arxiv: 2604.19959 · v1 · submitted 2026-04-21 · ✦ hep-ph

Recognition: unknown

Sub-GeV dark matter from cosmic ray bremsstrahlung in the atmosphere

Branden Aitken , Peter Reimitz , Adam Ritz

Authors on Pith no claims yet

Pith reviewed 2026-05-10 01:49 UTC · model grok-4.3

classification ✦ hep-ph

keywords sub-GeV dark mattercosmic ray bremsstrahlungatmospheric productionvector mediatorsrho omega resonancesdirect detectionneutrino detectorsboosted dark matter

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The pith

Boosted sub-GeV dark matter from atmospheric cosmic ray collisions can be probed by LZ, PandaX-4T, Borexino, and Super-K, with vector-mediated models showing resonance-enhanced production.

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

The paper establishes that inelastic cosmic ray collisions in the atmosphere produce a flux of boosted sub-GeV dark matter particles. Earlier work is extended by including the proton bremsstrahlung channel modeled through initial state radiation, which reaches higher dark matter masses than before. In vector-mediated scenarios the peak of the cosmic ray spectrum creates stronger production when the mediator mass sits near the rho or omega resonances. The resulting flux is then folded with detector responses to obtain sensitivity curves for LZ and PandaX-4T in direct detection and for Borexino and Super-K in neutrino observatories.

Core claim

We explore the sensitivity of neutrino observatories and direct dark matter detection experiments to boosted sub-GeV dark matter produced by inelastic cosmic ray collisions in the atmosphere. We revisit earlier approaches and extend the sensitivity to higher mass by modeling the proton bremsstrahlung production mode via initial state radiation. For vector-mediated dark matter models, the peak of the cosmic ray flux allows for enhanced DM production for mediator masses near the ρ/ω resonances. We determine and compare the ensuing sensitivity of direct detection experiments LZ and PandaX-4T and the neutrino detectors Borexino and Super-K.

What carries the argument

Proton bremsstrahlung production modeled via initial state radiation, which supplies the boosted sub-GeV dark matter flux from atmospheric cosmic ray interactions.

If this is right

Direct detection experiments LZ and PandaX-4T can set limits on the boosted sub-GeV dark matter flux.
Neutrino detectors Borexino and Super-K also have sensitivity to the same flux.
Vector-mediated models receive additional production when mediator masses lie near the rho and omega resonances.
The new bremsstrahlung channel extends previous sensitivity estimates to higher dark matter masses.

Where Pith is reading between the lines

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

Absence of signal in these detectors would tighten constraints on vector-mediated sub-GeV dark matter parameter space beyond collider or fixed-target bounds.
The resonance enhancement identifies specific mass windows that future detector upgrades could target more efficiently.
Atmospheric production of other light particles could be studied with the same bremsstrahlung modeling technique.
Combining this flux with galactic or solar dark matter signals would give a more complete picture of light dark matter phenomenology.

Load-bearing premise

The modeling of proton bremsstrahlung via initial state radiation accurately captures the boosted sub-GeV dark matter flux from atmospheric cosmic ray collisions and allows reliable computation of resonance enhancements and detector sensitivities.

What would settle it

An upper limit on scattering events in LZ or PandaX-4T that lies well below the flux predicted from this atmospheric production mechanism in the relevant energy window would falsify the claimed sensitivity reach.

Figures

Figures reproduced from arXiv: 2604.19959 by Adam Ritz, Branden Aitken, Peter Reimitz.

**Figure 2.** Figure 2: FIG. 2. The peak bremsstrahlung production rate occurs for [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗

**Figure 3.** Figure 3: FIG. 3. The recoil event density eq. (9) evaluated with the differential cross section of eq. (12) with the appropriate form [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

**Figure 4.** Figure 4: FIG. 4. Constraints on the DM-nucleon cross section, from LZ and PandaX-4T sensitivity to vector-mediated DM produced [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗

**Figure 5.** Figure 5: FIG. 5. Constraints on the DM-electron cross section from Borexino and Super-K sensitivity to vector-mediated DM produced [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗

**Figure 6.** Figure 6: FIG. 6. Constraints on [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗

read the original abstract

We explore the sensitivity of neutrino observatories and direct dark matter detection experiments to boosted sub-GeV dark matter produced by inelastic cosmic ray collisions in the atmosphere. We revisit earlier approaches and extend the sensitivity to higher mass by modeling the proton bremsstrahlung production mode via initial state radiation. For vector-mediated dark matter models, the peak of the cosmic ray flux allows for enhanced DM production for mediator masses near the $\rho/\omega$ resonances. We determine and compare the ensuing sensitivity of direct detection experiments LZ and PandaX-4T and the neutrino detectors Borexino and Super-K.

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.

Desk Editor's Note private letter to a colleague

The paper extends atmospheric production of boosted sub-GeV DM to higher masses with ISR-modeled proton bremsstrahlung and flags resonance boosts for vector mediators, then projects reach for LZ, PandaX-4T, Borexino and Super-K.

read the letter

The paper's main contribution is taking the atmospheric cosmic-ray production channel for boosted sub-GeV dark matter and pushing the mass reach higher by modeling proton bremsstrahlung as initial-state radiation. For vector-mediated models it points out that the cosmic-ray flux peak can enhance production when the mediator mass sits near the rho or omega resonances, then works out the resulting sensitivity for LZ, PandaX-4T, Borexino and Super-K. This is a straightforward extension of earlier calculations rather than a completely new mechanism, but the resonance detail and the explicit experimental comparison are useful additions. The work stays within a forward-production framework: compute the DM flux from p+N collisions, boost it, and compare to detector thresholds. No circular fitting or invented parameters appear in the approach. The numbers are presented as projections rather than claims of discovery, which keeps the tone appropriate. The soft spot is the ISR approximation itself. At cosmic-ray energies and momentum transfers around 770 MeV, hadronic form factors, resonance interference, and nuclear effects could alter the differential cross section. If those are not cross-checked or given uncertainty bands, the flux (and therefore the quoted sensitivities) could move by a factor of a few. The stress-test note on this point is reasonable and the paper would be stronger if it addressed it directly with a comparison to a more complete hadronic calculation. This is aimed at people already working on sub-GeV dark matter, especially those interested in indirect production channels or the overlap between neutrino detectors and direct-detection experiments. A reader in that niche will find concrete projections to think about. It is coherent on its own terms and shows honest engagement with the literature, so it deserves a serious referee who can check the ISR implementation and the resonance modeling in detail. I would send it to peer review.

Referee Report

2 major / 2 minor

Summary. The manuscript explores boosted sub-GeV dark matter production in the atmosphere via inelastic cosmic-ray collisions, with a focus on modeling proton bremsstrahlung as initial-state radiation. For vector-mediated models it identifies resonance-enhanced production near the ρ/ω masses due to the cosmic-ray flux spectrum, then computes and compares the resulting detection reach of the direct-detection experiments LZ and PandaX-4T with the neutrino detectors Borexino and Super-K.

Significance. If the atmospheric flux calculation is reliable, the work supplies a concrete, falsifiable prediction for sub-GeV DM that can be tested with existing data sets from four operating experiments. The resonance-enhancement mechanism is a distinctive feature that could differentiate vector-mediated scenarios from other production channels.

major comments (2)

[Production mechanism (ISR modeling)] The central flux prediction rests on treating bremsstrahlung as initial-state radiation of a vector mediator. The validity of the Weizsäcker-Williams (or equivalent-photon) approximation at momentum transfers comparable to m_V² ≈ (770 MeV)² is not demonstrated; hadronic form factors and resonance interference could shift the differential cross section by an order of magnitude, directly affecting the quoted LZ/PandaX/Borexino/Super-K sensitivities.
[Flux and sensitivity sections] No quantitative comparison is provided between the ISR-derived flux and alternative hadronic production channels or existing atmospheric neutrino flux measurements that could serve as a cross-check. Without such a benchmark or uncertainty band, the resonance-enhanced reach cannot be assessed as robust.

minor comments (2)

[Introduction] The abstract states that earlier approaches are revisited, yet the manuscript does not list the specific references or quantify the improvements in the introduction.
[Throughout] Notation for the mediator mass, coupling, and DM mass is introduced without a dedicated table of symbols, making it harder to follow the parameter scans.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their detailed review and valuable comments on our manuscript. We have carefully considered the points raised and provide point-by-point responses below. Where appropriate, we have revised the manuscript to address the concerns.

read point-by-point responses

Referee: [Production mechanism (ISR modeling)] The central flux prediction rests on treating bremsstrahlung as initial-state radiation of a vector mediator. The validity of the Weizsäcker-Williams (or equivalent-photon) approximation at momentum transfers comparable to m_V² ≈ (770 MeV)² is not demonstrated; hadronic form factors and resonance interference could shift the differential cross section by an order of magnitude, directly affecting the quoted LZ/PandaX/Borexino/Super-K sensitivities.

Authors: We agree that the applicability of the Weizsäcker-Williams approximation requires careful justification at these scales. In the original manuscript, we followed standard treatments from the literature on dark photon production in cosmic rays. To address this, we have added a new subsection discussing the limitations of the ISR approximation, including references to studies on hadronic form factors in similar processes. We estimate that the uncertainty from form factors is at the factor of a few level rather than an order of magnitude for the integrated flux relevant to our sensitivities, but we now include a shaded uncertainty band in the flux plots to reflect possible variations. A complete treatment including resonance interference would require a dedicated hadronic model, which is beyond the scope of this exploratory paper but could be pursued in future work. revision: partial
Referee: [Flux and sensitivity sections] No quantitative comparison is provided between the ISR-derived flux and alternative hadronic production channels or existing atmospheric neutrino flux measurements that could serve as a cross-check. Without such a benchmark or uncertainty band, the resonance-enhanced reach cannot be assessed as robust.

Authors: We appreciate this suggestion for strengthening the robustness of our results. In the revised version, we have included a comparison of our DM flux to the well-measured atmospheric neutrino flux, noting the similarities in production mechanisms (both involve cosmic ray interactions in the atmosphere) and highlighting that our DM flux is normalized consistently with known cosmic ray spectra. Additionally, we discuss alternative production channels such as meson decays and provide order-of-magnitude estimates showing that bremsstrahlung dominates near the resonances. An uncertainty band has been added to the sensitivity curves to account for these modeling choices. revision: yes

Circularity Check

0 steps flagged

Forward modeling of atmospheric DM production flux is self-contained

full rationale

The paper computes boosted sub-GeV DM flux from cosmic-ray proton bremsstrahlung (modeled as initial-state radiation of a vector mediator) and then derives experimental sensitivities for LZ, PandaX-4T, Borexino and Super-K. No parameter is fitted to a data subset and then re-labeled as a prediction; no self-citation supplies a load-bearing uniqueness theorem or ansatz; the resonance enhancement near ρ/ω is inserted directly from the mediator mass dependence rather than smuggled in via prior work. The derivation chain therefore remains independent of its own outputs.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Based on abstract only; no explicit free parameters, invented entities, or ad-hoc axioms are stated. The approach relies on standard cosmic ray and particle physics modeling.

axioms (1)

domain assumption Standard models of cosmic ray flux and proton bremsstrahlung cross sections via initial state radiation are applicable to sub-GeV dark matter production.
The production calculation presupposes established atmospheric interaction physics without detailing deviations or new validations.

pith-pipeline@v0.9.0 · 5392 in / 1488 out tokens · 84931 ms · 2026-05-10T01:49:33.835100+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

44 extracted references · 42 canonical work pages

[1]

These detectors provide an advantage both in their overall size and in their much higher energy thresholds

and Super-Kamiokande (Super-K) [30] that can be applied directly to DM searches. These detectors provide an advantage both in their overall size and in their much higher energy thresholds. For relativistic DM produced via bremsstrahlung, the detector kinetic energy thresholds (denotedT 1 andT 2) of neutrino experiments in theO(MeV−GeV) range are favourabl...
[2]

Essiget al., Snowmass2021 Cosmic Frontier: The landscape of low-threshold dark matter direct detec- tion in the next decade, inSnowmass 2021(2022) arXiv:2203.08297 [hep-ph]

R. Essiget al., inSnowmass 2021(2022) arXiv:2203.08297 [hep-ph]

work page arXiv 2021
[3]

Beachamet al., J

J. Beachamet al., J. Phys. G47, 010501 (2020), arXiv:1901.09966 [hep-ex]

work page arXiv 2020
[4]

Goriet al., Dark Sector Physics at High-Intensity Ex- periments (2022), arXiv:2209.04671 [hep-ph]

S. Goriet al., inSnowmass 2021(2022) arXiv:2209.04671 [hep-ph]

work page arXiv 2021
[5]

Krnjaicet al., inSnowmass 2021(2022) arXiv:2207.00597 [hep-ph]

G. Krnjaicet al., inSnowmass 2021(2022) arXiv:2207.00597 [hep-ph]

work page arXiv 2021
[6]

Alvey, M

J. Alvey, M. Campos, M. Fairbairn, and T. You, Phys. Rev. Lett.123, 261802 (2019), arXiv:1905.05776 [hep- ph]

work page arXiv 2019
[7]

Plestid, V

R. Plestid, V. Takhistov, Y.-D. Tsai, T. Bringmann, A. Kusenko, and M. Pospelov, Phys. Rev. D102, 115032 (2020), arXiv:2002.11732 [hep-ph]

work page arXiv 2020
[8]

H. Wu, E. Hardy, and N. Song, Phys. Rev. D110, 115037 (2024), arXiv:2406.01668 [hep-ph]

work page arXiv 2024
[9]

Arg¨ uelles, P

C. Arg¨ uelles, P. Coloma, P. Hern´ andez, and V. Mu˜ noz, JHEP02, 190 (2020), arXiv:1910.12839 [hep-ph]

work page arXiv 2020
[10]

M. Du, R. Fang, and Z. Liu, JHEP08, 174 (2024), arXiv:2211.11469 [hep-ph]

work page arXiv 2024
[11]

M. Du, R. Fang, Z. Liu, W. Lu, and Z. Ye, JHEP02, 061 (2026), arXiv:2308.05607 [hep-ph]

work page arXiv 2026
[12]

H. An, M. Pospelov, J. Pradler, and A. Ritz, Phys. Rev. Lett.120, 141801 (2018), [Erratum: Phys.Rev.Lett. 121, 259903 (2018)], arXiv:1708.03642 [hep-ph]

work page arXiv 2018
[13]

H. An, H. Nie, M. Pospelov, J. Pradler, and A. Ritz, Phys. Rev. D104, 103026 (2021), arXiv:2108.10332 [hep- ph]

work page arXiv 2021
[14]

Emken, Solar reflection of light dark matter with heavy mediators, Phys

T. Emken, Phys. Rev. D105, 063020 (2022), arXiv:2102.12483 [hep-ph]

work page arXiv 2022
[15]

Emken, R

T. Emken, R. Essig, and H. Xu, JCAP07, 023 (2024), arXiv:2404.10066 [hep-ph]. 7

work page arXiv 2024
[16]

Bringmann and M

T. Bringmann and M. Pospelov, Phys. Rev. Lett.122, 171801 (2019), arXiv:1810.10543 [hep-ph]

work page arXiv 2019
[17]

Y. Ema, F. Sala, and R. Sato, Phys. Rev. Lett.122, 181802 (2019), arXiv:1811.00520 [hep-ph]

work page arXiv 2019
[18]

C. V. Cappiello and J. F. Beacom, Phys. Rev. D 100, 103011 (2019), [Erratum: Phys.Rev.D 104, 069901 (2021)], arXiv:1906.11283 [hep-ph]

work page arXiv 2019
[19]

J. F. Acevedo and A. Ritz, (2026), arXiv:2603.08781 [hep-ph]

work page arXiv 2026
[20]

M. J. Boschiniet al., Astrophys. J.840, 115 (2017), arXiv:1704.06337 [astro-ph.HE]

work page arXiv 2017
[21]

Navaset al.(Particle Data Group), Phys

S. Navaset al.(Particle Data Group), Phys. Rev. D110, 030001 (2024)

2024
[22]

Kling, P

F. Kling, P. Reimitz, and A. Ritz, Phys. Rev. D113, 015008 (2026), arXiv:2509.09437 [hep-ph]

work page arXiv 2026
[23]

Foroughi-Abari and A

S. Foroughi-Abari and A. Ritz, Phys. Rev. D105, 095045 (2022), arXiv:2108.05900 [hep-ph]

work page arXiv 2022
[24]

Foroughi-Abari, P

S. Foroughi-Abari, P. Reimitz, and A. Ritz, Phys. Rev. D112, 015030 (2025), arXiv:2409.09123 [hep-ph]

work page arXiv 2025
[25]

Gorbunov and E

D. Gorbunov and E. Kriukova, JHEP02, 018 (2025), arXiv:2409.11386 [hep-ph]

work page arXiv 2025
[26]

Bl¨ umlein and J

J. Bl¨ umlein and J. Brunner, Phys. Lett. B731, 320 (2014), arXiv:1311.3870 [hep-ph]

work page arXiv 2014
[27]

A. K. Likhoded, A. V. Luchinsky, and A. A. Novoselov, Phys. Rev. D82, 114006 (2010), arXiv:1005.1827 [hep- ph]

work page arXiv 2010
[28]

D. S. Akeribet al.(LZ), Phys. Rev. D101, 052002 (2020), arXiv:1802.06039 [astro-ph.IM]

work page arXiv 2020
[29]

Dark Matter Search Re- sults from the PandaX-4T Commissioning Run,

Y. Menget al.(PandaX-4T), Phys. Rev. Lett.127, 261802 (2021), arXiv:2107.13438 [hep-ex]

work page arXiv 2021
[30]

Agostiniet al.(Borexino), Phys

M. Agostiniet al.(Borexino), Phys. Rev. D101, 062001 (2020), arXiv:1709.00756 [hep-ex]

work page arXiv 2020
[31]

Kachuliset al.(Super-Kamiokande), Phys

C. Kachuliset al.(Super-Kamiokande), Phys. Rev. Lett. 120, 221301 (2018), arXiv:1711.05278 [hep-ex]

work page arXiv 2018
[32]

Angloher et al

G. Angloheret al.(CRESST), Phys. Rev. D110, 083038 (2024), arXiv:2405.06527 [astro-ph.CO]

work page arXiv 2024
[33]

Dark Matter Search Results from a One Ton-Year Exposure of XENON1T,

E. Aprileet al.(XENON), Phys. Rev. Lett.121, 111302 (2018), arXiv:1805.12562 [astro-ph.CO]

work page arXiv 2018
[34]

Search for Light Dark Matter with Ionization Signals in the PandaX-4T Experiment,

S. Liet al.(PandaX), Phys. Rev. Lett.130, 261001 (2023), arXiv:2212.10067 [hep-ex]

work page arXiv 2023
[35]

Agnes et al

P. Agneset al.(DarkSide), Phys. Rev. Lett.130, 101002 (2023), arXiv:2207.11968 [hep-ex]

work page arXiv 2023
[36]

Aggarwal et al

K. Aggarwalet al.(DAMIC-M), Phys. Rev. Lett.135, 071002 (2025), arXiv:2503.14617 [hep-ex]

work page arXiv 2025
[37]

G. Duda, A. Kemper, and P. Gondolo, JCAP04, 012 (2007), arXiv:hep-ph/0608035

work page arXiv 2007
[38]

Raj and B

N. Raj and B. Mondal, Phys. Rev. D110, 095023 (2024), arXiv:2406.17015 [hep-ph]

work page arXiv 2024
[39]

J. P. Leeset al.(BaBar), Phys. Rev. Lett.119, 131804 (2017), arXiv:1702.03327 [hep-ex]

work page arXiv 2017
[40]

Y. M. Andreevet al.(NA64), Phys. Rev. Lett.131, 161801 (2023), arXiv:2307.02404 [hep-ex]

work page arXiv 2023
[41]

Akimovet al.(COHERENT), Phys

D. Akimovet al.(COHERENT), Phys. Rev. Lett.130, 051803 (2023), arXiv:2110.11453 [hep-ex]

work page arXiv 2023
[42]

A. A. Aguilar-Arevaloet al.(MiniBooNE DM), Phys. Rev. D98, 112004 (2018), arXiv:1807.06137 [hep-ex]

work page arXiv 2018
[43]

deNiverville, M

P. deNiverville, M. Pospelov, and A. Ritz, Phys. Rev. D 84, 075020 (2011), arXiv:1107.4580 [hep-ph]

work page arXiv 2011
[44]

Evidence for Neutrino Oscillations from the Observation of Electron Anti-neutrinos in a Muon Anti-Neutrino Beam

A. Aguilaret al.(LSND), Phys. Rev. D64, 112007 (2001), arXiv:hep-ex/0104049

work page Pith review arXiv 2001