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arxiv: 2604.22731 · v1 · submitted 2026-04-24 · 🌌 astro-ph.CO · gr-qc· hep-ph

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Precision Analysis for boldsymbol{H₀} Using Upcoming Multi-band Gravitational Wave Observations

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Pith reviewed 2026-05-08 09:50 UTC · model grok-4.3

classification 🌌 astro-ph.CO gr-qchep-ph
keywords primordial black holesHubble constantgravitational wavesmulti-band observationsFisher matrixscalar-induced GWHubble tension
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The pith

Multi-band gravitational wave observations from primordial black holes can constrain the Hubble constant to within 2 km/s/Mpc.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper examines how signals from primordial black holes observed across multiple frequency bands can tighten constraints on the Hubble parameter H0. It combines scalar-induced gravitational waves accessible to the Square Kilometre Array with merger-induced waves detectable by the Einstein Telescope, then uses signal-to-noise estimates and Fisher matrix analysis on the black hole mass and abundance to forecast errors. These parameter uncertainties are propagated to derive corresponding limits on H0. A sympathetic reader would care because the approach supplies an independent cosmological probe that avoids traditional distance-ladder systematics and could address the Hubble tension with entirely new observations.

Core claim

The central finding is that relative uncertainties of 10 percent or less on the primordial black hole parameters M_PBH and f_PBH translate into an uncertainty on H0 of at most 2 km s^{-1} Mpc^{-1} in a conservative multi-band analysis, improving to order 0.1 km s^{-1} Mpc^{-1} in an optimistic precision case, with the results largely insensitive to the fiducial H0 value and only moderately dependent on collapse efficiency.

What carries the argument

Fisher matrix propagation of uncertainties from the primordial black hole parameters M_PBH and f_PBH, obtained from the joint analysis of scalar-induced and merger-induced gravitational wave signals in multi-band data from SKA and ET.

If this is right

  • Multi-band gravitational wave observations supply an independent and complementary approach to constraining uncertainties in H0.
  • The resulting H0 uncertainties remain largely insensitive to the exact fiducial value chosen for H0.
  • The constraints show only moderate dependence on the assumed efficiency of primordial black hole collapse.
  • This framework offers a novel cosmic distance ladder-independent route to measuring the Hubble parameter.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If such primordial black hole signals are actually detected, the method could serve as a cross-check against other gravitational-wave determinations of H0 such as those from binary neutron star mergers.
  • The same multi-band framework could be extended to additional future detectors to achieve even tighter joint constraints on both black hole properties and cosmological parameters.
  • Absence of the predicted signals in real data would directly translate into stronger upper bounds on primordial black hole abundance in the relevant mass window.
  • Real observations might eventually test whether unmodeled systematics in the multi-band combination alter the propagated errors on H0 beyond the Fisher matrix estimates.

Load-bearing premise

Primordial black holes must exist in sufficient abundance to produce detectable scalar-induced and merger-induced gravitational wave signals with signal-to-noise ratio of at least 1 in the SKA and Einstein Telescope bands.

What would settle it

Observation of the expected multi-band gravitational wave signals from primordial black holes but with measured uncertainties in H0 that substantially exceed the forecasted values of 2 km/s/Mpc or smaller.

read the original abstract

We investigate how multi-band gravitational wave (GW) observations can constrain the uncertainties in the Hubble parameter ($H_0$) using primordial black holes (PBHs) as possible sources. Our framework combines scalar-induced and merger-induced GWs from PBHs, and forecasts on a combination of two future detectors Square Kilometre Array (SKA) and the Einstein Telescope (ET), enabling a multi-band analysis. We perform a statistical forecast of the PBH parameters, $M_{\rm PBH}$ and $f_{\rm PBH}$, using signal-to-noise ratio (SNR) estimates and Fisher matrix analysis. Imposing $\mathrm{SNR} \geq 1$, we identify the accessible PBH parameter space and propagate these uncertainties to estimate the corresponding uncertainties in $H_0$. For $\delta \theta_i/\theta_i \leq 0.1$, with $\theta_i \equiv M_{\rm PBH}(f_{\rm PBH})$, we find $\delta H_0 \lesssim 2~{\rm km\,s^{-1}\,Mpc^{-1}}$ in a conservative approach, improving to $\delta H_0 \lesssim \mathcal{O}(0.1)~{\rm km\,s^{-1}\,Mpc^{-1}}$ for $\delta \theta_i/\theta_i \leq 0.01$ for an optimistic approach of precision measurement. The results are further found to be largely insensitive to the fiducial choice of the $H_0$, with only moderate dependence on the PBH collapse efficiency. These findings demonstrate that multi-band GW observations provide an independent and complementary approach to constraining the uncertainties in $H_0$, with the potential to provide a novel, cosmic distance ladder-independent measure of the Hubble parameter.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript presents a forecast for constraining the Hubble constant H0 using multi-band gravitational wave observations of primordial black holes (PBHs). It combines scalar-induced gravitational waves and merger-induced signals from PBHs, using the Square Kilometre Array (SKA) and Einstein Telescope (ET) for multi-band analysis. The authors perform signal-to-noise ratio (SNR) estimates to identify the accessible parameter space for PBH mass M_PBH and abundance f_PBH, followed by Fisher matrix analysis to forecast uncertainties in these parameters. These uncertainties are then propagated to estimate the uncertainty in H0, yielding δH0 ≲ 2 km s^{-1} Mpc^{-1} for 10% relative precision on PBH parameters and δH0 ≲ O(0.1) km s^{-1} Mpc^{-1} for 1% precision. The results are reported to be insensitive to the fiducial H0 value and moderately dependent on PBH collapse efficiency.

Significance. If the error propagation from PBH parameters to H0 is rigorously demonstrated and the assumptions about PBH abundance and signal detectability hold, this work could provide a novel, independent probe of H0 that is free from the cosmic distance ladder. The multi-band approach combining SKA and ET is a positive aspect, as is the use of standard Fisher forecasting methods. The finding of insensitivity to fiducial H0 adds robustness. However, the significance is tempered by the reliance on PBHs existing in sufficient numbers to produce SNR ≥1 signals, which remains an open question in the field.

major comments (2)
  1. [§4 (Results and H0 propagation)] §4 (Results and H0 propagation): The central results for δH0 are obtained by imposing δθi/θi ≤ 0.1 and ≤ 0.01 on θi ≡ M_PBH(f_PBH) rather than using the uncertainties directly computed from the Fisher matrix in the SNR ≥1 region. The manuscript does not provide the explicit functional form of H0(M_PBH, f_PBH) or the error propagation formula (e.g., via partial derivatives ∂H0/∂M_PBH and ∂H0/∂f_PBH). This makes the quoted δH0 bounds conditional on external precision assumptions instead of being the direct output of the statistical forecast.
  2. [§3.2 (Fisher matrix analysis)] §3.2 (Fisher matrix analysis): While the Fisher matrix is applied to forecast σ(M_PBH) and σ(f_PBH), there is no demonstration that these computed uncertainties satisfy or relate to the imposed relative error thresholds used for the δH0 estimates. The paper should show the actual Fisher-derived relative errors for the accessible parameter space and then propagate those specifically to H0.
minor comments (2)
  1. [Abstract] Abstract: The notation 'O(0.1)' should be typeset as mathcal{O}(0.1) for consistency.
  2. [Methods] Ensure that all references to the PBH collapse efficiency parameter are clearly defined in the methods section with its range of values explored.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of our manuscript and for providing constructive comments that help improve the clarity and rigor of our analysis. We address each major comment point by point below, agreeing that revisions are needed to better connect the Fisher matrix results directly to the H0 uncertainty estimates.

read point-by-point responses
  1. Referee: [§4 (Results and H0 propagation)] The central results for δH0 are obtained by imposing δθi/θi ≤ 0.1 and ≤ 0.01 on θi ≡ M_PBH(f_PBH) rather than using the uncertainties directly computed from the Fisher matrix in the SNR ≥1 region. The manuscript does not provide the explicit functional form of H0(M_PBH, f_PBH) or the error propagation formula (e.g., via partial derivatives ∂H0/∂M_PBH and ∂H0/∂f_PBH). This makes the quoted δH0 bounds conditional on external precision assumptions instead of being the direct output of the statistical forecast.

    Authors: We thank the referee for this observation. The current presentation uses assumed relative precisions (10% and 1%) on M_PBH and f_PBH to delineate conservative and optimistic cases for δH0, as these thresholds illustrate the potential reach of multi-band observations within the SNR ≥1 region identified by our Fisher analysis. However, we agree that the manuscript would be strengthened by explicitly deriving the functional dependence H0(M_PBH, f_PBH) from the underlying GW signal models (e.g., via frequency or amplitude scalings in the scalar-induced and merger-induced spectra) and by providing the error propagation formula using partial derivatives. In the revised manuscript, we will add this derivation in §4, compute the actual Fisher-derived relative errors across the accessible parameter space, and propagate those specific uncertainties to obtain δH0. This will make the quoted bounds a direct output of the forecast rather than conditional on external assumptions. revision: yes

  2. Referee: [§3.2 (Fisher matrix analysis)] While the Fisher matrix is applied to forecast σ(M_PBH) and σ(f_PBH), there is no demonstration that these computed uncertainties satisfy or relate to the imposed relative error thresholds used for the δH0 estimates. The paper should show the actual Fisher-derived relative errors for the accessible parameter space and then propagate those specifically to H0.

    Authors: We acknowledge that the connection between the Fisher-computed uncertainties and the imposed thresholds is not explicitly demonstrated in the current version. The Fisher matrix in §3.2 yields σ(M_PBH) and σ(f_PBH) for the SNR ≥1 region, but these are not directly mapped to the 0.1 and 0.01 relative error levels used for δH0. In the revision, we will include a new figure or table in §3.2 (or §4) displaying the Fisher-derived relative errors δM_PBH/M_PBH and δf_PBH/f_PBH as a function of the PBH parameters within the detectable space. We will then use these computed values, together with the propagation formula, to derive the corresponding δH0, ensuring full consistency between the statistical forecast and the final H0 constraints. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation uses standard Fisher forecasting with conditional bounds on assumed precisions.

full rationale

The paper's chain consists of SNR-based identification of PBH parameter space, Fisher matrix estimation of uncertainties on M_PBH and f_PBH, and propagation to H0. The quoted δH0 values are presented as conditional on externally imposed relative precisions (δθi/θi ≤ 0.1 or 0.01) rather than direct outputs of the computed Fisher covariances. No equations reduce to each other by construction, no parameters are fitted and then renamed as predictions, and no load-bearing self-citations or imported uniqueness theorems appear in the abstract or description. The analysis remains self-contained against external benchmarks using standard statistical methods without self-referential loops.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The forecast rests on standard cosmological assumptions plus PBH-specific modeling choices whose independent evidence is not supplied in the abstract.

free parameters (1)
  • PBH collapse efficiency
    Mentioned as having moderate dependence; value chosen to model scalar-induced GW amplitude.
axioms (2)
  • domain assumption PBHs produce both scalar-induced and merger-induced GW backgrounds that can be jointly observed in radio and ground-based bands.
    Invoked to justify the multi-band framework and SNR ≥ 1 selection.
  • standard math Fisher matrix provides accurate uncertainty propagation from PBH parameters to H0.
    Standard assumption in forecast papers; no validation shown.

pith-pipeline@v0.9.0 · 5638 in / 1420 out tokens · 22987 ms · 2026-05-08T09:50:03.796503+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

76 extracted references · 66 canonical work pages · 6 internal anchors

  1. [1]

    Schutz,Determining the Hubble Constant from Gravitational Wave Observations, Nature323(1986) 310

    B.F. Schutz,Determining the Hubble Constant from Gravitational Wave Observations, Nature323(1986) 310. [4]LISA Cosmology Working Groupcollaboration,Reconstructing primordial curvature perturbations via scalar-induced gravitational waves with LISA,JCAP05(2025) 062 [2501.11320]. [5]LIGO Scientific, Virgocollaboration,Observation of Gravitational Waves from ...

  2. [2]

    Abramovici et al.,LIGO: The Laser interferometer gravitational wave observatory, Science256(1992) 325

    A. Abramovici et al.,LIGO: The Laser interferometer gravitational wave observatory, Science256(1992) 325

  3. [3]

    Abbott and M.B

    L.F. Abbott and M.B. Wise,Constraints on Generalized Inflationary Cosmologies,Nucl. Phys. B244(1984) 541

  4. [4]

    The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background

    B. Allen,The Stochastic Gravity Wave Background in Cosmological Space-Times,Phys. Rev. D37(1988) 2078. – 19 – [9]NANOGravcollaboration,The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background,Astrophys. J. Lett.951(2023) L8 [2306.16213]. [10]EPTA, InPTAcollaboration,The second data release from the European Pulsar Timing Array - III. Sear...

  5. [5]

    Search for an isotropic gravitational-wave background with the Parkes Pulsar Timing Array

    D.J. Reardon et al.,Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar Timing Array,Astrophys. J. Lett.951(2023) L6 [2306.16215]

  6. [6]

    Searching for the nano-Hertz stochastic gravitational wave background with the Chinese Pulsar Timing Array Data Release I

    H. Xu et al.,Searching for the Nano-Hertz Stochastic Gravitational Wave Background with the Chinese Pulsar Timing Array Data Release I,Res. Astron. Astrophys.23(2023) 075024 [2306.16216]

  7. [7]

    Zel’dovich and I.D

    Y.B. Zel’dovich and I.D. Novikov,The Hypothesis of Cores Retarded during Expansion and the Hot Cosmological Model,Sov. Astron.10(1967) 602

  8. [8]

    Hawking,Gravitationally collapsed objects of very low mass,Mon

    S. Hawking,Gravitationally collapsed objects of very low mass,Mon. Not. Roy. Astron. Soc. 152(1971) 75

  9. [9]

    Carr and S.W

    B.J. Carr and S.W. Hawking,Black holes in the early Universe,Mon. Not. Roy. Astron. Soc. 168(1974) 399

  10. [10]

    Carr and F

    B. Carr and F. Kuhnel,Primordial Black Holes as Dark Matter: Recent Developments,Ann. Rev. Nucl. Part. Sci.70(2020) 355 [2006.02838]

  11. [11]

    Primordial Black Holes as a dark matter candidate

    A.M. Green and B.J. Kavanagh,Primordial Black Holes as a dark matter candidate,J. Phys. G48(2021) 043001 [2007.10722]

  12. [12]

    Carr and F

    B. Carr and F. Kuhnel,Primordial black holes as dark matter candidates,SciPost Phys. Lect. Notes48(2022) 1 [2110.02821]

  13. [13]

    S. Bird, I. Cholis, J.B. Mu˜ noz, Y. Ali-Ha¨ ımoud, M. Kamionkowski, E.D. Kovetz et al.,Did LIGO detect dark matter?,Phys. Rev. Lett.116(2016) 201301 [1603.00464]

  14. [14]

    The clustering of massive Primordial Black Holes as Dark Matter: measuring their mass distribution with Advanced LIGO

    S. Clesse and J. Garc´ ıa-Bellido,The clustering of massive Primordial Black Holes as Dark Matter: measuring their mass distribution with Advanced LIGO,Phys. Dark Univ.15(2017) 142 [1603.05234]

  15. [15]

    Primordial Black Hole Scenario for the Gravitational-Wave Event GW150914

    M. Sasaki, T. Suyama, T. Tanaka and S. Yokoyama,Primordial Black Hole Scenario for the Gravitational-Wave Event GW150914,Phys. Rev. Lett.117(2016) 061101 [1603.08338]

  16. [16]

    Carr,The Primordial black hole mass spectrum,Astrophys

    B.J. Carr,The Primordial black hole mass spectrum,Astrophys. J.201(1975) 1

  17. [17]

    Primordial Black Holes - Perspectives in Gravitational Wave Astronomy -

    M. Sasaki, T. Suyama, T. Tanaka and S. Yokoyama,Primordial black holes—perspectives in gravitational wave astronomy,Class. Quant. Grav.35(2018) 063001 [1801.05235]

  18. [18]

    Generalised constraints on the curvature perturbation from primordial black holes

    A.S. Josan, A.M. Green and K.A. Malik,Generalised constraints on the primordial power spectrum from primordial black holes,Phys. Rev. D79(2009) 103520 [0903.3184]

  19. [19]

    Matarrese, S

    S. Matarrese, S. Mollerach and M. Bruni,Second-order perturbations of the Einstein-de Sitter universe,Phys. Rev. D58(1998) 043504 [astro-ph/9707278]

  20. [20]

    Ananda, C

    K.N. Ananda, C. Clarkson and D. Wands,The Cosmological gravitational wave background from primordial density perturbations,Phys. Rev. D75(2007) 123518 [gr-qc/0612013]

  21. [21]

    Baumann, P.J

    D. Baumann, P.J. Steinhardt, K. Takahashi and K. Ichiki,Gravitational Wave Spectrum Induced by Primordial Scalar Perturbations,Phys. Rev. D76(2007) 084019 [hep-th/0703290]. – 20 –

  22. [22]

    Di Valentino, O

    E. Di Valentino, O. Mena, S. Pan, L. Visinelli, W. Yang, A. Melchiorri et al.,In the realm of the Hubble tension—a review of solutions,Class. Quant. Grav.38(2021) 153001 [2103.01183]

  23. [23]

    E. Abdalla et al.,Cosmology intertwined: A review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies,JHEAp34(2022) 49 [2203.06142]. [30]Planckcollaboration,Planck 2018 results. VI. Cosmological parameters,Astron. Astrophys. 641(2020) A6 [1807.06209]. [31]eBOSScollaboration,Completed SDSS-IV extende...

  24. [24]

    A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team

    A.G. Riess et al.,A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km s −1 Mpc−1 Uncertainty from the Hubble Space Telescope and the SH0ES Team, Astrophys. J. Lett.934(2022) L7 [2112.04510]

  25. [25]

    Liu, X.-Y

    L. Liu, X.-Y. Yang, Z.-K. Guo and R.-G. Cai,Testing primordial black hole and measuring the Hubble constant with multiband gravitational-wave observations,JCAP01(2023) 006 [2112.05473]

  26. [26]

    Kohri and T

    K. Kohri and T. Terada,Semianalytic calculation of gravitational wave spectrum nonlinearly induced from primordial curvature perturbations,Phys. Rev. D97(2018) 123532 [1804.08577]

  27. [27]

    Saito and J

    R. Saito and J. Yokoyama,Gravitational wave background as a probe of the primordial black hole abundance,Phys. Rev. Lett.102(2009) 161101 [0812.4339]

  28. [28]

    Dom` enech,Induced gravitational waves in a general cosmological background, International Journal of Modern Physics D29(2020) 2050028

    G. Dom` enech,Induced gravitational waves in a general cosmological background, International Journal of Modern Physics D29(2020) 2050028

  29. [29]

    Dom` enech, Universe7, 398 (2021), arXiv:2109.01398 [gr-qc]

    G. Dom` enech,Scalar Induced Gravitational Waves Review,Universe7(2021) 398 [2109.01398]

  30. [30]

    and Sand, David J

    N. Vieira et al.,Search For a Counterpart to the Subsolar Mass Gravitational Wave Candidate S251112cm,2603.17009

  31. [31]

    Primordial

    M.R. Haque, F. Iocco and L. Visinelli,Primordial Black Hole interpretation of the sub-solar merger event S251112cm,2603.25795

  32. [32]

    Alabidi, K

    L. Alabidi, K. Kohri, M. Sasaki and Y. Sendouda,Observable Spectra of Induced Gravitational Waves from Inflation,JCAP09(2012) 017 [1203.4663]

  33. [33]

    Nakama and T

    T. Nakama and T. Suyama,Primordial black holes as a novel probe of primordial gravitational waves. II: Detailed analysis,Phys. Rev. D94(2016) 043507 [1605.04482]. [42]NANOGravcollaboration,The NANOGrav 15 yr Data Set: Search for Signals from New Physics,Astrophys. J. Lett.951(2023) L11 [2306.16219]

  34. [34]

    Gravitational wave astronomy with the SKA

    G. Janssen et al.,Gravitational wave astronomy with the SKA,PoSAASKA14(2015) 037 [1501.00127]

  35. [35]

    Weltman et al.,Fundamental physics with the Square Kilometre Array,Publ

    A. Weltman et al.,Fundamental physics with the Square Kilometre Array,Publ. Astron. Soc. Austral.37(2020) e002 [2002.11733]

  36. [36]

    Wang, Y.-F

    S. Wang, Y.-F. Wang, Q.-G. Huang and T.G.F. Li,Constraints on the Primordial Black Hole – 21 – Abundance from the First Advanced LIGO Observation Run Using the Stochastic Gravitational-Wave Background,Phys. Rev. Lett.120(2018) 191102 [1610.08725]

  37. [37]

    Raidal, V

    M. Raidal, V. Vaskonen and H. Veerm¨ ae,Gravitational Waves from Primordial Black Hole Mergers,JCAP09(2017) 037 [1707.01480]. [47]KAGRA, Virgo, LIGO Scientificcollaboration,Upper limits on the isotropic gravitational-wave background from Advanced LIGO and Advanced Virgo ˘2019s third observing run,Phys. Rev. D104(2021) 022004 [2101.12130]. [48]LIGO Scienti...

  38. [38]

    Punturo et al.,The Einstein Telescope: A third-generation gravitational wave observatory,Class

    M. Punturo et al.,The Einstein Telescope: A third-generation gravitational wave observatory,Class. Quant. Grav.27(2010) 194002

  39. [39]

    Maggiore, C

    M. Maggiore et al.,Science Case for the Einstein Telescope,JCAP03(2020) 050 [1912.02622]

  40. [40]

    Allen, inLes Houches School of Physics: Astrophysical Sources of Gravitational Radiation (1996) pp

    B. Allen,The Stochastic gravity wave background: Sources and detection,gr-qc/9604033

  41. [41]

    Detecting a stochastic background of gravitational radiation: Signal processing strategies and sensitivities

    B. Allen and J.D. Romano,Detecting a stochastic background of gravitational radiation: Signal processing strategies and sensitivities,Phys. Rev. D59(1999) 102001 [gr-qc/9710117]

  42. [42]

    Measuring gravitational waves from binary black hole coalescences: I. Signal to noise for inspiral, merger, and ringdown

    E.E. Flanagan and S.A. Hughes,The Basics of gravitational wave theory,Phys. Rev. D57 (1998) 4535 [gr-qc/9701039]

  43. [43]

    Gravitational Waves from Mergin Compact Binaries: How Accurately Can One Extract the Binary's Parameters from the Inspiral Waveform?

    C. Cutler and E.E. Flanagan,Gravitational waves from merging compact binaries: How accurately can one extract the binary’s parameters from the inspiral waveform?,Phys. Rev. D 49(1994) 2658 [gr-qc/9402014]

  44. [44]

    Gravitational waves from inspiraling co mpact binaries: Pa- rameter estimation using second-post-Newtonian wave forms

    E. Poisson and C.M. Will,Gravitational waves from inspiraling compact binaries: Parameter estimation using second postNewtonian asymptotics,Phys. Rev. D52(1995) 848 [gr-qc/9502040]

  45. [45]

    Musco and J

    I. Musco and J.C. Miller,Primordial black hole formation in the early universe: critical behaviour and self-similarity,Class. Quant. Grav.30(2013) 145009 [1201.2379]

  46. [46]

    Primordial black hole formation in the radiative era: investigation of the critical nature of the collapse

    I. Musco, J.C. Miller and A.G. Polnarev,Primordial black hole formation in the radiative era: Investigation of the critical nature of the collapse,Class. Quant. Grav.26(2009) 235001 [0811.1452]

  47. [47]

    Hawke and J.M

    I. Hawke and J.M. Stewart,The dynamics of primordial black hole formation,Class. Quant. Grav.19(2002) 3687

  48. [48]

    Near-Critical Gravitational Collapse and the Initial Mass Function of Primordial Black Holes

    J.C. Niemeyer and K. Jedamzik,Near-critical gravitational collapse and the initial mass function of primordial black holes,Phys. Rev. Lett.80(1998) 5481 [astro-ph/9709072]

  49. [49]

    Escriv` a and A.E

    A. Escriv` a and A.E. Romano,Effects of the shape of curvature peaks on the size of primordial black holes,JCAP05(2021) 066 [2103.03867]

  50. [50]

    Escriv` a,Simulation of primordial black hole formation using pseudo-spectral methods, Phys

    A. Escriv` a,Simulation of primordial black hole formation using pseudo-spectral methods, Phys. Dark Univ.27(2020) 100466 [1907.13065]. – 22 –

  51. [51]

    Escriv` a, C

    A. Escriv` a, C. Germani and R.K. Sheth,Analytical thresholds for black hole formation in general cosmological backgrounds,JCAP01(2021) 030 [2007.05564]

  52. [52]

    Escriv` a, Universe8, 66 (2022),2111.12693

    A. Escriv` a,PBH Formation from Spherically Symmetric Hydrodynamical Perturbations: A Review,Universe8(2022) 66 [2111.12693]

  53. [53]

    A new approach to the evolution of cosmological perturbations on large scales

    D. Wands, K.A. Malik, D.H. Lyth and A.R. Liddle,A New approach to the evolution of cosmological perturbations on large scales,Phys. Rev. D62(2000) 043527 [astro-ph/0003278]

  54. [54]

    Threshold of primordial black hole formation

    T. Harada, C.-M. Yoo and K. Kohri,Threshold of primordial black hole formation,Phys. Rev. D88(2013) 084051 [1309.4201]

  55. [55]

    Ajith et al., A Template bank for gravitational wave- forms from coalescing binary black holes

    P. Ajith et al.,A Template bank for gravitational waveforms from coalescing binary black holes. I. Non-spinning binaries,Phys. Rev. D77(2008) 104017 [0710.2335]

  56. [56]

    Ajith et al., Inspiral-merger-ringdown waveforms for black-hole binaries with non-precessing spins, Phys

    P. Ajith et al.,Inspiral-merger-ringdown waveforms for black-hole binaries with non-precessing spins,Phys. Rev. Lett.106(2011) 241101 [0909.2867]

  57. [57]

    Raidal, C

    M. Raidal, C. Spethmann, V. Vaskonen and H. Veerm¨ ae,Formation and Evolution of Primordial Black Hole Binaries in the Early Universe,JCAP02(2019) 018 [1812.01930]

  58. [58]

    Liu, Z.-K

    L. Liu, Z.-K. Guo and R.-G. Cai,Effects of the surrounding primordial black holes on the merger rate of primordial black hole binaries,Phys. Rev. D99(2019) 063523 [1812.05376]

  59. [59]

    Vaskonen and H

    V. Vaskonen and H. Veerm¨ ae,Lower bound on the primordial black hole merger rate,Phys. Rev. D101(2020) 043015 [1908.09752]

  60. [60]

    H¨ utsi, M

    G. H¨ utsi, M. Raidal, V. Vaskonen and H. Veerm¨ ae,Two populations of LIGO-Virgo black holes,JCAP03(2021) 068 [2012.02786]

  61. [61]

    TASI Lectures on Inflation

    D. Baumann,Inflation, inTheoretical Advanced Study Institute in Elementary Particle Physics: Physics of the Large and the Small, pp. 523–686, 2011, DOI [0907.5424]

  62. [62]

    R.-g. Cai, S. Pi and M. Sasaki,Gravitational Waves Induced by non-Gaussian Scalar Perturbations,Phys. Rev. Lett.122(2019) 201101 [1810.11000]

  63. [63]

    Sensitivity curves for searches for gravitational-wave backgrounds

    E. Thrane and J.D. Romano,Sensitivity curves for searches for gravitational-wave backgrounds,Phys. Rev. D88(2013) 124032 [1310.5300]

  64. [64]

    Science with the space-based interferometer eLISA. II: Gravitational waves from cosmological phase transitions

    C. Caprini et al.,Science with the space-based interferometer eLISA. II: Gravitational waves from cosmological phase transitions,JCAP04(2016) 001 [1512.06239]

  65. [65]

    Schmitz, JHEP01, 097 (2021), arXiv:2002.04615 [hep-ph]

    K. Schmitz,New Sensitivity Curves for Gravitational-Wave Signals from Cosmological Phase Transitions,JHEP01(2021) 097 [2002.04615]

  66. [66]

    Gowling and M

    C. Gowling and M. Hindmarsh,Observational prospects for phase transitions at LISA: Fisher matrix analysis,JCAP10(2021) 039 [2106.05984]

  67. [67]

    Dodelson,Modern Cosmology, Academic Press, Amsterdam (2003)

    S. Dodelson,Modern Cosmology, Academic Press, Amsterdam (2003)

  68. [68]

    Primordial black holes: constraints, potential evidence and prospects,

    B. Carr, A.J. Iovino, G. Perna, V. Vaskonen and H. Veerm¨ ae,Primordial black holes: constraints, potential evidence and prospects,2601.06024

  69. [69]

    Oncins,Constraints on PBH as dark matter from observations: a review,2205.14722

    M. Oncins,Constraints on PBH as dark matter from observations: a review,2205.14722

  70. [70]

    B. Carr, F. Kuhnel and M. Sandstad,Primordial Black Holes as Dark Matter,Phys. Rev. D 94(2016) 083504 [1607.06077]. – 23 –

  71. [71]

    Constraints on Earth-mass primordial black holes from OGLE 5-year microlensing events

    H. Niikura, M. Takada, S. Yokoyama, T. Sumi and S. Masaki,Constraints on Earth-mass primordial black holes from OGLE 5-year microlensing events,Phys. Rev. D99(2019) 083503 [1901.07120]

  72. [72]

    Microlensing constraints on primordial black holes with the Subaru/HSC Andromeda observation

    H. Niikura et al.,Microlensing constraints on primordial black holes with Subaru/HSC Andromeda observations,Nature Astron.3(2019) 524 [1701.02151]

  73. [73]

    Mr´ oz et al.,No massive black holes in the Milky Way halo,Nature632(2024) 749 [2403.02386]

    P. Mr´ oz et al.,No massive black holes in the Milky Way halo,Nature632(2024) 749 [2403.02386]

  74. [74]

    Nitz and Y.-F

    A.H. Nitz and Y.-F. Wang,Search for Gravitational Waves from the Coalescence of Subsolar-Mass Binaries in the First Half of Advanced LIGO and Virgo’s Third Observing Run,Phys. Rev. Lett.127(2021) 151101 [2106.08979]

  75. [75]

    Black Holes' Dark Dress: On the merger rate of a subdominant population of primordial black holes

    B.J. Kavanagh, D. Gaggero and G. Bertone,Merger rate of a subdominant population of primordial black holes,Phys. Rev. D98(2018) 023536 [1805.09034]. [88]Planckcollaboration,Planck 2018 results. VI. Cosmological parameters,Astron. Astrophys. 641(2020) A6 [1807.06209]. [89]H0DNcollaboration,The Local Distance Network: a community consensus report on the mea...

  76. [76]

    B.J. Carr, K. Kohri, Y. Sendouda and J. Yokoyama,New cosmological constraints on primordial black holes,Phys. Rev. D81(2010) 104019 [0912.5297]. – 24 –