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REVIEW 2 major objections 7 minor 78 references

Advanced Virgo during the LIGO-Virgo-KAGRA fourth observing run

T0 review · 2 major / 7 minor · reviewed 2026-07-30 · grok-4.5

Pith's one-line read Advanced Virgo finished its dual-recycled design for O4, ran at 68.9% duty cycle and 53 Mpc BNS range after taming a mid-band excess noise with power cut and intentional signal-recycling misalignment.

desk verdict Solid O4 instrument paper: first dual-recycled Virgo numbers (68.9% duty cycle, 53 Mpc median BNS range) with a clear commissioning narrative; excess-noise origin still open but does not undercut the reported performance. read the letter →

arxiv 2607.26872 v1 pith:3QALCQUH submitted 2026-07-29 gr-qc

Virgo Collaboration: F Acernese , A Agapito , D Agarwal , I-L Ahrend , L Aiello , A Ain , W Ali , A Allocca
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W Amar A Amato F Amicucci C Amra M Andia T Andri S Antier F Arciprete F Armato N Arnaud L Asprea M Assiduo S Assis de Souza Melo P Astone F Attadio F Aubin G Avallone N Avdeev S Babak S Bagnasco S Baimukhametova T Baka G Balbi G Baldi N Baldicchi G Ballardin M Ballelli B Banerjee M Baratti F Barone M Barsuglia D Barta A Basti M Bawaj M Bazzan F Beirnaert M Bejger C Bellani D Beltran-Martinez E Benedetti I Bentara S Bera D Bersanetti T Bertheas A Bertolini J Bezerra-Sobrinho V Biancalana F Bianchi M Bilicki A Binetti S Biot M Bitossi M-A Bizouard M Bloch G Boileau M Boldrini R Bonnand N Borghi V Boschi Y Bothra A Boudon A Bozzi C Bradaschia M Branchesi T Briant A Brillet M L Brozzetti G Bruno F Bucci A Buchicchio A Buggiani O Bulashenko T Bulik H J Bulten R Buscicchio N Busdon D Buskulic R Cabrita G Cagnoli E Calloni E Capocasa G Capoccia G Capurri F Carbognani M Carpinelli A Casallas-Lagos J Casanueva Diaz C Casentini R Cavalieri G Cella P Cerd E Cesarini W Chaibi E Chassande-Mottin S Chaty P Chessa F Chiadini A Chincarini A Chiummo A Chopra N Christensen G Ciani M Cie P Ciecielag M Cifaldi S Clesse F Cleva E Coccia E Codazzo P-F Cohadon A Colombo G Comp L Conti I Cordero-Carri S Corezzi S Cortese L A Corubolo A Cozzumbo K Csuk E Cuoco M Cusinato R R Cuzinatto B D'Angelo S D'Antonio L D'Onofrio D D'Urso G D S Dall'Osso T Dal Canton S Dal Pra S Danilishin V Dattilo A Daumas P Davis J Degallaix C J Delgado Mendez S Della Torre W Del Pozzo A Demagny G Demasi A Depasse J De Bolle M De Laurentis F De Lillo F De Marco F De Matteis C de Melo R De Pietri R De Rosa C De Rossi R De Simone S Dhage C Diaz F Diaz Guerra M A Dicorato D Diksha J Ding M Di Cesare M Di Giovanni S Di Pace I Di Palma D Di Piero F Di Renzo A Domiciano De Souza O Dorosh M Drago M Dubois U Dupletsa H Duval H Einsle V Ernst L Errico M Esposito F Fabrizi V Fafone M Fays E Fenyvesi A Feo G Fern T Fernandes S Ferraiuolo F Fidecaro P Figura I Fiori V Fiumara R Flaminio F Flocco J A Font A Fragkos N Franchini F Frappez F Frasconi A Freise O Freitas S Galaudage M Galimberti B Garaventa J Garc P Garc J Gargiulo X Garrido F Garufi C Gasbarra F Gautier G Gemme A Gennai V Gennari A Ghinassi Archisman Ghosh F Gittins F Glotin E Glowacki S Gomez Lopez A Goodwin-Jones M Gosselin C Gostiaux R Gouaty D Goupilliere A Grado M Granata V Granata G Greco A C Green C Grimaud G M Guidi F Gulminelli Y Guo M Haney S Harikumar J Harms M T Hartman B Haskell D Hegde H Heitmann G Hemming J Heynen S Hild D Hofman L Honet W-F Hsu L Iampieri G A Iandolo M Ianni A Ierardi P Iosif J Irwin C Jacquet T Jacquot J Janquart S Jaraba P Jaranowski G Joubert B Kacskovics A Karia W Kiendrebeogo S Koley A E Koloniari A Kr E Kraja S L Kranzhoff J Kubisz S Kuroyanagi N Lajili A Lakhal M Lalleman J A Lange A Lartaux-Vollard L Lavezzi C Lazzaro P Leaci F Legger A Lema R Lemrani Alaoui M Lenti M Leonardi M Lequime N Letendre M Lethuillier S Lexmond M Le Jean T G F Li F Liu J-P Locquet A Longo M Lopez Portilla M Lorenzini V Loriette M Lorusso G Losurdo D Lumaca L Lunghini A Macquet S S Madekar S Maenaut E Maggio M Magnozzi E Majorana N Man M Mancarella V Mangano M Mantovani M Mapelli S Marchetti F Marion S Marsat F Martelli M Martinez V Martinez A Martini J C Martins L Massaro A Masserot S Mastrogiovanni G Mastropasqua L Maurin L G Medeiros L Mereni C Michel E Milotti V Milotti E Minakaki Y Minenkov Ll. M Mir L Mirasola C-A Miritescu L Mobilia M Montani G Montefusco A Moreso Serra G Morras A Moscatello B Mours C M Mow-Lowry L Muccillo F Muciaccia D Nabari S Nadji A Nagar D Nanadoumgar-Lacroze V Napolano A Nardecchia I Nardecchia H Narola L Naticchioni L Negri A Nemmani T C K Ng S Nissanke F Nocera J Novak M Oertel G Oganesyan R Oliveira A Ouzriat M A Palaia C Palomba P T H Pang F Pannarale M Panzeri F Paoletti A Paoli A Paolone L Papalini G Papigkiotis A Paquis A Parisi D Pascucci A Pasqualetti D Passuello B Patricelli K Paul A Perreca J Perret D Pesios C Petrillo L Piccari M Pichot M Piendibene F Piergiovanni L Pierini G Pierra V Pierro M Pillas L Pinard I M Pinto M Pinto A Pisarski E Placidi R Poggiani E Polini M Polo J Pomper E Porcelli E K Porter M Pracchia G Principe G A Prodi P Prosperi P Prosposito M Punturo P Puppo G Qu I Rainho P Rapagnani M Razzano T Regimbau A I Renzini B Revenu A Revilla-Pe F Ricci M Ricci A Ricciardone A Riminucci F Robinet A Rocchi L Rolland R Romano A Romero-Rodr S Ronchini D Rosi S Roy D Rozza P Ruggi E Ruiz Morales F Safai Tehrani P Saffarieh T Sainrat S Sajith Menon L Salconi F Salemi M Sall M Salom S Salvador A Samajdar N Sanchis-Gual F Santoliquido F Sarandrea P Sassi B Sassolas M Schoor K Schouteden M Schulz M Scialpi M Seglar-Arroyo J W Seo V Sequino M Serra A Sevrin L Silenzi P J S Silva L Silvestri L Smith S Soares de Albuquerque Filho V Sordini F Sorrentino F Spada V Spagnuolo M Spera P Spinicelli D A Steer J Steinlechner S Steinlechner N Stergioulas M Suchenek S Sudhagar J Sun J Suresh A Svizzeretto B L Swinkels A Syx M J Szczepa M Tacca M Tagliazucchi I Takimoto Schmiegelow N Tamanini L Tao E N Tapia San Mart A Theodoropoulos J Tissino P Tiwari E Tofani M Toffano I Tosta e Melo E Tournefier A Trapananti R Travaglini F Travasso M C Tringali G Troian A Trovato L Trozzo M Turconi C Turski H Ubach M Vacatello M Valentini E Vallejo-Pag S Vallero M van Dael E Van den Bossche J F J van den Brand C Van Den Broeck M van der Kolk M van der Sluys A Van de Walle J van Dongen H van Haevermaet J V van Heijningen P Van Hove N van Remortel M Vardaro G Vedovato S Venikoudis P Verdier M Vereecken D Verkindt S Verma F Vetrano A Veutro A Vicer N Villanueva Espinosa J-Y Vinet S Viret H Vocca M Was M Wils I C F Wong T Wouters M Wright Z Wu N Yadav M Zanatta T Zelenova J-P Zendri M Zeoli M Zerrad J Zhang Y Zhao L Zhizhong L Zimmermann
This is my paper
classification gr-qc PACS 04.80.Nn95.55.Ym07.60.Ly
keywords AdvancedVirgoO4observingrundualrecyclingsignalexcessnoisehigher-ordermodesbinaryneutronstarrangedutycycle
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper reports how Advanced Virgo finally installed its signal-recycling mirror and ran the dual-recycled Fabry–Perot Michelson configuration through the LIGO–Virgo–KAGRA fourth observing run (April 2024–November 2025). The nearly unstable recycling cavities forced a cascade of control, thermal-compensation and alignment work-arounds; a dominant broadband excess noise between 50 and 200 Hz then limited sensitivity. The collaboration mitigated that noise by dropping input power to about 17 W and deliberately misaligning the signal-recycling mirror by roughly 2 µrad, which lowered the detector bandwidth from ~430 Hz to ~190 Hz and raised the binary-neutron-star range from ~40 Mpc to a median 53 Mpc at 68.9 % science duty cycle. The account documents both the successful upgrades (high-finesse output mode cleaner, filter-cavity squeezing source, Newtonian calibrator, scattered-light baffles) and the residual limitations that now motivate replacing the recycling cavities with stable ones.

What carries the argument

Nearly unstable dual-recycling cavities (g-factor ~0.999988, round-trip Gouy phase ~0.39°), which co-resonate carrier higher-order modes in the signal-recycling cavity and force the power-reduction plus intentional SR-misalignment mitigation that shaped the final O4 noise curve.

What would settle it

A direct measurement showing that the excess noise amplitude does not track the optical gain of higher-order modes inside the signal-recycling cavity when that cavity’s alignment or Gouy phase is deliberately varied.

Watch

Extended reading notes

Core claim

With the signal-recycling mirror installed, Advanced Virgo operated in its design dual-recycled configuration for O4 and achieved a 68.9 % science duty cycle and a median angle-averaged binary-neutron-star range of 53 Mpc after the dominant mid-band excess noise was reduced by lowering input power and intentionally misaligning the signal-recycling mirror.

Load-bearing premise

That the still-unidentified broadband excess noise is carried by carrier higher-order modes resonant in the nearly unstable signal-recycling cavity, so that misaligning that mirror correctly suppresses it.

Editorial extensions

If this is right

  • Stable recycling cavities are now the baseline upgrade path because they would remove the HOM co-resonance that drove both the excess noise and the control offsets.
  • Frequency-dependent squeezing remains ineffective until the intentional SR misalignment can be removed.
  • Future runs will need faster lock-acquisition sequences once dither-based set-point loops are no longer required.
  • Scattered-light and environmental couplings improved by the new baffles and seismometers will become limiting only after the mid-band excess noise is cured.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The same nearly-unstable cavity physics that limited Virgo will reappear in any dual-recycled detector whose recycling Gouy phase is kept this small, so cavity redesign is a network-wide lesson.
  • Once stable cavities restore the full detector bandwidth, the already-commissioned filter cavity should immediately deliver the missing low-frequency quantum-noise reduction.
  • The Newtonian calibrator’s sub-percent absolute accuracy is now available as a network reference once the other detectors adopt comparable systems.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

2 major / 7 minor

Summary. This manuscript reports the configuration, commissioning challenges, upgrades, and observational performance of Advanced Virgo during the LIGO–Virgo–KAGRA O4 run (10 April 2024 – 18 November 2025). After installing the signal-recycling mirror and completing the dual-recycled Fabry–Perot Michelson design, the detector was operated with reduced input power (~17 W) and intentional SR misalignment (~2 µrad) to mitigate a dominant broadband excess noise in the 50–200 Hz band associated with carrier higher-order modes resonant in the nearly unstable SRC. Headline results are a 68.9% science duty cycle and an angle-averaged median BNS range of 53 Mpc. The paper documents lock acquisition with ALS, thermal compensation of the central interferometer, automatic alignment (including double-dither SR control), laser-noise coupling control, scattered-light and environmental-noise work, and several successful subsystem upgrades (high-finesse OMC, squeezing path, IMC payload, Newtonian calibrator, electronics) whose net sensitivity impact was limited by the dual-recycling challenges.

Significance. As the definitive instrument-status account of Virgo in O4, the paper is of clear and lasting value to the gravitational-wave community. It supplies the operational configuration actually used for astrophysical analyses (misaligned SR, reduced power, bandwidth ~190 Hz), quantitative duty-cycle and range statistics, a simplified but useful noise budget, measured back-scatter fractions, a squeezing loss budget, and a candid diagnosis of nearly unstable recycling cavities. The consistency tests linking excess noise to SRC-resonant carrier HOMs (DARM-offset scaling, optical-response shape under misalignment, HOM redistribution after the WE swap) are carefully framed, and the residual unidentified physical origin is stated explicitly rather than over-claimed. The documented path to stable recycling cavities for O5 is a concrete outcome of the commissioning experience. Strengths include direct operational observables, cross-reference to the companion optical-parameter paper, and transparent tables (duty cycle, f_sc, squeezing losses).

major comments (2)
  1. [§5.2–5.3] §5.2–5.3 and Fig. 10: The case that excess noise is carried by SRC-resonant carrier HOMs is consistent and well argued (linear scaling with DARM offset, shape change under SR misalignment matching optical response plus HOM gain, direction change after WE swap). The manuscript correctly states that the physical origin of the noise that couples through HOMs “remains unidentified.” For the status claim this is acceptable, but the paper would be stronger if §5.3 briefly quantified residual alternatives still allowed (e.g., upper bounds on any residual displacement-like or RF-sideband contribution after the tests listed) so that future analyses know what has been closed versus left open.
  2. [§5.1, Fig. 9] §5.1 / Fig. 9: The excess-noise term is introduced as an empirical power law (−0.6 ± 0.1, or “1/f^{0.67}” in the caption text) multiplied by the detector optical response. Clarify in one place whether the quoted slope is fit in strain or in optical power at the dark port, and whether the same index is used for both the aligned and misaligned projections in Fig. 10; a one-sentence statement of the fit band and degrees of freedom would make the simplified budget fully reproducible from the text.
minor comments (7)
  1. [Abstract, §8] Abstract and §8: Duty cycle 68.9% and median BNS range 53 Mpc are clear; consider adding the O4b vs O4c_2 split (71.8% / 62.3%) in the abstract or early in §8 so readers see the post-break hardware impact without opening Table 3.
  2. [Fig. 9] Fig. 9 caption vs body: body uses −0.6 ± 0.1; caption writes 1/f^{0.67}. Harmonize the exponent notation.
  3. [§6.1.2, Table 1] Table 1: The factor-~7 rise in SDB1 f_sc from pre-O4 to O4 is attributed to a July 2024 waveplate intervention and/or SR misalignment; a short note on whether f_sc was re-measured after subsequent bench work would help.
  4. [§7.2] §7.2 / Table 2: Squeezing efficiency (41 ± 4)% in the aligned high-frequency band matches the loss budget well; the statement that no useful trade-off exists with SR misalignment is important—consider a single sentence pointing to the BNS-range optimum (~55 Mpc) versus high-frequency shot-noise cost so non-squeezing readers see the global figure of merit.
  5. [References] Many supporting results are cited as “in preparation” (TCS [10], alignment [28], injection [34], calibration [70], etc.). Where a public arXiv or TDS number already exists, adding it would improve citability; otherwise leave as is.
  6. [§2, Appendix A] Appendix A: Eq. (4) in the main text and Eq. (17) in the appendix are the same content; a forward reference in §2 to Appendix A is present—ensure symbol r_SRC vs r_SR is consistent throughout.
  7. Typographical: “inteferometer” (§6.1), “Superattanuator” (§7.6), “guarantees” style inconsistencies in author list footnotes; standard copy-edit pass.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: O4 performance metrics and commissioning narrative are direct measurements, not quantities forced by definition or self-citation chains.

full rationale

This is an instrumentation status paper reporting measured duty cycle (68.9%), BNS range (53 Mpc median), noise spectra, lock procedures, and upgrade outcomes for Advanced Virgo in O4. The strongest claims are operational observables (science time fraction, calibrated range, strain spectra) obtained from detector data, not quantities derived from fitted parameters that are then re-presented as predictions. The dominant excess-noise discussion (Sec. 5) adds an empirical power-law term shaped by the optical response to close the noise budget; it does not claim a first-principles derivation that forces the observed spectrum, and explicitly states the physical origin coupling through HOMs “remains unidentified.” Self-citations and “in preparation” notes supply methods, prior optical parameters, or companion analyses; they are not load-bearing uniqueness theorems or ansatzes that redefine the headline results. No equation reduces a claimed prediction to its own fitted input by construction. Circularity score is therefore zero.

Assumptions & free parameters 4 free parameters · 5 assumptions · 1 invented entities

Status/instrumentation paper resting on standard interferometer physics and on the collaboration’s prior optical-parameter measurements. No new fundamental entities. Free parameters are empirical noise-model slopes and operating setpoints chosen to maximize range, not theory constants fitted to force a claim.

free parameters (4)
  • excess_noise_power_law_slope = -0.6 ± 0.1
    Broadband excess in 50–200 Hz modeled empirically as frequency dependence −0.6±0.1 times the detector optical response (Fig. 9, §5.1); not derived from a first-principles noise mechanism.
  • SR_misalignment_angle_and_direction = ~2 µrad (bandwidth ~190 Hz)
    Chosen operationally (~2 µrad) to maximize BNS range by trading excess noise against shot noise and bandwidth (§5.3); direction retuned after WE mirror replacement.
  • input_laser_power_O4 = 17 W
    Reduced from attempted 31–40 W to 17 W because higher power made recycling fields bistable/unstable (§3.2, §5.3).
  • MICH_setpoint_offset = set to minimize PSTAB→DARM coupling
    Adjusted via 1501 Hz intensity dither to minimize intensity-noise coupling to DARM (§3.4); residual coupling quoted as 6.5e-17 strain/RIN.
assumptions (5)
  • domain assumption Cavity geometric stability requires 0 < g < 1; Virgo recycling cavities have design g ≈ 0.999988 and round-trip Gouy phase ≈ 0.39°.
    Section 2; standard resonator theory (Siegman/Kogelnik) applied to measured/design RoCs.
  • domain assumption Carrier HOMs that are anti-resonant in the arm cavities reverse the FP reflection sign and therefore resonate in a SRC tuned for carrier anti-resonance (Appendix A Airy gain).
    Appendix A derivation; load-bearing for the HOM-excess-noise interpretation.
  • domain assumption Pound–Drever–Hall and Ward techniques plus ALS green-light CARM offset provide valid longitudinal/angular error signals for lock acquisition.
    Section 3.1; standard GW-detector control assumptions.
  • domain assumption BNS range is the sky- and orientation-averaged distance for SNR=8 canonical binary neutron star merger.
    Footnote in §6; community convention used for the 53 Mpc headline.
  • domain assumption Optical parameters (losses, gains, sideband build-up) measured in the companion O4 optical characterization paper are accurate inputs to the noise and squeezing budgets.
    Repeated reliance on Ref. [5] throughout §§2–5, 7.
invented entities (1)
  • unidentified excess noise carried by SRC-resonant carrier HOMs
    purpose: Account for the 50–200 Hz strain noise above the sum of modeled quantum, coating, and control noises after all known projections.
    Introduced in §5 as an empirical residual; HOM carrier is inferred from scaling tests but the microscopic noise source is explicitly unidentified. Not a new particle/force—an unmodeled noise term.

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Cite this review

Pith. "Pith review of Advanced Virgo during the LIGO-Virgo-KAGRA fourth observing run." pith.science (2026). https://pith.science/paper/3QALCQUH

@misc{pith2026260726872,
  author       = {Pith},
  title        = {Pith review of: Advanced Virgo during the LIGO-Virgo-KAGRA fourth observing run},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/3QALCQUH}},
  note         = {Machine review of arXiv:2607.26872}
}
read the original abstract

From April 10, 2024 to November 18, 2025 Advanced Virgo participated in the fourth observing run of the network of gravitational-wave detectors, together with Advanced LIGO and KAGRA. For this observing run Advanced Virgo has completed its design optical configuration with the installation of a signal recycling mirror. In this paper we describe the challenges encountered in commissioning this optical configuration, alongside the other upgrades performed between the third and fourth observing run. The Virgo detector operated with a 68.9% duty cycle and with an angle-averaged median range to binary neutron star mergers of 53 Mpc.

Figures

Figures reproduced from arXiv: 2607.26872 by the authors.

Figure 1
Figure 1. Optical configuration of the Advanced Virgo detector during O4. The 1064 nm laser is going through the input mode cleaner (IMC) towards the core optics: power recycling mirror, beam splitter, north input and end mirrors, west input and end mirrors, and signal recycling mirror. Different colored lines represent the carrier and sidebands, with the modulation frequencies listed in the caption at the bottom of the schem… view at source ↗
Figure 2
Figure 2. ALS lock and introduction of the CARM offset in the arm cavities of Virgo. The top row shows the infrared power in transmission through the arms’ end mirrors as a function of time, the middle row the ALS beam power in transmission of the arms’ input mirrors (the auxiliary beams are injected through the end mirrors, as per figure 1), and the bottom row the actuation voltage on the IM. The colored boxes show the diffe… view at source ↗
Figure 3
Figure 3. Dynamics of PR CHRoCC. The points indicates the equivalent PR RoC correction, expressed as ∆ [PITH_FULL_IMAGE:figures/full_fig_p017_3.png] view at source ↗
Figures from the paper (18 more)
Figure 4
Figure 4. Figure 4: Dynamics of NI CH on the left plot and of WI CH on the right one. The points are the values of HWS-measured Gaussian weighted curvature related to different injected powers, the solid lines represent the linear fit and the dashed lines are the 95% confidence bounds. Th…
Figure 5
Figure 5. Figure 5: The 1D Gaussian weighted curvatures induced by WI CH and compensated by WI DAS. The blue line represents the curvature extracted from the barycentre row and the red line from the column one. The yellow line is the average curvature. gain frequency of a few Hz. To mitig…
Figure 6
Figure 6. Figure 6: Effects of a scan of the setpoint of the MICH control loop: top-left: MICH setpoint, top-right: coupling between laser intensity noise and DARM, bottom-left: error signal obtained by demodulating DARM error signal at the frequency of the monitor line, bottom-right: pow…
Figure 7
Figure 7. Figure 7: Projection of the laser intensity noise compared with the quiet strain noise curve. from simulations, it also improves the balance between the upper and lower 56 MHz sidebands power in transmission of the interferometer. All these loops based on dither signals are slow…
Figure 8
Figure 8. Figure 8: Projection of the laser frequency stabilization in-loop signal and the loop sensing noise compared with the quiet detector noise curve. The total frequency noise is the quadratic sum of these two components. We also discuss the effect of the intentional SR mirror misal…
Figure 9
Figure 9. Figure 9: Simplified noise budget of the Virgo strain noise curve on June 11, 2025, in the misaligned SR configuration used during O4. The measured strain spectrum is shown together with the main modeled noise contributions, including coating thermal noise, quantum shot noise, c…
Figure 10
Figure 10. Figure 10: Comparison of inferred excess noise for two different conditions of the SR mirror alignment. The black solid line represents a simple model for the excess noise in the aligned case, which is a power law shaped by the optical response; the black dashed line represents …
Figure 11
Figure 11. Figure 11: Left: 3D drawing of the SDB1 bench where the newly installed diaphragms are indicated by the red arrows. The main infrared beams are shown as red tubes. The green beam represents the optical path of the Hartmann wavefront sensor light, which overlaps with the main inf…
Figure 12
Figure 12. Figure 12: Examples of beam dumps and diaphragms installed on the optical benches to block the ghost beams. Circular absorbing glass beam dumps (1) were integrated on the highly reflective mirror mounts to dump the ghost beams induced by the spurious transmission through the hig…
Figure 13
Figure 13. Figure 13: Projection of back-scattered light noise from the optical benches SDB1, SNEB, SWEB compared to the strain noise curve. Left: Data from February 12, 2025, during a period of low bench motion. The maximum bench speed measured was around the median of the annual speed di…
Figure 14
Figure 14. Figure 14: Projections of magnetic noise in the central experimental halls, compared with quiet detector noise curve. the corresponding environmental noise under quiet (no injections) conditions can be estimated by projecting the witness sensor spectrum X(f) through the measured…
Figure 15
Figure 15. Figure 15: Projections of acoustic noise for the central experimental hall compared with the quiet detector noise curve. The faint colored curves show upper-limit estimates, while the bold dots are measurements [PITH_FULL_IMAGE:figures/full_fig_p036_15.png]
Figure 16
Figure 16. Figure 16: Projections of acoustic noise based on injections performed at the NEB and at the WEB, respectively before and after the installation of the WE payload baffle. The black curve is a reference strain noise in quiet conditions. The faint colored curves are upper-limit es…
Figure 17
Figure 17. Figure 17: Squeezing efficiency in Virgo before and during the O4b run, for different detector bandwidth frequencies. The median values of the investigated frequency bands are reported along the x-axis. The red line corresponds to the measurements taken with aligned configuratio…
Figure 18
Figure 18. Figure 18: Weekly breakdown of the Virgo detector activities during the O4b and O4c runs. periods and global strong earthquakes). The last 2% of the time were associated with short Virgo downtimes required to make more invasive actions on the Virgo detector (Detector upgrade). T…
Figure 19
Figure 19. Figure 19: Evolution of the Virgo BNS range in O4, from the start of O4b at 15:00 UTC on April 10, 2024, to the end of O4c at 16:00 UTC on November 18, 2025. The data has been taken from the online range computation , which uses 84-second sliding estimates with FFTs of 4 seconds…
Figure 20
Figure 20. Figure 20: Distribution of the Virgo BNS range in O4, divided into O4b plus the first part of O4c until spring break, and the rest of O4c. Vertical dashed lines represent the median ranges for the O3 and O4 subruns. These curves have been produced with the same data shown in fig…
Figure 21
Figure 21. Figure 21: Circulating Airy distributions of equation (17) inside the SRC for different detunings of the SRC round-trip phase ϕSRC for the fundamental, 1st and 10th order modes. where rSRC and rFP are the amplitude field reflection coefficients for the signal recycling mirror an…

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Pith tools

Reviewed July 30, 2026 · model on record in the stance chip above.