Euclid Definition Study Report
Pith reviewed 2026-05-08 21:54 UTC · model claude-opus-4-7
The pith
Euclid is engineered to decide whether dark energy is Einstein's cosmological constant or something that evolves, by mapping shapes and redshifts of roughly a billion galaxies from L2.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Euclid is presented as a feasible, cost-bounded space mission whose specific instrument and survey choices — a 1.2 m Korsch telescope, a 0.1 arcsec-pixel visible imager with a tightly stabilised PSF, a near-IR photometer in Y/J/H, and a slitless near-IR spectrograph at R≈250 — are jointly necessary and sufficient to measure the dark-energy equation of state to ~1% in wp and ~10% in wa, the growth-rate index γ to ~0.02, the summed neutrino mass to better than 0.03 eV, and primordial non-Gaussianity fNL to ~2, by combining weak lensing tomography and a galaxy-clustering redshift survey over the same 15,000 deg² volume.
What carries the argument
The combination of two probes over a single shared survey volume: cosmic-shear tomography of ~30 resolved galaxies per arcmin² with photometric redshifts (σz/(1+z)<0.05), and a spectroscopic Hα redshift survey at σz/(1+z)≈0.001 down to a line flux of 3×10⁻¹⁶ erg s⁻¹ cm⁻². The shear measurement does the geometric work; the redshift survey supplies BAO standard rulers and redshift-space distortions for the growth rate; their cross-use breaks the dark-energy-versus-modified-gravity degeneracy and self-calibrates galaxy bias and intrinsic alignments.
If this is right
- A figure of merit above 400 from lensing plus clustering alone, rising past 1500 once cluster counts and the integrated Sachs-Wolfe signal are added and beyond 4000 when combined with Planck, would represent more than a hundredfold tightening over the constraints available at the time of the report.
- The summed neutrino mass would be measured to ~0.02 eV, enough to decide the neutrino mass hierarchy if the total mass is small.
- Primordial non-Gaussianity fNL would be constrained to ~2, a level competitive with or better than CMB-only bounds and able to discriminate among inflationary scenarios.
- The same data set yields a legacy archive — over a billion galaxy images at HST-like resolution, ~50 million NIR spectra, ~10⁵ strong-lens systems, deep fields with thousands of z>6 candidates — that becomes the default near-IR reference catalogue for follow-up with JWST, E-ELT, ALMA, SKA precursors and eROSITA.
- Required ground-based optical photometry over the survey footprint pushes the Dark Energy Survey, Pan-STARRS, KiDS and eventually LSST into the role of mandatory partners, fixing the data-flow architecture of late-2010s observational cosmology.
Where Pith is reading between the lines
- Choosing Hα slitless spectroscopy from space — rather than fibre spectroscopy of luminous red galaxies from the ground — bets that the dominant systematic at z≈1–2 is atmospheric and selection-driven, not instrumental confusion from overlapping spectra; the deep-field calibration strategy is essentially an admission that this bet must be checked in flight.
- The mission's real scientific lever is not either probe alone but the cross-correlation between the shear field and the galaxy density field on the same sky, which lets galaxy bias and intrinsic alignments be solved for rather than marginalised away; this is what lifts the projected figure of merit out of the regime achievable by any single ground-based survey.
- Because the figure of merit is dominated by low-redshift contributions, dropping the blue end of the spectroscopic range (z<0.7) trades nominal FoM for signal-to-noise and confusion control, conceding that low-z BAO is better left to ground-based programmes — a division of labour rather than a limitation.
- The 0.1% requirement on the mean redshift per Δz=0.1 bin is the quietest but most demanding number in the report; if it cannot be verified with ~10⁵ external spectroscopic redshifts and the deep-field self-calibration, the BAO distance ladder picks up a coherent bias that the FoM headline number does not advertise.
Load-bearing premise
That instrument-induced distortions of galaxy shapes and contamination of slitless spectra can be controlled to parts in ten thousand over six years of operations — the systematics budget the whole science case rests on.
What would settle it
Run the planned wide survey and measure the dark-energy equation of state w(z) and the growth index γ; if w(z) is consistent with −1 and γ with 0.55 at the projected ~1% and ~0.02 precisions with subdominant systematics, the cosmological-constant + General Relativity model survives. Any statistically clean departure at that precision falsifies it. The mission's own internal falsifier is that weak lensing and galaxy clustering, analysed independently on the same volume, must agree; persistent disagreement beyond the quoted error budgets would indicate uncontrolled systematics rather than new ph
read the original abstract
Euclid is a space-based survey mission from the European Space Agency designed to understand the origin of the Universe's accelerating expansion. It will use cosmological probes to investigate the nature of dark energy, dark matter and gravity by tracking their observational signatures on the geometry of the universe and on the cosmic history of structure formation. The mission is optimised for two independent primary cosmological probes: Weak gravitational Lensing (WL) and Baryonic Acoustic Oscillations (BAO). The Euclid payload consists of a 1.2 m Korsch telescope designed to provide a large field of view. It carries two instruments with a common field-of-view of ~0.54 deg2: the visual imager (VIS) and the near infrared instrument (NISP) which contains a slitless spectrometer and a three bands photometer. The Euclid wide survey will cover 15,000 deg2 of the extragalactic sky and is complemented by two 20 deg2 deep fields. For WL, Euclid measures the shapes of 30-40 resolved galaxies per arcmin2 in one broad visible R+I+Z band (550-920 nm). The photometric redshifts for these galaxies reach a precision of dz/(1+z) < 0.05. They are derived from three additional Euclid NIR bands (Y, J, H in the range 0.92-2.0 micron), complemented by ground based photometry in visible bands derived from public data or through engaged collaborations. The BAO are determined from a spectroscopic survey with a redshift accuracy dz/(1+z) =0.001. The slitless spectrometer, with spectral resolution ~250, predominantly detects Ha emission line galaxies. Euclid is a Medium Class mission of the ESA Cosmic Vision 2015-2025 programme, with a foreseen launch date in 2019. This report (also known as the Euclid Red Book) describes the outcome of the Phase A study.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript is the Euclid Definition Study Report ("Red Book"), documenting the outcome of the ESA Phase A study for a 1.2 m Korsch space telescope carrying a visible imager (VIS) and a near-infrared imager/slitless spectrometer (NISP). The mission is optimised for two primary cosmological probes — weak gravitational lensing (WL) and galaxy clustering / BAO — over a 15,000 deg² wide survey plus two 20 deg² deep fields. The headline performance claim is a dark-energy Figure-of-Merit FoM > 400 from the two primary probes, σ(γ) < 0.02 on the growth index, σ(Σmν) < 0.03 eV, and σ(f_NL) ≈ 2 in combination with Planck. The document also lays out the science rationale (§2), level-1/level-2 requirements (§3), payload (§4), mission design (§5), expected end-to-end performance from simulations (§6), ground segment (§7), and management/programmatics (§8).
Significance. If realised at the quoted performance, Euclid would deliver an order-of-magnitude improvement on dynamical-dark-energy constraints, the first competitive cosmological measurement of Σmν at the inverted-hierarchy threshold, and an f_NL constraint complementary to Planck. The combination of HST-like optical imaging over 15,000 deg² with space-based NIR photometry and slitless H-α spectroscopy is genuinely unique; no ground-based facility can match the NIR depth or PSF stability over this area. The legacy value (§2.4) — z>7 LBGs and quasars, ~10⁵ strong lenses, brown-dwarf census, resolved stellar populations to 5 Mpc — is substantial and largely independent of the cosmology forecasts. The Phase-A study has clearly converged on a self-consistent payload concept with two competing industrial designs (TAS, Astrium) and explicit mass/power margin, and the requirements are traceable from level-0 science goals down to instrument-level specs (Tables 3.1–3.6), which is the appropriate standard for a definition study.
major comments (5)
- [§3.3.1, Fig. 3.3] The σ²_sys ≤ 10⁻⁷ additive-shear-systematic budget is the load-bearing assumption behind the FoM>400 claim, but the manuscript only argues feasibility by appeal to (i) Paulin-Henriksson et al. decomposition and (ii) extrapolated algorithmic progress beyond Bridle et al. (2009). The text explicitly states that current methods reach μ~2×10⁻³ and c~10⁻³, i.e. at — not below — the requirement, and asserts 'μ≪10⁻³ is likely by the time Euclid is launched.' Given Fig. 3.3's near-linear bias-vs-σ²_sys scaling, a factor-of-few miss on σ²_sys translates directly into a comparable bias on w_p, w_a. A more defensible treatment would (a) quote the FoM under a less aggressive systematics floor (e.g. σ²_sys=10⁻⁶) so the reader can see how 'subdominant systematics' degrades, and (b) show that the PSF stability requirements σ(e_PSF)<2×10⁻⁴ and σ(R²)/R²<10⁻³ are met by the as-designed thermo-mechanical m
- [§3.2.3 / §3.3.2] The photo-z calibration plan requires ≥10⁵ spectroscopic redshifts to RIZ_AB≈24.5 with catastrophic-failure fraction <10⁻⁴, and requires the mean redshift in each tomographic bin known to σ(<z>)<0.002(1+z). §3.2.5 lists ongoing/planned spectroscopic surveys (VVDS, zCOSMOS, VUDS, BOSS, etc.) but does not demonstrate that any combination of these reaches 10⁻⁴ outlier rate at the relevant magnitude — current deep redshift surveys typically quote outlier rates at the 10⁻²–10⁻³ level. Please add an explicit accounting of how the 10⁻⁴ figure is to be achieved (cross-checks across instruments? multi-wavelength priors? deep-field self-calibration via §6.2?) and quantify the residual FoM degradation if the achieved rate is 10⁻³.
- [§3.2.4] The ground-based optical photometry plan (DES + Pan-STARRS PS1+PS2 + KiDS/VST or LSST) is presented as a set of options rather than a baseline with secured commitments. Because the photo-z (and hence the entire WL tomography) depends on griz at the stated depths over the full 15,000 deg², the risk that one or more of these surveys does not deliver to the required depth/area on the required timescale is a programmatic risk to the level-1 WL requirements. The report should state the contingency: what is the WL performance if only DES+KiDS data are available at launch, and what is the minimum acceptable ground-based dataset?
- [§3.3.2, Fig. 3.4–3.5] The galaxy-clustering systematics requirement (mean redshift in each Δz=0.1 bin known to 0.1%) is to be verified using a 140,000-galaxy deep-survey calibration sample with 99% purity. The argument for achieving 99% purity with slitless spectroscopy at H-α depth ~5×10⁻¹⁷ erg s⁻¹ cm⁻² rests on multiple roll-angle dithers and split-grism observations. A quantitative end-to-end demonstration of the achieved purity in §6.1.3 simulations as a function of source density and roll-angle coverage would substantially strengthen the case; at present the link between the deep-survey strategy and the required 0.1% mean-z accuracy is asserted rather than shown.
- [§2.3.1 / Table 2.2] The 'Euclid All' and 'Euclid+Planck' FoM numbers (1540, 4020) include forecasts from clusters and ISW that, by the report's own admission, depend on cluster mass-observable calibration (selection function, photo-z based richness) and on tomographic ISW with an assumed photo-z error model. Given that these secondary probes are sold as cross-checks, but here are co-added into the headline FoM, the report should make clear which FoM number is the science requirement (the primary-probes-only 430) versus which is aspirational. The Executive Summary's '>400' should be tied unambiguously to the primary-probes-only forecast under the stated systematics assumptions.
minor comments (9)
- [Mission Summary table (p.3)] The Mission Summary lists 'foreseen launch date in 2019' in the abstract but '2017 and 2018' in the Foreword and '2018' in §1. Please harmonise.
- [§2.1.2] The statement that the cosmological constant is '10⁶⁰ times smaller than that predicted from theory' uses a particular cutoff convention; the more common figure quoted in the literature is 10¹²⁰ (Planck-scale cutoff) or 10⁶⁰ (electroweak-scale cutoff). A one-line clarification of which cutoff is assumed would help the non-specialist reader.
- [§2.3.1] The intrinsic-alignment self-calibration grid (Joachimi & Bridle 2010) is mentioned but the number of nuisance parameters and the prior assumed are not given. Since IA marginalisation can degrade the WL FoM substantially, please state these explicitly.
- [Fig. 2.6] The right-hand panel labels (Q, G, B for quasars, galaxies, brown dwarfs) are not defined in the caption itself — the reader has to infer from the body text.
- [Table 2.1] The pivot redshift / pivot scale factor a_p convention is introduced in §2.1.2 but not stated in Table 2.1 where w_p is first defined; a footnote would help.
- [§3.2.6 / Table 3.4] The phrase 'flux limit ≤ 3×10⁻¹⁶ erg cm⁻² s⁻¹' is stated as the limit for a 1-arcsec-diameter source at 1600 nm at 3.5σ; please ensure this aperture/wavelength specification is repeated in Table 3.4, since the table is what readers will cite.
- [§2.4.7] The microlensing exoplanet survey toward the bulge (Fig. 2.9) is described as a possible additional survey but the impact on the cosmology survey timeline is not quantified. A sentence on whether this is mission-extension-only or could be interleaved with the wide survey would be useful.
- [§6.1.1] The CTI correction is said to require readout noise <4.5 e⁻; given the relevance to the WL systematics budget, please state whether the as-designed CCD273 readout noise meets this with margin under end-of-life radiation conditions.
- [Throughout] Several acronyms (EOAT, ECB, ECL, EMC, SGS, SDC) are used before the acronym list at the back. A forward reference at first use would help.
Simulated Author's Rebuttal
We thank the referee for the careful and constructive report and for the recommendation to accept. The five major comments all concern the quantitative defensibility of the headline performance claims rather than the mission concept itself, and we agree that each can be sharpened in a revision. In summary: (i) we will make the FoM-vs-σ²_sys scaling explicit and remove the 'μ≪10⁻³ is likely' phrasing in favour of a documented requirement-and-development-plan statement; (ii) we will expand §3.2.5 to describe how the 10⁻⁴ photo-z outlier rate is reached via cross-instrument confirmation, and add a FoM degradation calculation for a 10⁻³ achieved rate; (iii) we will re-cast §3.2.4 with an explicit baseline ground-based programme, a defined fallback (DES+KiDS only), and the minimum acceptable dataset; (iv) we will add to §6.1.3 a quantitative purity-vs-roll-coverage demonstration for the deep-survey calibration sample; and (v) we will tie the Executive Summary 'FoM>400' unambiguously to the primary-probes-only forecast (430), reframing the 'Euclid All' and 'Euclid+Planck' numbers as forecasts that include secondary probes and external data. Two items remain as honest standing caveats, listed below: the closure of shape-measurement algorithm performance and the assumption of independent photo-z failure modes between calibration facilities are both community-level development items that this Definition Study Report can document but not finally resolve.
read point-by-point responses
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Referee: σ²_sys ≤ 10⁻⁷ budget is load-bearing; current shape-measurement methods reach μ~2×10⁻³ and c~10⁻³ at — not below — the requirement. Please quote FoM under a less aggressive systematics floor (e.g. σ²_sys=10⁻⁶) and show that the PSF stability requirements σ(e_PSF)<2×10⁻⁴, σ(R²)/R²<10⁻³ are met by the as-designed thermo-mechanical model.
Authors: We agree this is the dominant assumption underpinning the WL forecast and will strengthen §3.3.1 accordingly. In the revision we will (i) add a table/figure showing the FoM degradation as σ²_sys is relaxed from 10⁻⁷ to 10⁻⁶ in half-decade steps, so the reader can see the scaling implied by Fig. 3.3 made explicit; and (ii) reference the end-to-end PSF stability budget that supports the σ(e_PSF)<2×10⁻⁴ and σ(R²)/R²<10⁻³ allocations — namely the thermal stability analysis summarised in §6.1.1 (PSF reconstructed from ≥1800 stars per field with the demonstrated residuals) and the thermo-mechanical stability of the SiC bench discussed in §4 and §5.4.5. We will note explicitly in §3.3.1 that current algorithmic performance (μ~2×10⁻³, c~10⁻³) sits at the requirement boundary and that ongoing community shape-measurement challenges (GREAT/handbook efforts) are the path to the assumed margin — not extrapolation alone. The revised text will avoid the phrase 'μ≪10⁻³ is likely' in favour of a more measured statement of what is required and what is currently demonstrated. revision: yes
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Referee: Photo-z calibration requires ≥10⁵ spectroscopic redshifts at RIZ~24.5 with catastrophic-failure fraction <10⁻⁴, but current deep redshift surveys quote outlier rates of 10⁻²–10⁻³. Demonstrate how 10⁻⁴ is achieved and quantify FoM degradation if achieved rate is 10⁻³.
Authors: The referee is correct that no single existing or planned survey delivers a 10⁻⁴ outlier rate at the calibration depth. Our intended strategy, which we will state more explicitly in §3.2.5, is multi-instrument cross-confirmation: a redshift is retained in the calibration sample only when it is independently confirmed by two facilities (e.g. VIMOS + Keck/DEIMOS, or VLT + JWST/NIRSpec for the faintest objects), reducing the joint outlier rate to the product of single-survey rates (~10⁻²×10⁻²=10⁻⁴). This is supplemented by Euclid's own deep-field slitless spectroscopy (§6.1.3) for high-z star-forming galaxies, where the redshift is established from multiple emission lines (Hα, [OIII], [OII], Hβ where in band) and by COSMOS-style multi-wavelength priors. We will add a short sub-section quantifying the FoM penalty if only a 10⁻³ outlier rate is achieved, propagated through the bin-by-bin σ(<z>) requirement; preliminary calculations indicate a ~15–20% FoM degradation, still within the >400 primary-probes science requirement but with reduced margin. revision: yes
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Referee: Ground-based griz photometry plan (DES, Pan-STARRS PS1+PS2, KiDS/VST, LSST) is presented as options rather than secured commitments. State the contingency: WL performance if only DES+KiDS data are available at launch, and the minimum acceptable ground-based dataset.
Authors: We accept this is a programmatic risk and not adequately quantified in the present text. We note that since submission, MoUs have advanced with DES and the Pan-STARRS consortium, and the Euclid Consortium has formed an External Data Working Group whose explicit charge is to secure the ground-based complementary data. For the revision we will (i) re-cast §3.2.4 with a clearly identified baseline (DES South + a defined Northern programme) and explicit fallback options rather than a parallel listing; (ii) add a contingency analysis showing the WL FoM in the limiting case where only DES (5,000 deg²) and KiDS (1,500 deg²) data are available, in which the photo-z performance is degraded over ~60% of the Euclid footprint and the FoM falls to a level we will quote; and (iii) define the minimum acceptable ground dataset as griz to within 0.3 mag of the depths in §3.2.3 over the full 15,000 deg². We will also note that LSST data, while not required, would substantially over-deliver against requirements over its footprint. revision: yes
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Referee: The 99% purity claim for the 140,000-galaxy deep-survey calibration sample (needed for 0.1% mean-z accuracy in Δz=0.1 bins) rests on roll-angle dithers and split-grism observations but is asserted rather than demonstrated. Provide an end-to-end demonstration in §6.1.3 of achieved purity vs source density and roll-angle coverage.
Authors: This is a fair criticism. The end-to-end NISP spectroscopic simulations summarised in §6.1.3 do include the multi-roll, split-grism strategy and were used to derive the wide-survey completeness/purity numbers, but the deep-survey-specific purity-vs-roll-coverage curve is not shown. We will add to §6.1.3 a figure showing simulated redshift purity as a function of (a) number of distinct roll angles and (b) source surface density, for the deep-survey exposure depth, demonstrating that ≥4 well-separated roll angles plus the red/blue grism split achieve >99% purity for the calibration subsample at the relevant flux. We will also describe the planned ground-based spectroscopic follow-up of a deep-field subset that provides an external cross-check on the purity figure independent of the slitless self-consistency. revision: yes
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Referee: Table 2.2 'Euclid All' (FoM=1540) and 'Euclid+Planck' (FoM=4020) numbers include clusters and ISW, which depend on calibrations sold elsewhere as cross-checks. Make clear which FoM is the science requirement (primary-probes-only=430) and which is aspirational; tie the Executive Summary '>400' unambiguously to the primary-probes-only forecast.
Authors: We agree and will revise the presentation. In the Mission Summary and Executive Summary the headline FoM>400 will be explicitly tagged as 'primary probes (WL + galaxy clustering) only, under the stated systematics assumptions', matching the 'Euclid Primary' row of Table 2.2 (FoM=430). The 'Euclid All' and 'Euclid+Planck' numbers will be retained but framed unambiguously as forecasts that include secondary probes (clusters, ISW) and external CMB data, with a sentence noting that they are subject to additional astrophysical-calibration assumptions (cluster mass–observable scatter, photo-z error model for ISW) and should not be read as the formal mission requirement. The level-0 science requirement of FoM>400 from the primary probes will be the requirement that flows down through §3. revision: yes
- For the σ²_sys ≤ 10⁻⁷ requirement, while we will quantify the FoM-vs-systematics scaling and tighten the language, ultimate demonstration that shape-measurement algorithms reach μ<10⁻³ at Euclid depths is a community development that cannot be closed within this Definition Study Report; we can only document the requirement, the current state of the art, and the development plan.
- The 10⁻⁴ photo-z outlier rate argument relies on cross-instrument confirmation under the assumption of independent failure modes between facilities. We cannot rigorously prove that assumption from existing data; it remains a working hypothesis to be validated during the implementation phase using overlapping calibration fields.
Circularity Check
Mission design report; forecasts are Fisher-matrix projections from stated assumptions, not circular derivations.
full rationale
This is a mission definition study (the Euclid Red Book), not a theoretical paper claiming to derive a novel result from first principles. Its central quantitative claims — FoM>400, σ(γ)<0.02, σ(Σmν)<0.03 eV, σ(fNL)~2 — are explicitly presented as Fisher-matrix forecasts conditional on stated survey parameters (15,000 deg², 30 gal/arcmin², σz/(1+z)<0.05, σ²_sys≤10⁻⁷, etc.) and a fiducial ΛCDM cosmology. The paper is transparent about this: §2.3.1 lists the fiducial parameter values, the parameterisations (w(a)=wp+wa(ap−a); f(z)=Ωm(z)^γ), and the assumed priors on nuisance parameters (intrinsic alignments, galaxy bias). The requirements flow-down in §3 derives Level-2 instrument requirements from Level-1 science requirements via standard error-propagation (e.g. Paulin-Henriksson et al. 2008 for PSF→shear bias), which is engineering, not circular reasoning. The skeptic's concern — that σ²_sys≤10⁻⁷ and the 10⁵-spec-z/<10⁻⁴-outlier calibration are aspirational rather than demonstrated — is a correctness/feasibility risk, not a circularity. The paper does not claim these floors are achieved; it claims they are required, and acknowledges current shape-measurement performance sits at the requirement (μ~2×10⁻³, c~10⁻³) with extrapolated improvement. That is an assumption the reader can challenge on its merits, but the FoM forecast does not reduce to its own input by definition: changing σ²_sys changes the predicted FoM in the documented linear way (Fig. 3.3), so the forecast has independent content given the assumption. Self-citation is present (Kitching et al., Amara & Refregier, Joachimi & Bridle, Wang et al.) but is used to import standard forecasting machinery, not to import the conclusion. No 'uniqueness theorem' is invoked; no fitted parameter is renamed as a prediction; no result is defined in terms of itself. Score 1 reflects the normal level of in-consortium methodological self-reference expected in a mission study.
Axiom & Free-Parameter Ledger
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A Systematic Study of Behavioral Cloning for Scientific Data Annotation
Introduces 9 synthetic annotation tasks and benchmarks for behavioral cloning, finding hierarchical skill learning, scaling benefits, effective multi-task pretraining, and shared internal representations of task phase...
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Reassessing the Statistical Necessity of Stellar Velocity Anisotropy in Strong-Lensing Cosmology with Lens-by-Lens Photometric Constraints
Analysis of 107 matched strong-lensing and supernova pairs with lens-specific luminosity slopes finds that free stellar anisotropy is statistically required and reveals negative redshift evolution in early-type galaxy...
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Extracting redshifts from 2D slitless spectroscopic images using deep learning for the CSST galaxy survey
A Bayesian CNN maps 2D slitless spectral images to redshift estimates with NMAD precision 0.0104 for SNR_GI >=1 and better for brighter sources, while remaining robust to wavelength calibration errors via spatial augm...
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Radio sirens: inferring $H_0$ with binary black holes and neutral hydrogen in the era of the Einstein Telescope and the SKA Observatory
Using simulated binary black hole mergers and neutral hydrogen maps, the radio sirens method constrains H0 to 8% precision with 3000 high-SNR events, offering a 90% improvement over standard dark siren analyses.
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Measuring cosmic bulk flow with kinetic Sunyaev-Zel'dovich velocity reconstruction
Kinetic Sunyaev-Zel'dovich reconstruction from WISExSuperCOSMOS and unWISE galaxies with Planck data yields tight upper limits on bulk velocities consistent with LambdaCDM out to 2000 h^{-1} Mpc while showing tension ...
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Unveiling $f(R)$ Gravity with Void-Galaxy Cross-Correlation Multipoles
Semi-analytical calculation of void-galaxy cross-correlation multipoles in Hu-Sawicki f(R) gravity reveals size-dependent deviations from LambdaCDM up to 29.7 percent for small voids, amplified by nonlinear evolution ...
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Unveiling $f(R)$ Gravity with Void-Galaxy Cross-Correlation Multipoles
Void-galaxy cross-correlation multipoles exhibit amplified size-dependent deviations from LCDM in f(R) gravity due to the scalaron fifth force and nonlinear shell dynamics, providing a new probe for modified gravity.
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Matter Clustering in Astrid: Reduced Baryonic Suppression from Realistic Black Hole Dynamics
Realistic black hole dynamics in Astrid reduce baryonic suppression of the matter power spectrum at low redshifts compared to repositioning schemes used in other simulations.
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Euclid preparation. CosmoPostProcess: A simulation calibrated framework for weak lensing selection bias in richness-selected galaxy clusters
CosmoPostProcess delivers simulation-calibrated radial corrections for projection-induced selection bias (20-40% amplitude near 1 h^{-1} Mpc) and baryonic effects in Euclid richness-selected cluster weak lensing profiles.
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Diffusion-based Galaxy Simulations for the Roman High Latitude Survey
A denoising diffusion model trained on transformed JWST observations generates multi-band galaxy images that match key statistical properties of real galaxies for Roman weak lensing simulations.
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Backlighting the Cosmic Web with Fast Radio Bursts: An Anthology of Dispersion Measure Cross-Correlations with Large-Scale Structure and Baryon Tracers
FRB DMs correlate at 2.6-5 sigma with galaxies, weak lensing, CIB, CMB lensing, tSZ, X-ray clusters, SXRB and radio continuum, consistent with moderate feedback models while ruling out weak feedback at 3.5 sigma via SXRB-DM.
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Spontaneous Symmetry Breaking and the Vacuum Displacement Principle: From Galactic Scales to Cosmic Fine-Tuning
A Higgs-type scalar vacuum field displaced by baryonic matter yields a Yukawa-corrected gravitational potential that replaces dark matter and dynamically relaxes the cosmological constant.
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Signatures of Suppressed Matter Clustering revealed by Fast Radio Bursts
FRB dispersion measures directly constrain suppression of the matter power spectrum due to feedback at k ~ 0.1-3 h/Mpc, reduce posterior variance by a factor of ~8 at k~1 h/Mpc, and exclude extreme large-scale feedbac...
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Old Universe, Young SNe Ia: A Statistical Analysis of Type Ia Supernova Progenitor Age from 6,983 TITAN Host Galaxies, and Implications for Cosmology
Large sample of SN Ia hosts shows young mean progenitor age of 3.5 Gyr and only 1.5 Gyr evolution, leading to negligible cosmological bias of 0.007 mag.
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Constraining Neutrino Mass with the Void Weak Lensing Effect
Simulations of void-shear cross-correlation demonstrate that void lensing can constrain total neutrino mass to σ(M_ν)=0.096 eV without shape noise and 0.340 eV with Stage-III-like noise.
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Quantifying Weighted Morphological Content of Large-Scale Structures via Simulation-Based Inference
Simulation-based inference on Big Sobol Sequence halos at z=0.5 shows CMD+MFs improves σ8 and Ωm precision by ~27% over MFs alone and outperforms PS by ~45% in mass-selected samples at matched scales.
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Impact of projection-induced optical selection bias on the weak lensing mass calibration of galaxy clusters
Projection-induced selection bias causes 20-50% overestimation of weak lensing masses for optically selected galaxy clusters, larger on scales >3 Mpc.
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Parity Violation in Galaxy Shapes: Primordial Non-Gaussianity
The parity-odd intrinsic alignment power spectrum probes the collapsed limit of the parity-odd primordial trispectrum and can tighten constraints on parity-violating PNG when bias parameters are calibrated from N-body...
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GWTC-4.0: Constraints on the Cosmic Expansion Rate and Modified Gravitational-wave Propagation
Statistical redshifts inferred from mass spectrum features and galaxy catalogs for 142 GW events yield H0 = 76.6 km s^{-1} Mpc^{-1} and Ξ0 = 1.2, consistent with general relativity.
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Modeling and measuring the anisotropic halo 3-point correlation function: a coordinated study
Novel implementation of anisotropic 3PCF model and estimator tested on 298 halo catalogs shows degeneracy breaking between f and b1 in 3PCF-only analysis but limited added value in joint 2PCF+3PCF due to tree-level mo...
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LSST: from Science Drivers to Reference Design and Anticipated Data Products
LSST will image 18,000 square degrees of sky about 800 times across six bands over 10 years to a coadded depth of r~27.5, producing a public database of 40 billion objects and 32 trillion observations.
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Cosmology-dependent covariance in galaxy cluster number counts: consequences for parameter inference
Fixing the covariance at an incorrect cosmology in cluster count analyses leaves Ω_c, σ_8, and w estimates unbiased but distorts their uncertainties, driven by S_8 amplitude effects; a single update at the recovered b...
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pop-cosmos: Galaxy size evolution across structural and star-formation classifications in COSMOS-Web
Galaxy size-mass relations exhibit double power-law breaks at different pivot masses for quiescent versus bulge-dominated samples, coinciding with AGN activity scales.
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Revisiting the 'Lensing is Low' Problem with UNIONS
New UNIONS galaxy-galaxy lensing data around CMASS galaxies indicates no significant lensing is low problem, with joint HOD fits to GGL and GC favoring a slightly lower matter power spectrum amplitude than Planck.
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Bounding the Effect of HOD Assumptions on Small-Scale Clustering Constraints
The fraction of AbacusSummit cosmologies excluded at 3σ by small-scale clustering multipoles drops from 81% to 25% when moving from fixed HOD parameters to broad marginalization over the five-parameter HOD model.
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(The) Wiggles going non-linear
N-body simulations calibrate a one-parameter damping model that predicts the non-linear matter power spectrum from wiggly primordial spectra to sub-percent accuracy when wiggle frequency is high enough.
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Exploring non-Poisson satellite occupation in HOD models and its impact on 2- and 3-point galaxy clustering
Replacing Poisson satellite occupation with Conway-Maxwell-Poisson in HOD models produces up to 10% shifts in small-scale projected clustering and 30% in counts-in-cylinders but under 2% change in tree-level bispectru...
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Cosmological constraints from neighbor-density-weighted marked correlation functions
Neighbor-density-weighted marked correlation functions improve FoM for Ω_m–σ_8 by 1.7–2.5× over standard 2PCF using emulators from 129 w0waCDM+∑m_ν simulations.
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Cosmological constraints from neighbor-density-weighted marked correlation functions
Neighbor-density-weighted marked correlation functions improve FoM for Ωm–σ8 by 1.7–2.5× over standard 2PCF using Gaussian-process emulators on 129 w0waCDM+∑mν simulations.
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The dual effect of group-scale environments on galaxy quenching during cluster infall: pre-processing and protection
Group-scale halos produce a dual effect on infalling galaxies: pre-processing raises quiescent fraction early, while protection delays cluster-driven quenching to smaller d_R.
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Towards precision cosmology with Void x CMB correlations (II): Impact of mock catalogs on the Void x CMB lensing signal
Void x CMB lensing from Roman mocks is robust to catalog construction choices and forecasts S/N of 13-31 sigma with Planck, SO, and CMB-S4-like data for 2D and 3D voids.
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Euclid preparation: Testing multi-field inflation with galaxy power spectrum and bispectrum
Validates redshift-space power spectrum and bispectrum analysis on Abacus-PNG mocks to recover unbiased f_NL constraints for Euclid spectroscopic sample.
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Information Content of the Cosmic Web
An information-theoretic analysis of the cosmic web using tidal tensor eigenvalues defines morphological entropy that identifies filaments as dominant information carriers and relates to the growth rate f(z).
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