{"id":"2003e1e9-4cce-4b3c-8fe5-8c504e56437b","arxiv_id":"2411.19827","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"A first search of ALMA Band 3 archival data for narrowband technosignatures finds no signals from 28 galactic stars and sets EIRP limits above about 7×10^17 W for the nearest star.","lead":"This paper presents the first SETI search using ALMA archival data, looking for narrowband radio signals from 28 stars in calibrator fields at about 90 GHz. It finds no signals and sets upper limits on transmitter power for these stars, opening up millimeter wavelengths for technosignature searches.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The quoted EIRP_min limits are valid only for transmitters with |drift| ≲ 400 Hz/s, but the null-detection statement does not carry that caveat; even within the assumed drift bound, channel-edge splitting can halve SNR.","rationale":"The paper's central claim is a null detection with a specific sensitivity floor, so the load-bearing condition is that any transmitter with EIRP above the quoted limit would remain detectable in the chosen analysis. The drift-rate prior is the weakest link in that chain: Section 2.2 adopts ±400 Hz/s by linear scaling from 1 GHz, Section 4 splits the data into sub-75 s chunks to avoid smearing, and Section 5 explicitly labels the drift rate as the biggest limitation, yet the abstract and Table 2 present EIRP_min without a drift caveat. The reader's weakest_assumption identifies the same issue, and I agree. I also note that even inside the assumed ±400 Hz/s bound, a signal can straddle channel boundaries and lose up to a factor of two in SNR, so the exact 'no signals with EIRP_min > 6.91×10^17 W' statement is not strictly supported for the full assumed population without a trial over channel-start phase. The concrete injection test above would settle whether the quoted limits are robust, and the fix is straightforward: either add a drift-conditional caveat to the limits or implement a coarse drift search. Since the proof-of-concept value of the survey does not depend on this correction, and the reader's CONDITIONAL verdict already captures the need for revision, no verdict change is needed.","tokens_in":12484,"tokens_out":11472,"duration_ms":111393,"concrete_test":"Using the calibrated visibilities for the J1832-1035 field, inject a synthetic narrowband signal at the position of Gaia DR3 4154920820659128192 with flux density 5×rms (EIRP_min = 6.91×10^17 W at d = 1.010 kpc) and with constant drift rates of 0, 100, 200, 400, and 800 Hz/s, varying the starting frequency offset within a channel to sample worst-case splitting. Re-run the exact channel-map SNR>5 search. If the 400 Hz/s injection is not recovered in at least one channel, or if the recovered SNR drops below 5 for some starting offsets, then the EIRP_min quoted in Table 2 is valid only for slower-drifting signals and should be restated with an explicit drift caveat.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The headline null result and Table 2 EIRP_min values are conditional on the drift-rate prior of Eq. (7): ±400 Hz/s at ~90 GHz, obtained by scaling Breakthrough Listen's ±4 Hz/s at 1 GHz linearly with frequency. This is a survey design choice, not a physical upper bound. A transmitter with line-of-sight acceleration above ~1.3 m/s^2 (c × 400 / 9×10^10) drifts faster than 400 Hz/s; over the 30–60 s scan lengths used in Section 4, it sweeps an appreciable fraction of or more than the 30.52 kHz channel, so its flux is split across multiple channels and the single-channel SNR>5 search can miss it even if EIRP is well above the quoted limit. More subtly, even within the assumed ±400 Hz/s, a signal starting near a channel edge can straddle two channels over a 60 s integration, reducing peak SNR by up to ~2×; the quoted limits do not account for this worst-case splitting. The authors themselves call the drift rate 'probably the biggest limitation' (Section 5) and note that existing Doppler-tracking algorithms handle rates two orders of magnitude smaller, but the central 'no signals with EIRP_min > 6.91×10^17 W' statement and Table 2 carry no such caveat. Thus the survey demonstrates ALMA's viability, but its headline sensitivity claim is not robust for the full assumed drift population.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents a radio SETI survey using archival ALMA Band 3 observations of four calibrator fields, targeting 28 Gaia DR3 stars located within the primary beam. The authors search for narrowband signals in 30.52 kHz channels with an SNR > 5 threshold, splitting the data into 30-60 s scans to mitigate drift. No candidates are found. They derive EIRP_min limits for each star using Eq. (8), with the best limit of 6.91e17 W for the closest star, and compare their survey's figure of merit with previous SETI surveys. The paper also discusses the challenges of high-frequency SETI, including primary beam size, drift rates, and spectral confusion.","tokens_in":12753,"tokens_out":8723,"duration_ms":75414,"significance":"The significance lies in demonstrating that archival ALMA data can be used for technosignature searches, opening a new frequency window (90-93 GHz) and providing the first SETI limits at these frequencies toward 28 stars. The null result is a direct measurement with a transparent detection threshold and no fitted parameters in the EIRP calculation. The comparison with other surveys using the CWFTM is useful. However, the quantitative limits are weakened by two issues: the neglect of primary beam attenuation for off-axis stars and the unqualified assumption of the ±400 Hz/s drift-rate bound. These issues are repairable and do not affect the null detection itself, but they do affect the stated EIRP_min values that are a central product of the paper.","major_comments":[{"comment":"The EIRP_min calculation assumes the full sensitivity of the array at the star's position, but it does not account for attenuation by the primary beam for stars away from the pointing center. For the 12-m ALMA antennas at ~90 GHz, the primary beam FWHM is ~63\" (Table 1). A star at an angular offset of 25-30\" from the calibrator center experiences a response loss of roughly 40-50% (e.g., for a Gaussian primary beam). Since the r.m.s. noise is approximately uniform across the image, the minimum detectable flux density for an off-axis star is SNR × rms / P(θ), and the quoted EIRP_min underestimates the true limit by a factor of roughly 1.5-2 for stars near the edge of the 59\" field. This affects most rows of Table 2 and propagates into the CWFTM and transmitter-rate comparisons in Section 5. The authors should either apply the primary beam correction or explicitly state that the limits apply to on-axis transmitters.","section":"Section 4, Eq. (8), Table 2"},{"comment":"The EIRP_min limits assume that a narrowband signal remains within a single 30.52 kHz channel for the full integration time (60 s or 30 s). Even under the assumed maximum drift rate of ±400 Hz/s derived in Eq. (7), a signal whose start frequency is near a channel edge will spend part of the integration in a neighboring channel, reducing the peak single-channel SNR by up to a factor of ~2. More fundamentally, the ±400 Hz/s maximum drift rate is a heuristic scaling from ±4 Hz/s at 1 GHz and is not a physical upper bound; a transmitter with larger line-of-sight acceleration would sweep through multiple channels and could be missed entirely even at EIRP well above the quoted values. The authors acknowledge in Section 5 that drift is \"probably the biggest limitation,\" but the headline statement \"we detect no signals with an EIRP_min > 6.91×10^17 W\" (Section 4) and the entries of Table 2 are presented without this caveat. The abstract, Section 4, and Table 2 should explicitly state that the limits apply to signals with drift rates within ±400 Hz/s and to signals that remain within a single channel for the integration time.","section":"Section 2.2 and Section 4"}],"minor_comments":[{"comment":"The Data Availability section lists project ID 2017.1.01704.S, while Section 3 and Section 6 state 2017.1.01794.S; please verify the correct project code and use it consistently.","section":"Data Availability"},{"comment":"The header for the third field reads \"J200-1748\" but the text refers to \"J2000-1748\"; please make the notation consistent.","section":"Table 2"},{"comment":"In Eq. (7), the term \"ν0/1 GHz\" should be written with parentheses, e.g., \"ν0/(1 GHz)\", and the units of the drift rate at 1 GHz (Hz/s) should be stated explicitly in the following sentence.","section":"Eq. (7)"},{"comment":"The discussion of time-average smearing uses a maximum baseline of 16 km, but the actual project used a maximum baseline of 314 m; for this configuration the undistorted field of view is much larger than the primary beam, so the conclusion is unchanged, but the text should clarify which baseline is being used for the estimates.","section":"Section 2.1"},{"comment":"The text states \"We assume a Gaussian distribution for a pixel across all frequency channels\" but does not present a normality test; consider adding a brief validation, for example by comparing the number of pixels exceeding 5σ with the Gaussian expectation.","section":"Section 4"},{"comment":"The abstract quotes the limit as \"EIRP_min > 7×10^17 W\" while Section 4 gives 6.91×10^17 W; please ensure the abstract and body report the same rounded value.","section":"Abstract and Section 4"}],"recommendation":"major_revision","confidential_remarks":"The paper is a well-written first demonstration of ALMA-based SETI, and the null detection itself is robust. The main concerns are quantitative: the EIRP_min values in Table 2 need primary beam correction for off-axis stars, and the drift-rate caveat should be propagated into the headline limits. Both issues are straightforward to address without new observations. I would support publication after these revisions."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"You should read this as a proof-of-concept paper: it is the first SETI search using ALMA data, and it shows the bycatch method works at 90 GHz. The authors take archival Band 3 calibrator observations, find 28 Gaia stars in the fields, search for narrowband signals after continuum subtraction, and get a clean null. That null is robust: they search SNR>5 per channel, no candidates, and the limits are derived from measured noise and catalog distances with no free parameters in the output.\n\nWhat it does well: the paper is honest about the main technical obstacle, drift rate. They scale the Breakthrough Listen bound to 400 Hz/s at 90 GHz, show that a signal drifts out of a 30 kHz channel in ~75 s, and therefore split scans into shorter segments. They also explicitly say the drift rate is 'probably the biggest limitation' and note current Doppler-tracking algorithms handle two orders of magnitude less. That is the right framing.\n\nThe soft spots are real but correctable. First, the EIRP limits in Table 2 ignore primary beam attenuation. The rms per field is a single number, so off-axis stars have limits that are too optimistic by factors of maybe 1.4–4. That should be fixed before publication. Second, the headline statement 'we detect no signals with EIRP_min > 6.91×10^17 W' is conditional on the drift-rate prior and on continuous emission. The drift issue is acknowledged in the text, but the headline number does not carry the caveat. The stress-test note also points out that even within the assumed drift bound, a signal starting at a channel edge can split across two channels and lose up to 2× in SNR; that is a minor effect, not a fatal one. Neither issue threatens the central null, but the quoted limits should be interpreted as upper sensitivity bounds under specific assumptions.\n\nThe comparison figures (CWFTM, EIRP vs frequency) are standard and appropriate. The paper is modest in constraining power — Kardashev I scale only — but that is expected for a first look at a new frequency regime.\n\nBottom line: this deserves serious peer review. It is a clean, reproducible archival analysis that opens a new frequency window for SETI. I would recommend asking for revisions to (a) apply primary beam attenuation corrections to the EIRP limits and (b) soften the headline claim to carry the drift-rate and spectral-splitting caveats. After that, it is a solid contribution.","headline":"First ALMA technosignature search with a credible null result, but the sensitivity numbers are over-sold and need caveats before publication.","tokens_in":13457,"tokens_out":1958,"would_cite":true,"duration_ms":17391,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper reports the first technosignature search using ALMA data, a null detection that limits powerful extraterrestrial transmitters at 90–93 GHz toward 28 nearby stars.","keywords":["SETI","technosignatures","ALMA","millimetre astronomy","narrowband signals","drift rate","archival data","EIRP limits"],"falsifier":"Re-analyse the same ALMA calibration-subtracted data cubes with a search that explicitly corrects for drift rates up to at least ±4000 Hz/s (for example, by de-drifting into several inertial reference frames before searching) and check whether any pixel associated with the 28 stars yields a signal with SNR > 5. If such a signal appears, the null result and its EIRP limits are overturned; if none appears, the drift assumption is not the reason for the null.","tokens_in":12246,"feed_emoji":"📡","tokens_out":8701,"duration_ms":65894,"temperature":0.7,"pith_summary":"The paper reports the first search for extraterrestrial technosignatures using archival data from the Atacama Large Millimeter/Submillimeter Array (ALMA). The authors look for narrowband signals at 90–93 GHz toward 28 stars that happen to lie within the fields of view of four ALMA calibrator observations, a 'stellar bycatch' strategy that reuses data taken for other purposes. They detect nothing above a signal-to-noise ratio of 5, placing an upper limit of about $6.91 \\times 10^{17}$ W on the equivalent isotropic radiated power of any transmitter toward the closest star. The result matters because it opens a new, largely unexplored frequency window for SETI and shows that ALMA's sensitivity can be harnessed for technosignature searches despite the small field of view and large signal drift rates at millimetre wavelengths.","feed_headline":"First ALMA SETI search finds no signals in 28 stars","feed_subtitle":"Null result at 90-93 GHz opens the millimetre band to technosignature searches","key_machinery":"The argument is carried by three pieces: (i) the 'stellar bycatch' method, which harvests stars from the Gaia DR3 catalogue that fall within the interferometer's undistorted field of view of calibrator scans, allowing archival ALMA data to be reused for SETI; (ii) the drift-rate scaling relation $\\dot{\\nu}_{\\rm max} = \\dot{\\nu}_{1\\,{\\rm GHz}} \\, (\\nu_0 / 1\\,{\\rm GHz})$, which assumes a maximum drift of $\\pm 4$ Hz/s at 1 GHz and yields $\\pm 400$ Hz/s at 90 GHz, setting the 75-second integration limit that preserves sensitivity to drifting narrowband signals; and (iii) the EIRP-limit formula ${\\rm EIRP}_{\\rm min} = 4\\pi d^2 S_{\\rm min}\\delta\\nu$, which converts per-channel rms noise and source distance into a transmitter power limit. Together they define which stars can be searched, for how long, and what power limits the null result sets.","core_discovery":"To the best of the authors' knowledge, this is the first technosignature search conducted with ALMA data. Using two spectral windows centred on 90.642 GHz and 93.151 GHz from ALMA Band 3 observations of star-forming clumps, they identify 28 galactic stars with reliable Gaia DR3 distances within the undistorted fields of view of four calibrators. After subtracting the continuum calibrator sources and splitting the data into scans shorter than 75 seconds to limit drift smearing, they search for signals with SNR > 5 in the pixels of each star and in adjacent pixels out to 1.1 arcseconds. No candidate signals are found, so they derive upper limits on the EIRP of any putative transmitter for each star, with the best limit being $6.91 \\times 10^{17}$ W for the closest star. The paper argues that ALMA therefore places the first constraints on extremely powerful transmitters at millimetre frequencies and demonstrates a viable path for high-frequency SETI.","pith_inferences":["The quoted EIRP limits rest on the assumption that any signal drifts by no more than about 400 Hz/s at 90 GHz; a transmitter on a close-in planet, whose orbital acceleration can exceed the scaled Earth-bound value, would drift through the 30.52 kHz channel in less than the integration time and be missed, so the limits should be read as applying to transmitters on Earth-like or more slowly accelera","A straightforward testable extension is to re-run the same calibration-subtracted data cubes with a drift-rate search that covers a range of reference frames (for example, ±4000 Hz/s); the computational cost is high but the data already exist, so this could directly probe whether the null result is an artefact of the drift assumption.","The 'stellar bycatch' approach could be generalised to other ALMA spectral windows (Band 6 and 7) with similar spectral resolution, potentially extending SETI limits to even higher frequencies where the field of view shrinks but the drift-rate challenge grows.","If a dedicated SETI backend were installed on ALMA, the telescope's combination of sensitivity, frequency coverage, and RFI-quiet site would make it competitive with cm-wave facilities for probing very powerful, beamed transmitters, despite the small field of view."],"forward_implications":["ALMA can be used for SETI at frequencies above 35 GHz, expanding the search parameter space by more than an order of magnitude in frequency compared with most previous surveys.","The null detection places the first constraints on transmitters with EIRP above about $10^{17}$–$10^{19}$ W at 90–93 GHz toward 28 stars, complementing limits at lower frequencies.","At millimetre wavelengths, propagation effects from the ionised interstellar medium are much weaker, so intrinsically narrow signals can survive as narrow, drifting features even after long path lengths.","The same archival bycatch approach can be applied to other ALMA projects and to other high-frequency interferometers, increasing the number of stars searched without new observing time.","Future ALMA SETI searches would benefit from a specialised backend with finer spectral resolution and beamforming, which could push sensitivity toward Arecibo-level EIRP limits at millimetre wavelengths."],"supporting_citations":[{"why":"Supplies the maximum drift rate of ±4 Hz/s at 1 GHz that is scaled to ±400 Hz/s at ~90 GHz, determining the integration time split and the survey's sensitivity to drifting signals.","marker":"Price et al. 2020"},{"why":"Provides the drift-rate equation linking relative acceleration and rest frequency to the observed drift, and notes current algorithms handle only two orders of magnitude smaller drifts.","marker":"Sheikh et al. 2019"},{"why":"Supplies geometric distances for stars with moderately uncertain parallaxes, and these distances directly enter the EIRP_min calculation for several targets.","marker":"Bailer-Jones et al. 2021"},{"why":"Defines EIRP_min and the continuous-wave transmitter figure of merit used to compare this survey with other SETI searches.","marker":"Enriquez et al. 2017"},{"why":"Provides the bandwidth and time-average smearing formulae that define the undistorted interferometer field of view and justify the choice of stars in the sample.","marker":"Wrobel 1995"},{"why":"Demonstrates the stellar bycatch approach to commensal SETI with archival data that this paper applies to ALMA.","marker":"Wlodarczyk-Sroka et al. 2020"}],"fun_headline_variants":["First ALMA SETI hunt: 28 stars, zero signals","ALMA's millimetre SETI debut draws blank on 28 stars","No alien transmitters: ALMA checks 28 stars at 90 GHz","Millimetre SETI: ALMA finds no technosignatures in 28 stars"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The survey assumes that any artificial signal drifts in frequency by no more than about 400 Hz per second at 90 GHz, an assumption scaled from a 1-GHz search; a transmitter with a larger line-of-sight acceleration would smear across many channels and evade detection, weakening the quoted power limits.","fun_headline_variants_meta":{"raw":{"variants":["First ALMA SETI hunt: 28 stars, zero signals","ALMA's millimetre SETI debut draws blank on 28 stars","No alien transmitters: ALMA checks 28 stars at 90 GHz","Millimetre SETI: ALMA finds no technosignatures in 28 stars"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000506,"raw_usage":{"total_tokens":2465,"prompt_tokens":940,"completion_tokens":1525,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":556,"completion_tokens_details":{"reasoning_tokens":1441}},"tokens_in":556,"tokens_out":1525,"duration_ms":12659,"temperature":1.0,"reasoning_tokens":1441,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T05:47:46.338446+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Re-analyse the same ALMA calibration-subtracted data cubes with a search that explicitly corrects for drift rates up to at least ±4000 Hz/s (for example, by de-drifting into several inertial reference frames before searching) and check whether any pixel associated with the 28 stars yields a signal with SNR > 5. If such a signal appears, the null result and its EIRP limits are overturned; if none appears, the drift assumption is not the reason for the null.","supporting_citations":[{"cited_title":"M., 1995, in Zensus J","cited_arxiv_id":null,"evidence_quote":"Provides the bandwidth and time-average smearing formulae that define the undistorted interferometer field of view and justify the choice of stars in the sample."}],"review_version":1}