Constraints on primordial black holes

By B. Carr, K. Kohri, Y. Sendouda, J. Yokoyama. Reports on progress in physics. Physical Society, 2020

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We update the constraints on the fraction of the Universe that may have gone into primordial black holes (PBHs) over the mass range 10−5 to 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 extragalactic γ-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 and μ-distortions arising from the effect of acoustic reheating on the CMB, if PBHs are created from the high-σ peaks 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.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/5ea1d2df44ccc5f3703a73c518ad293c27073b20

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Citations in the corpus

Primordial black holes as dark matter candidates (2021, methodology): “In Reference [181] this method is applied for various PBH mass functions and this analysis is updated in Reference [16].”
Solar-mass primordial black holes explain NANOGrav hint of gravitational waves (2020, neutral): “[75]).”
Primordial Black Holes as Dark Matter: Recent Developments (2020, methodology): “[27].”
Detecting high-frequency gravitational waves with microwave cavities (2021, background): “[95] Bernard Carr, Kazunori Kohri, Yuuiti Sendouda, and Jun’ichi Yokoyama, “Constraints on primordial black holes,” Rept.”
A Brief Review on Primordial Black Holes as Dark Matter (2021, background): “Several recent reviews are devoted to discuss PBHs in great detail (see, e.g., Sasaki et al., 2018; Carr and Kühnel, 2020; Carr et al., 2020; Green and Kavanagh, 2021).”