) to SMBH and IMBH detections and BH inspiralling (Hz to mHz, and eventually µHz). One would ultimately approach the pulsar timing array sensitivities (NANOGrav, SKA) at nanohertz frequencies to enable exploration of first order very early universe phase transitions, and presence of loop decays in a network of cosmic strings [30].
We next address various “smoking-gun” signatures that may identify PBHs, notably including high redshift mergers and sub-solar mass PBHs.
This paper is available on arxiv under CC BY 4.0 DEED license.