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REVIEW 2 major objections 5 minor 101 references

This paper argues that axion-like particles produced in neutron stars are best sought in the MeV band, where archival COMPTEL data already constrain previously open parameter space and the future COSI telescope could test much more.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

T0 review · deepseek-v4-flash

2026-08-05 00:33 UTC pith:IOK4B3DP

load-bearing objection Solid, honest ALP flux study of four pulsars that makes a good case for MeV searches, but its headline COMPTEL exclusion sits on a nucleon-coupling benchmark five times above the SN1987A bound quoted in the same paper. the 2 major comments →

arxiv 2608.00589 v1 pith:IOK4B3DP submitted 2026-08-01 astro-ph.HE hep-ph

Gamma Rays from ALP-Photon Conversion and Inverse Compton Reprocessing in Neutron Star Magnetospheres

classification astro-ph.HE hep-ph
keywords axion-like particlesneutron starsmagnetarsALP-photon conversioninverse Compton scatteringMeV gamma-ray astronomyCOMPTELCOSI
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

The paper tries to establish where axion-like particles (ALPs) produced inside neutron stars would appear as gamma rays. For the young pulsars and magnetar-like pulsars it models, ALP emission is dominated by nucleon-nucleon bremsstrahlung, and the photons produced by ALP-photon conversion land in the hard X-ray and MeV band rather than in Fermi-LAT's GeV range. Inverse Compton scattering can upscatter some of these photons above 100 MeV, but the predicted flux is too weak for Fermi-LAT to detect. The paper concludes that existing COMPTEL data already exclude parts of the ALP parameter space, including some previously untested high masses, and that a future MeV telescope such as COSI can probe substantially more. If correct, the science case for MeV gamma-ray observatories is strengthened and a previously untested region of the ALP mass-coupling plane is closed.

Core claim

On the paper's own terms, the central claim is that neutron-star magnetospheres do produce observable ALP-induced gamma rays, but in the MeV gap rather than in the Fermi-LAT band. The chain runs from a core temperature of about 10^9 K, through T^6-scaling ALP emissivities, through ALP-photon conversion at radii roughly 10^3 to 10^4 stellar radii where the QED vacuum-polarization term, the plasma term, and the ALP mass term balance in the mixing matrix, to a resulting photon flux peaking below about 1 MeV. Inverse Compton reprocessing by magnetospheric electrons can shift emission above 100 MeV, but the resulting energy flux stays around 10^-11 MeV cm^-2 s^-1, below Fermi-LAT sensitivity. The

What carries the argument

The load-bearing object is the photon-ALP mixing system in the neutron-star magnetosphere, described by a three-state Schr\"odinger-like equation with diagonal photon terms from plasma frequency and QED vacuum birefringence, an ALP mass term, and an off-diagonal mixing term proportional to g_a\gamma B sin\theta. Efficient conversion occurs where the accumulated phase difference becomes of order one, defining a conversion radius, typically far from the stellar surface because strong-field QED suppresses mixing close to the star. The plasma density entering the mixing is taken from the standard corotating magnetospheric charge-density model, with a steep atmospheric layer near the surface and

Load-bearing premise

The absolute ALP luminosity rests on two imported inputs: a core temperature of about 10^9 K from the standard cooling law, and nucleon couplings g_an = g_ap = 5e-9 GeV^-1, which exceed the SN1987A bound of about 1e-9 GeV^-1 that the paper itself quotes; since every flux scales as the square of these couplings, a smaller coupling or colder core weakens the derived exclusions by a comparable factor.

What would settle it

Measure the 0.2-5 MeV spectrum of the Crab with COSI and test whether adding an ALP-conversion component improves the fit over a pure astrophysical pulsar model: if the residual is consistent with no ALP component across the masses where the paper predicts a best-fit feature, the central signal claim for those masses is falsified; conversely, a detection of the predicted oscillatory spectral feature would confirm it. A direct measurement or improved inference of the Crab's core temperature would also test the T_core normalization on which all predicted fluxes scale.

Watch this falsifier. Get emailed when new claim-graph text bears on it.

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If this is right

  • Fermi-LAT is not the right instrument for this channel: null results in the 100 MeV-to-GeV band do not constrain NS-produced ALPs, because the primary converted flux sits below about 1 MeV.
  • Existing COMPTEL data on the Crab already exclude part of the ALP parameter space, and for m_a above about 10^-5 eV the limits reach previously unconstrained region.
  • A future MeV telescope with COSI-like sensitivity could probe g_a\gamma values below current CAST limits for light ALPs and extend into new high-mass territory.
  • The Crab, being the closest target, gives the strongest projected sensitivity despite its lower magnetic field, while magnetar-like pulsars add complementary reach through their stronger fields and different plasma environments.
  • Combining several pulsar targets in a joint analysis should harden the constraints, since conversion probability depends on magnetic-field strength, distance, and magnetospheric conditions.

Where Pith is reading between the lines

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

  • Our inference: if the nucleon couplings were lowered to the SN1987A bound that the paper itself quotes, roughly a factor of five below the adopted benchmark, all fluxes and derived g_a\gamma exclusions would shrink by the same factor-squared, likely erasing the new high-mass exclusion; this is a straightforward re-run rather than a paper claim.
  • Our inference: the no-GeV-signal conclusion is conditional on the adopted magnetospheric pair spectrum and multiplicity; at the high end of the pair-multiplicity range, inverse-Compton reprocessing could bring the >100 MeV flux closer to Fermi-LAT sensitivity, so the negative GeV result is model-dependent.
  • Our inference: the same production-and-conversion machinery could be applied to additional high-field neutron stars with accurately known distances to build a target list for MeV surveys, exploiting the diversity of magnetic fields, ages, and plasma densities in the population.
  • Our inference: the assumption of radial, equatorial propagation maximizes the transverse magnetic field and thus likely sets an upper bound on conversion; a full ray-tracing treatment with non-dipolar field geometry could raise or lower individual source predictions, so source-by-source flux uncertainties are probably larger than the central values shown.

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

2 major / 5 minor

Summary. The paper studies ALP production in neutron star cores via nucleon-nucleon bremsstrahlung, pion-assisted processes, electron bremsstrahlung, and Primakoff conversion, then calculates ALP-photon conversion in the NS magnetosphere and the Galactic magnetic field for four representative pulsars (Crab, PSR J1119-6127, PSR J1846-0258, PSR J1341-6220). It further considers inverse-Compton reprocessing of the converted photons. The central quantitative conclusions are (i) the ALP-induced flux is too small to be detectable in the Fermi-LAT band, (ii) the unconverted flux lies in the MeV gap and can be probed by COMPTEL and future instruments such as COSI, and (iii) for m_a ≳ 10^-5 eV the COMPTEL Crab data begin to exclude previously unconstrained (m_a, g_aγ) parameter space. The derivation chain is standard and transparently presented, and the paper is unusually honest about its limitations, explicitly disclaiming the COMPTEL best-fit points and the detectability of the IC-boosted component.

Significance. If the conclusions hold, the paper strengthens the scientific case for MeV gamma-ray observatories and provides a concrete, falsifiable target for COSI. The manuscript's main strengths are the clarity of the production/conversion formalism, the use of external validated codes and data (iminuit, 4FGL, 3PC, COMPTEL), and an honest assessment of systematics. The central result that the signal sits in the MeV gap rather than the Fermi-LAT band is robust to the main modeling uncertainties. However, the quantitative claim of a new high-mass COMPTEL exclusion rests on a benchmark nucleon coupling that exceeds the SN1987A bound quoted in the same paper, and the sensitivity of that claim to g_N and T_core is not quantified. This makes the headline exclusion provisional rather than established.

major comments (2)
  1. [Sec. 2.6, Sec. 5, Fig. 9] The COMPTEL exclusion for m_a ≳ 10^-5 eV is controlled by the ALP luminosity, which is set by the benchmark g_an = g_ap = 5×10^-9 GeV^-1 adopted in Sec. 2.6. This value exceeds the SN1987A bound g_ap ~ g_an < 10^-9 GeV^-1 that the paper itself quotes in Sec. 1 [13,14]. Since the emissivities (Eqs. 6, 8, 9) scale as g_N^2 and the flux (Eq. 48) scales as g_N^2 g_aγ^2, the derived upper limit on g_aγ scales inversely with g_N. Lowering g_N to the quoted 10^-9 GeV^-1 shifts the blue exclusion curve in Fig. 9 upward by a factor of about 5. The paper does not quantify the margin between this curve and the gray astrophysical bounds; if the margin is smaller than this factor, the claimed exclusion of previously unconstrained parameter space disappears. The same rescaling weakens the COSI projections in Fig. 11. The authors should either adopt a benchmark consistent with the quoted SN1987A bound
  2. [Eq. (1), Sec. 2.6, Sec. 5] The absolute ALP luminosity inherits a strong sensitivity to the core temperature, T_core, because the dominant nucleon-bremsstrahlung emissivities scale as T^6 and the electron channels as T^4. Equation (1) uses the simple cooling law T_core ~ 10^9 K (10^3 yr/t_NS)^(1/6), and the paper does not propagate any uncertainty in T_core into the exclusion or sensitivity curves. A factor-of-2 decrease in T_core reduces the ALP luminosity by a factor of 64 and weakens the derived g_aγ limits by a factor of about 8. This is comparable to or larger than the g_N rescaling discussed above, and could also erase the reported high-mass COMPTEL exclusion. The authors should provide a sensitivity band or a representative alternative cooling model (e.g., including superfluid pairing or different EoS) to show that the new exclusion is not an artifact of a single optimistic temperature choice.
minor comments (5)
  1. [Eq. (55)] The expression for the target photon density, nγ(E,r) ≃ 1/(4πr^2) dNγ/dE dt, is dimensionally inconsistent unless one works in units with c=1. The authors should either include the factor 1/c or explicitly state that c=1 is used throughout. As written, readers who reinstate c will find the IC emissivity (Eq. 51) and flux (Eq. 56) to be off by powers of c.
  2. [Sec. 2.6] The phrase 'benchmark values motivated by current limits' is misleading for g_ap = g_an = 5×10^-9 GeV^-1, since Sec. 1 quotes a stricter SN1987A bound of <10^-9 GeV^-1. Please rephrase to clarify that this is an optimistic benchmark, not a limit-satisfying value.
  3. [Sec. 4.1] Typo: 'PSR 1116-6127' should be 'PSR J1119-6127'.
  4. [Eq. (6)] Typo: 'where where' should be 'where'.
  5. [Fig. 9 caption] The right-panel axis label '2 = 2 null 2 best' is garbled; it should read 'χ²_null − χ²_best'.

Circularity Check

0 steps flagged

No significant circularity: the predicted fluxes are compared to independent external data (COMPTEL/Crab) and the production/conversion inputs are taken from external references, not fitted to the target.

full rationale

The derivation chain is self-contained against external anchors. ALP production rates (Eqs. 6, 8, 9, 13, 16, 19, 24) are taken from independent literature [22,56,62,68]; the core temperature scaling (Eq. 1) comes from Yakovlev–Pethick; the magnetospheric conversion uses the standard Raffelt–Stodolsky mixing formalism with Goldreich–Julian densities and QED polarization from Adler; and the Galactic conversion adopts the Jansson–Farrar magnetic-field model with a cross-check against Pshirkov et al. The observable flux of Eq. (48) is then compared to archival COMPTEL data through a profile-likelihood test, with no parameter fitted to the target being renamed as a prediction. The benchmark choice g_ap = g_an = 5e-9 GeV^-1 in Sec. 2.6 exceeds the SN1987A bound quoted in Sec. 1, and since all fluxes scale as g_N^2 the derived g_aγ exclusions scale inversely as g_N; this is a parameter-normalization/robustness concern, not circularity, because the prediction is not defined in terms of the data and is not a self-consistent reduction. Existing self-citations (e.g., [79] for Galactic propagation) are non-load-bearing and are independently cross-checked within the paper.

Axiom & Free-Parameter Ledger

7 free parameters · 6 axioms · 0 invented entities

The paper's genuine contribution is the pipeline: production spectra in NS interiors, magnetospheric plus Galactic conversion, IC reprocessing, and the COMPTEL/COSI statistical analysis. Almost all physics inputs are imported from prior literature: emissivities from [22, 56, 62, 68], conversion formalism from [47, 22, 72], Galactic field from [80, 81, 82], plasma density from [73], electron spectra from [90-94]. The free parameters listed above set the absolute normalization of every prediction and constraint; the largest is the benchmark nucleon coupling, which exceeds the SN1987A bound quoted in the paper's own introduction. No new entities (particles, forces, dimensions) are postulated.

free parameters (7)
  • Pair multiplicity kappa = 10^4 (stated range 10^2-10^5)
    Sets the magnetospheric electron density n_e(r) = kappa n_GJ(r) in Eq. (31), is used to compute n_e,0 in Table 1, and enters both the conversion probability and the IC scattering rates. A factor of 100 in kappa shifts the plasma-frequency floor and the IC optical depth.
  • Benchmark nucleon couplings g_an, g_ap = 5x10^-9 GeV^-1
    Fixed in Sec. 2.6 as 'motivated by current limits', but exceeding the SN1987A bound (g_ap ~ g_an < 10^-9 GeV^-1) that the paper itself quotes in Sec. 1. ALP production scales as g_N^2, so this benchmark sets the absolute normalization of every flux, limit, and projection.
  • Benchmark electron coupling g_ae = 1.3x10^-13 GeV^-1
    Fixed in Sec. 2.6 from the red-giant bound [12]; affects only the subdominant electron bremsstrahlung channels.
  • Core temperature T_core(t_NS) = 0.0465-0.086 MeV for the four pulsars (Eq. 1)
    Comes from the analytic cooling law T_core ~ 10^9 K (10^3 yr/t_NS)^(1/6). Emissivities scale steeply with T (Q ~ T^6 for nucleon bremsstrahlung), so a factor 2 in T changes the flux by more than an order of magnitude.
  • Magnetospheric integration radius R_max = 10^4 r0
    The conversion probability of Sec. 3.1 and the IC integral of Eq. (56) are integrated up to R_max = 10^4 r0. For the Crab (r0 ~ 13 km, light cylinder ~ 10^8 cm), this extends beyond the light cylinder where the dipole field and GJ plasma description break down.
  • Pion-nucleon correction factor C_pi = 1/4
    Taken from Appendix C of [22] to correct the one-pion-exchange overestimate; enters the dominant nucleon-bremsstrahlung emissivity linearly (Eqs. 6, 8, 9).
  • IC electron spectrum parameters = p1 ~ 1.5 +/- 0.5, p2 ~ 2.5 +/- 0.5, gamma_break ~ 10^5, gamma_min ~ 10-100, gamma_max ~ 10^7-10^8
    Broken power law of Eq. (49) borrowed from pulsar cascade models [90-94]; used for the IC reprocessing channel, which the paper ultimately finds negligible.
axioms (6)
  • domain assumption The adopted emissivity formulas of Eqs. (6)-(24) correctly describe ALP production in neutron star matter
    The central production module is imported wholesale from Refs. [22, 56, 62, 68], including OPE-based rates and the pion-fugacity treatment; the paper does not re-derive or cross-check these.
  • domain assumption The neutron star core is isothermal and thermally relaxed, with T_core from Eq. (1)
    Stated in Sec. 2.1: 'we assume the core has already thermalized'. Real pulsars have temperature gradients, and Q ~ T^6 makes this input critical.
  • domain assumption The magnetosphere is a rotating vacuum dipole with Goldreich-Julian charge density and constant pair multiplicity kappa
    Sec. 3.1, Eqs. (26) and (31). Ignores field-line curvature, current sheets, and regions beyond the light cylinder, and assumes radial equatorial propagation, which maximizes B_T and P(a->gamma) by an unquoted sin^2 theta factor ([72]).
  • standard math The short-wavelength / perturbative conversion probability of Eq. (44) is valid
    Raffelt-Stodolsky mixing formalism imported from [47, 22, 72]; the paper notes the resonant regime is neglected, following [72].
  • domain assumption Resonant cyclotron absorption and pair production do not attenuate the signal
    Sec. 4.1 concludes tau_cyc is small except possibly for the Crab at 0.1 keV, and sets the total optical depth to 3.5x10^-3; absorption is then dropped from the flux pipeline.
  • domain assumption The Jansson-Farrar Galactic magnetic field model with the [82] update and the [85] electron-density model describe propagation to Earth
    Sec. 3.2 adopts a specific field realization for kiloparsec-scale conversion; a cross-check with Pshirkov et al. shows 'minor quantitative differences' that are not propagated into the limits.

pith-pipeline@v1.3.0-alltime-deepseek · 30931 in / 26429 out tokens · 296200 ms · 2026-08-05T00:33:30.150038+00:00 · methodology

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Cite this review

Pith. "Pith review of Gamma Rays from ALP-Photon Conversion and Inverse Compton Reprocessing in Neutron Star Magnetospheres." pith.science (2026). https://pith.science/paper/IOK4B3DP

@misc{pith2026260800589,
  author       = {Pith},
  title        = {Pith review of: Gamma Rays from ALP-Photon Conversion and Inverse Compton Reprocessing in Neutron Star Magnetospheres},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/IOK4B3DP}},
  note         = {Machine review of arXiv:2608.00589}
}
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read the original abstract

Exploring axion-like particle (ALP) signatures from neutron stars (NSs) in the \emph{Fermi}-LAT energy range remains largely unexplored. Neutron stars with exceptionally strong magnetic fields, such as magnetars and pulsars with magnetar-like magnetic fields, provide particularly promising environments for ALP--photon conversion. Magnetars are characterized by surface magnetic fields as large as $B_0\sim(10^{14}$--$10^{15})\,\mathrm{G}$; however, despite their extreme magnetic fields, no steady magnetar emission has been firmly detected in the \emph{Fermi}-LAT energy range, with high-energy activity generally associated with rare flaring episodes. In this work, we investigate ALP production in the interiors of different classes of NSs and the subsequent conversion of ALPs into photons in their magnetospheres. The ALP emissivity is determined by the stellar density and temperature $T$, while the conversion probability is enhanced by the strong magnetic fields surrounding the star. We further account for photon propagation through the Galactic magnetic field, which can provide an additional contribution to the observable photon flux. We investigate the resulting gamma-ray signatures and assess whether ALP-induced emission from NS magnetospheres could be detectable at energies $E\gtrsim100,\mathrm{MeV}$ in the \emph{Fermi}-LAT band. In addition, we consider if the reprocessing of the magnetospheric photons through inverse Compton scattering can shift part of the emission to higher energies and provide an additional observational signature. We use the resulting fluxes to derive constraints from existing gamma-ray observations and to estimate the sensitivity of future MeV--GeV observations, taking COSI as a representative example.

Figures

Figures reproduced from arXiv: 2608.00589 by Bradley J. Kavanagh, Conrado A. Torres, Federica Giacchino, Giorgio Galanti, Jose M. Diego, Maria A. P\'erez-Garc\'ia.

Figure 1
Figure 1. Figure 1: Energy spectra of ALPs [MeV−1 s −1 ] produced for different internal NS temperatures: T = 108 K, 109 K, 5 ×109 K, and 1010 K, showing separately the contributions from the various production mechanisms. In each of these panels, the total is represented as a black solid line; the nucleon bremsstrahlung contributions from neutron–neutron, proton–proton, and neutron–proton interactions are shown by a blue das… view at source ↗
Figure 2
Figure 2. Figure 2: Total ALP energy spectra [ MeV−1 s −1 ] obtained by summing all individual production channels, for the four temperatures considered (blue, red, green, and orange lines). gap = gan = 5 × 10−9 GeV−1 , gaγ = 10−11 GeV−1 , gae = 1.3 × 10−13 GeV−1 . θˆ component contributes, yielding BT = B0  r0 r 3 sin θ , (28) where r0 ≡ R denotes the stellar radius and r ≥ r0. For simplicity, we consider an equatorial tra… view at source ↗
Figure 3
Figure 3. Figure 3: Parameter space of ALP energy E vs radius r for four PSRs (B0 and ne,0 of each PSR are shown in Tab.1). The color gradient is the logarithmic ratio of the QED term over the plasma term. The solid lines mark the resonance condition of Eq. (42). The ALP mass is fixed at ma = 10−9 eV (white), ma = 10−8 eV (yellow), ma = 10−7 eV (cyan), ma = 10−6 eV (pink). We define a quantity related to the oscillation lengt… view at source ↗
Figure 4
Figure 4. Figure 4: Probability of conversion ALP into photons in PSR 1119-6127, PSR 1341-6220, PSR 0534 [PITH_FULL_IMAGE:figures/full_fig_p015_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Probability of conversion ALP→ γ from ALP produced in PSR J1119-6127 (top left), PSR J1341-6220 (top right), PSR J0534-2200 (bottom left), PSR J1846-0258 (bottom right), for different masses from ma = 10−11 eV to ma = 10−6 eV, and fixed ALP-photon coupling gaγ = 10−11 GeV−1 . 3.3. Photon Spectrum The differential photon flux is given by dΦγ dE = 1 4πd 2 dNa dEdt Pa→γ(E) [MeV−1 cm−2 s −1 ] (48) with d the d… view at source ↗
Figure 6
Figure 6. Figure 6: Top left: Observed flux of PSR J1119-6127 at T = 109 K; Top right: Observed flux of PSR J1341-6220 at T = 5 × 108 K; Bottom left: Observed flux of PSR J0534-2200 at T = 109 K; Bottom right: Observed flux of PSR J1846-0258 at T = 5 × 108 K. All fluxes are computed for gaγ = 10−11 GeV−1 and six ALP mass values (from 10−11 to 10−6 eV). 4. Inverse Compton (IC) and gamma-ray flux In the previous section we have… view at source ↗
Figure 7
Figure 7. Figure 7: Contour plot of electron Lorentz factor γ from Inverse Compton. The parameter space is given by initial photon energy produced in ALP-photon conversion E i γ vs final photon energy in Fermi-LAT range E f γ . The color is the γ given applying the Eq. (50) if we are in Thomson regime, otherwise we have approximated with γ = Ef /me in KN regime. The white line is the limit of the two regimes, γ = me/E i γ . a… view at source ↗
Figure 8
Figure 8. Figure 8: Photon flux after Inverse Compton for the four PSRs applying Eq. ( [PITH_FULL_IMAGE:figures/full_fig_p020_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Constraints on the ALP-photon coupling derived from the COMPTEL observations of the Crab pulsar [ [PITH_FULL_IMAGE:figures/full_fig_p022_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: Photon conversion probability P(E; a → γ) for energy E = 1 MeV, as a function of the ALP mass ma [eV] and the photon–ALP coupling gaγ [GeV−1 ]. Existing hard X-ray and MeV observations, including archival COMPTEL data, can already constrain part of the ALP parameter space, although the sensitivity is limited by the instrumental coverage and by the astrophysical back￾grounds. Our projections show that futu… view at source ↗
Figure 11
Figure 11. Figure 11: Parameter space tested at 95% C.L. by COSI after [PITH_FULL_IMAGE:figures/full_fig_p024_11.png] view at source ↗

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Reference graph

Works this paper leans on

101 extracted references · 22 canonical work pages · 12 internal anchors

  1. [1]

    Arvanitaki, S

    A. Arvanitaki, S. Dimopoulos, S. Dubovsky, N. Kaloper, J. March-Russell, String Axiverse, Phys. Rev. D 81 (2010) 123530.arXiv:0905.4720,doi:10.1103/PhysRevD.81.123530

  2. [2]

    Jaeckel, A

    J. Jaeckel, A. Ringwald, The Low-Energy Frontier of Particle Physics, Ann. Rev. Nucl. Part. Sci. 60 (2010) 405–437.arXiv:1002.0329,doi:10.1146/annurev.nucl.012809.104433

  3. [3]

    Ringwald, Exploring the Role of Axions and Other WISPs in the Dark Universe, Phys

    A. Ringwald, Exploring the Role of Axions and Other WISPs in the Dark Universe, Phys. Dark Univ. 1 (2012) 116–135.arXiv:1210.5081,doi:10.1016/j.dark.2012.10.008

  4. [4]

    R. D. Peccei, H. R. Quinn, CP Conservation in the Presence of Instantons, Phys. Rev. Lett. 38 (1977) 1440– 1443.doi:10.1103/PhysRevLett.38.1440

  5. [5]

    R. D. Peccei, H. R. Quinn, Constraints Imposed by CP Conservation in the Presence of Instantons, Phys. Rev. D 16 (1977) 1791–1797.doi:10.1103/PhysRevD.16.1791

  6. [6]

    Hook, TASI Lectures on the Strong CP Problem and Axions, PoS TASI2018 (2019) 004.arXiv:1812

    A. Hook, TASI Lectures on the Strong CP Problem and Axions, PoS TASI2018 (2019) 004.arXiv:1812. 02669,doi:10.22323/1.333.0004

  7. [7]

    Arias, D

    P. Arias, D. Cadamuro, M. Goodsell, J. Jaeckel, J. Redondo, A. Ringwald, WISPy Cold Dark Matter, JCAP 06 (2012) 013.arXiv:1201.5902,doi:10.1088/1475-7516/2012/06/013

  8. [8]

    Albertus, et al., WISPedia – the WISPs Encyclopedia (2 2026).arXiv:2602.09089

    C. Albertus, et al., WISPedia – the WISPs Encyclopedia (2 2026).arXiv:2602.09089

  9. [9]

    O’Hare, cajohare/axionlimits: Axionlimits,https://cajohare.github.io/AxionLimits/(Jul

    C. O’Hare, cajohare/axionlimits: Axionlimits,https://cajohare.github.io/AxionLimits/(Jul. 2020). doi:10.5281/zenodo.3932430

  10. [10]

    Altenmüller, et al., New Upper Limit on the Axion-Photon Coupling with an Extended CAST Run with a Xe-Based Micromegas Detector, Phys

    K. Altenmüller, et al., New Upper Limit on the Axion-Photon Coupling with an Extended CAST Run with a Xe-Based Micromegas Detector, Phys. Rev. Lett. 133 (22) (2024) 221005.arXiv:2406.16840,doi:10. 1103/PhysRevLett.133.221005

  11. [11]

    Payez, C

    A. Payez, C. Evoli, T. Fischer, M. Giannotti, A. Mirizzi, A. Ringwald, Revisiting the SN1987A gamma-ray limit on ultralight axion-like particles, JCAP 02 (2015) 006.arXiv:1410.3747,doi:10.1088/1475-7516/ 2015/02/006

  12. [12]

    Capozzi, G

    F. Capozzi, G. Raffelt, Axion and neutrino bounds improved with new calibrations of the tip of the red-giant branch using geometric distance determinations, Phys. Rev. D 102 (8) (2020) 083007.arXiv:2007.03694, doi:10.1103/PhysRevD.102.083007

  13. [13]

    Lella, P

    A. Lella, P. Carenza, G. Co’, G. Lucente, M. Giannotti, A. Mirizzi, T. Rauscher, Getting the most on supernova axions, Phys. Rev. D 109 (2) (2024) 023001.arXiv:2306.01048,doi:10.1103/PhysRevD.109.023001

  14. [14]

    Carenza, T

    P. Carenza, T. Fischer, M. Giannotti, G. Guo, G. Martínez-Pinedo, A. Mirizzi, Improved axion emissivity from a supernova via nucleon-nucleon bremsstrahlung, JCAP 10 (10) (2019) 016, [Erratum: JCAP 05, E01 (2020)]. arXiv:1906.11844,doi:10.1088/1475-7516/2019/10/016

  15. [15]

    M. S. Pshirkov, S. B. Popov, Conversion of Dark matter axions to photons in magnetospheres of neutron stars, J. Exp. Theor. Phys. 108 (2009) 384–388.arXiv:0711.1264,doi:10.1134/S1063776109030030

  16. [16]

    B. R. Safdi, Z. Sun, A. Y . Chen, Detecting Axion Dark Matter with Radio Lines from Neutron Star Populations, Phys. Rev. D 99 (12) (2019) 123021.arXiv:1811.01020,doi:10.1103/PhysRevD.99.123021. 25

  17. [17]

    A. Hook, Y . Kahn, B. R. Safdi, Z. Sun, Radio Signals from Axion Dark Matter Conversion in Neutron Star Mag- netospheres, Phys. Rev. Lett. 121 (24) (2018) 241102.arXiv:1804.03145,doi:10.1103/PhysRevLett. 121.241102

  18. [18]

    F. P. Huang, K. Kadota, T. Sekiguchi, H. Tashiro, Radio telescope search for the resonant conversion of cold dark matter axions from the magnetized astrophysical sources, Phys. Rev. D 97 (12) (2018) 123001.arXiv: 1803.08230,doi:10.1103/PhysRevD.97.123001

  19. [19]

    S. J. Lloyd, P. M. Chadwick, A. M. Brown, H.-k. Guo, K. Sinha, Axion Constraints from Quiescent Soft Gamma-ray Emission from Magnetars, Phys. Rev. D 103 (2) (2021) 023010.arXiv:2001.10849,doi: 10.1103/PhysRevD.103.023010

  20. [20]

    T. D. P. Edwards, B. J. Kavanagh, L. Visinelli, C. Weniger, Transient Radio Signatures from Neutron Star Encounters with QCD Axion Miniclusters, Phys. Rev. Lett. 127 (13) (2021) 131103.arXiv:2011.05378, doi:10.1103/PhysRevLett.127.131103

  21. [21]

    Agrawal, et al., Feebly-interacting particles: FIPs 2020 workshop report, Eur

    P. Agrawal, et al., Feebly-interacting particles: FIPs 2020 workshop report, Eur. Phys. J. C 81 (11) (2021) 1015. arXiv:2102.12143,doi:10.1140/epjc/s10052-021-09703-7

  22. [22]

    Fortin, H.-K

    J.-F. Fortin, H.-K. Guo, S. P. Harris, E. Sheridan, K. Sinha, Magnetars and axion-like particles: probes with the hard X-ray spectrum, JCAP 06 (2021) 036.arXiv:2101.05302,doi:10.1088/1475-7516/2021/06/036

  23. [23]

    R. A. Battye, B. Garbrecht, J. I. McDonald, S. Srinivasan, Radio line properties of axion dark matter conversion in neutron stars, JHEP 09 (2021) 105.arXiv:2104.08290,doi:10.1007/JHEP09(2021)105

  24. [24]

    Noordhuis, A

    D. Noordhuis, A. Prabhu, C. Weniger, S. J. Witte, Axion Clouds around Neutron Stars, Phys. Rev. X 14 (4) (2024) 041015.arXiv:2307.11811,doi:10.1103/PhysRevX.14.041015

  25. [25]

    S. Roy, A. Prabhu, C. Thompson, S. J. Witte, C. Blanco, J. Zhang, Searching for axion dark matter near relaxing magnetars, Phys. Rev. D 113 (4) (2026) 043001.arXiv:2505.20450,doi:10.1103/glnt-t93q

  26. [26]

    Bhura, et al., Axion search with telescope for radio astronomy (ASTRA): forecast for observations between 0.5 and 4~GHz (3 2026).arXiv:2603.13194

    U. Bhura, et al., Axion search with telescope for radio astronomy (ASTRA): forecast for observations between 0.5 and 4~GHz (3 2026).arXiv:2603.13194

  27. [27]

    D. R. Lorimer, M. Kramer, Handbook of Pulsar Astronomy, V ol. 4, 2004

  28. [28]

    A. A. Abdo, et al., Search for Gamma-ray Emission from Magnetars with the Fermi Large Area Telescope, Astrophys. J. Lett. 725 (1) (2010) L73–L78.arXiv:1011.0091,doi:10.1088/2041-8205/725/1/L73

  29. [29]

    J. Li, N. Rea, D. F. Torres, E. de Oña-Wilhelmi, Gamma-ray Upper Limits on Magnetars with Six Years of Fermi-LAT Observations, Astrophys. J. 835 (1) (2017) 30.arXiv:1607.03778,doi:10.3847/1538-4357/ 835/1/30

  30. [30]

    Search for transient gamma-ray emission from magnetar flares using Fermi-LAT

    V . Ramakrishnan, S. Desai, Search for transient gamma-ray emission from magnetar flares using Fermi-LAT, JCAP 07 (2025) 050.arXiv:2412.03900,doi:10.1088/1475-7516/2025/07/050

  31. [31]

    V . M. Kaspi, A. Beloborodov, Magnetars, Ann. Rev. Astron. Astrophys. 55 (2017) 261–301.arXiv:1703. 00068,doi:10.1146/annurev-astro-081915-023329

  32. [32]

    Esposito, N

    P. Esposito, N. Rea, G. L. Israel, Magnetars: a short review and some sparse considerations, Astrophys. Space Sci. Libr. 461 (2020) 97–142.arXiv:1803.05716,doi:10.1007/978-3-662-62110-3_3

  33. [33]

    Ballet, P

    J. Ballet, P. Bruel, T. H. Burnett, B. Lott, Fermi Large Area Telescope Fourth Source Catalog Data Release 4 (4FGL-DR4) (7 2023).arXiv:2307.12546

  34. [34]

    D. A. Smith, et al., The Third Fermi Large Area Telescope Catalog of Gamma-Ray Pulsars, Astrophys. J. 958 (2) (2023) 191.arXiv:2307.11132,doi:10.3847/1538-4357/acee67

  35. [36]

    Raffelt, A

    G. Raffelt, A. Caputo, Astrophysical axion bounds: The 2024 edition, in: Proceedings of 1st General Meeting and 1st Training School of the COST Action COSMIC WSIPers — PoS(COSMICWISPers), COSMICWIS- Pers, Sissa Medialab, 2024, p. 041.doi:10.22323/1.454.0041. URLhttp://dx.doi.org/10.22323/1.454.0041

  36. [37]

    Li, T.-R

    C.-C. Li, T.-R. Hu, F.-K. Guo, U.-G. Meißner, Pion axioproduction revisited, Physical Review D 109 (7) (Apr. 2024).doi:10.1103/physrevd.109.075050. URLhttp://dx.doi.org/10.1103/PhysRevD.109.075050

  37. [38]

    D. G. Yakovlev, C. J. Pethick, Neutron star cooling, Annual Review of Astronomy and Astrophysics 42 (2004) 169–210.doi:10.1146/annurev.astro.42.053102.134013

  38. [40]

    Schönfelder, H

    V . Schönfelder, H. Aarts, K. Bennett, H. de Boer, R. Diehl, W. Hermsen, G. Lichti, D. Morris, J. Ryan, A. Strong, D. J. Thompson, et al., Instrument Description and Performance of the Imaging Gamma-Ray Tele- scope COMPTEL aboard the Compton Gamma-Ray Observatory, Astrophys. J. Suppl. Ser. 86 (1993) 657–692. doi:10.1086/191794

  39. [41]

    Compton Telescopes for Gamma-ray Astrophysics

    C. Kierans, T. Takahashi, G. Kanbach, Compton Telescopes for Gamma-ray Astrophysics (8 2022).arXiv: 2208.07819,doi:10.1007/978-981-16-4544-0_46-1

  40. [42]

    Beechert, et al., Calibrations of the Compton Spectrometer and Imager, Nucl

    J. Beechert, et al., Calibrations of the Compton Spectrometer and Imager, Nucl. Instrum. Meth. A 1031 (2022) 166510.arXiv:2203.00695,doi:10.1016/j.nima.2022.166510

  41. [43]

    Gallego, et al., Preflight Background Estimates for COSI, Astrophys

    S. Gallego, et al., Preflight Background Estimates for COSI, Astrophys. J. 997 (2) (2026) 284.doi:10.3847/ 1538-4357/ae32f4

  42. [44]

    Berge, M

    D. Berge, M. N. Mazziotta, M. Tavani, V . Tatischeff, U. Oberlack, newASTROGAM: The New MeV to GeV Gamma-ray Observatory, PoS ICRC2025 (2025) 572.arXiv:2507.08133,doi:10.22323/1.501.0572

  43. [45]

    Georgi, D

    H. Georgi, D. B. Kaplan, L. Randall, Manifesting the Invisible Axion at Low-energies, Phys. Lett. B 169 (1986) 73–78.doi:10.1016/0370-2693(86)90688-X

  44. [46]

    Darmé, F

    L. Darmé, F. Giacchino, E. Nardi, M. Raggi, Invisible decays of axion-like particles: constraints and prospects, JHEP 06 (2021) 009.arXiv:2012.07894,doi:10.1007/JHEP06(2021)009

  45. [47]

    Raffelt, L

    G. Raffelt, L. Stodolsky, Mixing of the Photon with Low Mass Particles, Phys. Rev. D 37 (1988) 1237.doi: 10.1103/PhysRevD.37.1237

  46. [48]

    G. G. Raffelt, Stars as laboratories for fundamental physics: The astrophysics of neutrinos, axions, and other weakly interacting particles, 1996

  47. [49]

    De Angelis, M

    A. De Angelis, M. Roncadelli, O. Mansutti, Evidence for a new light spin-zero boson from cosmological gamma-ray propagation?, Phys. Rev. D 76 (2007) 121301.arXiv:0707.4312,doi:10.1103/PhysRevD. 76.121301

  48. [50]

    K. A. Hochmuth, G. Sigl, Effects of Axion-Photon Mixing on Gamma-Ray Spectra from Magnetized As- trophysical Sources, Phys. Rev. D 76 (2007) 123011.arXiv:0708.1144,doi:10.1103/PhysRevD.76. 123011

  49. [51]

    M. A. Sanchez-Conde, D. Paneque, E. Bloom, F. Prada, A. Dominguez, Hints of the existence of Axion- Like-Particles from the gamma-ray spectra of cosmological sources, Phys. Rev. D 79 (2009) 123511.arXiv: 0905.3270,doi:10.1103/PhysRevD.79.123511

  50. [52]

    Galanti, Axion-like Particle Effects on Photon Polarization in High-Energy Astrophysics, Universe 10 (8) (2024) 312.arXiv:2407.21421,doi:10.3390/universe10080312

    G. Galanti, Axion-like Particle Effects on Photon Polarization in High-Energy Astrophysics, Universe 10 (8) (2024) 312.arXiv:2407.21421,doi:10.3390/universe10080312

  51. [53]

    Fortin, C

    M. Fortin, C. Providência, A. R. Raduta, F. Gulminelli, J. L. Zdunik, P. Haensel, M. Bejger, Neutron star radii and crusts: Uncertainties and unified equations of state, Phys. Rev. C94 (3) (2016) 035804.arXiv: 1604.01944,doi:10.1103/PhysRevC.94.035804

  52. [54]

    Prakash, T

    M. Prakash, T. L. Ainsworth, J. M. Lattimer, Equation of state and the maximum mass of neutron stars, Physical Review Letters 61 (22) (1988) 2518–2521.doi:10.1103/PhysRevLett.61.2518

  53. [55]

    Haensel, A

    P. Haensel, A. Y . Potekhin, D. G. Yakovlev, Neutron stars 1: Equation of state and structure, V ol. 326, Springer, New York, USA, 2007.doi:10.1007/978-0-387-47301-7

  54. [56]

    Carenza, M

    P. Carenza, M. Giannotti, J. Isern, A. Mirizzi, O. Straniero, Axion astrophysics, Phys. Rept. 1117 (2025) 1–102. arXiv:2411.02492,doi:10.1016/j.physrep.2025.02.002

  55. [57]

    Carenza, B

    P. Carenza, B. Fore, M. Giannotti, A. Mirizzi, S. Reddy, Enhanced Supernova Axion Emission and its Impli- cations, Phys. Rev. Lett. 126 (7) (2021) 071102.arXiv:2010.02943,doi:10.1103/PhysRevLett.126. 071102

  56. [58]

    D. J. Dean, M. Hjorth-Jensen, Pairing in nuclear systems: from neutron stars to finite nuclei, Rev. Mod. Phys. 75 (2003) 607.doi:10.1103/RevModPhys.75.607

  57. [59]

    J. A. Pons, D. Viganò, Magnetic, thermal and rotational evolution of isolated neutron stars, Liv. Rev. Comput. Astrophys. 5 (1) (2019) 3.arXiv:1911.03095,doi:10.1007/s41115-019-0006-7

  58. [60]

    B. Fore, S. Reddy, Pions in hot dense matter and their astrophysical implications, Phys. Rev. C 101 (2020) 035809.doi:10.1103/PhysRevC.101.035809. URLhttps://link.aps.org/doi/10.1103/PhysRevC.101.035809

  59. [61]

    S. P. Harris, B. Fore, S. Reddy, Bulk viscosity of nuclear matter with pions in the neutrino-trapped regime, 27 Phys. Rev. C 111 (1) (2025) 015802.arXiv:2407.18890,doi:10.1103/PhysRevC.111.015802

  60. [62]

    Iwamoto, Axion Emission from Neutron Stars, Phys

    N. Iwamoto, Axion Emission from Neutron Stars, Phys. Rev. Lett. 53 (1984) 1198–1201.doi:10.1103/ PhysRevLett.53.1198

  61. [63]

    C. J. Horowitz, M. A. Pérez-García, J. Piekarewicz, Neutrino-“pasta” scattering: The opacity of nonuniform neutron-rich matter, Phys. Rev. C 69 (2004) 045804.doi:10.1103/PhysRevC.69.045804. URLhttps://link.aps.org/doi/10.1103/PhysRevC.69.045804

  62. [64]

    Haensel, A

    P. Haensel, A. Y . Potekhin, D. G. Yakovlev, Neutron Stars 1: Equation of State and Structure, V ol. 326 of Astrophysics and Space Science Library, Springer, 2007

  63. [65]

    J. A. Pons, D. Viganò, N. Rea, A unified approach to the evolution of isolated neutron stars, Physical Review D 99 (2019) 103009

  64. [66]

    Barba-González, C

    D. Barba-González, C. Albertus, M. A. Pérez-García, Crystallization in single- and multicomponent neutron star crusts, Phys. Rev. C 106 (2022) 065806.doi:10.1103/PhysRevC.106.065806. URLhttps://link.aps.org/doi/10.1103/PhysRevC.106.065806

  65. [67]

    Anomalous thermal relaxation in warm ion plasmas

    D. Barba-González, C. Albertus, M. Á. Pérez-García, Anomalous thermal relaxation in warm ion plasmas, Mon. Not. Roy. Astron. Soc. 537 (2) (2025) 723–729.arXiv:2406.01700,doi:10.1093/mnras/staf040

  66. [68]

    Carenza, O

    P. Carenza, O. Straniero, B. Döbrich, M. Giannotti, G. Lucente, A. Mirizzi, Constraints on the coupling with photons of heavy axion-like-particles from Globular Clusters, Phys. Lett. B 809 (2020) 135709.arXiv:2004. 08399,doi:10.1016/j.physletb.2020.135709

  67. [69]

    S. J. Witte, D. Noordhuis, T. D. P. Edwards, C. Weniger, Axion-photon conversion in neutron star magne- tospheres: The role of the plasma in the Goldreich-Julian model, Phys. Rev. D 104 (10) (2021) 103030. arXiv:2104.07670,doi:10.1103/PhysRevD.104.103030

  68. [70]

    J. I. McDonald, S. J. Witte, Generalized ray tracing for axions in astrophysical plasmas, Phys. Rev. D 108 (10) (2023) 103021.arXiv:2309.08655,doi:10.1103/PhysRevD.108.103021

  69. [71]

    E. U. Ginés, D. Noordhuis, C. Weniger, S. J. Witte, Numerical analysis of resonant axion-photon mixing, Phys. Rev. D 110 (8) (2024) 083007.arXiv:2405.08865,doi:10.1103/PhysRevD.110.083007

  70. [72]

    D. F. G. Fiorillo, Á. Gil Muyor, H.-T. Janka, G. G. Raffelt, E. Vitagliano, Axion-photon conversion in transient compact stars: Systematics, constraints, and opportunities (9 2025).arXiv:2509.13322

  71. [73]

    Goldreich, W

    P. Goldreich, W. H. Julian, Pulsar electrodynamics, Astrophys. J. 157 (1969) 869.doi:10.1086/150119

  72. [74]

    A. N. Timokhin, A. K. Harding, On the polar cap cascade pair multiplicity of young pulsars, Astrophys. J. 810 (2) (2015) 144.arXiv:1504.02194,doi:10.1088/0004-637X/810/2/144

  73. [75]

    Heisenberg, H

    W. Heisenberg, H. Euler, Consequences of Dirac’s theory of positrons, Z. Phys. 98 (11-12) (1936) 714–732. arXiv:physics/0605038,doi:10.1007/BF01343663

  74. [76]

    V . S. Weisskopf, K. Dan. Vidensk. Selsk. Mat. Fys. Medd. 14 (1936) 6

  75. [77]

    J. S. Schwinger, On gauge invariance and vacuum polarization, Phys. Rev. 82 (1951) 664–679.doi:10.1103/ PhysRev.82.664

  76. [78]

    S. L. Adler, Photon splitting and photon dispersion in a strong magnetic field, Annals Phys. 67 (1971) 599–647. doi:10.1016/0003-4916(71)90154-0

  77. [79]

    Galanti, F

    G. Galanti, F. Tavecchio, M. Roncadelli, C. Evoli, Blazar VHE spectral alterations induced by photon-ALP oscillations, Mon. Not. R. Astron. Soc.487 (1) (2019) 123–132.arXiv:1811.03548,doi:10.1093/mnras/ stz1144

  78. [80]

    Jansson, G

    R. Jansson, G. R. Farrar, A New Model of the Galactic Magnetic Field, Astrophys. J.757 (1) (2012) 14.arXiv: 1204.3662,doi:10.1088/0004-637X/757/1/14

  79. [81]

    Jansson, G

    R. Jansson, G. R. Farrar, The Galactic Magnetic Field, Astrophys. J. Lett.761 (1) (2012) L11.arXiv:1210. 7820,doi:10.1088/2041-8205/761/1/L11

  80. [82]

    Unger, G

    M. Unger, G. R. Farrar, Uncertainties in the Magnetic Field of the Milky Way, in: 35th International Cosmic Ray Conference (ICRC2017), V ol. 301 of International Cosmic Ray Conference, 2017, p. 558.arXiv:1707. 02339,doi:10.22323/1.301.0558

Showing first 80 references.