REVIEW
Memory of Initial Conditions in Gravitational Clustering
Astrophysics · Submitted 15 Sep 2005 · 14 references
Pith's verdict: The propagator formula in Eq. (41) is the durable contribution here — parameter-free, tested against simulations, and the finite-volume analysis in Section IV D is a genuine second result rather than an afterthought.
T0 · AI review
Why Pith says this
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Referee report
The paper
The paper claims
Gravity gradually erases the memory of the early universe, and this paper gives a parameter-free formula for how fast it does so, scale by scale and epoch by epoch.
The reading
What carries the argument
The load-bearing object is the nonlinear propagator itself, $G_{ab}(k,eta) delta_D(k-k') = <delta Psi_a(k,eta)/delta phi_b(k')>$, a two-point Green's function that measures how much of a final Fourier mode still traces its initial value. The machinery that carries the argument is a diagrammatic expansion in which the initial power spectrum, the mode-coupling vertex and the linear propagator are the three ingredients, combined with a resummation of the 'principal-path' diagrams — the trees where the main line interacts only with modes arriving straight from the initial conditions. In the large-$k$ limit the vertex matrix becomes proportional to the identity, $bar gamma_{ab} approx (1/2) k q_n x_n delta_{ab}$, which lets the $2n$ time integrals and $(2n-1)!!$ pairings collapse into a single exponential. The final step is an interpolation ansatz: write the one-loop result as a sum of a growing and a decaying term, both negative, and exponentiate each, which is claimed to be the only grouping consistent with the required asymptotics at large $a$ and large $k$.
Extended reading notes
Core claim
The central claim is that the nonlinear propagator $G_{ab}(k,a)$, defined as the ensemble-averaged functional derivative of the final density or velocity-divergence field with respect to the initial field, is the right bookkeeping device for the survival of initial conditions, and that it can be computed in closed form. The authors show that for Gaussian initial conditions $G_{ab}$ is proportional to the cross-correlation coefficient between initial and final states with the dependence on the final power spectrum divided out, which removes a known ambiguity in that coefficient. They then resum the subset of diagrams in which every interaction lies along the principal path, prove that in the large-$k$ limit each such vertex preserves the growing mode so the series sums to a Gaussian, $G_{ab}=g_{ab}(a)e^{-k^2 sigma_v^2 (a-1)^2/2}$, and interpolate to all $k$ by grouping the one-loop correction into growing and decaying pieces and exponentiating them, Eq. (41). The resulting expression, with $a$ replaced by the linear growth factor $D_+$, reproduces measurements in a $479 h^{-1}$ Mpc simulation across three redshifts without tuning. A corollary the authors emphasise is that the decay scales $k_delta = sqrt(105/61), sigma_v^{-1}$ and $k_theta = sqrt(5/9), sigma_v^{-1}$ define the nonlinear scale far better than the usual criterion $4pi k_{nl}^3 P_L(k_{nl})=1$, which at high redshift can be off by more than an order of magnitude.
Load-bearing premise
The calculation assumes that the diagrams where every interaction sits along the principal path dominate the propagator at all wavenumbers, not only in the large-$k$ limit, and the authors say outright that they could not sum the remaining diagrams to show this.
Editorial extensions
If this is right
- The nonlinear power spectrum in renormalized perturbation theory can now be computed, since the propagator is the ingredient that was missing from the mode-coupling series.
- Baryon acoustic oscillations should be damped by a factor near $e^{-1/2} approx 0.6$ over a smooth component at the scale $k_delta(z)$, giving a concrete estimate of where the wiggles survive.
- High-redshift surveys should use $k_delta$ and $k_theta$ rather than $4pi k_{nl}^3 P_L = 1$ to decide which scales are still in the linear regime, since the standard criterion underestimates nonlinearity badly at large $z$.
- Simulations built to study the high-redshift universe need boxes of roughly $240 h^{-1}$ Mpc to get the propagator decay scale right to ten percent, independent of redshift.
- Finite-volume simulations suppress the propagator decay while also suppressing mode-coupling power, and the two errors cancel in the total power spectrum but not in its dependence on cosmological parameters, since their ratio tracks the linear spectrum.
Reading between the lines
- If the propagator is really the cleanest clock of memory loss, then the same exponential form should describe the damping of any small perturbation imprinted in the initial conditions, including non-Gaussianity shapes, so the damping factor could be measured once and applied to several observables.
- The finite-volume bias identified here is a systematic that grows with the steepness of the spectrum, which suggests that small-box simulations of steep, high-redshift spectra are the most exposed, and that a box-size convergence test on the propagator is a cheap diagnostic for any simulation campaign.
- Because the resummation rests on the dominance of principal-path diagrams, the intermediate-$k$ regime between one-loop and the Gaussian tail is where a numerical diagram-by-diagram summation would be most informative; a direct comparison of the omitted two-loop classes against Eq. (41) would turn the authors' stated inability to prove dominance into a quantitative error bar.
- The same functional-derivative definition applied to the velocity field suggests a joint density-velocity propagator matrix whose off-diagonal entries test whether velocities decohere faster than densities, which the paper's Fig. 5 hints at but does not exploit.
Original abstract
We study the nonlinear propagator, a key ingredient in renormalized perturbation theory (RPT) that allows a well-controlled extension of perturbation theory into the nonlinear regime. We show that it can be thought as measuring the memory of density and velocity fields to their initial conditions. This provides a clean definition of the validity of linear theory, which is shown to be much more restricted than usually recognized in the literature. We calculate the nonlinear propagator in RPT and compare to measurements in numerical simulations, showing remarkable agreement well into the nonlinear regime. We also show that N-body simulations require a rather large volume to recover the correct propagator, due to the missing large-scale modes. Our results for the nonlinear propagator provide an essential element to compute the nonlinear power spectrum in RPT.
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.
The abstract, sentence by sentence
We study the nonlinear propagator, a key ingredient in renormalized perturbation theory (RPT) that allows a well-controlled extension of perturbation theory into the nonlinear regime. We show that it can be thought as measuring the memory of density and velocity fields to their initial conditions. This provides a clean definition of the validity of linear theory, which is shown to be much more restricted than usually recognized in the literature. We calculate the nonlinear propagator in RPT and compare to measurements in numerical simulations, showing remarkable agreement well into the nonlinear regime. We also show that N-body simulations require a rather large volume to recover the correct propagator, due to the missing large-scale modes. Our results for the nonlinear propagator provide an essential element to compute the nonlinear power spectrum in RPT.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We study the nonlinear propagator, a key ingredient in renormalized perturbation theory (RPT) that allows a well-controlled extension of perturbation theory into the nonlinear regime. | contribution 0.66 | 0.53 | 0.07 | asserted 0.99 |
| s1 | We show that it can be thought as measuring the memory of density and velocity fields to their initial conditions. | interpretation 0.96 | 0.86 | 0.23 | asserted 0.92 |
| s2 | This provides a clean definition of the validity of linear theory, which is shown to be much more restricted than usually recognized in the literature. | interpretation 0.76 | 0.83 | 0.30 | asserted 1.00 |
| s3 | We calculate the nonlinear propagator in RPT and compare to measurements in numerical simulations, showing remarkable agreement well into the nonlinear regime. | result 0.92 | 0.96 | 0.21 | asserted 1.00 |
| s4 | We also show that N-body simulations require a rather large volume to recover the correct propagator, due to the missing large-scale modes. | result 0.85 | 0.88 | 0.06 | asserted 1.00 |
| s5 | Our results for the nonlinear propagator provide an essential element to compute the nonlinear power spectrum in RPT. | interpretation 0.71 | 0.87 | 0.17 | asserted 1.00 |
What was examined, and what was not
- arXiv listing abstract v2
- full text
- figures and tables
- references and citing sentences
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- P abstract
- S sections
- T body sentences
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- R cross-paper relations
Figures
Figures reproduced from arXiv:astro-ph/0509419 by the authors.
References
How later papers used it
106 later papers cite it
3 later papers by other authors are listed below: 3 used its method or tool.
Uses its method or tool 3 of 20 papers with this label
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Computed its k-star following this paper and another work in its approximation of the nonlinear damping of the wiggled part in redshift space.
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: single-probe measurements from CMASS anisotropic galaxy clustering (2013) · 1.00 · paraphrased: the licence does not allow quoting
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The matter power spectra are denoised on large scales based on a treatment updated from the one described in [ref] using the propagator method based on perturbation theory [ref] .
Exploring the baryonic effect signature in the Hyper Suprime-Cam Year 3 cosmic shear two-point correlations on small scales: the $S_8$ tension remains present (2024) · DarkEmulator2 · 0.92
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The two-halo term is damped at quasi-linear scales following the calculation of [ref] , which means that only $P'_1H$ in HMcode depends on $p$ and $q$, not the 2-halo term (unlike the vanilla halo model).
On constraining Cosmology and the Halo Mass Function with Weak Gravitational Lensing (2023) · The Halo Model and HMcode · 0.80
How the literature uses it
78 arXiv papers cite this in 184 sentences
Papers citing it · 113 sentences without a confident label
Contests it 1 paper
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The most generic case of scale dependent growth factors is precluded to the approaches such as [ref] , while it can be properly treated here.
Flowing with Time: a New Approach to Nonlinear Cosmological Perturbations · Comparison to other approaches · contest 0.74
Builds on it 3 papers
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This is a remarkable result that extends in a concrete and simple way the findings of [ref] for Gaussian initial conditions.
Multi-Point Propagators for Non-Gaussian Initial Conditions · The $α$-method · 1.00
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To extend the validity of this approach to $Λ$CDM, we will reinterpret the variable $η$ as the logarithm of the linear growth factor of the growing mode, i.e. [ref] , η=ln(D/D_in) , and we redefine the field in Eq. ([ref]) as ([ φ_1 ( k, η); φ_2 ( k, η) ]) ≡e^-η ( [ δ_m ( k, η); -θ( k, η)/H f ]) ,
Next-to-leading resummations in cosmological perturbation theory · Nonlinear fluid equations and the Propagator · 0.83
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When transforming the equations of motion into Fourier space as in Eq. [ref], this implies that the non-linear vertices satisfy the property γ_abc(p⃗,q⃗) = δ_ac(δ_bθq⃗·p⃗/2p^2-δ_b w_i(q⃗×p⃗)_i/2p^2)+ O(p^0) , in the limit $p⃗→0$, generalizing the result in [ref] to include vorticity.
Perturbation theory with dispersion and higher cumulants: non-linear regime · Galilean invariance · 1.00
Uses its method or tool 14 papers
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To include the effect of non-linear structure formation on the BAOs, we first calculate the dewiggled power spectrum [equation] where $P_lin(k)$ is the linear matter power spectrum, $P_nw(k)$ is the no-wiggle or pure CDM power spectrum calculated using Eq.(29) from [ref] , and $k_⋆$ is marginalized over[Although $k_⋆$ can be computed by renormalization perturbation theory [ref] , doing so requires knowing the amplitude of the power spectrum, which is also marginalized over in this study.] with a flat prior over the range of 0.09 to 0.13 $h$Mpc$^-1$.
Measurements of H(z) and D_A(z) from the Two-Dimensional Two-Point Correlation Function of Sloan Digital Sky Survey Luminous Red Galaxies · Theoretical Two-Dimensional Two-Point Correlation Function · 0.99
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The nonlinear damping effect of the wiggled part in redshift space can be well approximated by [ref] [equation] where $k_⋆$ could be computed by [ref] [equation] The dewiggled power spectrum is [equation] $μ_k$ is the cosine of the angle between $k$ and the line of sight (LOS).
Modeling the Anisotropic Two-Point Galaxy Correlation Function on Small Scales and Improved Measurements of H(z), D_A(z), and f(z)sigma_8(z) from the Sloan Digital Sky Survey DR7 Luminous Red Galaxies · Modeling 2D Correlation Function for Large Scales · 0.94
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The nonlinear damping effect of the “wiggled” part, in redshift space, can be well approximated following [ref] by [equation] where $μ_k$ is the cosine of the angle between $k$ and the LOS, $f$ is the growth rate, and $k_⋆$ is computed following [ref] by [equation] The dewiggled power spectrum is [equation]
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: single-probe measurements and the strong power of normalized growth rate on constraining dark energy · Theoretical Two-Dimensional Two-Point Correlation Function · 1.00
Compares with it 6 papers
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We stress again that the difference between the propagator computed along the lines described in this section and the one in [ref] is entirely due to the different interpolation procedures, while the classes of diagrams resummed are exactly the same.
Next-to-leading resummations in cosmological perturbation theory · Factorization and the Crocce-Scoccimarro propagator · 0.99
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In order to facilitate comparison with the known expressions for the case of a single component fluid [ref] , we define:
Cosmological perturbation theory for baryons and dark matter I: one-loop corrections in the RPT framework · Momentum integrals arising in computing $1_ab(,η)$ · 0.98
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Due to the factor of $e^-η$ in the definition of the two–component field in equation [ref] the first term in the linear propagator reduces to a time independent constant matrix in contrast to the growing mode of the linear propagator of [ref] that grows as $e^η$.
Large-k Limit of Multi-Point Propagators in the RG Formalism · Evolution of Cosmic Fields · 0.97
Cites it as support 1 paper
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The full validity of this identity was overlooked in early papers but was successfully checked in numerical simulations in [ref] .
Exact Results for Propagators in the Geometrical Adhesion Model · Propagators and correlators, general properties · 0.97
Cites it as background 30 papers
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[ref] we review eulerian PT in the compact form discussed in [ref] , the diagrammatic approach to the PT expansion, and we recall the exact expressions for the fully nonlinear propagator and PS, which provide the starting points for their evolution equations.
Nonlinear Power Spectrum from Resummed Perturbation Theory: a Leap Beyond the BAO Scale · Introduction · 0.94
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The renormalized perturbation theory (RPT) [ref] is a representative pioneering work, and since it appeared, various approaches have been subsequently proposed [ref] .
Next-to-leading resummation of cosmological perturbations via the Lagrangian picture: 2-loop correction in real and redshift spaces · Introduction · 0.91
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A diversity of modeling methods have been developed ranging from simulation-based methods such as emulator [ref] , fast simulations [ref] , and machine learning [ref] to analytical methods such as Standard Perturbation Theory (SPT) [ref] , Lagrangian Perturbation Theory (LPT) [ref] , Effective-Field Theory of Large Scale Structure (EFTofLSS) [ref] , and various Renormalized Perturbation Theory (RPT) [ref] , including RegPT [ref] .
Perturbation Theory Remixed: Improved Nonlinearity Modeling beyond Standard Perturbation Theory · Introduction · 0.98
Discussion
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