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Abstract
We update the constraints on the fraction of the Universe that may have gone into primordial black holes (PBHs) over the mass range 10-5to 1050 g. Those smaller than ∼1015 g would have evaporated by now due to Hawking radiation, so their abundance at formation is constrained by the effects of evaporated particles on big bang nucleosynthesis, the cosmic microwave background (CMB), the Galactic and extragalacticγ-ray and cosmic ray backgrounds and the possible generation of stable Planck mass relics. PBHs larger than ∼1015 g are subject to a variety of constraints associated with gravitational lensing, dynamical effects, influence on large-scale structure, accretion and gravitational waves. We discuss the constraints on both the initial collapse fraction and the current fraction of the dark matter (DM) in PBHs at each mass scale but stress that many of the constraints are associated with observational or theoretical uncertainties. We also consider indirect constraints associated with the amplitude of the primordial density fluctuations, such as second-order tensor perturbations andμ-distortions arising from the effect of acoustic reheating on the CMB, if PBHs are created from the high-σpeaks of nearly Gaussian fluctuations. Finally we discuss how the constraints are modified if the PBHs have an extended mass function, this being relevant if PBHs provide some combination of the DM, the LIGO/Virgo coalescences and the seeds for cosmic structure. Even if PBHs make a small contribution to the DM, they could play an important cosmological role and provide a unique probe of the early Universe.
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Affiliation(s)
- Bernard Carr
- School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom
- Research Center for the Early Universe (RESCEU), Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
| | - Kazunori Kohri
- Theory Center, IPNS, KEK, Tsukuba, Ibaraki 305-0801, Japan
- The Graduate University for Advanced Studies (SOKENDAI), Tsukuba, Ibaraki 305-0801, Japan
- Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, Kashiwa, Chiba 277-8568, Japan
| | - Yuuiti Sendouda
- Graduate School of Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561, Japan
| | - Jun'ichi Yokoyama
- Research Center for the Early Universe (RESCEU), Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
- Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, Kashiwa, Chiba 277-8568, Japan
- Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
- Trans-Scale Quantum Science Institute, The University of Tokyo, Tokyo 113-0033, Japan
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