{"id":"c45fe7fb-c2dc-4d38-a26a-302c652f612d","arxiv_id":"2501.08930","paper_version":2,"verdict":"UNVERDICTED","confidence":"MODERATE","novelty_score":2.0,"correctness_risk":"low","formal_verification":"none","parameter_count":1,"one_line_summary":"KAGRA is prepared to search for ultralight vector dark matter by mirror forces and axion dark matter by laser polarization rotation; this report reviews the 2020 vector limits and the 2025 axion run plans.","lead":"This paper reviews plans to use Japan's KAGRA gravitational wave detector to search for two types of ultralight dark matter: vector particles that push mirrors and axions that rotate laser polarization. It summarizes the first vector search results from 2020 data and describes optics installed for the axion search in 2025.","discovery_kind":"review","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Section 3's readiness claim is unsupported by any measurement or reference; the only new empirical assertion in the paper, it needs verification before it can carry the central message.","rationale":"The paper is a review/status paper. I read the O3GK limit and the ADAM-GD projections as honestly attributed to prior work; the figures clearly label projections, and the text distinguishes achieved limits from planned sensitivity. The one statement that is both new and central is the hardware-readiness declaration at the end of Sec. 3. If that declaration is wrong, the paper's claimed first-axion-search readiness disappears, although the review content remains valid. I therefore do not allege an error in the physics; I identify a missing-support gap on the only original empirical claim. The reader's weakest_assumption concerned future designed sensitivity; I agree that is important, but the readiness claim is more immediately checkable and more central to the paper's title promise of searches 'with KAGRA.' A concrete check of the 2021 installation records and transmitted-port optical performance would settle whether the concern lands. Since the claim is plausible and probably true, the correct disposition is conditional rather than rejection: the authors should either substantiate the readiness statement with a technical reference or commissioning data, or downgrade it to a plan. I also note the paper's positive features: it correctly separates achieved O3GK limits from projected sensitivity, and the cited prior work provides independent derivations and published limits.","tokens_in":4896,"tokens_out":14545,"duration_ms":155167,"concrete_test":"Consult KAGRA's optical layout drawings and 2021 shutdown commissioning records to confirm installation of polarizers, waveplates, and photodetectors at both ETM transmission ports; then, in the next engineering run, measure the transmitted arm-cavity power and the static/dynamic polarization extinction ratio at these ports while the interferometer is locked. If no transmitted beam is available, or if the extinction ratio is insufficient for the ADAM-GD scheme (i.e., the projected signal in Fig. 1 right falls below the measured orientation-noise floor), the readiness claim is false; otherwise it is verified.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The only new load-bearing assertion in this manuscript is in Sec. 3: \"we installed polarization optics at the transmission ports of the two arm cavities in 2021 and are now ready to collect the first axion data during the upcoming O4c observing run in 2025.\" Everything else — the O3GK vector limit, the ADAM-GD sensitivity projections in Fig. 1, and the axion polarization equations — is carried by refs. 6, 7, 13, 16, and 31. The readiness statement is therefore what distinguishes a progress report from a proposal, yet no commissioning evidence is presented: no measured transmitted power at the ETM ports, no polarization extinction ratio, no noise spectrum, and no reference to a KAGRA technical document. If the optics are not actually in place, or if the transmitted-beam power or extinction is too poor for the ADAM-GD readout, the claim that KAGRA is ready for the first axion search fails and the paper reduces to a review. This is a missing-support gap, not an internal contradiction; it is directly testable by inspecting the detector.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper reviews the status of ultralight vector and axion dark matter searches using the KAGRA gravitational wave detector. It summarizes the published O3GK upper limit on the B-L gauge coupling from KAGRA's 2020 data, and it reports the installation of polarization optics at the arm cavity transmission ports in 2021, stating that KAGRA is ready for the first axion dark matter search in the planned O4c run of 2025. The theoretical background, sensitivity projections, and limits from other experiments are taken from earlier work by the authors and from published LIGO-Virgo-KAGRA results.","tokens_in":5122,"tokens_out":2601,"duration_ms":29053,"significance":"If the hardware-readiness claim is correct, the paper documents KAGRA as the first gravitational-wave detector equipped to search for axion dark matter via polarization rotation, complementing its already-published vector dark matter limit. The paper is a concise and well-referenced status report rather than a technical derivation; its novelty rests almost entirely on the Section 3 installation claim. The ability to verify that claim will determine whether the paper carries new information beyond a review of existing results.","major_comments":[{"comment":"The sole new empirical assertion in the manuscript is the sentence \"we installed polarization optics at the transmission ports of the two arm cavities in 2021 and are now ready to collect the first axion data during the upcoming O4c observing run in 2025.\" No supporting evidence is provided: there is no measured transmitted power at the end test mass ports, no polarization extinction ratio, no noise spectrum, and no citation to a KAGRA technical document or commissioning note. Because this statement underlies the paper's central claim that KAGRA is hardware-ready for a first axion search, it is load-bearing. The authors should either cite a verifiable technical reference or present quantitative commissioning data (e.g., achieved extinction ratio or transmitted power) to support the readiness claim.","section":"Section 3"},{"comment":"The text states \"Once the detector reaches its designed sensitivity, it will surpass equivalence principle test limits\" and Fig. 1 shows projected sensitivities. The paper does not explicitly state which auxiliary length channels (MICH, PRCL, SRCL) are assumed to reach design noise in the projections, nor does it quantify the margin by which they would surpass limits. Since the projected reach depends directly on the noise in those channels, a sentence clarifying that the curves assume the design sensitivity in each channel and referencing the noise model would make the basis of the projection transparent.","section":"Section 2"}],"minor_comments":[{"comment":"In the left panel caption, \"fifth-fore searches\" should read \"fifth-force searches.\"","section":"Figure 1 caption"},{"comment":"The coupling is introduced as ϵ_B-L, but later in the same paragraph the quantity g_B-L/M appears; the relation between ϵ_B-L and g_B-L should be defined explicitly to avoid notational confusion.","section":"Section 2, around Eq. (1)"},{"comment":"Reference 27 is formatted inconsistently: \"C. P. Salemi C P et al.\" should be \"C. P. Salemi et al.\"","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The paper is a very short status report whose scientific content is mostly a summary of prior published work. Its only new claim is the detector-readiness statement in Section 3, which is currently unsupported. If the authors can provide a verifiable reference to a KAGRA technical note or commissioning data, the paper would be a suitable progress report. Without that, the paper reduces to a review of the authors' own proposals and published limits. The main concern is not internal consistency but unverified load-bearing empirical content."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is a review/status report, not a new measurement. The only genuinely new claim is that KAGRA installed polarization optics at the arm-cavity transmission ports in 2021 and plans to take axion data in O4c in 2025. Everything else—the O3GK vector limits, the ADAM-GD sensitivity projections, the axion polarization equations—is already in the cited papers (refs. 6, 7, 13, 16, 31). The authors are transparent about this; the abstract and intro frame it as a review.\n\nWhat the paper does well: it gives a clean, accurate summary of the vector force search using auxiliary length channels (MICH, PRCL, SRCL), explains why KAGRA's mixed-material mirrors (sapphire vs. fused silica) give a unique advantage over LIGO/Virgo, and lays out the ADAM-GD axion scheme clearly. The sensitivity curves in Fig. 1 match the published versions. The citation pattern looks appropriate; no sign of overclaiming or hiding prior work.\n\nThe soft spot is exactly the one the stress test flags: the readiness statement in Sec. 3. \"We installed polarization optics... in 2021 and are now ready\" carries no supporting evidence—no measured extinction ratio, no transmitted power, no noise spectrum, no reference to a KAGRA technical note. For a review paper that's a smallish flaw; for a paper whose central message is that KAGRA is hardware-ready for the first axion search, it's load-bearing. If the optics are in place and working, the paper is a useful status update. If not, it's just a proposal dressed as a report. This is easily fixed by adding a reference to commissioning documentation or a brief description of the measured performance.\n\nThe other caveat is the designed-sensitivity assumption. The text says \"once the detector reaches its designed sensitivity\"—that's a projection, not a result. The paper doesn't hide this, but a reader skimming Fig. 1 could take the projected reach as actual sensitivity.\n\nBottom line: it's a solid review with one unsupported empirical claim. It deserves peer review in the sense that a referee can quickly verify the references and ask for the commissioning evidence. I'd bring it to a reading group if you're interested in GW-detector dark matter searches, but I wouldn't cite it for anything beyond the status update. For the record, the stress-test concern holds up; that's the one thing I'd push on.","headline":"A clean review/status report whose one genuinely new claim—that KAGRA is hardware-ready for an axion search—needs commissioning evidence before it can carry the paper's message.","tokens_in":5684,"tokens_out":1694,"would_cite":false,"duration_ms":16681,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["95.35.+d","04.80.Nn","14.80.Va"],"model":"deepseek-v4-flash","headline":"This paper reports that KAGRA, a laser interferometric gravitational wave detector in Japan, has used its first joint observing run with GEO600 to set upper limits on the B-L gauge coupling at the 10^-19 level for ultralight vector dark…","keywords":["ultralight dark matter","vector dark matter","axion dark matter","KAGRA","gravitational wave detector","B-L gauge boson","axion-photon coupling","polarization rotation"],"falsifier":"Measure the noise spectral density in the MICH, PRCL, and SRCL channels and at the transmission ports during the O4c run; if the integrated noise exceeds the design curves used to generate Fig. 1 by more than an order of magnitude, the claimed readiness and projected sensitivities for both searches are contradicted.","tokens_in":4714,"feed_emoji":"🔭","tokens_out":6332,"duration_ms":55351,"temperature":0.7,"pith_summary":"This paper reports on two concrete steps toward using the KAGRA gravitational wave detector as a dark matter instrument. An analysis of data from the 2020 O3GK run with GEO600 set upper limits on the B-L gauge coupling of ultralight vector dark matter at the $10^{-19}$ level in the mass range $10^{-13}\\,\\mathrm{eV} \\lesssim m_A \\lesssim 10^{-12}\\,\\mathrm{eV}$. The team also installed polarization optics at the arm cavity transmission ports in 2021, making KAGRA ready to collect its first axion dark matter data during the O4c observing run in 2025. The projected sensitivities in both channels could surpass existing equivalence-principle and astrophysical bounds if the detector reaches its designed noise performance.","feed_headline":"KAGRA targets dark matter: first vector limits, axion search next","feed_subtitle":"A gravitational wave observatory's auxiliary channels and new optics aim to probe ultralight particles.","key_machinery":"The vector search relies on KAGRA being the only gravitational wave detector with test masses (sapphire) and auxiliary mirrors (fused silica) of different materials, so an oscillating force from a B-L gauge boson field produces a differential signal in the MICH, PRCL, and SRCL channels instead of cancelling as it does in the common DARM channel. The axion search uses the axion-photon coupling, which induces a tiny oscillating circular birefringence; the ADAM-GD scheme detects the resulting polarization rotation, and reading out the beam transmitted through the arm cavity rather than reflected makes the rotation add coherently over the odd number of cavity transits.","core_discovery":"Using the auxiliary length channels (MICH, PRCL, SRCL) that sense differential acceleration between KAGRA's sapphire test masses and fused silica auxiliary mirrors, the O3GK analysis produced the first KAGRA upper limit on B-L vector dark matter: a $10^{-19}$ level bound on the coupling $\\epsilon_{B-L}$ over $10^{-13}\\,\\mathrm{eV} \\lesssim m_A \\lesssim 10^{-12}\\,\\mathrm{eV}$. For axions, the paper shows that measuring oscillating polarization rotation of the beams transmitted through the 3-km arm cavities avoids the cancellation that affects reflected-beam readouts at the anti-symmetric port, and reports that the required polarization optics are now installed and ready for the 2025 run.","pith_inferences":["A null axion result in the O4c run could still be significant if the achieved limits improve on astrophysical bounds from SN1987A or M87 in the low-mass region, though the paper does not quantify this.","The mixed-material strategy could be adopted by future detectors or retrofits, potentially extending the technique to other observatories and mass ranges.","The polarization-rotation hardware may also be sensitive to axion-like particles over a broader mass range if cavity parameters are optimized, which the current configuration does not fully explore."],"forward_implications":["If KAGRA reaches its designed sensitivity, the vector dark matter limits will surpass the best equivalence-principle tests in the mass range near $10^{-13}$ to $10^{-12}\\,\\mathrm{eV}$.","The upcoming O4c run in 2025 is expected to deliver the first axion dark matter constraints from a gravitational wave detector, complementing tabletop experiments such as DANCE.","The demonstration that auxiliary length channels are scientifically useful will motivate dedicated noise reduction in these channels, turning them into standard dark matter observables.","If no signal is found, the new bounds will tighten constraints on ultralight vector and axion dark matter parameter space in mass windows not fully covered by existing experiments."],"supporting_citations":[{"why":"Supplies the KAGRA O3GK vector dark matter result that sets the $10^{-19}$ level upper limits.","marker":"16"},{"why":"Proposes using KAGRA's mixed-material mirrors to search for B-L vector dark matter via auxiliary length channels.","marker":"13"},{"why":"Provides the theoretical treatment of DARM sensitivity to vector dark matter from residual phase and light-travel-time effects.","marker":"14"},{"why":"Introduces the ADAM-GD scheme for detecting axion polarization rotation in gravitational wave detectors.","marker":"6"},{"why":"Shows that the transmitted beam avoids cancellation and gives better axion sensitivity at lower masses.","marker":"7"},{"why":"Describes the pipeline that accounts for the stochastic nature of ultralight dark matter signals in the O3GK analysis.","marker":"31"},{"why":"Provides the LIGO-Virgo O3 vector dark matter limits that KAGRA's result is compared against.","marker":"15"}],"fun_headline_variants":["KAGRA reports first vector dark matter limits from 2020 run","Axion search via polarization rotation to debut at KAGRA in 2025","KAGRA's 3-km arms to sense axion polarization, vector limits done","KAGRA: first vector DM result, axion optics installed for next run"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The projected dark matter sensitivities assume KAGRA will reach its designed noise levels in the auxiliary length channels and at the arm-cavity transmission ports; if those channels remain several orders of magnitude above design during the 2025 run, the projected reach will not be achieved.","fun_headline_variants_meta":{"raw":{"variants":["KAGRA reports first vector dark matter limits from 2020 run","Axion search via polarization rotation to debut at KAGRA in 2025","KAGRA's 3-km arms to sense axion polarization, vector limits done","KAGRA: first vector DM result, axion optics installed for next run"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000406,"raw_usage":{"total_tokens":2027,"prompt_tokens":778,"completion_tokens":1249,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":394,"completion_tokens_details":{"reasoning_tokens":1162}},"tokens_in":394,"tokens_out":1249,"duration_ms":10092,"temperature":1.0,"reasoning_tokens":1162,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T20:13:52.720692+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the noise spectral density in the MICH, PRCL, and SRCL channels and at the transmission ports during the O4c run; if the integrated noise exceeds the design curves used to generate Fig. 1 by more than an order of magnitude, the claimed readiness and projected sensitivities for both searches are contradicted.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the KAGRA O3GK vector dark matter result that sets the $10^{-19}$ level upper limits."},{"cited_title":"Michimura et al","cited_arxiv_id":null,"evidence_quote":"Proposes using KAGRA's mixed-material mirrors to search for B-L vector dark matter via auxiliary length channels."},{"cited_title":"Morisaki et al","cited_arxiv_id":null,"evidence_quote":"Provides the theoretical treatment of DARM sensitivity to vector dark matter from residual phase and light-travel-time effects."},{"cited_title":"Nagano, T","cited_arxiv_id":null,"evidence_quote":"Introduces the ADAM-GD scheme for detecting axion polarization rotation in gravitational wave detectors."},{"cited_title":"Nagano et al","cited_arxiv_id":null,"evidence_quote":"Shows that the transmitted beam avoids cancellation and gives better axion sensitivity at lower masses."},{"cited_title":"Nakatsuka et al","cited_arxiv_id":null,"evidence_quote":"Describes the pipeline that accounts for the stochastic nature of ultralight dark matter signals in the O3GK analysis."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the LIGO-Virgo O3 vector dark matter limits that KAGRA's result is compared against."}],"review_version":1}