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Computations of primordial black hole formation

General Relativity and Quantum Cosmology · Submitted 13 Dec 2004 · 47 references

Pith's verdict: A careful, well-designed numerical study that lowers the PBH threshold to δc ≈ 0.43–0.47 for growing-mode initial data; the new number is plausible and independently consistent, but the initial-data prescription behind it is asserted rather than checked.

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arXiv IDgr-qc/0412063 (version 2)
Pith IDEQ5ZO2PG, Pith's permanent record of this paper and its review
Citation2), 3); ((1) SISSA, England; (3) Department of Physics, Ilia Musco (1), INFN, International School for Advanced Studies, Italy; (2) Department of Physics (Astrophysics), John C. Miller (1, Louisiana State University, Luciano Rezzolla (1, University of Oxford, USA). "Computations of primordial black hole formation." arXiv:gr-qc/0412063 (2004). https://pith.science/paper/EQ5ZO2PG
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Referee report
The paper

The paper claims

The threshold for primordial black hole formation falls to about 0.45 when perturbations begin as pure growing modes.

The reading

The paper asks how large a density perturbation in the radiation-dominated early universe must be for it to collapse into a primordial black hole. Its central move is to start from a pure growing-mode perturbation while it is still larger than the horizon, rather than from data imposed at horizon crossing, and then follow the collapse numerically. The authors find that the threshold fractional mass excess drops from about $0.67$–$0.71$ in earlier work to about $0.43$ for a Mexican-hat profile and $0.47$ for a polynomial profile, while the power-law slope of the black-hole mass with distance above threshold stays near $0.36$–$0.37$. That matters because a lower threshold means more perturbations of a given amplitude make black holes, so abundance estimates tied to the older number need revisiting.

What carries the argument

The load-bearing machinery is a two-stage numerical scheme built around the initial-data choice. A super-horizon linear growing mode is specified with density perturbation $��e$ and velocity perturbation $��u = -��e/4$, then evolved with the Misner-Sharp cosmic-time equations until a null slice can be constructed; the collapse is continued with a Hernandez-Misner outgoing-null-slice code, where the lapse $f$ is fixed to unity at the outer FRW observer and evolved inward using $D_k[(��+U)/f] = -4��R(e+p)f$. The null slicing keeps singularity formation from halting the computation, and the paper reports that this alternative $f$ equation, rather than the more direct equation (24), is what preserves the synchronization $D_kR �� 0$ as $f �� 0$.

Extended reading notes

Core claim

The paper's central claim is that the threshold amplitude for primordial black-hole formation is substantially lower than previously reported when the initial perturbation is a pure growing mode. For Mexican-hat perturbations the critical fractional mass excess is $��_c �� 0.43$, and for polynomial perturbations $��_c �� 0.47$, compared with $��_c �� 0.67$ and $0.71$ obtained with horizon-crossing initial data. The authors explain the shift by noting that the earlier initial data contained a decaying-mode component which rapidly disappeared, so the effective growing-mode amplitude available for collapse was smaller than the nominal $��$. The scaling law $M_{��m BH} = K(��-��_c)^�� M_H(t_H)$ survives with $�� �� 0.36$–$0.37$, and adding a positive cosmological constant raises $��_c$ linearly while lowering $��$. For sub-critical perturbations close to threshold, the collapse rebounds, drives strong compression and rarefaction waves, and can produce a second, more violent bounce.

Load-bearing premise

The revised threshold depends on the assumption that a super-horizon perturbation from inflation is well represented by the linear growing mode with velocity perturbation $��u = -��e/4$; if that prescription misstates the actual perturbation, the lower $��_c$ is an artifact of the setup.

Editorial extensions

If this is right

  • For a fixed inflationary perturbation spectrum, using $��_c �� 0.43$–$0.47$ instead of $0.67$–$0.71$ raises the predicted number of primordial black holes, because more perturbations cross the collapse threshold.
  • The mass scaling $M_{��m BH} \propto (��-��_c)^��$ with $�� �� 0.36$–$0.37$ survives the change in initial data, so near-threshold black-hole masses are controlled mainly by $��-��_c$ rather than by the initial-data convention.
  • A positive cosmological constant makes collapse harder: it shifts $��_c$ upward by about $0.98\,y$ and lowers $��$ by about $8.3\,y$ for small vacuum-energy fraction $y$.
  • Near-threshold sub-critical perturbations do not fade quietly; they generate strong compression waves and a second, more violent bounce, so the surrounding medium can be dynamically disturbed even when no black hole forms.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If a decaying-mode component can inflate the apparent $��_c$ by roughly 0.2, then threshold values quoted across the literature are not directly comparable unless the initial-data slicing and mode content are specified.
  • The shift from $0.67$ to $0.43$ is large enough that primordial-black-hole abundance constraints on the inflationary spectral index should be recomputed with the lower threshold; a constraint derived with the older value may be too conservative.
  • The linear $��$ corrections suggest a possible consistency check: any measured primordial-black-hole abundance that requires a nonzero vacuum-energy fraction would also require a correlated change in the scaling exponent, not just in the threshold.
  • The second-bounce compression waves in near-critical sub-critical cases may be a source of secondary perturbations or gravitational radiation; simulating them with a shock-capturing code would test whether they leave an observable imprint.
Original abstract

Results are presented from general relativistic numerical computations of primordial black-hole formation during the radiation-dominated era of the universe. Growing-mode perturbations are specified within the linear regime and their subsequent evolution is followed as they become nonlinear. We use a spherically symmetric Lagrangian code and study both super-critical perturbations, which go on to produce black holes, and sub-critical perturbations, for which the overdensity eventually disperses into the background medium. For super-critical perturbations, we confirm the results of previous work concerning scaling-laws but note that the threshold amplitude for a perturbation to lead to black-hole formation is substantially reduced when the initial conditions are taken to represent purely growing modes. For sub-critical cases, where an initial collapse is followed by a subsequent re-expansion, strong compressions and rarefactions are seen for perturbation amplitudes near to the threshold. We have also investigated the effect of including a significant component of vacuum energy and have calculated the resulting changes in the threshold and in the slope of the scaling law.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 5,060 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.30 · human participants 0.01 · controlled comparison 0.16 · randomized assignment 0.01 · states quantitative result 0.12 · compares with prior results 0.95 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

Results are presented from general relativistic numerical computations of primordial black-hole formation during the radiation-dominated era of the universe. Growing-mode perturbations are specified within the linear regime and their subsequent evolution is followed as they become nonlinear. We use a spherically symmetric Lagrangian code and study both super-critical perturbations, which go on to produce black holes, and sub-critical perturbations, for which the overdensity eventually disperses into the background medium. For super-critical perturbations, we confirm the results of previous work concerning scaling-laws but note that the threshold amplitude for a perturbation to lead to black-hole formation is substantially reduced when the initial conditions are taken to represent purely growing modes. For sub-critical cases, where an initial collapse is followed by a subsequent re-expansion, strong compressions and rarefactions are seen for perturbation amplitudes near to the threshold. We have also investigated the effect of including a significant component of vacuum energy and have calculated the resulting changes in the threshold and in the slope of the scaling law.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 Results are presented from general relativistic numerical computations of primordial black-hole formation during the radiation-dominated era of the universe. contribution 0.97 0.92 0.07 asserted 0.99
s1 Growing-mode perturbations are specified within the linear regime and their subsequent evolution is followed as they become nonlinear. method 0.99 0.85 0.04 asserted 0.95
s2 We use a spherically symmetric Lagrangian code and study both super-critical perturbations, which go on to produce black holes, and sub-critical perturbations, for which the overdensity eventually disperses into the background medium. method 0.89 0.95 0.08 asserted 0.97
s3 For super-critical perturbations, we confirm the results of previous work concerning scaling-laws but note that the threshold amplitude for a perturbation to lead to black-hole formation is substantially reduced when the initial conditions are taken to represent purely growing modes. result 1.00 0.88 0.44 asserted 1.00
s4 For sub-critical cases, where an initial collapse is followed by a subsequent re-expansion, strong compressions and rarefactions are seen for perturbation amplitudes near to the threshold. result 1.00 0.93 0.05 asserted 1.00
s5 We have also investigated the effect of including a significant component of vacuum energy and have calculated the resulting changes in the threshold and in the slope of the scaling law. contribution 0.54 0.97 0.13 asserted 1.00

What kind of paper the classifier reports this is: simulation study 1.00 · evidence from simulation or computation 1.00.

What was examined, and what was not

sources read
  • arXiv listing abstract v2
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. Scaling behaviour for MBH as a function of (δ − δc) calculated for growing-mode Mexican-hat perturbations specified within the linear regime. The filled circles refer to the standard calculation discussed in section 3.2, while the open circles are for a calculation including a non-zero cosmological constant Λ, as discussed in section 3.3, giving y = 3.0 × 10−3 . Following these initial calculations to reproduce previous results, we then carried out further ones starting from growing-mode perturbations specified within the linear regime and with length-scales larger than the…
Figure 2. A typical evolution leading to black hole formation: the initial perturbation had a Mexican-hat profile and gave (δ − δc) = 2.37 × 10−3 at the horizon crossing time. The top left-hand panel shows the behaviour of the lapse function (the time sequence of the curves goes from bottom to top on the right hand side); the top right-hand panel shows the fluid-element worldlines (the time is measured in units of the horizon-crossing time tH). The bottom left-hand panel shows the profile of 2M/R at different times, with the inset showing the approach of the maximum value of 2M/R → 1; the bott
Figure 3. Worldlines for a Mexican-hat perturbation with (δ − δc) = −3.0 × 10−3 ). This plot shows alternating collapse and expansion of the perturbed region while the outer material continues to expand uniformly. The “cosmic” time is measured in units of the time at horizon crossing. the outer matter until eventually it starts to re-contract shortly after horizon crossing. The maximum infall velocity reached is, however, rather small [see row (a) of
Figure 4. Plots of local quantities as functions of R/RH(tH): the velocity U/c is shown in the left-hand column and the energy density e/eb in the right-hand column. The frames correspond to the following values of (t − t0)/tH: (a) 7.02; (b) 25.92, (c) 31.67; (d) 33.64; (e) 40.11 . Note that RH is increasing with time and so points with R/RH(tH) > 1 can be within the current horizon scale at times after horizon-crossing
Figure 5. Evolution of the energy density e and radial velocity U at three (comoving) locations: near to the centre of the perturbation, at an intermediate region and at the edge of the grid where the fluid is unperturbed. Each quantity is measured in units of its initial value at the same comoving location

Figures reproduced from arXiv:gr-qc/0412063 by the authors.

References
How the literature uses it

158 arXiv papers cite this in 216 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 128 sentences without a confident label

Uses its method or tool 7 papers
Uses its data or values 38 papers
  • The mass of the resulting PBH depends on the horizon mass and the amplitude of the density perturbation $δ$ defined in the comoving gauge from which it formed, and is given by [ref] [equation] where $$ is the horizon mass at the time of horizon re-entry, and during radiation domination the constants have been numerically found to be given by $k=3.3, γ=0.36, δ_c=0.453$ (the values depend upon the radial profile of the perturbations being considered; we use the values given here in order to be concrete).

    Primordial black holes with an accurate QCD equation of state · Extended mass function of primordial black hole formation · 0.91

  • where $t_PBH$ is the time of production of the PBH, which can be obtained when the density contrast between inside and outside of the Hubble volume exceeds the critical value $δ_c=0.45$ [ref] .

    Primordial black holes as a probe of strongly first-order electroweak phase transition · PBH and GW productions from first-order phase transition · 0.86

  • We use $δ_c ≃0.42$ [ref] (see also Refs. [ref] ), $k=3.3$ [ref] and $γ=0.36$ [ref] .

    Primordial Black Holes from Thermal Inflation · Primordial black holes · 1.00

Compares with it 1 paper
Cites it as support 2 papers
Cites it as background 37 papers

Discussion

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