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REVIEW 3 major objections 4 minor 23 references

The cosmic-ray sea explains the Galactic $\gamma$-ray and $\nu$ diffuse emissions from GeV to PeV

T0 review · 3 major / 4 minor · reviewed 2026-08-06 · deepseek-v4-flash

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Pith's one-line read LHAASO's measured Milky Way diffuse glow from 1 TeV to 1 PeV is produced by the ordinary hadronic cosmic-ray sea — with the proton spectrum following KASCADE — so no extra cosmic-ray source component is needed to explain the data.

desk verdict A solid consistency check showing LHAASO diffuse gamma-ray data match a pre-existing CR sea model, but the no-extra-component conclusion is conditional on the disputed KASCADE proton spectrum and the Max rejection lacks systematics. read the letter →

arxiv 2507.07083 v2 pith:4BNJHBPO submitted 2025-07-09 astro-ph.HE

Pedro De La Torre Luque , Daniele Gaggero , Dario Grasso , Antonio Marinelli , Manuel Rocamora This is my paper
classification astro-ph.HE
keywords Galacticdiffuseemissioncosmic-rayseaLHAASOgamma-rayastronomytransportneutrinoPeVgammarays
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper claims that the diffuse gamma-ray glow of the Milky Way, as measured by LHAASO from 1 TeV to 1 PeV, is produced entirely by the ordinary hadronic cosmic-ray sea colliding with interstellar gas. The authors take pre-existing transport models built to match the local cosmic-ray spectra measured by CALET, DAMPE, and KASCADE, apply the LHAASO sky mask, and find agreement over more than four energy decades. No extra cosmic-ray source component, whether a new accelerator population or exotic emission, is required. The same models stay consistent with Fermi-LAT data from GeV energies and with the diffuse neutrino emission discovered by IceCube. If correct, this makes LHAASO's diffuse measurement a clean probe of the Galactic cosmic-ray population rather than evidence for new physics.

What carries the argument

The load-bearing object is the gamma-optimized Min model: a numerical cosmic-ray transport setup whose interstellar proton spectrum follows CALET and DAMPE at lower energies and KASCADE from 10 TeV to 10 PeV, embedded in a spatially dependent diffusion halo (the upgraded KRA-gamma scenario). Convolving this cosmic-ray sea with the interstellar gas distribution and accounting for gamma-ray attenuation produces the diffuse gamma-ray and neutrino sky. Applying the LHAASO mask to the model makes the comparison unbiased; the mask is also what hides the difference between conventional and space-dependent transport, and what the authors argue suppresses unresolved source contamination.

What would settle it

An unmasked LHAASO measurement of the inner Galactic plane whose diffuse flux falls significantly below the gamma-optimized Min prediction above 100 TeV would falsify the claim that the hadronic cosmic-ray sea alone explains the diffuse emission; an IceCube or KM3NeT template fit using the gamma-optimized Min model that required a normalization far from unity would do the same.

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Extended reading notes

Core claim

The paper's central claim is that LHAASO's 1 TeV–1 PeV Galactic diffuse gamma-ray emission, in the inner and outer Galactic-plane windows defined by the experiment, is the hadronic emission of the Galactic cosmic-ray sea. Using the Min setup — in which the interstellar proton spectrum follows KASCADE measurements — the gamma-ray flux predicted by pre-existing models reproduces the LHAASO spectrum and angular distributions across more than four energy decades, with reduced chi-square of 0.8 in the inner window and 0.6 in the outer window. The Max setup, based on the harder IceTop/LHAASO proton spectra, is incompatible at more than 10 standard deviations. The authors conclude that no extra source component is required, that unresolved sources contribute only marginally in the LHAASO-masked sky, and that the same framework is consistent with Fermi-LAT GeV data and with IceCube's diffuse neutrino emission.

Load-bearing premise

The load-bearing premise is that the KASCADE-based Min proton spectrum represents the true interstellar cosmic-ray spectrum across the Galaxy; if the harder IceTop/LHAASO proton measurements are the local reality, the paper's central agreement fails and transport models would need revision.

Editorial extensions

If this is right

  • LHAASO's diffuse gamma-ray measurement becomes a direct probe of the interstellar cosmic-ray spectrum above 100 TeV, complementary to local direct-detection measurements.
  • The more-than-10-sigma rejection of the Max setup implies that if the IceTop or LHAASO proton spectra represent the true local cosmic-ray population, current cosmic-ray transport models need revision.
  • The gamma-optimized Min model predicts a specific neutrino diffuse flux and is expected to serve as a better IceCube template than the older KRA-gamma model, pending a dedicated reanalysis.
  • Unmasked LHAASO data already favor space-dependent transport models, and future mask refinement or SWGO observations near the Galactic Centre can break the remaining degeneracy between conventional and space-dependent transport.
  • A validated cosmic-ray template for the TeV–PeV diffuse glow sharpens searches for point sources, extended sources, and dark-matter annihilation in the same energy band.

Reading between the lines

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

  • The paper's logic implies a sharp, testable asymmetry: a future measurement that lowers the masked inner-plane diffuse flux would force either a revision of the local cosmic-ray spectrum or the introduction of a subdominant new component, while a higher flux would point to unresolved sources leaking through the mask.
  • The Min/Max bracket effectively predicts that the unresolved tension between KASCADE and the IceTop/LHAASO proton measurements will be settled closer to KASCADE; direct cosmic-ray experiments should eventually decide the question.
  • A natural extension is to run the IceCube cascade analysis with the gamma-optimized Min template; the predicted shift relative to KRA-gamma is a smaller flux above 10 TeV, small enough that distinguishing it may require combining IceCube with KM3NeT.
  • The LHAASO mask carries two distinct roles in this argument — suppressing source contamination and hiding transport-model differences — and a quantitative source-population simulation of the masked sky would test whether those roles can be separated.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 4 minor

Summary. Using the recently released LHAASO WCDA+KM2A measurements of the Galactic diffuse emission (GDE) from 1 TeV to 1 PeV in the inner and outer Galactic plane regions, the paper compares these data with two pre-existing DRAGON/HERMES models, Min and Max, that bracket the uncertainty in the proton and helium injection spectra. The gamma-optimized Min model, normalized to CALET, DAMPE, and KASCADE data, reproduces the masked LHAASO spectra over four decades in energy, whereas the Max model, closer to IceTop/LHAASO proton measurements, is reported as incompatible at more than 10 sigma. The paper also compares conventional and spatially dependent transport models, discusses the LHAASO mask and unresolved-source contamination, and argues that the IceCube neutrino Galactic diffuse emission is consistent with the gamma-optimized Min model.

Significance. If correct, the result resolves a key question in Galactic astroparticle physics: the LHAASO GDE from 1 TeV to 1 PeV is explained by hadronic interactions of the Galactic cosmic-ray sea, with no extra source component, and the KASCADE-based proton spectrum is favored over the harder IceTop/LHAASO measurements. The paper's strengths are that the models were not fitted to LHAASO data, a consistent mask is applied to models and Fermi-LAT data, CMB attenuation is included, and the comparison spans more than four decades in energy. The main weakness is that the no-extra-component conclusion is contingent on the KASCADE-based Min choice and on a quantitative rejection of the Max model that is not correctly established in the paper.

major comments (3)
  1. [Sec. 1, 'more than 10σ' claim] The claim that the Max model is rejected at more than 10σ is not supported by reduced chi-squared values alone (the paper quotes reduced χ² = 9.5 vs 0.8 in the inner region and 1.9 vs 0.6 in the outer region). Reduced chi-square is not a significance; no number of degrees of freedom or covariance is given, and LHAASO systematic uncertainties (energy scale, cosmic-ray background subtraction) are not propagated. Please replace this statistic with a proper likelihood or chi-square test that includes systematics and reports a p-value or confidence level.
  2. [Sec. 1 and Sec. 4] The central conclusion is conditional on the Min setup, which adopts the KASCADE proton spectrum, while the harder IceTop and LHAASO measurements motivate the Max setup. The paper offers no physical argument for preferring KASCADE, and the >10σ rejection of Max is the only quantitative basis for that preference; once that rejection is corrected for systematics, the distinction may weaken. If the true interstellar spectrum is closer to Max, the same transport and gas assumptions overproduce the LHAASO GDE, so the no-extra-component claim would fail. The manuscript should state this dependence explicitly as a limitation and provide a sensitivity analysis of the LHAASO data to the proton-spectrum choice.
  3. [Sec. 1 and Sec. 2 (unresolved sources)] The assertion that resolved and unresolved sources can only give a minor contribution in the LHAASO sky windows is not demonstrated quantitatively in this manuscript; it is delegated to refs. [15,19]. Since the 'no extra CR source component' conclusion depends on this assumption, please include a quantitative estimate (e.g., source-count distribution or residual flux in the masked windows) or clearly mark the statement as inherited from the cited works.
minor comments (4)
  1. [Sec. 2] The text 'While one would aspect the offset' contains a typo; 'aspect' should be 'expect'. Also, 'taken in mind' should be 'borne in mind'.
  2. [Fig. 2] The provenance of the 'unmasked LHAASO data' should be clarified; the LHAASO public release is masked, so the reader needs to know whether these points come from a reanalysis or from the Tibet-ASγ data shown in the same panel.
  3. [Sec. 1 and Fig. 1] The term 'gamma-optimized' is used without a definition; please state explicitly what was optimized and with respect to which data.
  4. [Sec. 3] The notation 'KRA5γ' is inconsistent with 'KRA-γ' used elsewhere in the same section; please unify the notation.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the LHAASO comparison is a forward test of pre-existing Min/Max models, not a fit.

full rationale

The paper's central comparison is a genuine prediction: the Min and Max gamma-ray models were fixed in earlier work from direct CR measurements and lower-energy gamma-ray data, and the paper explicitly states that 'the models do not represent a fit of LHAASO data rather they were determined on the basis of CR and lower energy gamma-ray data' (Sec. 1 and Fig. 1 caption). The LHAASO data are then overlaid on these pre-existing predictions; agreement for Min and incompatibility for Max is reported as a test, not as a redefinition of the model. The preference for Min over Max is an a posteriori selection between two pre-existing bracketing hypotheses, and the paper openly presents the Max tension with IceTop/LHAASO direct measurements, including the possibility that 'a revision of current CR models' may be required. Self-citations to KRA-gamma, DRAGON, HERMES, and to the authors' earlier papers supply the models and templates, but the load-bearing evidence is external: LHAASO, Fermi-LAT, IceCube, and ANTARES data are compared with the models rather than used to construct them. Some caveats about systematics, the role of unresolved sources, and the external prior on the interstellar proton spectrum are legitimate scientific concerns, but they are not circularity: the derivation chain does not reduce to its own inputs by construction.

Assumptions & free parameters 5 free parameters · 5 assumptions · 0 invented entities

The central claim adds no new free parameters or invented entities; it is a forward-modeling comparison. All adjustable numbers are inherited from prior fits to CR, Fermi-LAT, and B/C data. The load-bearing inputs are the local CR spectra, the transport prescription, the gas and source distributions, and the neglect of unresolved sources in masked windows.

free parameters (5)
  • CR proton injection spectrum normalization (Min setup) = not quoted in text, calibrated to CALET/DAMPE/KASCADE
    Sets the absolute scale of hadronic gamma-ray emission and is fitted to direct CR spectra in prior work.
  • CR proton injection spectral index and break (Min setup) = broken power-law parameters, not quoted
    Chosen to match KASCADE between 10 TeV and 10 PeV; the Max setup uses a harder IceTop/LHAASO spectrum instead.
  • CR helium injection spectrum = not quoted
    Helium contributes to gamma-ray and neutrino emission; heavier nuclei are treated as negligible.
  • CR transport parameters (diffusion coefficient, halo height, reacceleration) = not quoted
    Inherited from DRAGON fits to CR data, including B/C ratios and secondary-to-primary ratios.
  • Spatial-dependent diffusion normalization (gamma-optimized) = not quoted
    Introduced in the KRA-gamma framework to reproduce Fermi-LAT inner Galaxy data; affects high-energy gamma predictions.
assumptions (5)
  • domain assumption The local CR spectra measured by CALET, DAMPE, and KASCADE are representative of the interstellar CR population in the regions probed by LHAASO.
    The Min model normalizes the source spectrum to these local measurements; if the local spectrum is not representative, the gamma-ray prediction changes. Invoked in the Introduction and Fig. 1 caption.
  • domain assumption The KASCADE proton spectrum is the correct one among conflicting direct measurements, rather than the harder IceTop or LHAASO spectra.
    The central no-extra-component claim holds for the Min setup only; the paper notes the Max setup is incompatible with LHAASO gamma data. See Introduction and Sec. 1.
  • domain assumption Standard CR transport as implemented in DRAGON correctly describes diffusion, reacceleration, and energy losses over the whole Galaxy.
    The gamma and neutrino fluxes are computed by propagating source spectra with DRAGON; transport errors propagate into all predicted maps. Mentioned in Sec. 1.
  • domain assumption The interstellar gas (HI and H2) and CR source spatial distributions used in the model are accurate.
    Hadronic gamma-ray emissivity is proportional to the gas column, and the peaked gas distribution strongly affects inner and outer region predictions. See Sec. 1.
  • domain assumption Unresolved gamma-ray sources contribute negligibly to the LHAASO masked sky windows.
    The no-extra-component conclusion relies on the mask removing source contamination; the paper argues Tibet data may be contaminated but does not quantify residual contribution in LHAASO windows. See Introduction and Sec. 2.

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Cite this review

Pith. "Pith review of The cosmic-ray sea explains the Galactic $\gamma$-ray and $\nu$ diffuse emissions from GeV to PeV." pith.science (2026). https://pith.science/paper/4BNJHBPO

@misc{pith2026250707083,
  author       = {Pith},
  title        = {Pith review of: The cosmic-ray sea explains the Galactic $\gamma$-ray and $\nu$ diffuse emissions from GeV to PeV},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/4BNJHBPO}},
  note         = {Machine review of arXiv:2507.07083}
}
read the original abstract

The LHAASO collaboration has recently released the spectrum and the angular distribution of the gamma-ray Galactic diffuse emission from 1 TeV to 1 PeV measured with the Kilometer-2 Array (KM2A) and the Water Cherenkov Detector Array (WCDA). We show that those data are in remarkably good agreement with a set of pre-existing models that assume the emission to be produced by the Galactic population of cosmic rays if its spectral shape traces that measured by CALET, DAMPE as well as KASCADE at higher energies. No extra-components besides the CR sea is needed to explain LHAASO results. Spatial dependent CR transport models, although not required to reproduce LHAASO results, are in better agreement with them respect to conventional ones and needed to consistently reproduce Fermi-LAT and neutrino data.

Figures

Figures reproduced from arXiv: 2507.07083 by the authors.

Figure 1
Figure 1. The Galactic 𝛾-ray diffuse emission spectra computed with the 𝛾-optimized Min and Max models [16] are compared with LHAASO (KM2A + WCDA) [4] and Fermi-LAT data in the inner and outer Galactic Plane regions (see also [15]). We shaded the energy region covered by the WCDA and KM2A in different colors, for clarity. We obtained Fermi-LAT diffuse data points applying the LHAASO mask and subtracting contribution from sour… view at source ↗
Figure 2
Figure 2. We show here the GDE spectra computed with (left panels) and without (right panels) the mask used by LHAASO in the inner and outer regions probed by that experiment. In the first case the models are compared with LHAASO KM2A and WCDA data. In the second with not-masked LHAASO and Tibet data. In the outer region Tibet data – taken in a slightly different region – are rescaled for illustrative reasons. the TeV [17]. I… view at source ↗
Figure 3
Figure 3. The spectra of the Galactic diffuse emission from the 𝛾-optimized and Base models in the Min configuration are compared to the recent diffuse LHAASO-WCDA data (only statistical errors are available) and Fermi-LAT data (with errorbars indicating statistical and systematic uncertainties from the effective area) in the 15◦ < 𝑙 < 50◦ , |𝑏| < 5 ◦ region. The LHAASO mask is applied to all data sets as well as to the model… view at source ↗
Figures from the paper (1 more)
Figure 4
Figure 4. Figure 4: The predicted full-sky 𝜈 diffuse emission fluxes (per flavor) from the 𝛾-optimized models are compared to the best-fit IceCube flux (1𝜎 bands) extracted from the KRA-𝛾 (cutoff energy of E𝑐 = 5 PeV) and 𝜋 0 models. The predicted flux from the KRA5 𝛾 model is also report…

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