Gravitational-wave astronomy offers a promising opportunity to directly observe scalar-induced gravitational waves originating from the early universe. Experiments—including ground-based interferometers such as LIGO and Virgo, and pulsar timing arrays (PTAs) based on facilities such as FAST and SKA—are poised to significantly enhance sensitivity to these signals. In this paper, we combine Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillation (BAO) datasets with upper or lower limits on the stochastic gravitational-wave background provided by FAST or SKA to constrain scalar-induced gravitational waves. To provide a comprehensive forecast, we consider two scenarios at a given frequency: one in which FAST or SKA does not detect scalar-induced gravitational waves, thereby setting an upper limit on the fractional energy density; and another in which these waves are detected, thus establishing a lower limit. In the ΛCDM+r model, the scalar spectral index of the power-law power spectrum is constrained to from the combination of CMB+BAO+SKA datasets in the upper-limit scenario where scalar-induced gravitational waves propagate at the speed of light. The constraint shifts to in the lower-limit scenario. Compared with the constraint from the combination of CMB+BAO datasets, the scalar spectral index in the upper-limit scenario exhibits significant changes, which could serve as an indicator of scalar-induced gravitational waves. In the ΛCDM+ +r and ΛCDM+ + +r models, the running of the scalar spectral index and the running of the running also show notable variations, suggesting potential indicators. The numerical findings clearly demonstrate the impact of the upper and lower limits provided by FAST or SKA.

The detection of gravitational waves from binary black hole and neutron star mergers by ground-based interferometers, as well as the evidence for a gravitational wave background from pulsar timing array experiments, has marked a new era in astrophysics and cosmology. These experiments also have great potential for discovering new physics through gravitational wave detection. One of the most motivated sources of gravitational waves that can be realized only within a beyond-the-Standard-Model framework is first-order phase transitions. In this work we release PT2GWFinder , a Mathematica package designed to compute phase transition parameters and the gravitational wave power spectrum for an arbitrary scalar theory exhibiting a first-order phase transition, in scenarios where a single scalar acquires a vacuum expectation value. PT2GWFinder performs the phase tracing, computes the bounce profile and action using FindBounce , calculates the relevant temperatures and phase transition parameters, and finally evaluates the gravitational wave spectrum. Additionally, it offers a user-friendly interface with DRalgo , which enables the computation of the dimensionally reduced effective potential in the high-temperature regime. This work includes a user manual and two models that demonstrate the capability and performance of PT2GWFinder . As a supplement, for one of these models we obtain the bounce solution and action analytically in the thin-wall approximation and demonstrate excellent agreement with the numerical approach. Program title : PT2GWFinder CPC Library link to program files: https://doi.org/10.17632/s69t25dw2j.1 Developer’s repository link : https://github.com/finshky/PT2GW Licensing provisions : GNU General Public License 3 Programming language : Mathematica Nature of problem : Search and characterization of cosmological first-order phase transitions, computation of the generated gravitational wave spectra. Solution method : Construction of the Euclidean bounce action function, using FindBounce , and application of integral criteria to determine the transition temperatures. Restrictions : Mathematica version 13 or above, applicable to single-field models.

We propose a new strategy to probe nontensorial polarizations in the stochastic gravitational wave (GW) background. Averaging over polarization angles, we find that three-point correlations of the GW signal vanish for tensor and vector modes, while scalar modes generically leave a nonzero imprint. This property makes the GW bispectrum a distinctive and robust diagnostic of scalar polarizations predicted in theories beyond general relativity. We derive the corresponding response functions for ground-based interferometers, pulsar timing arrays, and astrometric observables, and we construct an optimal estimator together with simple Fisher forecasts for pulsar timing sensitivity. As a proof of principle, we show that second-order GWs sourced by primordial magnetogenesis can be characterized by large three-point functions. Our results demonstrate that GW three-point correlations provide a novel observational window on physics beyond general relativity.

The thermosphere serves as a pivotal region for Sun–Earth interactions, and thermospheric winds are of great scientific importance for deepening insights into atmospheric dynamics, climate formation mechanisms, and space environment evolution. This study designed and developed a Ground-based Doppler Asymmetric Spatial Heterodyne Interferometer (GDASHI). Targeting the nightglow of the oxygen atomic red line (OI 630.0 nm), this instrument enables high-precision observation of thermospheric winds. The GDASHI was deployed at Gemini Astronomical Manor (26.7°N, 100.0°E), and has obtained one year of nighttime meridional and zonal wind data. To verify the reliability of GDASHI-derived winds, a collocated observation comparison was performed against the Dual-Channel Optical Interferometer stationed at Binchuan Station (25.6°N, 100.6°E), Yunnan. The winds of the two instruments are basically consistent in both their diurnal variation trends and amplitudes. Further Deming regression and correlation analysis were conducted for the two datasets, with the meridional and zonal winds yielding fitting slopes of 0.808 and 0.875 and correlation coefficients of 0.754 and 0.771, respectively. An uncertainty analysis of the inter-instrument comparison was also carried out, incorporating instrumental measurement uncertainties, instrumental parameter errors, and small-scale perturbations induced by observational site differences; the synthesized total uncertainties of zonal and meridional winds are determined to be 20.24 m/s and 20.77 m/s, respectively. This study not only verifies the feasibility and reliability of GDASHI for ground-based thermospheric wind detection but also provides critical observational support for analyzing the spatiotemporal variation characteristics of mid-low latitude thermospheric wind fields and exploring their underlying physical mechanisms.

HighlightsWhat are the main findings?A gNB 5G base station can be effectively used as a ground-based radar interferometer for monitoring structural displacements.A regression-based compensation method is proposed to estimate and remove antenna mast motion and atmospheric disturbances directly from radar data, achieving better performance than approaches relying on auxiliary sensors.What are the implications of the main findings?Using existing 5G infrastructures for radar sensing significantly reduces deployment and maintenance costs for large-scale Structural Health Monitoring.Radar interferometry can be used even for health monitoring of a gNB telecommunication mast itself.Radar interferometry can provide important information for Structural Health Monitoring (SHM) of bridges and other transportation structures. In this article, joint communication and sensing (JCAS) telecommunication infrastructure is tested as a ground-based radar, offering advantages in terms of long-term costs, deployment and maintenance. This work specifically addresses the estimation of the radar support movement (i.e., pylon or mast), which represents a major challenge in this kind of measurements. Movements of the radar system combine with the true target motion and, if not correctly compensated, can compromise the accuracy of the results. A technique for estimating radar movements based on the displacement tracking of multiple permanent scatterers (PSs) in the scenario is presented. True target displacements can then be retrieved by applying linear regression methods to fixed PSs located at different viewing angles, accounting for both radar movements and atmospheric displacement components. The technique was validated using real data acquired during an experimental campaign on a bridge test site. First, results obtained for a target subject to known displacements are shown. A second measurement session was aimed at testing the method for bridge dynamic monitoring. Finally, the same technique was applied antenna mast monitoring in terms of modal analysis and vibration characterization.

Abstract. Scattered airglow emissions in the lower atmosphere can bias ground-based interferometer observations of thermospheric winds, particularly when airglow brightness becomes spatially uneven due to auroras. During two geomagnetic storms with visible auroras on 10 May and 10 October 2024, the Doppler Asymmetric Spatial Heterodyne (DASH) and Fabry-Perot (FP) interferometers concurrently detected atypical winds at Siziwang (SIZW, 41.83° N, 111.93° E), suspected to be caused by scattering. These atypical winds, characterized by horizontal differences exceeding 400 m s−1 between opposite cardinal directions (N-S or E-W) and downwelling exceeding 100 m s−1, showed a strong temporal association with airglow brightness. By modelling the transmission of scattered airglow emissions, we calculate post-scattering wind speeds as the initial wind speeds weighted by both scattered and direct intensities. With fixed initial winds (100 m s−1 westward, 400 m s−1 southward, zero vertical wind), the simulation reproduces horizontal differences of approximately 400 m s−1 on 10 May and 100 m s−1 on 10 October, both capturing the temporal characteristics of the atypical winds. The simulation shows that scattering-induced biases on line-of-sight speed take their sign from the brighter region, while their magnitude varies directionally with the angle to that region: at 45° elevation, biases 135–180° azimuth away exceed those in the brighter region by more than 10 times. Limited by uncertainties in airglow images and optical depth of model inputs, the simulation incurs numerical errors of roughly 75 % during some periods. Effective correction of the scattering impact will require improved accuracy of model inputs in the future.

Since the first detection of gravitational waves (GWs), the field of experimental gravitation is steadily working on improving the current detectors as well as developing new instruments in order to expand the range of observable frequencies and improve the reconstruction of the GW direction and source parameters. In such a context, the Astrometric GW Antenna, consisting of at least three pairs of lines of sight assembled in a very compact configuration, represents a promising concept to achieve the above goals. Therefore, its detection capabilities and performances should be characterised. We derive the pattern functions of the Astrometric GW Antenna to estimate its directional response, allowing initial comparisons with other detectors and among different configurations. Our analysis shows that the Astrometric GW Antenna is almost equally sensitive to GWs coming from any direction, and better suited for detecting relatively nearby events. The implication is that the Astrometric GW Antenna can be an optimal detector for GW sources located within our Galaxy and can boost the instantaneous sky coverage of current ground-based interferometers. Moreover, the complementarity with the observations of LISA space antenna is emphasised. Finally, the detection range can be further expanded by combining simultaneous observations of a few replicas of the Astrometric GW Antenna.

Abstract The dynamics of stellar mass black holes (sBHs) embedded in active galactic nuclei (AGNs) could produce highly eccentric orbits near the central supermassive black hole, leading to repeated close encounters that emit gravitational waves in the Laser Interferometer Gravitational-Wave Observatory (LIGO) frequency band. Many works have focused on the mergers of sBHs in the disk that produce gravitational waves; however, sBHs in hyperbolic orbits also emit gravitational-wave bremsstrahlung that can be detected by ground-based interferometers like LIGO. In this work, we analyze the scattering of sBHs in an AGN disk as they migrate inside the disk, focusing on gravitational-wave bremsstrahlung emission. We determine how the gravitational-wave emission depends on the different parameters of the scattering experiments, such as the mass of the supermassive black hole and the sBH migration rate and mass ratio. We find that scattering with detectable gravitational-wave bremsstrahlung is more frequent around lower-mass supermassive black holes (∼105−6 M ⊙). We then conduct a suite of Monte Carlo simulations and estimate the rate for ground-based gravitational-wave detections to be in the range of 0.08–1194 Gpc−3 yr−1, depending on migration forces and detection thresholds, with large uncertainties accounting for variations in possible AGN environments. The expected rate for our Fiducial parameters is 3.2 Gpc−3 yr−1. Finally, we provide first-principle gravitational-wave templates produced by the encounters.

Using gravitational waves to probe the geometry of the ringing remnant black hole formed in a binary black hole coalescence is a well-established way to test Einstein's theory of general relativity. However, doing so requires knowledge of when the predictions of black hole perturbation theory, i.e., quasinormal modes (QNMs), are a valid description of the emitted gravitational wave as well as what the amplitudes of these excitations are. In this work, we develop an algorithm to systematically extract QNMs from the ringdown of black hole merger simulations. Our algorithm improves upon previous ones in three ways: it fits over the two-sphere, enabling a complete model of the strain; it performs a reverse search in time for QNMs using a more robust nonlinear least squares routine called varpro; and it checks the variance of QNM amplitudes, which we refer to as ``stability,'' over an interval matching the natural timescale of each QNM. Using this algorithm, we not only demonstrate the stability of a multitude of QNMs and their overtones across the parameter space of quasicircular, nonprecessing binary black holes, but we also identify new quadratic QNMs that may be detectable in the near future using ground-based interferometers. Furthermore, we provide evidence which suggests that the source of remnant black hole perturbations is roughly independent of the overtone index in a given angular harmonic across binary parameter space, at least for overtones with $n\ensuremath{\lesssim}2$. This finding may hint at the spatiotemporal structure of ringdown perturbations in black hole coalescences, as well as the regime of validity of perturbation theory in the ringdown of these events.

The atmospheric wind field is a key parameter for the middle and upper atmosphere, with significant applications in civil and military domains. Currently, the development of ground-based Doppler asymmetric spatial heterodyne wind interferometers is still in its early stages. Moreover, research on the spatial distribution of horizontal wind speed and direction in real wind fields remains limited. To address this, we present the design and development of a ground-based Doppler asymmetric spatial heterodyne wind interferometer for observing the nocturnal airglow of the oxygen green line at 557.7 nm. The instrument’s performance was comprehensively evaluated through optical modeling, laboratory wind speed simulation experiments, and outdoor observation tests. In addition, a preliminary investigation was conducted into the spatial distribution of horizontal wind speed and direction. Experimental results demonstrate that the instrument achieved a calibration error standard deviation of 2.97 m/s in laboratory tests and less than 5 m/s during outdoor observations. These findings validate the instrument’s observation accuracy and confirm the reliability of the inversion calculation formula, demonstrating its effectiveness in investigating the spatial distribution of horizontal wind speed and direction. Furthermore, the instrument meets the precision requirements for wind field measurements at altitudes of 90 to 110 km, providing reliable technical support for middle-atmosphere wind field studies.

Grand unified theory (GUT) phase transition is generally considered unobservable due to its ultrahigh energy scale, and the monopole problem associated with GUT phase transition is one motivation of inflation. We propose that if a first-order GUT phase transition happens during inflation, the induced gravitational waves (GWs) are redshifted and deformed, and might be observed today in GW observatories. We review the formalism of inflated GWs and derive the general deformation function between inflated and uninflated GW spectra in the instant-source or transitory-source application. It is valid for any e-folding number of instant or transitory source. Applying the formalism to GUT phase transition, we find that the e-folding number at 15 or 25 can shift the GWs to 10 Hz or mHz hands, respectively, which might be tested in the future ground-based or space-based interferometers. We further generalise the discussion to inflated GWs via phase transition below the GUT scale. It is worth mentioning that, due to the deformation of the spectrum, the peak of inflated GWs is not simply a redshift of the peak of uninflated GWs.

We investigate the influence of an early matter-dominated era in cosmic history on the dynamics of cosmic strings and the resulting stochastic gravitational waves. Specifically, we examine the case where this era originates from the dark matter dilution mechanism within the framework of the minimal left-right symmetric model. By numerically solving the Boltzmann equations governing the energy densities of the relevant components, we meticulously analyze the modifications to the cosmological scale factor, the number density of cosmic string loops, and the gravitational wave spectrum. Our results reveal that the early matter-dominated era causes a characteristic suppression in the high-frequency regime of the gravitational wave spectrum, providing distinct and testable signatures for future ground-based interferometer experiments.

We quantify the advantages of a recently proposed data processing technique to search for continuous gravitational wave (GW) signals from isolated rotating asymmetric neutron stars in data measured by ground-based GW interferometers. This technique relies on the symmetry of the motion around the Sun of an Earth-bound gravitational wave interferometer. By multiplying the measured data time series with a half-year time-shifted copy of it, we obtain two advantages: (i) the main Doppler phase modulation of a monochromatic gravitational wave signal is exactly removed, and (ii) the signal in the product data are located at twice the GW signal frequency. The first significantly reduces the size of the signal’s parameter space over which a search is to be performed. The second is advantageous at low frequencies; we find that, with currently available computer processing speeds, this technique is capable of achieving sensitivity that is comparable to or even better than coherent and other possibly non-coherent methods. Further, since our proposed method is implemented over a year-long data segment, it requires processing time comparable to the data acquisition time of currently available computers.

Gravitational waveform (GW) models are a core ingredient for the analysis of compact binary mergers observed by current ground-based interferometers. We focus here on a specific class of such models known as phenomx, which has gained popularity in recent years thanks to its computational efficiency. We introduce a new description of the ``twisting-up'' mapping underpinning the construction of precessing waveforms within this family. The new description is an adaptation to the frequency domain of a technique previously implemented in time-domain models, where the orbit-averaged post-Newtonian spin-precession dynamics is numerically solved on the fly. We also present an improved version of the gravitational wave strain amplitudes approximating the signal in the coprecessing frame. We demonstrate that the new description yields improved matches against numerical relativity simulations, with only a modest computational overhead. We also show that the new model can be reliably employed in parameter estimation follow-ups of GW events, returning equivalent or more stringent measurements of the source properties compared to its predecessor.

Stochastic gravitational-wave background (SGWB) is one of the major targets for contemporary gravitational wave (GW) observations, including pulsar timing array (PTA), ground-based laser interferometer (GbLI), and space-based laser interferometer (SbLI). The data analysis of SGWB involves cross-correlating the outputs of a pair of detectors to find the functional form of the correlations, which is referred to as the overlap reduction function (ORF). While conventional approaches employ detector-specific approximations for ORF calculations, in this paper, we present a universal formula to calculate the precise ORF for isotropic SGWB detection with PTA and laser interferometer detectors. Since no approximations are employed, the exact value of the ORF can be obtained for all three types of detectors.

The detection of gravitational waves with ground-based laser interferometers has opened a new window to test and constrain General Relativity (GR) in the strong, dynamical, and non-linear regime. In this paper, we follow an agnostic approach and we study the quasi-normal modes of gravitational perturbations of Johannsen black holes under the assumptions of the validity of the Einstein Equations and of low values of the black hole spin parameter and deformation parameters. We find that the deformation parameter α13 has a stronger impact on the quasi-normal modes than the other leading order deformation parameters (α22, α52, and ϵ3). We derive a fitting formula for the fundamental modes with l=2 and l=3 for the deformation parameter α13 valid in the slow rotation approximation (a∗<0.4). Finally, we constrain α13 from the event GW170104; within our analysis, we find that the data of GW170104 are consistent with the predictions of GR.

We present a Fisher information matrix study of the parameter estimation precision achievable by a class of future space-based, “mid-band”, gravitational wave interferometers observing monochromatic signals. The mid-band is the frequency region between that accessible by the Laser Interferometer Space Antenna (LISA) and ground-based interferometers. We analyze monochromatic signals observed by the TianQin mission, gLISA (a LISA-like interferometer in a geosynchronous orbit) and a descoped gLISA mission, gLISAd, characterized by an acceleration noise level that is three orders of magnitude worse than that of gLISA. We find that all three missions achieve their best angular source reconstruction precision in the higher part of their accessible frequency band, with an error box better than 10−10 sr in the frequency band [10−1,10] Hz when observing a monochromatic gravitational wave signal of amplitude h0=10−21 that is incoming from a given direction. In terms of their reconstructed frequencies and amplitudes, TianQin achieves its best precision values in both quantities in the frequency band [10−2,4×10−1] Hz, with a frequency precision σfgw=2×10−11 Hz and an amplitude precision σh0=2×10−24. gLISA matches these precisions in a frequency band slightly higher than that of TianQin, [3×10−2,1] Hz, as a consequence of its smaller arm length. gLISAd, on the other hand, matches the performance of gLISA only over the narrower frequency region, [7×10−1,1] Hz, as a consequence of its higher acceleration noise at lower frequencies. The angular, frequency, and amplitude precisions as functions of the source sky location are then derived by assuming an average signal-to-noise ratio of 10 at a selected number of gravitational wave frequencies covering the operational bandwidth of TianQin and gLISA. Similar precision functions are then derived for gLISAd by using the amplitudes resulting in the gLISA average SNR being equal to 10 at the selected frequencies. We find that, for any given source location, all three missions display a marked precision improvement in the three reconstructed parameters at higher gravitational wave frequencies.

The direct detection of gravitational waves from a binary black hole merger has opened a new window in observational astronomy. The first three observing runs of the LIGO/Virgo groundbased interferometers have produced a broad range of scientific results, including the first observationsof a binary neutron star merger and a neutron star-black hole merger. The observations include some exceptional events and other mergers reported in the GWTC-1, GWTC-2, GWTC-2.1, GWTC-3 catalogues, that have allowed tests of general relativity and studies of black hole and neutron star populations. The paper is a concise review of ground-based gravitational wave astronomy and related multi-messenger observations over the electromagnetic spectrum and the neutrino domain. Since the spectrum of gravitational waves extends over a broad frequency range, other techniques for gravitational wave detection outside the sensitivity band of ground-based interferometers will also be discussed.

Ground-based Doppler asymmetric spatial heterodyne interferometry retrieves upper atmospheric winds by calculating the phase shift in the interferogram resulting from the Doppler shift of airglow emission lines. However, in practical applications, interferogram distortion, such as fringe bending and tilting, can adversely affect wind accuracy. This paper presents a distortion correction method based on the resampling matrix that can be obtained from an interferogram of airglow lines or a calibration lamp. The method is straightforward to implement, capable of addressing various types of distortions, and notably reduces wind uncertainty in interferograms with low signal-to-noise ratios. Laboratory tests and field results verify that the interferograms corrected by this method not only yield accurate wind measurements but also reduce the standard deviation of retrieved wind for the average fringes corresponding to different rows of the interferogram.

针对地基多普勒非对称空间外差干涉仪中干涉模块两臂光栅装调偏差引发的条纹倾斜现象，系统分析其对仪器风速测量标定结果的影响。基于倾斜条纹的相位分布特性，开展仪器标定精度分析研究：通过对比空域法相位校正、频域法相位校正及未校正三种处理方法的反演结果，量化分析倾斜条纹对仪器风速测量标定的影响。结果表明，仪器标定误差为2.9 m/s，三种处理方法的误差分别为0.4、0.5、0.4 m/s。所提出的标定方案能够满足仪器的风速测量标定需求，且标定后的仪器展现出高精度测量性能。此外，三种处理方法的测量结果具有高度一致性，倾斜条纹对测量精度无显著影响。