Abstract Gravitational wave signals from asymmetric binary black hole systems have been shown to exhibit additional chirps beyond the primary merger chirp in the post-merger region of the time-frequency domain. These secondary post-merger chirps correlate to the evolving geometry of the common horizon that forms as the binary merges and were previously studied through numerical relativity simulation in a zero-spin regime. In this work, we investigate the post-merger time-frequency structure in systems with both aligned and precessing spin using widely available waveform models. We find that the inclusion of strong aligned spin (ξ = 0.75) induces further post-merger time-frequency peaks. Additionally we show that even a mild precessing spin (χp = 0.25) strongly affects the distribution of post-merger radiative power across the celestial sky of the final black hole. Our results support the theory of a correlation between the post-merger signal and horizon geometry.

Abstract We present a passive (i.e. not requiring feedback) ultraviolet (UV) charge management system for the fused silica test masses (TMs) in ground-based laser interferometric gravitational wave detectors. The system uses photoelectron emission from low work-function gold (Au) coatings illuminated by 275–285 nm UV light to neutralize unwanted electric charge on electrically floating TMs, maintaining them at zero potential relative to surrounding components. Two implementation schemes are described: (1) distributed discharge of the TMTs illuminated by UV LEDs mounted at the eight surrounding earthquake stops, and (2) a conductively linked TMT design enabling centralized discharge on the TM barrel, with potential extension to annular coatings around the high-reflectivity and anti-reflective surfaces. Experimental results show photoelectric currents ≥10 pA for 1.0 mW of incident UV, enabling discharge rates ≥10 V/s for a 1 pF capacitor. With 0.2 mW UV power, charge neutralization of the TM conductive areas to ≤1 pC can be achieved in less than 5 to 75 minutes; where the TM maximal potential and capacitance to ground are calculated values that include a combined safety margin of about one order of magnitude. This technique offers a vacuum-compatible alternative to ion sprayers, significantly reducing operational downtime, though not addressing the discharge of the TM dielectric surfaces. For the conductive-barrel configuration, we also propose a balanced electrostatic actuator using four parallel-plate capacitors for combined control of TM axial displacement, tilt, and azimuth, with reduced drive voltages.

Abstract In addition to the gravitational-wave (GW) tensor modes of general relativity, more general metric theories of gravity allow up to four additional polarization states. Sensitivity curves for these additional GW polarizations are key quantities for assessing how well a detector can constrain such theories. In this work, we derive analytical expressions and high-accuracy approximate formulas for the sensitivity curves for the vector- x , vector- y , breathing, and longitudinal modes of the second-generation time-delay interferometry (TDI). Our analysis covers the TDI Michelson, $$(\alpha ,\beta ,\gamma ),$$ ( α , β , γ ) , Monitor, Beacon, Relay, and Sagnac combinations, together with the orthogonal A , E , T channels constructed from them. The validity of analytical expressions is confirmed by Monte Carlo integration. We find that, in the high-frequency limit, the sensitivity curves for the tensor and breathing modes scale as $$f^{2},$$ f 2 , whereas those for the vector and longitudinal modes approach the explicit asymptotic forms $$\frac{c^{\textrm{op}}f^{2}}{\ln f}$$ c op f 2 ln f and $$\frac{4c^{\textrm{op}}}{\pi ^{2} L^{2}} f,$$ 4 c op π 2 L 2 f , respectively. In the low-frequency limit, for all GW modes, the sensitivity curves of the $$\zeta $$ ζ combination and of the T channel scale as $$f^{-6},$$ f - 6 , whereas those of the other TDI combinations and of the A , E channels scale as $$f^{-4}.$$ f - 4 . In this limit, the sensitivity curves for the tensor and vector modes coincide, and likewise for the breathing and longitudinal modes. For the breathing mode, the sensitivity curves of the $$(\alpha ,\beta ,\gamma )$$ ( α , β , γ ) and $$\zeta $$ ζ combinations and of the T channel exhibit singularities at frequencies $$f = k/L$$ f = k / L and do not exhibit a frequency range with nearly flat sensitivity. LISA and Taiji exhibit better sensitivity for $$f \lesssim 0.01$$ f ≲ 0.01 Hz due to their longer arm lengths, whereas TianQin performs better at $$f \gtrsim 0.1$$ f ≳ 0.1 Hz. We also highlight the advantage of utilizing the uncorrelated A , E , T channels to maximize the signal-to-noise ratio. These analytical formulas are useful for estimating the capability of future space-based GW detectors to constrain additional GW polarizations.

We investigate the formation of primordial black holes (PBHs) induced by a first-order electroweak phase transition in a realistic renormalizable framework, the complex singlet extension of the Standard Model. We perform a quantitative analysis of the PBH abundance and identify parameter regions consistent with current microlensing constraints. Furthermore, we show that the same parameter space predicts observable stochastic gravitational waves within the sensitivities of future space-based detectors, as well as a sizable deviation in the Higgs triple coupling that can be probed at future lepton colliders. Our results highlight a comprehensive multimessenger framework in which PBHs, gravitational waves, and collider observations can jointly test the dynamics of a strongly first-order electroweak phase transition in the early Universe.

Space gravitational wave detection is performed via a laser interferometry system across hundreds of thousands to millions of kilometers for picometer-level displacement measurement, using phasemeters to read gravitational wave-induced displacement changes. A critical yet unresolved challenge is the coupling of Doppler frequency shift—resulting from relative satellite motion—into the phase measurements, as well as its consequent impact. To address this, we analyzed the Doppler effect principle, built a laser interferometry signal model, and obtained signal frequency ranges via orbit simulation. We then conducted time- and frequency-domain analyses of the phasemeter, theoretically deriving steady-state phase errors to clarify how Doppler shift affects phasemeter noise. A hardware system was constructed for verification, showing that phase noise curves rise significantly at a 100 Hz/s Doppler shift rate, and increasing phasemeter bandwidth increases low-frequency phase noise. This study provides a theoretical and experimental basis for phasemeter parameter optimization and ground experiments of phasemeters in space gravitational wave detection.

Gravitational wave interferometers have studied compact object mergers and solidified our understanding of strong gravity. Their increasing precision raises the possibility of detecting new physics, especially in a neutron star binary system that may contain hidden-sector particles. In particular, a new vector force between binary constituents, giving rise to dark electromagnetic phenomena, could measurably alter the inspiral waveforms and thus be constrained by gravitational wave observations. In this work, we critically examine the mechanisms for neutron stars to acquire enough hidden-sector particles with requisite couplings to furnish a detectable signature from dark electromagnetism. In particular, we explore three plausible mechanisms for achieving a sufficient dark mass fraction, and we derive quite general limitations on the amount of charge that can be accumulated by any of these mechanisms. We demonstrate that the repulsive nature of vector forces imposes stringent constraints on any putative particle physics model or astrophysical environment which could give rise to such gravitational signatures. We argue that absent an extreme fine-tuning of parameters, such signatures are well out of reach of any current or near-future gravitational wave observatory.

Gravitational waves from first-order phase transitions assisted by temperature-enhanced scatterings

PT2GWFinder: A Package for Cosmological First-Order Phase Transitions and Gravitational Waves

In order for an inflationary universe to evolve into a hot universe, a process known as reheating is required. However, the precise mechanism of reheating remains unknown. We show that if the reheating is triggered by thermal dissipation effects, distinctive features appear in the spectrum of primordial gravitational waves. This suggests a possible way to observationally probe the physics of reheating.

Towards an anomaly detection pipeline for gravitational waves at the Einstein telescope

Investigating optical and ring-down gravitational wave properties of a rotating black hole in a Dehnen galactic dark matter halo

Observations of Cosmic Microwave Background (CMB) B-mode polarization provide a way to probe primordial gravitational waves and test inflationary predictions. Extragalactic point sources become a major source of contamination after foreground cleaning and can bias estimates of the tensor-to-scalar ratio r at the 10-3 level. We introduce Generalized Point Spread Function Fitting (GPSF), a method for removing point-source contamination in polarization maps. GPSF uses the full pixel-domain covariance, including off-diagonal terms, and models overlapping sources. This allows accurate flux estimation under realistic conditions, particularly for small-aperture telescopes with large beams that are more susceptible to source blending. We test GPSF on simulated sky maps, apply foreground cleaning using the Needlet Internal Linear Combination (NILC) method, and compare its performance with standard masking and inpainting. The results show GPSF reduces point-source contamination without significantly affecting the background signal, as seen in both the maps and their power spectra. For the constraint on r, GPSF reduces the bias from 1.67 × 10-3 to 2.9 × 10-4, with only a 2% increase in standard deviation. Compared to inpainting and masking, GPSF yields lower bias while maintaining comparable variance. This suggests that it may serve as a promising method for future CMB experiments targeting measurements of r ∼ 10-3.

Abstract The Legacy Survey of Space and Time (LSST) is expected to observe up to ∼100 million quasars in the next decade. In this work, we show that it is possible to use such data to measure the characteristic frequency evolution of a “chirp” induced by gravitational waves, which can serve as robust evidence for the presence of a compact supermassive black hole binary. Following the LSST specifications, we generate mock lightcurves consisting of (i) a post-Newtonian chirp produced by orbital motion through, e.g., relativistic Doppler boosting, (ii) a damped random walk representing intrinsic quasar variability, and (iii) Gaussian photometric errors, while assuming nonuniform observations with extended gaps over a period of 10 yr. Through a fully Bayesian analysis, we show that we can simultaneously measure the chirp and noise parameters with little degeneracy between the two. For chirp signals with an amplitude of A = 0.5 mag and a range of times to merger ( t m = 15–10 4 yr), we can typically measure a nonzero amplitude and positive frequency derivative with over 5 σ credibility. For binaries with t m = 50 yr, we achieve 3 σ (5 σ ) confidence that the signal is chirping for A ≳ 0.1 ( A > 0.2). The median runtime of our analysis is 5.6 minutes, with a minimum as low as 35 s, making it scalable to a large number of lightcurves. This implies that LSST could, on its own, establish the presence of a compact supermassive black hole binary, and thus discover gravitational wave sources detectable by LISA and by Pulsar Timing Arrays.

Gravitational wave standard sirens from GWTC-3 combined with DESI DR2 and DESY5: A late-universe probe of the Hubble constant and dark energy

Ultralight dark matter constraints from nano-Hertz gravitational waves

This paper explores whether primordial black hole hydrogen-like atoms (PBH-H protoatoms) could be detectable through their distinctive spectroscopic signatures. Background Building on theoretical work proposing that gravitational binding between primordial black holes and electrons may create exotic quantum systems, we investigate the observational prospects for these hypothetical atomic structures. Methods We develop a comprehensive detection framework combining simulated spectroscopic signatures, sensitivity analyses for current space-based infrared telescopes, and machine-learning classification algorithms to distinguish genuine signals from astrophysical contaminants. Our approach integrates deep spectroscopic surveys targeting dark matter halos, multi-messenger coordination with gravitational wave triggers, and time-domain analysis of spectral evolution. Results Our simulations predict that PBH-H protoatoms would emit characteristic far-infrared transitions spanning one to fifty micrometers, with the dominant n equals two to n equals one line occurring at five point four micrometers, placing it within the detection range of the James Webb Space Telescope Mid-Infrared Instrument. The spectral features exhibit significant broadening from Hawking radiation-induced quantum blur and rapid temporal evolution on timescales of minutes to hours as electrons spiral toward the black hole nuclei. Sensitivity analysis confirms that the James Webb Space Telescope can probe PBH-H densities as low as one thousand per cubic parsec in the Galactic Center, while the Atacama Large Millimeter Array and Very Large Array can access higher-order millimeter and centimeter wavelength transitions. Conclusions Successful detection of PBH-H protoatoms would validate primordial black holes as dark matter constituents and provide unprecedented tests of quantum gravity at atomic scales, representing a transformative advancement in understanding dark matter composition and quantum gravitational phenomena.

Insights into the properties of dense, neutron-rich matter emerge from the interplay between nuclear experiments and astrophysical observations. Measurements of parity-violating electron scattering on 48Ca (CREX) and 208Pb (PREX-2), together with electric dipole polarizability data, offer stringent probes of isovector dynamics in nuclei. In this study, a set of relativistic energy density functionals is employed to investigate how these nuclear signatures correlate with neutron star observables, such as stellar radii and tidal deformabilities. By confronting the theoretical predictions with data from both terrestrial experiments and multimessenger observations—including the gravitational wave event GW170817—constraints are derived on the symmetry energy and the high-density behavior of the equation of state. The analysis highlights the influence of including the fourth-order term in the isospin-asymmetry expansion of the energy density on neutron star radius and tidal deformability predictions. At the same time, discrepancies between constraints from CREX and PREX-2 underscore the need for improved experimental precision and additional astrophysical input to refine our understanding of dense matter.

The symmetry energy is a key quantity for the structure of finite nuclei and the bulk properties of neutron stars. Therefore, its investigation has special significance in nuclear astrophysics, especially given the uncertainty that presents in the high density region and the large error in data from corresponding experiments. A way to get an indication about the behavior of symmetry energy in high densities is to examine it in the context of neutron stars. The recent observations of gravitational waves emitted from binary neutron star mergers provide useful information on characteristics such as the radius and the tidal deformability, i.e. two quantities that are in direct relation to the symmetry energy. Our work aims to examine the symmetry energy under this point of view and specifically obtain constraints on the structure of finite nuclei. In this effort, we deploy a methodology that is based on parameterization of the equation of state of asymmetric and symmetric nuclear matter through the introduction of a parameter called η=(K0L2)1/3, which combines the incompressibility K0 and the slope parameter L. In fact, the parameter η serves as a regulator of the stiffness of the equation of state. This quantity affects both the properties of finite nuclei and the properties of neutron stars, where the isovector interaction plays a significant role. Hence, we expect that the obtained constraints, through the values of η, will provide insights on the properties of neutron stars and finite nuclei vice versa. Our investigation proposes a simple and self-consistent method to examine the effects of η on both kind of properties, which led us to derive constraints on the latter systems by using recent experiments (PREX-2) and astrophysical observables (observations from LIGO/VIRGO collaboration).

Abstract Physics-Informed Neural Networks (PINNs) embed the partial differential equations (PDEs) governing the system under study directly into the training of Neural Networks, ensuring solutions that respect physical laws. While effective for single-system problems, standard PINNs scale poorly to datasets containing many realizations of the same underlying physics with varying parameters. To address this limitation, we present a complementary approach by including auxiliary physically-redundant information in loss (APRIL), i.e. augment the standard supervised output-target loss with auxiliary terms which exploit exact physical redundancy relations among outputs. We mathematically demonstrate that these terms preserve the true physical minimum while reshaping the loss landscape, improving convergence toward physically consistent solutions. As a proof-of-concept, we benchmark APRIL on a fully-connected neural network for gravitational wave (GW) parameter estimation (PE). We use simulated, noise-free compact binary coalescence (CBC) signals, focusing on inspiral-frequency waveforms to recover the chirp mass $\mathcal{M}$, the total mass $M_\mathrm{tot}$, and symmetric mass ratio $\eta$ of the binary. In this controlled setting, we show that APRIL achieves up to an order-of-magnitude improvement in test accuracy, especially for parameters that are otherwise difficult to learn. This method provides a physically consistent training approach for more realistic GW analysis applications.

Upper Limits on Microhertz Gravitational Waves from Supermassive Black Hole Binaries Using PSR J1909–3744 Data from the Second IPTA Data Release