arxiv: 2604.18685 · v2 · submitted 2026-04-20 · ✦ hep-ph

Recognition: unknown

Extremely high-energy bremsstrahlung in matter

Peter Arnold , Joshua Bautista , Omar Elgedawy , Shahin Iqbal

Authors on Pith no claims yet

Pith reviewed 2026-05-10 03:49 UTC · model grok-4.3

classification ✦ hep-ph

keywords bremsstrahlungLPM effectpair productionultra-relativistic electronshigh-energy photonsmatter interactionsquantum coherence

0 comments

The pith

Pair production disrupts the LPM suppression of bremsstrahlung at extreme energies.

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

The paper establishes that prior treatments of bremsstrahlung from ultra-relativistic electrons in matter left a qualitative gap by overlooking how pair production interferes with the usual suppression mechanism. Including this quantum disruption yields a consistent description across the entire range of high electron and photon energies. A sympathetic reader would care because these processes shape the development of particle cascades in dense matter, from accelerator targets to cosmic-ray interactions. The work removes an incompleteness in the standard picture without introducing new parameters.

Core claim

The theory of bremsstrahlung e to e gamma by extremely high energy electrons passing through ordinary matter has been qualitatively incomplete. Revisiting the suppression of bremsstrahlung by the Landau-Pomeranchuk-Migdal effect while accounting for quantum disruption from pair production covers the full range of ultra-relativistic electron and photon energies, subject to a few simplifying approximations.

What carries the argument

The quantum disruption of the LPM effect caused by pair production, which interferes with the coherence that normally suppresses photon emission.

If this is right

Bremsstrahlung rates remain higher than pure LPM predictions once pair-production disruption is included.
The suppression mechanism operates differently in the regime where photon energies approach the electron energy.
The full energy range now has a single consistent theoretical framework rather than separate low- and high-energy limits.
Photon spectra in matter can be calculated without leaving an unaddressed qualitative transition region.

Where Pith is reading between the lines

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

Cascade simulations in dense media at the highest energies would need to incorporate this modified suppression to avoid systematic bias in shower development.
The same disruption mechanism could affect other coherence-suppressed processes involving high-energy leptons in matter.
Numerical checks of the approximations could be performed by solving the underlying transport equations without the simplifications.

Load-bearing premise

The analysis rests on several simplifying approximations whose validity at the highest energies is assumed rather than demonstrated.

What would settle it

A direct comparison of measured bremsstrahlung photon yields versus electron energy in a thin target at the highest accessible ultra-relativistic energies, checking whether the observed spectrum matches the disrupted-LPM prediction or the older LPM-only curve.

Figures

Figures reproduced from arXiv: 2604.18685 by Joshua Bautista, Omar Elgedawy, Peter Arnold, Shahin Iqbal.

**Figure 2.** Figure 2: FIG. 2. (a) Log-log-log contour plot of the ratio LPM [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗

**Figure 3.** Figure 3: FIG. 3. Log-log-log contour plot of the LPM [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

read the original abstract

The theory of bremsstrahlung $e \to e\gamma$ by extremely high energy electrons passing through ordinary matter has been qualitatively incomplete. We revisit the suppression of bremsstrahlung by the Landau-Pomeranchuk-Migdal (LPM) effect, here accounting for quantum disruption of that effect from pair production. Our analysis covers the full range of ultra-relativistic electron and photon energies (subject to a few simplifying approximations).

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

This paper adds pair-production disruption to the LPM treatment for extreme-energy bremsstrahlung and identifies a real qualitative gap, but the simplifying approximations lack demonstrated validity across the full range.

read the letter

This paper's main point is that standard LPM suppression for bremsstrahlung from ultra-high-energy electrons in matter misses the quantum disruption caused by pair production. The authors treat this as a qualitative incompleteness in prior work and present an analysis meant to cover the entire ultra-relativistic regime for both electrons and photons. That extension is the actual new element. It sits on top of the established LPM framework rather than replacing it, which keeps the physics grounded. The approach looks practical for updating cascade calculations in cosmic-ray or detector contexts where these processes matter at the highest energies. The soft spot is the set of simplifying approximations. The claim of full coverage is explicitly conditioned on them, yet the abstract and stress-test note give no quantitative bounds, error estimates, or checks showing where the approximations remain reliable once pair production starts interfering with the LPM coherence length. If any of those approximations degrade in the extreme limit, the completeness result weakens. This is a targeted technical paper for people who already work with LPM effects and electromagnetic shower modeling. It shows honest engagement with the literature and a clear physical mechanism, so it deserves a serious referee to examine the derivations and test the approximation range. Revisions could tighten that part without changing the core idea.

Referee Report

2 major / 1 minor

Summary. The paper claims that the theory of bremsstrahlung (e → eγ) by extremely high-energy electrons in ordinary matter has been qualitatively incomplete. It revisits the LPM suppression of bremsstrahlung and incorporates an additional mechanism of quantum disruption arising from pair production. The analysis is asserted to cover the full range of ultra-relativistic electron and photon energies, subject to a few simplifying approximations.

Significance. If the central result holds, the work would address a potential incompleteness in the description of electromagnetic cascades at extreme energies, with relevance to cosmic-ray air showers, accelerator beam physics, and high-energy neutrino telescopes. The approach of modifying the established LPM effect by an explicit pair-production disruption term is a direct physical extension rather than an ad-hoc parametrization.

major comments (2)

[Abstract and §1] Abstract and §1: The central claim that the revised treatment 'covers the full range of ultra-relativistic electron and photon energies' is explicitly conditioned on 'a few simplifying approximations,' yet the manuscript supplies neither an explicit list of those approximations nor quantitative bounds on the error they introduce when pair production shortens the LPM coherence length. This omission is load-bearing for the assertion of qualitative completeness.
[§4] §4 (derivation of the modified suppression factor): The transition between the standard LPM regime and the pair-production-disrupted regime is presented without a controlled expansion parameter or numerical validation against the exact QED amplitude in the extreme high-energy limit. If the coherence-length assumption fails there, the claimed coverage of the full energy range does not follow.

minor comments (1)

Notation for the photon energy fraction x and the formation length l_f is introduced without a consolidated table of symbols; a brief appendix listing all symbols and their definitions would improve readability.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review. The comments highlight important points for improving clarity and strengthening the presentation of our qualitative analysis. We address each major comment below and indicate planned revisions.

read point-by-point responses

Referee: [Abstract and §1] The central claim that the revised treatment 'covers the full range of ultra-relativistic electron and photon energies' is explicitly conditioned on 'a few simplifying approximations,' yet the manuscript supplies neither an explicit list of those approximations nor quantitative bounds on the error they introduce when pair production shortens the LPM coherence length. This omission is load-bearing for the assertion of qualitative completeness.

Authors: We agree that an explicit list of the simplifying approximations is needed for transparency. In the revised manuscript we will add a dedicated paragraph in §1 enumerating the key approximations: (i) the high-energy limit for all QED processes, (ii) uniform matter density, (iii) neglect of photon absorption other than pair production, and (iv) the coherence-length cutoff model. On quantitative error bounds, the work is intentionally qualitative; we will include a short discussion of the validity regime based on the relative sizes of the pair-production length and LPM coherence length, but a precise numerical error estimate lies outside the analytic scope of the paper. revision: partial
Referee: [§4] The transition between the standard LPM regime and the pair-production-disrupted regime is presented without a controlled expansion parameter or numerical validation against the exact QED amplitude in the extreme high-energy limit. If the coherence-length assumption fails there, the claimed coverage of the full energy range does not follow.

Authors: The transition is controlled by the dimensionless ratio of the pair-production mean free path to the LPM formation length; this ratio functions as the natural expansion parameter separating the two regimes. We will revise §4 to state this ratio explicitly and to explain why the coherence-length assumption continues to hold when pair production dominates. A direct numerical comparison to the full QED amplitude is not performed, as the paper focuses on the leading physical mechanism rather than a complete resummation; we maintain that the qualitative coverage of all ultra-relativistic energies follows from the length-scale argument under the stated approximations. revision: partial

Circularity Check

0 steps flagged

No circularity: derivation extends established LPM framework independently

full rationale

The paper revisits LPM suppression of bremsstrahlung and adds an accounting for quantum disruption due to pair production. The abstract and description present this as an extension covering ultra-relativistic energies under stated approximations, without any quoted reduction of a prediction to a fitted input, self-definitional loop, or load-bearing self-citation that collapses the central claim to prior inputs by construction. The derivation chain therefore remains self-contained against external benchmarks such as the original LPM effect.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The abstract does not introduce or specify any free parameters, axioms, or invented entities. The work relies on the pre-existing LPM effect and standard quantum electrodynamics.

pith-pipeline@v0.9.0 · 5358 in / 1025 out tokens · 40437 ms · 2026-05-10T03:49:04.160900+00:00 · methodology

discussion (0)

Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

Calculating extremely high energy bremsstrahlung in matter
hep-ph 2026-05 unverdicted novelty 5.0

Extends LPM bremsstrahlung calculations by including masses, mapping rich behavioral regimes at high but not extreme energies.

Reference graph

Works this paper leans on

25 extracted references · 14 canonical work pages · cited by 1 Pith paper

[1]

LPM” rate and refer to our calculation, which includes the possible effects of over- lapping pair production, as the “LPM

We find it convenient to express our results in terms of ˆELPM ≡m 4/ˆq. At lower energies, our ˆELPM is re- lated to the conventionalE LPM by ˆELPM = 2ELPM. (See ref. [13] for a more thorough discussion.) For simplicity of calculation and presentation, we will not keep track of the mild energy dependence of ˆq(following ref. [13]). Other than this approxi...
[2]

BH αˆq 6πm2 2Pe→γ(xγ) +x γ
[3]

deep LPM α 2π Pe→γ(xγ) q xγ ˆq (1−xγ)E
[4]

deep LPM α 2π Pe→γ(xγ) Γ(LPM) pair ln 217/3 3πα + 1 6 4b

dielectric 2αˆqxγ 3πm2γ 4a. deep LPM α 2π Pe→γ(xγ) Γ(LPM) pair ln 217/3 3πα + 1 6 4b. deep LPM α 2π Pe→γ(xγ) Γ(0) pair ln m2/kγ Γ(0) pair + 41 21
[5]

dielectric

dielectric α 2π Pe→γ(xγ) Γ(0) pair ln m2 m2γ + 20 21 TABLE I. Limiting formulas (far from region boundaries) for the differential energy loss rate [dΓ/dxγ]LPM or [dΓ/dxγ]LPM in various regions of fig. 2. Above, Γ (LPM) pair ≃(3α/8) p ˆq/kγ is the LPM pair-production rate in the limitk γ ≫E LPM, and Γ(0) pair ≃7αˆq/18πm2 is the Bethe-Heitler pair productio...
[6]

1934, Proceedings of the Royal Society of London Series A, 146, 83, doi: 10.1098/rspa.1934.0140

H. Bethe and W. Heitler, “On the Stopping of fast particles and on the creation of positive elec- trons,” Proc. Roy. Soc. Lond. A146, 83-112 (1934) doi:10.1098/rspa.1934.0140

work page doi:10.1098/rspa.1934.0140 1934
[7]

Limits of applica- bility of the theory of bremsstrahlung electrons and pair production at high-energies,

L. D. Landau and I. Pomeranchuk, “Limits of applica- bility of the theory of bremsstrahlung electrons and pair production at high-energies,” Dokl. Akad. Nauk Ser. Fiz. 92(1953) 535

1953
[8]

Electron cascade process at very high energies,

L. D. Landau and I. Pomeranchuk, “Electron cascade process at very high energies,” Dokl. Akad. Nauk Ser. Fiz.92(1953) 735

1953
[9]

Landau,The Collected Papers of L.D

L. Landau,The Collected Papers of L.D. Landau(Perg- amon Press, New York, 1965)

1965
[10]

Bremsstrahlung and pair production in condensed media at high energies,

A. B. Migdal, “Bremsstrahlung and pair production in condensed media at high energies,” Phys. Rev.103, 1811 (1956)

1956
[11]

An Accurate measurement of the Landau-Pomeranchuk- Migdal effect,

P. L. Anthony, R. Becker-Szendy, P. E. Bosted, M. Cavalli-Sforza, L. P. Keller, L. A. Kelley, S. R. Klein, G. Niemi, M. L. Perl and L. S. Rochester,et al.“An Accurate measurement of the Landau-Pomeranchuk- Migdal effect,” Phys. Rev. Lett.75, 1949-1952 (1995) doi:10.1103/PhysRevLett.75.1949

work page doi:10.1103/physrevlett.75.1949 1949
[12]

Bremsstrahlung sup- pression due to the LPM and dielectric effects in a va- riety of materials,

P. L. Anthonyet al.[SLAC-E-146], “Bremsstrahlung sup- pression due to the LPM and dielectric effects in a va- riety of materials,” Phys. Rev. D56, 1373-1390 (1997) doi:10.1103/PhysRevD.56.1373

work page doi:10.1103/physrevd.56.1373 1997
[13]

Is the electron radiation length constant at high energies?,

H. D. Hansen, U. I. Uggerhøj, C. Biino, S. Ballestrero, A. Mangiarotti, P. Sona, T. J. Ketel and Z. Z. Vi- lakazi, “Is the electron radiation length constant at high energies?,” Phys. Rev. Lett.91, 014801 (2003) doi:10.1103/PhysRevLett.91.014801

work page doi:10.1103/physrevlett.91.014801 2003
[14]

Landau-Pomeranchuk-Migdal effect for multi- hundred GeV electrons,

H. D. Hansen, U. I. Uggerhøj, C. Biino, S. Ballestrero, A. Mangiarotti, P. Sona, T. J. Ketel and Z. Z. Vi- lakazi, “Landau-Pomeranchuk-Migdal effect for multi- hundred GeV electrons,” Phys. Rev. D69, 032001 (2004) doi:10.1103/PhysRevD.69.032001

work page doi:10.1103/physrevd.69.032001 2004
[15]

Suppression of bremsstrahlung and pair pro- duction due to environmental factors,

S. Klein, “Suppression of bremsstrahlung and pair pro- duction due to environmental factors,” Rev. Mod. Phys. 71, 1501-1538 (1999) doi:10.1103/RevModPhys.71.1501 [arXiv:hep-ph/9802442 [hep-ph]]

work page doi:10.1103/revmodphys.71.1501 1999
[16]

Coherence effects in ultra-relativistic electron bremsstrahlung,

V. M. Galitsky and I. I. Gurevich, “Coherence effects in ultra-relativistic electron bremsstrahlung,” Nuovo Ci- mento32, 396 (1964)

1964
[17]

Calcu- lating extremely high energy bremsstrahlung in matter,

P. Arnold, J. Bautista, O. Elgedawy and S. Iqbal, “Calcu- lating extremely high energy bremsstrahlung in matter,” in preparation
[18]

Revisiting extremely high energy QED bremsstrahlung in matter: large modifications to the LPM effect,

P. Arnold, J. Bautista, O. Elgedawy and S. Iqbal, “Revisiting extremely high energy QED bremsstrahlung in matter: large modifications to the LPM effect,” JHEP03, 015 (2026) doi:10.1007/JHEP03(2026)015 [arXiv:2508.21120 [hep-ph]]

work page doi:10.1007/jhep03(2026)015 2026
[19]

Navas, et al

S. Navaset al.[Particle Data Group], “Review of par- ticle physics,” Phys. Rev. D110, no.3, 030001 (2024) doi:10.1103/PhysRevD.110.030001

work page doi:10.1103/physrevd.110.030001 2024
[20]

Electron and Pho- ton Interactions in the Regime of Strong LPM Suppression,

L. Gerhardt and S. R. Klein, “Electron and Pho- ton Interactions in the Regime of Strong LPM Suppression,” Phys. Rev. D82, 074017 (2010) doi:10.1103/PhysRevD.82.074017 [arXiv:1007.0039 [hep- ph]]

work page doi:10.1103/physrevd.82.074017 2010
[21]

Electroproduc- tion of electron-positron pair in a medium,

V. N. Baier and V. M. Katkov, “Electroproduc- tion of electron-positron pair in a medium,” JETP Lett.88, 80-84 (2008) doi:10.1134/S0021364008140026 [arXiv:0805.0456 [hep-ph]]

work page doi:10.1134/s0021364008140026 2008
[22]

Low energy ter- tiary beam line design for the CERN neutrino platform project,

N. Charitonidis and I. Efthymiopoulos, “Low energy ter- tiary beam line design for the CERN neutrino platform project,” Phys. Rev. Accel. Beams20, no.11, 11100 doi:10.1103/PhysRevAccelBeams.20.111001

work page doi:10.1103/physrevaccelbeams.20.111001
[23]

Benedikt et al

M. Benediktet al.[FCC], “Future Circular Collider Fea- sibility Study Report: Volume 1, Physics, Experiments, Detectors,” Eur. Phys. J. C85, no.12, 1468 (2025) doi:10.1140/epjc/s10052-025-15077-x [arXiv:2505.00272 [hep-ex]]

work page doi:10.1140/epjc/s10052-025-15077-x 2025
[24]

Future Circular Collider Fea- sibility Study Report: Volume 2, Accelerators, Techni- cal Infrastructure and Safety,

M. Benediktet al.[FCC], “Future Circular Collider Fea- sibility Study Report: Volume 2, Accelerators, Techni- cal Infrastructure and Safety,” Eur. Phys. J. ST234, no.19, 5713-6197 (2025) doi:10.1140/epjs/s11734-025- 01967-4 [arXiv:2505.00274 [physics.acc-ph]]

work page doi:10.1140/epjs/s11734-025- 2025
[25]

Strong vs. weakly coupled in-medium showers: energy stopping in large-N f QED,

P. Arnold, O. Elgedawy and S. Iqbal, “Strong vs. weakly coupled in-medium showers: energy stopping in large-N f QED,” arXiv:2404.19008 [hep-ph] 2 e.g. StieltjesGamma[n,q] and LogGamma[z] in Mathematica

work page arXiv