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1. Automated evaluation of environmental coupling for Advanced LIGO gravitational wave detections

   https://doi.org/10.1088/1361-6382/ad5139  

   Helmling-Cornell, A F; Nguyen, P; Schofield, R_M S; Frey, R (June 2024, Classical and Quantum Gravity)

   Abstract The extreme sensitivity required for direct observation of gravitational waves by the Advanced LIGO detectors means that environmental noise is increasingly likely to contaminate Advanced LIGO gravitational wave signals if left unaddressed. Consequently, environmental monitoring efforts have been undertaken and novel noise mitigation techniques have been developed which have reduced environmental coupling and made it possible to analyze environmental artifacts with potential to affect the 90 gravitational wave events detected from 2015–2020 by the Advanced LIGO detectors. So far, there is no evidence for environmental contamination in gravitational wave detections. However, automated, rapid ways to monitor and assess the degree of environmental coupling between gravitational wave detectors and their surroundings are needed as the rate of detections continues to increase. We introduce a computational tool,PEMcheck, for quantifying the degree of environmental coupling present in gravitational wave signals using data from the extant collection of environmental monitoring sensors at each detector. We study its performance when applied to 79 gravitational waves detected in LIGO’s third observing run and test its performance in the case of extreme environmental contamination of gravitational wave data. We find thatPEMcheck’s automated analysis identifies only a small number of gravitational waves that merit further study by environmental noise experts due to possible contamination, a substantial improvement over the manual vetting that occurred for every gravitational wave candidate in the first two observing runs. Building on a first attempt at automating environmental coupling assessments used in the third observing run, this tool represents an improvement in accuracy and interpretability of coupling assessments, reducing the time needed to validate gravitational wave candidates. With the validation provided herein;PEMcheckwill play a critical role in event validation during LIGO’s fourth observing run as an integral part of the data quality report produced for each gravitational wave candidate. 

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2. Measured limits on amplitude dependence of mechanical loss in substrate-transferred $\mathrm{Ga}\mathrm{As}/{\mathrm{Al}}_{0.92}{\mathrm{Ga}}_{0.08}\mathrm{As}$ coatings

   https://doi.org/10.1103/PhysRevD.106.042001  

   Gretarsson, Elizabeth M.; Gretarsson, Andri M.; Cole, Garrett D.; Harry, Gregory M.; Kinley-Hanlon, Maya M.; Jones, R. Jason; Penn, Steven D. (August 2022, Physical Review D)

   AIP (Ed.)

   In this Perspective, we summarize the status of technological development for large-area and low-noise substrate-transferred GaAs/AlGaAs (AlGaAs) crystalline coatings for interferometric gravitational-wave (GW) detectors. These topics were originally presented as part of an AlGaAs Workshop held at American University, Washington, DC, from 15 August to 17 August 2022, bringing together members of the GW community from the laser interferometer gravitational-wave observatory (LIGO), Virgo, and KAGRA collaborations, along with scientists from the precision optical metrology community, and industry partners with extensive expertise in the manufacturing of said coatings. AlGaAs-based crystalline coatings present the possibility of GW observatories having significantly greater range than current systems employing ion-beam sputtered mirrors. Given the low thermal noise of AlGaAs at room temperature, GW detectors could realize these significant sensitivity gains while potentially avoiding cryogenic operation. However, the development of large-area AlGaAs coatings presents unique challenges. Herein, we describe recent research and development efforts relevant to crystalline coatings, covering characterization efforts on novel noise processes as well as optical metrology on large-area (∼10 cm diameter) mirrors. We further explore options to expand the maximum coating diameter to 20 cm and beyond, forging a path to produce low-noise mirrors amenable to future GW detector upgrades, while noting the unique requirements and prospective experimental testbeds for these semiconductor-based coatings. 

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3. Substrate-transferred GaAs/AlGaAs crystalline coatings for gravitational-wave detectors

   https://doi.org/10.1063/5.0140663  

   Cole, G. D.; Ballmer, S. W.; Billingsley, G.; Cataño-Lopez, S. B.; Fejer, M.; Fritschel, P.; Gretarsson, A. M.; Harry, G. M.; Kedar, D.; Legero, T.; et al (March 2023, Applied Physics Letters)

   In this Perspective, we summarize the status of technological development for large-area and low-noise substrate-transferred GaAs/AlGaAs (AlGaAs) crystalline coatings for interferometric gravitational-wave (GW) detectors. These topics were originally presented as part of an AlGaAs Workshop held at American University, Washington, DC, from 15 August to 17 August 2022, bringing together members of the GW community from the laser interferometer gravitational-wave observatory (LIGO), Virgo, and KAGRA collaborations, along with scientists from the precision optical metrology community, and industry partners with extensive expertise in the manufacturing of said coatings. AlGaAs-based crystalline coatings present the possibility of GW observatories having significantly greater range than current systems employing ion-beam sputtered mirrors. Given the low thermal noise of AlGaAs at room temperature, GW detectors could realize these significant sensitivity gains while potentially avoiding cryogenic operation. However, the development of large-area AlGaAs coatings presents unique challenges. Herein, we describe recent research and development efforts relevant to crystalline coatings, covering characterization efforts on novel noise processes as well as optical metrology on large-area (∼10 cm diameter) mirrors. We further explore options to expand the maximum coating diameter to 20 cm and beyond, forging a path to produce low-noise mirrors amenable to future GW detector upgrades, while noting the unique requirements and prospective experimental testbeds for these semiconductor-based coatings. 

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4. Methods for estimating neutron star parameters using multiple mechanisms for gravitational wave emission associated with pulsar glitches

   https://doi.org/10.1093/mnras/staf2176  

   Ball, Matthew; Frey, Raymond (December 2025, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Several mechanisms for gravitational wave (GW) emission are believed to be associated with pulsar glitches. This emission may be split between long-duration continuous waves and short-duration bursts. In the Advanced LIGO era, searches for GWs associated with pulsar glitches have only considered continuous wave emission. The increasing sensitivity of the detectors and the prospects for future detectors suggest that astrophysically motivated analyses involving multiple mechanisms may be possible. Here, we present a framework for combining two simple models for GW emission – long-duration continuous waves and short-duration bursts – to derive more constraining astrophysical implications than a single model would allow. The best limits arise from using models that predict a specific amount of GW emission; however, there are relatively few models that make such predictions. We apply these methods to the 2016 December Vela pulsar glitch and make predictions for how well future observing runs and detectors would improve results. As part of this analysis, we performed a targeted search for GW bursts associated with this glitch and find no signal. 

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5. Accounting for numerical-relativity calibration uncertainty in gravitational-wave modeling and inference

   https://doi.org/10.1103/5kbh-83k7  

   Pompili, Lorenzo; Buonanno, Alessandra; Pürrer, Michael (August 2025, Physical Review D)

   The increasing sensitivity of current and upcoming gravitational-wave (GW) detectors poses stringent requirements on the accuracy of the GW models used for data analysis. If these requirements are not met, systematic errors could dominate over statistical uncertainties, hindering our ability to extract astrophysical and cosmological information, and conduct precise tests of general relativity. In this work, we present a novel method to mitigate the impact of waveform-systematic errors, by incorporating and marginalizing over waveform-uncertainty estimates, which are modeled as probability distributions for the numerical-relativity calibration parameters of effective-one-body waveform models. By analyzing simulated GW signals of loud “golden” binary-black-hole systems, we show that our method significantly reduces biases in the recovered parameters, highlighting its potential to improve the robustness of GW parameter estimation with upcoming observing runs and next-generation ground-based facilities, such as the Einstein Telescope and Cosmic Explorer. 

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