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arxiv: 2604.08393 · v1 · submitted 2026-04-09 · 🌌 astro-ph.CO

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Ray-traced weak lensing convergence in screened modified gravity theories

Mattia Pantiri , Matthieu Schaller , Alessandra Silvestri , Jeger C. Broxterman , Joop Schaye
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Pith reviewed 2026-05-10 17:13 UTC · model grok-4.3

classification 🌌 astro-ph.CO
keywords weak lensingmodified gravityconvergence power spectrumscreening mechanismsray-tracinghydrodynamical simulationsbaryonic feedbackcosmological probes
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The pith

Ray-traced maps show that screened modified gravity alters the weak lensing convergence power spectrum at levels exceeding baryonic feedback variations.

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

The paper sets out to show that extensions of general relativity that change the lensing equation produce observable differences in the statistics of weak lensing convergence when ray-tracing is applied to hydrodynamical simulation outputs. A reader would care because Stage IV surveys will measure lensing to high precision on both linear and nonlinear scales, so any unmodeled modification to the lensing kernel could be mistaken for shifts in cosmological parameters or baryonic effects. The authors implement a time-dependent modification function together with a simple scale-dependent screening prescription, generate full convergence maps, and measure the resulting power spectrum. They find that the MG-induced changes are larger than the shifts produced by varying baryonic feedback strength within the same simulation suite. This leads them to conclude that modified lensing must be treated as a standard component when analyzing modified-gravity simulations.

Core claim

Starting from the FLAMINGO hydrodynamical density fields, the authors apply ray-tracing with a lensing convergence equation modified by a phenomenological function Σ_mg whose time evolution is analytic and whose scale dependence is chosen to emulate screening. The resulting convergence power spectra exhibit clear excess power on intermediate scales relative to general-relativity runs; these excesses remain larger than the variations obtained by changing either cosmological parameters or the strength of baryonic feedback inside the same simulation framework. The authors therefore state that modified lensing should become a standard ingredient in the analysis of modified-gravity simulations.

What carries the argument

Ray-tracing through density maps with a modified lensing convergence equation parametrized by the function Σ_mg that carries both analytic time dependence and a phenomenological scale dependence representing screening.

If this is right

  • The convergence power spectrum acquires distinct scale-dependent signatures once the modified lensing kernel is included.
  • These signatures can exceed the amplitude shifts produced by plausible changes in baryonic feedback strength.
  • Cosmological parameter inference from weak lensing in modified gravity must marginalize over the screening scale to remain unbiased.
  • Future simulation pipelines for modified gravity should incorporate the modified lensing step as a default rather than an optional add-on.

Where Pith is reading between the lines

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

  • If the power-spectrum excesses survive comparison with real survey data, the amplitude of the screening scale could itself become a measurable parameter in Stage IV analyses.
  • The same ray-tracing pipeline could be applied to other two-point statistics such as galaxy-galaxy lensing or CMB lensing cross-correlations to test consistency of the Σ_mg prescription.
  • Full self-consistent modified gravity N-body runs without the phenomenological screening function could be used as a direct numerical check on the size of any approximation error.

Load-bearing premise

The chosen phenomenological scale dependence for screening accurately reproduces the true behavior of the underlying modified gravity models without introducing large artifacts into the ray-traced convergence maps.

What would settle it

If the measured convergence power spectrum from Stage IV weak-lensing data shows no excess power at the scales and redshifts predicted by the Σ_mg model after all standard cosmological and baryonic variations have been marginalized, the claim that MG lensing effects dominate baryonic ones would be ruled out.

Figures

Figures reproduced from arXiv: 2604.08393 by Alessandra Silvestri, Jeger C. Broxterman, Joop Schaye, Matthieu Schaller, Mattia Pantiri.

Figure 1
Figure 1. Figure 1: We plot a 20x20 degrees portion of the overdensity map in the first shell to illustrate our two screening methods. The pixels inside the colored contours are screened, thus undergoing regular GR lensing, while the regions outside have MG lensing. Left: screening is performed inside spherical shells of radius 𝑅200c centered on haloes of mass 𝑀200𝑐 > 𝑀thresh = 1013M⊙ (red contours). Right: screening is perfo… view at source ↗
Figure 2
Figure 2. Figure 2: Top: angular power spectra of the MG weak lensing convergence obtained from CAMB (black line) and obtained from the ray-tracing algorithm (cyan line) with a purely time dependent Σ(𝑎). Bottom: ratio to the CAMB power spectrum. The resolution of the density maps in the ray-traced case is 𝑁side = 4096. The small scale suppression is due to the pixelization of the Healpix map. suppress the fifth force in the … view at source ↗
Figure 3
Figure 3. Figure 3: Ratios of the angular power spectra of the integrated convergence map with respect to the standard GR lensing prescription (continuous black line). The dashed cyan line corresponds to MG lensing without screening, while the dotted red and dot dashed green lines correspond to MG lensing with screening implemented using the halo method (with 𝑀thresh = 1013M⊙) and using the overdensity method (with 𝛿thresh = … view at source ↗
Figure 4
Figure 4. Figure 4: Ratio of the convergence power spectrum with source distribution as 𝑛(𝑧) = 𝛿D (𝑧 = 1) with respect to the standard GR convergence spectrum. Regular GR lensing is in continuous black, while the colored lines are MG lensing with the same screening radii for all haloes and equal to 0.5 Mpc, 1 Mpc and 1.5 Mpc respectively for dot dashed blue, dotted orange and dashed green. Vertical lines with corresponding co… view at source ↗
Figure 6
Figure 6. Figure 6: Ratio of the convergence power spectrum obtained via MG lensing with the overdensity based method with respect to the standard GR lensing spectrum. Different colors and line styles represent different choices of the overdensity threshold 𝛿thresh. from DESI favoring Σ0 > 0, to explore the full range of possibilities. Considering a negative value will also be helpful later, when we will compare the MG model … view at source ↗
Figure 7
Figure 7. Figure 7: Ratio of the convergence power spectrum obtained via MG lensing with the overdensity based method with respect to the standard GR lensing. Different colors and line styles represent different choices of the MG param￾eter Σ0. 102 103 104 ` 0.8 0.9 1.0 1.1 C`/CGR,D3A ` GR lensing, D3A GR lensing, Planck MG lensing, D3A GR lensing, LS8 [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Comparison of the effect on the convergence power spectrum of changing the cosmology with respect to changing the lensing prescription. The lines are obtained as the ratio of the power spectrum with the standard GR lensing, fiducial cosmology spectrum (continuous black): the GR lensing Planck cosmology in dotted silver, the GR lensing low 𝜎8 cosmology in dot dashed pink and the MG lensing (with overdensity… view at source ↗
Figure 10
Figure 10. Figure 10: Best-fitting values of the cosmological parameters Ωm (left) and 𝜎8 (right) when fitting the convergence power spectrum with a standard GR DMO ΛCDM model. The black points are fit to a GR DMO spectrum, the purple points to a hydrodynamical GR spectrum and the green points to a MG DMO spectrum (with Σ0 = 0.044). All three spectra have been produced with the fiducial D3A cosmology, whose parameter values ar… view at source ↗
read the original abstract

Weak gravitational lensing is one of the primary cosmological probes, providing powerful constraints on the cosmological model. As Stage IV surveys are expected to deliver data of unprecedented precision, accurate modeling of weak gravitational lensing observables across both linear and non-linear scales becomes increasingly important. In this work, we investigate weak lensing in modified gravity (MG) models, extensions of the standard $\Lambda$CDM cosmology in which gravity deviates from general relativity, generally introducing modifications to the lensing equation. We parametrize these modifications through the common phenomenological function $\Sigma_\mathrm{mg}$ and apply ray-tracing to the density maps of N-body and hydrodynamical simulations. We model the time dependence of $\Sigma_\mathrm{mg}$ analytically, while we introduce a phenomenological scale dependence to represent the screening mechanisms by which MG models reduce to general relativity in high-density environments. Starting from the output of the FLAMINGO hydrodynamical simulations, we generate fully ray-traced convergence maps using our modified lensing model. We analyze how the parameters of our prescription affect the weak lensing convergence power spectrum and compare these effects to other known sources of variation, in particular cosmological parameters and baryonic feedback. We find that the modifications to the lensing equation deriving from the MG model produce non-negligible signatures in the convergence power spectrum and that, within extensions of the $\Lambda$CDM framework, these effects can be larger than those induced by baryonic physics. Our results indicate that modified lensing should become a standard ingredient of the analysis of modified gravity simulations.

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 ray-tracing method for weak lensing convergence in screened modified gravity (MG) theories. It parametrizes deviations from GR in the lensing equation via the phenomenological function Σ_mg, with analytic time dependence and an ad-hoc scale dependence introduced to represent screening. Density maps are taken from the GR FLAMINGO hydrodynamical simulations; modified lensing kernels are applied post hoc to produce convergence maps. The effects on the convergence power spectrum are quantified and compared against variations induced by cosmological parameters and baryonic feedback, with the conclusion that MG modifications produce non-negligible signatures that can exceed baryonic effects within ΛCDM extensions.

Significance. If the phenomenological prescription holds, the work demonstrates an efficient route to explore MG lensing signatures using existing GR simulations and highlights that modified lensing can dominate over baryonic uncertainties on relevant scales. This has direct implications for Stage IV survey analyses, supporting the recommendation that modified lensing become standard in MG simulation pipelines. The approach leverages high-resolution hydrodynamical outputs and full ray-tracing, providing a concrete, reproducible framework for such studies.

major comments (2)
  1. [Methods (phenomenological scale dependence prescription)] The central claim that MG-induced changes to the lensing equation produce signatures larger than baryonic feedback rests on the ad-hoc scale dependence chosen for Σ_mg to model screening. Because the density fields are taken from GR FLAMINGO runs and only the lensing kernel is altered, without direct validation against self-consistent MG N-body simulations (e.g., f(R) or symmetron), it is unclear whether the reported excess power on intermediate scales is physical or an artifact of the functional form. This is load-bearing for the quantitative comparison in the results.
  2. [Results (comparison to baryonic feedback)] The analysis does not account for possible MG-induced modifications to the underlying matter density field itself, only to the lensing kernel. This assumption may bias the convergence power spectrum differences relative to a fully consistent MG simulation, undermining the claim that the MG effects are non-negligible and larger than baryonic physics when the density maps remain GR-based.
minor comments (2)
  1. [Abstract] The abstract summarizes the qualitative finding but omits any numerical values, error bars, or specific scale ranges for the power spectrum differences, making it harder to assess the magnitude of the reported effects without reading the full results section.
  2. [Introduction/Methods] Notation for the time and scale dependence of Σ_mg should be introduced with an explicit equation early in the text rather than described only in prose, to improve clarity for readers unfamiliar with the parametrization.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for the constructive comments, which have helped us improve the clarity and scope of our work. We address each major comment in detail below and have made targeted revisions to the manuscript.

read point-by-point responses

  1. Referee: [Methods (phenomenological scale dependence prescription)] The central claim that MG-induced changes to the lensing equation produce signatures larger than baryonic feedback rests on the ad-hoc scale dependence chosen for Σ_mg to model screening. Because the density fields are taken from GR FLAMINGO runs and only the lensing kernel is altered, without direct validation against self-consistent MG N-body simulations (e.g., f(R) or symmetron), it is unclear whether the reported excess power on intermediate scales is physical or an artifact of the functional form. This is load-bearing for the quantitative comparison in the results.

    Authors: We agree that the scale dependence of Σ_mg is a phenomenological choice introduced to capture screening. This enables efficient use of the existing high-resolution GR FLAMINGO hydrodynamical outputs rather than requiring new MG runs for every model. The functional form is motivated by the scale-dependent suppression typical of screening mechanisms in theories such as f(R) and symmetron. In the revised manuscript we have expanded the Methods section with additional justification, explicit references to screening literature, and a new set of robustness tests that vary the scale-dependence parameters. We also added a clear statement that the results illustrate the isolated effect of modified lensing on GR densities and are not intended as a direct prediction for any specific MG model. Direct validation against self-consistent MG N-body simulations remains a valuable next step but lies outside the present scope. revision: partial

  2. Referee: [Results (comparison to baryonic feedback)] The analysis does not account for possible MG-induced modifications to the underlying matter density field itself, only to the lensing kernel. This assumption may bias the convergence power spectrum differences relative to a fully consistent MG simulation, undermining the claim that the MG effects are non-negligible and larger than baryonic physics when the density maps remain GR-based.

    Authors: We acknowledge that a fully consistent MG simulation would modify both the density field and the lensing kernel. Our post-hoc application isolates the contribution of the modified lensing equation, which is a distinct and observationally relevant feature of screened MG models. This separation allows us to exploit existing high-fidelity hydrodynamical simulations while quantifying the lensing-only signature. In the revised manuscript we have inserted a new paragraph in the Discussion section that explicitly notes this approximation, discusses its implications for the baryonic comparison, and states that the total MG effect in a self-consistent run could differ. Within the framework of our phenomenological model, however, the lensing modification alone produces changes that remain non-negligible relative to baryonic feedback, supporting the original claim as an indicative result rather than a final quantitative prediction. revision: partial

Circularity Check

0 steps flagged

No significant circularity; numerical exploration of phenomenological MG lensing is self-contained

full rationale

The paper computes ray-traced convergence maps by post-processing GR FLAMINGO density fields with an explicitly phenomenological modification to the lensing kernel (analytic time dependence for Σ_mg plus ad-hoc scale dependence to model screening). The reported non-negligible signatures in the power spectrum and the statement that MG effects can exceed baryonic feedback are direct numerical outputs of this setup rather than quantities defined in terms of themselves or statistically forced by a fit. No self-definitional equations, fitted inputs renamed as predictions, load-bearing self-citations, or smuggled ansatzes appear in the derivation chain. The work is a controlled numerical study of the chosen parametrization and remains independent of its inputs.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The central claim rests on the accuracy of the FLAMINGO density fields and on the phenomenological Σ_mg parametrization being a faithful representation of screened modified gravity lensing.

free parameters (1)
  • Σ_mg scale-dependence parameters
    Phenomenological parameters introduced to model screening; their specific values control the amplitude of MG signatures in the power spectrum.
axioms (2)
  • domain assumption FLAMINGO hydrodynamical simulations provide accurate density and potential fields for ray-tracing
    The maps are generated directly from these simulation outputs without additional validation shown in the abstract.
  • domain assumption The Σ_mg parametrization with analytic time dependence and phenomenological scale dependence correctly modifies the lensing equation
    Standard phenomenological approach invoked without derivation from a specific MG Lagrangian in the abstract.

pith-pipeline@v0.9.0 · 5596 in / 1484 out tokens · 65777 ms · 2026-05-10T17:13:58.833260+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

1 extracted references · 1 canonical work pages

  1. [1]

    Abbott T. M. C., et al., 2022, Phys. Rev. D, 105, 023520 Abbott T. M. C., et al., 2023, Phys. Rev. D, 107, 083504 Abdalla E., et al., 2022, Journal of High Energy Astrophysics, 34, 49 Amendola L., Kunz M., Sapone D., 2008, J. Cosmology Astropart. Phys., 2008, 013 Amon A., et al., 2023, MNRAS, 518, 477 Anderson L., et al., 2014, MNRAS, 441, 24 Babichev E.,...

    work page arXiv 2022