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arxiv: 2511.17817 · v2 · submitted 2025-11-21 · ✦ hep-ex · gr-qc

Search for high-frequency gravitational waves via re-analysis of cavity axion data

Younggeun Kim , Jordan Gu\'e , Changhao Xu , Diego Blas , Dmitry Budker , Sungjae Bae , Claudio Gatti , Junu Jeong
show 12 more authors
Jihn E. Kim Kiwoong Lee Arjan F. van Loo Yasunobu Nakamura Seonjeong Oh Wolfram Ratzinger Taehyeon Seong Yannis K. Semertzidis Kristof Schmieden Mattias Schott Sergey Uchaikin SungWoo Youn
This is my paper

Pith reviewed 2026-05-17 19:50 UTC · model grok-4.3

classification ✦ hep-ex gr-qc
keywords high-frequency gravitational wavesaxion haloscopesuperradianceblack holesresonant cavitystrain limitsCAPP experiment
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The pith

Reanalysis of axion cavity data sets 90 percent limits on high-frequency gravitational wave strain down to 3.9 times 10 to the minus 21.

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

The paper reanalyzes existing data from a resonant cavity experiment built to search for axions, now scanning the same records for monochromatic high-frequency gravitational waves across a 2 megahertz band centered at 5.311 gigahertz. No candidate signals appear after the reprocessing. The lack of detections translates into exclusion limits on the gravitational wave strain amplitude. When the limits are read through models of axion clouds forming around spinning black holes by superradiance, they rule out black holes of mass roughly 1.22 times 10 to the minus 6 solar masses lying within about 0.01 astronomical units of Earth. The exercise shows that electromagnetic cavities already in use for particle searches can also function as detectors for this class of gravitational waves.

Core claim

No rescan candidates were found in the reanalysis of the CAPP-12T MC axion haloscope data, which permits setting 90 percent confidence-level exclusion limits on the gravitational-wave strain reaching h0 approximately 3.9 times 10 to the minus 21 in the most sensitive sky regions. Interpreted in the context of black-hole superradiance from axion clouds, the results exclude black holes with mass M_BH approximately 1.22 times 10 to the minus 6 solar masses within distances of order 10 to the minus 2 astronomical units from Earth under benchmark assumptions. The work demonstrates the potential of electromagnetic resonant cavities as novel detectors of monochromatic high-frequency gravitational 2

What carries the argument

Re-use of the resonant cavity's electromagnetic response, originally tuned for axion-induced signals, to place limits on gravitational-wave-induced effects in the same frequency band.

If this is right

  • The non-observation sets strain limits of h0 approximately 3.9 times 10 to the minus 21 at 90 percent .
  • Black holes of mass 1.22 times 10 to the minus 6 solar masses are excluded at distances of order 0.01 astronomical units under the stated superradiance assumptions.
  • Resonant electromagnetic cavities can serve as detectors for monochromatic high-frequency gravitational waves.
  • The same technique motivates dedicated follow-up searches for both long-lived and transient gravitational-wave signals.

Where Pith is reading between the lines

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

  • Other existing datasets from axion haloscope runs could be reprocessed in the same way to widen the frequency coverage or sky area searched for gravitational waves.
  • Designing future cavities explicitly for gravitational-wave sensitivity rather than axion coupling could tighten the strain limits further.
  • Time-domain analysis of cavity data might reveal transient gravitational-wave bursts in addition to the steady signals considered here.

Load-bearing premise

The mapping from measured strain limits to excluded black-hole masses and distances rests on specific benchmark assumptions about how axion clouds form, persist, and radiate gravitational waves.

What would settle it

A confirmed detection of a continuous monochromatic gravitational wave at 5.311 gigahertz with strain amplitude above 3.9 times 10 to the minus 21 arriving from a nearby sky direction would directly contradict the reported exclusions.

Figures

Figures reproduced from arXiv: 2511.17817 by Arjan F. van Loo, Changhao Xu, Claudio Gatti, Diego Blas, Dmitry Budker, Jihn E. Kim, Jordan Gu\'e, Junu Jeong, Kiwoong Lee, Kristof Schmieden, Mattias Schott, Seonjeong Oh, Sergey Uchaikin, Sungjae Bae, SungWoo Youn, Taehyeon Seong, Wolfram Ratzinger, Yannis K. Semertzidis, Yasunobu Nakamura, Younggeun Kim.

Figure 1
Figure 1. Figure 1: FIG. 1. Schematic of the CAPP-12T MC haloscope setup [35]. Red solid lines (between the 50 [PITH_FULL_IMAGE:figures/full_fig_p006_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Schematic of the GW propagation plane with respect to the cylindrical cavity. The external [PITH_FULL_IMAGE:figures/full_fig_p009_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Gravitational coupling coefficients as a function of [PITH_FULL_IMAGE:figures/full_fig_p010_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Relative location of the GW source and the cavity in the equatorial coordinates. The GW [PITH_FULL_IMAGE:figures/full_fig_p010_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Gravitational-wave with cross polarization coupling coefficients in equatorial coordinates [PITH_FULL_IMAGE:figures/full_fig_p011_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. Analysis procedure. (a) Raw spectrum with its baseline (red solid line). The peak at [PITH_FULL_IMAGE:figures/full_fig_p012_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7. (Left) Vertical grand spectrum for a gravitational-wave source located at (0 [PITH_FULL_IMAGE:figures/full_fig_p013_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: FIG. 8. Exclusion limit on the GW strain amplitude [PITH_FULL_IMAGE:figures/full_fig_p014_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: FIG. 9. Averaged [PITH_FULL_IMAGE:figures/full_fig_p015_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: FIG. 10. Distributions of normalized excess values obtained from 600 white-noise samples with [PITH_FULL_IMAGE:figures/full_fig_p022_10.png] view at source ↗
read the original abstract

Monochromatic high-frequency gravitational waves (HFGW) provide a distinctive probe of new physics scenarios, most notably axion clouds around rotating black holes formed via superradiance. We reanalyzed data from the CAPP-12T MC (multi-cell) axion haloscope experiment [Phys. Rev. Lett. 133,051802 (2024)]. The study covers a continuous $2\,$MHz frequency span centered at $5.311\,$GHz. No rescan candidates were found, and we set 90% confidence-level exclusion limits on the gravitational-wave strain, reaching $h_0 \approx 3.9 \times 10^{-21}$ in the most sensitive regions of the sky. Interpreted in the context of black-hole superradiance from axion clouds, the results exclude black holes with mass $M_{\mathrm{BH}} \simeq 1.22 \times 10^{-6}\,M_\odot$ within distances of $O(10^{-2})\,$AU from Earth, under benchmark assumptions. This work demonstrates the potential of electromagnetic resonant cavities as novel detectors of monochromatic HFGW and motivates future searches for both long-lived and transient signals.

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.

Referee Report

2 major / 2 minor

Summary. The paper re-analyzes existing data from the CAPP-12T MC axion haloscope experiment over a continuous 2 MHz frequency span centered at 5.311 GHz to search for monochromatic high-frequency gravitational waves. No rescan candidates are identified, yielding 90% CL exclusion limits on the gravitational-wave strain reaching h0 ≈ 3.9 × 10^{-21} in the most sensitive sky regions. These limits are interpreted, under benchmark assumptions for axion clouds formed via black-hole superradiance, as excluding black holes with mass M_BH ≃ 1.22 × 10^{-6} M_⊙ within distances of O(10^{-2}) AU from Earth.

Significance. If the strain limits hold, the work usefully demonstrates that resonant-cavity axion detectors can be repurposed for high-frequency GW searches, providing a new experimental handle on monochromatic signals. The experimental bound itself is obtained via standard statistical treatment of existing data and constitutes the primary deliverable; the superradiance interpretation adds context but is secondary and model-dependent.

major comments (2)
  1. [Data re-analysis and results] Data-analysis and results sections: the manuscript provides no full details on systematic uncertainties, data selection cuts, or how sky-position dependence was incorporated when converting the cavity power spectrum into the quoted strain limits h0 ≈ 3.9 × 10^{-21}. These omissions are load-bearing for the central experimental claim.
  2. [Interpretation] Interpretation section: the translation of the strain limits into exclusions on M_BH ≃ 1.22 × 10^{-6} M_⊙ at O(10^{-2}) AU rests entirely on external benchmark values for superradiance efficiency, cloud lifetime against GW emission, and the precise axion-GW coupling strength; no sensitivity study or cross-check of these assumptions is performed within the paper. If any benchmark is optimistic by a factor of a few, the excluded region shrinks substantially while the raw h0 limit remains unchanged.
minor comments (2)
  1. [Abstract and introduction] The abstract and introduction could more explicitly separate the model-independent strain limit from the benchmark-dependent black-hole exclusion to avoid conflating the two claims.
  2. [Throughout] Notation for the strain amplitude (h0) and frequency band should be defined at first use with a brief reminder of the conversion from cavity power to strain.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review. We address the two major comments point by point below, indicating where revisions will be made to improve clarity while preserving the manuscript's focus on the experimental strain limits.

read point-by-point responses

  1. Referee: [Data re-analysis and results] Data-analysis and results sections: the manuscript provides no full details on systematic uncertainties, data selection cuts, or how sky-position dependence was incorporated when converting the cavity power spectrum into the quoted strain limits h0 ≈ 3.9 × 10^{-21}. These omissions are load-bearing for the central experimental claim.

    Authors: We agree that additional explicit details will strengthen the paper. The re-analysis employs the identical power spectrum, data selection cuts, and systematic uncertainty estimates already documented in the original CAPP-12T publication (Phys. Rev. Lett. 133, 051802 (2024)). The conversion from cavity power to GW strain h0 follows the standard resonant-cavity response formula, which includes the cavity form factor, loaded quality factor, and the directional sensitivity to GW polarization and wave vector. The quoted 3.9 × 10^{-21} limit corresponds to the most sensitive sky directions under this response. In the revised manuscript we will insert a concise subsection that reproduces the key conversion equations, states the sky-position assumption, and explicitly references the original paper for the full cuts and systematics tables. revision: yes

  2. Referee: [Interpretation] Interpretation section: the translation of the strain limits into exclusions on M_BH ≃ 1.22 × 10^{-6} M_⊙ at O(10^{-2}) AU rests entirely on external benchmark values for superradiance efficiency, cloud lifetime against GW emission, and the precise axion-GW coupling strength; no sensitivity study or cross-check of these assumptions is performed within the paper. If any benchmark is optimistic by a factor of a few, the excluded region shrinks substantially while the raw h0 limit remains unchanged.

    Authors: We concur that the superradiance interpretation is model-dependent and secondary to the primary experimental result. The manuscript already qualifies the exclusion with the phrase “under benchmark assumptions.” To respond to the concern we will add a short paragraph that illustrates the scaling of the excluded mass and distance with plausible variations in superradiance efficiency and cloud lifetime drawn from the existing literature. This will make the dependence transparent without performing a full Monte-Carlo scan, which lies outside the scope of a re-analysis paper whose central deliverable is the model-independent h0 bound. revision: partial

Circularity Check

0 steps flagged

No circularity: strain limits from independent data re-analysis; BH exclusions are qualified interpretation under external benchmarks

full rationale

The paper's core result is a null search and 90% CL gravitational-wave strain limit h0 ≈ 3.9 × 10^{-21} obtained by re-analyzing existing CAPP-12T MC cavity data over a 2 MHz band. This experimental bound is produced by standard data-analysis techniques applied to external measurements and does not reduce to any fitted parameter that is then relabeled as a prediction. The subsequent mapping to black-hole mass and distance exclusions is explicitly labeled as relying on 'benchmark assumptions' about superradiance, cloud lifetime, and GW coupling; these assumptions are adopted from external literature rather than derived or self-cited within the present work. No self-definitional equations, uniqueness theorems imported from the same authors, or ansatzes smuggled via prior self-citation appear in the reported chain. The derivation therefore remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claims rest on standard statistical methods for setting exclusion limits from null results and on external astrophysical models for axion superradiance; no new free parameters are introduced in the re-analysis itself, but the interpretation step imports several benchmark assumptions from prior work.

axioms (2)
  • standard math Standard 90% confidence level frequentist exclusion procedure for monochromatic signals in the presence of noise
    Invoked when converting non-detection into strain upper limits.
  • domain assumption Benchmark superradiance model relating axion cloud properties to gravitational wave strain and black hole mass
    Used to translate h0 limits into excluded M_BH and distance ranges.

pith-pipeline@v0.9.0 · 5606 in / 1571 out tokens · 62831 ms · 2026-05-17T19:50:05.339632+00:00 · methodology

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