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Nonlinear evolution of cosmological power spectra

Astrophysics · Submitted 8 Mar 1996 · 1 reference

Pith's verdict: The spectrum-dependent HKLM fit is the real deliverable and it holds up; the one untested claim is that the factor-2 index shift in Eq. (22) doesn't matter, which is asserted exactly where the (1+n/3) exponents bite hardest.

T0 · AI review

How this review was made: An AI referee (selfhosted/deepseek-v4.1-flash) read the paper on November 13, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

  1. T0 AI review An AI read the paper and answered a fixed list of questions.
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  3. T2 Compute The paper's code or calculations re-run with the same results.
  4. T3 Formal statement The claims written out in a formal math language a computer can read.
  5. T4 Proof Those claims proved, and the proof checked by computer.

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arXiv IDastro-ph/9603031 (version 1)
Pith ID7GKDVI7B, Pith's permanent record of this paper and its review
CitationEdinburgh), J.A. Peacock, S.J. Dodds (Royal Observatory. "Nonlinear evolution of cosmological power spectra." arXiv:astro-ph/9603031 (1996). https://pith.science/paper/7GKDVI7B
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Claim paper

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Referee report
The paper

The paper claims

A single closed-form recipe, with one slope-dependent correction and one growth factor, converts a linear density power spectrum into its nonlinear counterpart across open, flat, and cosmological-constant universes.

The reading

The paper asks whether one closed-form rule can carry a linear density power spectrum into the nonlinear regime across the cosmologies people actually consider — open low-density universes and flat universes with a cosmological constant, not just the Einstein–de Sitter case. The earlier scaling ansatz of Hamilton and collaborators worked well near spectral index $-1$ but was known to fail for steeper, more negative indices, which is exactly where cold dark matter spectra spend their small scales. The authors run a library of N-body simulations covering $-2

What carries the argument

The carrying object is the generalized Hamilton–Kumar–Lu–Matthews mapping: nonlinear power at wavenumber $k_{NL}$ is read off linear power at a shifted, smaller wavenumber $k_L=[1+2_{NL}(k_{NL})]^{-1/3}k_{NL}$, and the two are related by a fitting function with a linear-growth term, a quasilinear power law, and a virialized $x^{3/2}$ asymptote, softened by a parameter $1$. The new ingredient is that the quasilinear coefficients $A$, $B$, $1$, $1$, $V$ are not constants but scale with $(1+n/3)$ raised to fitted powers, with $n$ taken from the tangent slope of the linear spectrum at $k_L/2$ — a factor-of-two shift the authors adopt because using the unshifted slope left the CDM results systematically below the power-law fits. The $g^3$ denominator on the virialized term is the only place the cosmological model appears.

Extended reading notes

Core claim

The central claim is that the nonlinear-to-linear mapping $f_{NL}$ is not universal, but is well described by a five-parameter family whose coefficients are simple power laws in $(1+n/3)$, where $n$ is the tangent spectral index of the linear spectrum evaluated at half the linear wavenumber: $n_L(k_L) 1 d1$ at $k=k_L/2$. Fitted globally to power-law and CDM simulations, this gives about 14 per cent rms in $f_{NL}(x)$ over $0.1<2.5$ in $1$, and about 7 per cent scatter in the direction that governs reconstructing a spectrum from nonlinear data. The cosmological dependence — open versus flat-with-$1$, and the value of $1$ — is carried entirely by the $g^3(1)$ factor that sets the amplitude of the stable-clustering asymptote $f_{NL}(x)1$. The qualitative result is that nonlinear effects boost small-scale power more strongly for more negative spectral indices and for lower densities, but that a cosmological constant softens the boost relative to an open universe of the same $1$.

Load-bearing premise

The load-bearing premise is that the tangent spectral index should be read at half the linear wavenumber being predicted; the paper asserts that the exact size of this shift is not critical, but never shows a sensitivity scan, and the whole cold-dark-matter branch of the fit depends on it.

Editorial extensions

If this is right

  • Linearizing an observed nonlinear clustering spectrum to recover the underlying linear spectrum becomes a numerical iteration using a single formula, rather than a separate simulation campaign for each cosmology.
  • The earlier conclusion that small-scale clustering data imply a linear spectral index near $-1.5$ survives: in the regime those data actually covered ($2_{NL}1$), the deduced linear power shifts by at most about 20 per cent.
  • Because the quasilinear slope $f_{NL}1$ with $1$–$4.5$ is steeper than the stable-clustering answer, the predicted growth of nonlinear power with time is faster than linear growth, which bears on the weak angular clustering of faint galaxies.
  • An observed nonlinear slope of about 1.8 would imply a linear index near $-2.2$ through the paper's relation between $1$ and $n$, rather than the $n=0$ that stable clustering alone would suggest.
  • The method is proposed as general for any convex hierarchical spectrum, with hot or warm dark matter cutoffs explicitly excluded as needing separate treatment.

Reading between the lines

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

  • The finding that cosmology enters only through $g(1)$ is close to a statement that quasilinear evolution is Zeldovich-like: if final positions are initial displacements scaled by a universal factor, then matching displacement amplitude should erase the cosmology. That suggests the residual cosmological dependence could be computed analytically from the known Zeldovich power spectrum rather than fi
  • Reading the tangent index at a smaller scale than the one being predicted makes the mapping implicitly non-local in $k$. A spectrum with a sharp feature — a baryon oscillation, a mild cutoff — would then be mispredicted in a way a smooth CDM spectrum conceals, which is a testable weakness rather than a defect of the present fit.
  • The steep quasilinear slope offers a growth-rate probe: measuring the nonlinear slope at a fixed nonlinear amplitude across two epochs constrains the growth factor more sharply than linear growth alone, and this is checkable against existing simulations at earlier output times.
  • The calibration used boxes of $100\,h^{-1}$ Mpc with final $1$ in the range 0.4–1, so applying the formula to very high normalizations or to much smaller boxes is an extrapolation the paper does not test.
Original abstract

Hamilton et al. have suggested an invaluable scaling formula which describes how the power spectra of density fluctuations evolve into the nonlinear regime of hierarchical clustering. This paper presents an extension of their method to low-density universes and universes with nonzero cosmological constant. We pay particular attention to models with large negative spectral indices, and give a spectrum-dependent fitting formula which is of significantly improved accuracy by comparison with an earlier version of this work. The tendency of nonlinear effects to increase power on small scales is stronger for spectra with more negative spectral indices, and for lower densities. However, for low-density models with a cosmological constant, the nonlinear effects are less strong than for an open universe of the same $\Omega$.

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, 4,234 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.05 · states limitation 0.26 · human participants 0.01 · controlled comparison 0.32 · randomized assignment 0.01 · states quantitative result 0.09 · compares with prior results 0.95 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

Hamilton et al. have suggested an invaluable scaling formula which describes how the power spectra of density fluctuations evolve into the nonlinear regime of hierarchical clustering. This paper presents an extension of their method to low-density universes and universes with nonzero cosmological constant. We pay particular attention to models with large negative spectral indices, and give a spectrum-dependent fitting formula which is of significantly improved accuracy by comparison with an earlier version of this work. The tendency of nonlinear effects to increase power on small scales is stronger for spectra with more negative spectral indices, and for lower densities. However, for low-density models with a cosmological constant, the nonlinear effects are less strong than for an open universe of the same $\Omega$.

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 Hamilton et al. have suggested an invaluable scaling formula which describes how the power spectra of density fluctuations evolve into the nonlinear regime of hierarchical clustering. background 1.00 0.03 0.03 asserted 0.67
s1 This paper presents an extension of their method to low-density universes and universes with nonzero cosmological constant. contribution 1.00 0.86 0.07 asserted 0.98
s2 We pay particular attention to models with large negative spectral indices, and give a spectrum-dependent fitting formula which is of significantly improved accuracy by comparison with an earlier version of this work. contribution 0.95 0.94 0.15 asserted 1.00
s3 The tendency of nonlinear effects to increase power on small scales is stronger for spectra with more negative spectral indices, and for lower densities. result 0.99 0.83 0.35 asserted 1.00
s4 However, for low-density models with a cosmological constant, the nonlinear effects are less strong than for an open universe of the same $\Omega$. result 1.00 0.84 0.14 asserted 1.00

What kind of paper the classifier reports this is: method or tool 0.72 · evidence from simulation or computation 0.82.

What was examined, and what was not

sources read
  • arXiv listing abstract v1
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. The generalized HKLM function relating nonlinear power to linear power, for an Ω = 1 Einstein-de Sitter universe and power-law spectra with n = 0, −1, −1.5, −2. The solid lines show the fitting formula of Section 3.3. For spectra with n >∼ −1, the function shows very little spectral dependence. For flatter spectra, the nonlinear power at a given linear power is higher; in particular the slope of the quasilinear portion around ∆2 NL ∼ 10 increases as n decreases, from approximately fNL(x) ∝ x 3 for n = 0 to fNL(x) ∝ x 4 for n = −2. This contains 5 free parameters, each of which i
Figure 2. The generalized HKLM function relating nonlinear power to linear power, for Ωm = 1 & 0.2 and zero vacuum energy. (a) an n = 0 spectrum; (b) n = −1.5. The solid lines show the fitting formula of Section 3.3. As Ω decreases, the nonlinear power increases and the quasilinear portion steepens. However, these changes are largely associated with the increase of fNL in the virialized regime with ∆2 NL >∼ 100. via the power-law model corresponding to neff at the non￾linear scale. However, it seemed to us that the whole phi￾losophy of the HKLM method is that the nonlinear power at kNL…
Figure 5. The present fitting formula for the nonlinear function (solid lines) compared with the spectrum-independent form sug￾gested by PD (dashed lines), for the cases n = −1 & −1.5 and open models with Ωm = 1, 0.5, 0.2. The PD formula was an ap￾proximation to the average effect of these different spectra, but the detailed agreement is often poor, particularly at low Ω for flatter spectra. However, these deviations are small in the regime of the data used by PD (∆2 NL <∼ 3). than the power spectrum. It is probably best to proceed nu￾merically with the forward nonlinear function as a…

Showing 3 of the paper's 5 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:astro-ph/9603031 by the authors.

References
How later papers used it

46 later papers cite it

Evidence: substantial. 46 of the citing papers share no author with it, and 12 of those carry a confident label from Pith's citation classifier.

Pith read 22 of the 56 citing sentences, choosing only those whose citation markers point at this paper alone, and wrote the paraphrases from them. The summary, the counts, the evidence level, the links and the quotes come from code; the summary counts the papers listed below. A later paper is listed under a label when Pith's citation classifier gives one of its sentences that label at probability 0.8 or more (0.95 for support), Pith's reading finds that the citing paper itself did it, and a second check confirms the paraphrase against the sentence. This section lists uses only. It does not list criticism or disagreement, so their absence here says nothing about how the paper has been received. Papers that share an author with this one are listed apart, under "By the same authors". A quote is the citing authors' own sentence, shown when their paper's licence is CC BY, CC BY-SA or CC0. JSON

Uses its method or tool 3 of 7 papers with this label
Compares with it 1 of 3 papers with this label
How the literature uses it

37 arXiv papers cite this in 47 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 · 28 sentences without a confident label

Contests it 2 papers
Uses its method or tool 7 papers
  • Here we take into account the effect of uncorrelated large scale structure projected along the line of sight on the error covariance matrix $C^lss_ij$ as $C=C^stat+C^lss$, where $C^lss$ is given as [ref] [equation] Here $C^κκ(l)$ is the weak-lensing power spectrum as a function of angular multipole $l$ evaluated for a given source population and a cosmology, and $Ĵ_0(lθ_i)$ is the Bessel function of the first kind and order zero averaged over the $i$th annulus between $θ_i,1$ and $θ_i,2 (>θ_i,1)$, given as [equation] We will assume the concordance $Λ$CDM cosmological model of [ref] and use the fitting formula of [ref] to compute the nonlinear mass power spectrum that enters in equation ([ref]).

    A Precise Cluster Mass Profile Averaged from the Highest-Quality Lensing Data · Combining Weak and Strong Lensing · 0.98

  • There are two approaches to compute the $P_δ^NL(k,z)$ that have been extensively tested and used in the literature: the more recent Halofit [ref] model, which is included in CAMB [ref] and the Peacock and Dodds (PD) [ref] method (generalized for dark energy cosmologies by [ref] ).

    Non-Gaussianity and the CMB Bispectrum: confusion between Primordial and Lensing-Rees Sciama contribution? · Bispectrum calculation and expected signal-to-noise · 0.97

  • We demonstrate that by integrating the mapping approach recommended in [ref] , it is feasible to derive a concise expression for the nonlinear power spectrum based on its linear counterpart and several critical cosmological parameters.

    $\texttt{SPINE}$: Symbolic Models to Predict the Evolution of the $\Lambda$CDM Nonlinear Power Spectrum · Introduction · 0.92

Compares with it 3 papers
Cites it as background 6 papers

Discussion

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