No torque mechanism studied supplies enough angular momentum for the innermost light-PBH shells around a heavy seed, so the spike core is swallowed and far less dense than a WIMP spike.
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Formation and Evolution of Primordial Black Hole Binaries in the Early Universe
Canonical reference. 78% of citing Pith papers cite this work as background.
abstract
The abundance of primordial black holes (PBHs) in the mass range $0.1 - 10^3 M_\odot$ can potentially be tested by gravitational wave observations due to the large merger rate of PBH binaries formed in the early universe. To put the estimates of the latter on a firmer footing, we first derive analytical PBH merger rate for general PBH mass functions while imposing a minimal initial comoving distance between the binary and the PBH nearest to it, in order to pick only initial configurations where the binary would not get disrupted. We then study the formation and evolution of PBH binaries before recombination by performing N-body simulations. We find that the analytical estimate based on the tidally perturbed 2-body system strongly overestimates the present merger rate when PBHs comprise all dark matter, as most initial binaries are disrupted by the surrounding PBHs. This is mostly due to the formation of compact N-body systems at matter-radiation equality. However, if PBHs make up a small fraction of the dark matter, $f_{\rm PBH} \lesssim 10\%$, these estimates become more reliable. In that case, the merger rate observed by LIGO imposes the strongest constraint on the PBH abundance in the mass range $2 - 160 M_\odot$. Finally, we argue that, even if most initial PBH binaries are perturbed, the present BH-BH merger rate of binaries formed in the early universe is larger than $\mathcal{O}(10)\,{\rm Gpc}^{-3} {\rm yr}^{-1}\, f_{\rm PBH}^3$
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representative citing papers
In the ADD extra-dimension model, microscopic primordial black holes undergo runaway accretion and grow to macroscopic scales, allowing them to comprise all dark matter with initial abundances as low as 10^{-44}.
BHL-type post-recombination accretion can raise late three-body PBH merger rates enough for TianQin detections at f~10^{-6} and for LVK limits to bound delayed virialization.
Curvaton self-interactions in non-quadratic potentials produce a local non-Gaussian map that enables supermassive primordial black hole formation at peak amplitudes of order 10^{-5} while remaining consistent with μ-distortion bounds.
O4a gravitational-wave data give 95% CL upper limits f_PBH ~ 1e-2 to 1e-4 for monochromatic primordial black holes with mean masses 0.6-100 M_sun, with no evidence of a PBH merger component.
GW231123's masses and high spins are consistent with primordial black holes that accreted mass and angular momentum in the early universe within the standard PBH framework.
Monte Carlo solutions of the Smoluchowski equation for PBH clusters yield finite runaway timescales and evolving mass distributions that form high-redshift SMBHs, shortened further by mass segregation.
Galactic synchrotron emissions above 20 MHz can set tighter upper limits on the abundance of primordial black holes with masses above 10^16 grams than previous cosmic-ray electron data.
Simulations of ET and CE networks show delays degrade localization metrics far more than SNR, with LIGO India greatly reducing the impact for multi-messenger and stochastic searches.
Weak initial clustering of primordial black holes reduces the PBH fraction needed to explain LIGO-Virgo-KAGRA mergers in the two-body channel, while strong clustering suppresses the rate via three-body formation.
For monochromatic primordial black holes, the low-frequency scalar-induced gravitational-wave peak and the high-frequency binary-merger ISCO frequency are linked by fISCO ≈ 3.4×10^20 Hz × (fSIGW/Hz)^2.
Using HBI on GWTC-4 data the authors compute lensed SGWBs for ABHs and PBHs and conclude that LIGO and ET can distinguish the two formation channels in specific frequency ranges, with ET offering broader coverage.
Multi-band GW observations of PBHs can reduce H0 uncertainty to ≲2 km/s/Mpc (conservative) or O(0.1) km/s/Mpc (optimistic) via Fisher forecasts on M_PBH and f_PBH.
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The swallowed spike: the formation of light primordial black hole structures around heavy seeds
No torque mechanism studied supplies enough angular momentum for the innermost light-PBH shells around a heavy seed, so the spike core is swallowed and far less dense than a WIMP spike.
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Microscopic primordial black holes as macroscopic dark matter from large extra dimensions
In the ADD extra-dimension model, microscopic primordial black holes undergo runaway accretion and grow to macroscopic scales, allowing them to comprise all dark matter with initial abundances as low as 10^{-44}.
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Effect of post-recombination accretion on primordial binary black hole mergers within virialized dark matter halos
BHL-type post-recombination accretion can raise late three-body PBH merger rates enough for TianQin detections at f~10^{-6} and for LVK limits to bound delayed virialization.
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Memoirs of the curvaton: non-perturbative non-Gaussianity and supermassive primordial black holes
Curvaton self-interactions in non-quadratic potentials produce a local non-Gaussian map that enables supermassive primordial black hole formation at peak amplitudes of order 10^{-5} while remaining consistent with μ-distortion bounds.
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Constraints on primordial black holes from the first part of LIGO-Virgo-KAGRA fourth observing run
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GW231123: A Possible Primordial Black Hole Origin
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Smoluchowski Coagulation Equation and the Evolution of Primordial Black Hole Clusters
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Constraints on Primordial Black Holes from Galactic Diffuse Synchrotron Emissions
Galactic synchrotron emissions above 20 MHz can set tighter upper limits on the abundance of primordial black holes with masses above 10^16 grams than previous cosmic-ray electron data.
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Impact of facility timing and coordination for next-generation gravitational-wave detectors
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Merger rate of initially clustered primordial black holes for the two-body channel
Weak initial clustering of primordial black holes reduces the PBH fraction needed to explain LIGO-Virgo-KAGRA mergers in the two-body channel, while strong clustering suppresses the rate via three-body formation.
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Gravitational Waves from Primordial Black Holes: Connecting Low-Frequency Scalar-Induced Signatures to High-Frequency Binary Mergers
For monochromatic primordial black holes, the low-frequency scalar-induced gravitational-wave peak and the high-frequency binary-merger ISCO frequency are linked by fISCO ≈ 3.4×10^20 Hz × (fSIGW/Hz)^2.
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Effects of formation channels and gravitational lensing on stochastic gravitational wave background
Using HBI on GWTC-4 data the authors compute lensed SGWBs for ABHs and PBHs and conclude that LIGO and ET can distinguish the two formation channels in specific frequency ranges, with ET offering broader coverage.
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Precision Analysis for $\boldsymbol{H_0}$ Using Upcoming Multi-band Gravitational Wave Observations
Multi-band GW observations of PBHs can reduce H0 uncertainty to ≲2 km/s/Mpc (conservative) or O(0.1) km/s/Mpc (optimistic) via Fisher forecasts on M_PBH and f_PBH.
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Using SKAO to Understand the Clustering of Gravitational Wave Sources
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Science with the Einstein Telescope: a comparison of different designs
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Primordial Black Holes as Dark Matter: Recent Developments
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Machine Learning for Multi-messenger Probes of New Physics and Cosmology: A Review and Perspective
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