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DOE OSTI2022

Quantifying modeling uncertainties when combining multiple gravitational-wave detections from binary neutron star sources

Here, with the increasing sensitivity of gravitational-wave detectors, we expect to observe multiple binary neutron-star systems through gravitational waves in the near future. The combined analysis of these gravitational-wave signals offers the possibility to constrain the neutron-star radius and the equation of state of dense nuclear matter with unprecedented accuracy. However, it is crucial to ensure that uncertainties inherent in the gravitational-wave models will not lead to systematic biases when information from multiple detections is combined. To quantify waveform systematics, we perform an extensive simulation campaign of binary neutron-star sources and analyze them with a set of four different waveform models. For our analysis with 38 simulations, we find that statistical uncertainties in the neutron-star radius decrease to ± 250 m (2% at 90% credible interval) but that systematic differences between currently employed waveform models can be twice as large. Hence, it will be essential to ensure that systematic biases will not become dominant in inferences of the neutron-star equation of state when capitalizing on future developments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Magnets are Weber Bar Gravitational Wave Detectors

When a gravitational wave (GW) passes through a dc magnetic field, it couples to the conducting wires carrying the currents which generate the magnetic field, causing them to oscillate at the GW frequency. The oscillating currents then generate an ac component through which the GW can be detected-thus forming a resonant mass detector or a nagnetic Weber bar. We quantify this claim and demonstrate that magnets can have exceptional sensitivity to GWs over a frequency range demarcated by the mechanical and electromagnetic resonant frequencies of the system; indeed, we outline why a magnetic readout strategy can be considered an optimal Weber bar design. The concept is applicable to a broad class of magnets, but can be particularly well exploited by the powerful magnets being deployed in search of axion dark matter, for example, by DMRadio and ADMX-EFR. Explicitly, we demonstrate that the MRI magnet that is being deployed for ADMX-EFR can achieve a broadband GW strain sensitivity of ∼10^{-20}/sqrt[Hz] from a few kHz to about 10 MHz, with a peak sensitivity down to ∼10^{-22}/sqrt[Hz] at a kHz exploiting a mechanical resonance.

Domcke, Valerie↗
DOE OSTI2022

Asteroids for μ Hz gravitational-wave detection

A major challenge for gravitational-wave (GW) detection in the μHz band is engineering a test mass (TM) with sufficiently low acceleration noise. We propose a GW detection concept using asteroids located in the inner Solar System as TMs. Our main purpose is to evaluate the acceleration noise of asteroids in the μHz band. We show that a wide variety of environmental perturbations are small enough to enable an appropriate class of ~10 km-diameter asteroids to be employed as TMs. This would allow a sensitive GW detector in the band (few) × 10 -7 Hz ≲ fGW ≲ (few) × 10 -5 Hz, reaching strain hc ~ 10 -19 around f GW ~10 μHz, sufficient to detect a wide variety of sources. To exploit these asteroid TMs, human-engineered base stations could be deployed on multiple asteroids, each equipped with an electromagnetic transmitter/receiver to permit measurement of variations in the distance between them. We discuss a potential conceptual design with two base stations, each with a space-qualified optical atomic clock measuring the round-trip electromagnetic pulse travel time via laser ranging. Trade space exists to optimize multiple aspects of this mission: for example, using a radio-ranging or interferometric link system instead of laser ranging. This motivates future dedicated technical design study. This mission concept holds exceptional promise for accessing this GW frequency band.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

The Binary–Host Connection: Astrophysics of Gravitational-Wave Binaries from Host Galaxy Properties

Gravitational waves from the merger of binary neutron stars (BNSs) are accompanied by electromagnetic counterparts, making it possible to identify the associated host galaxy. In this work, we explore how properties of the hosts relate to the astrophysical processes leading to the mergers. It is thought that the BNS merger rate within a galaxy at a given epoch depends primarily on the galaxy's star formation history, as well as the underlying merger time-delay distribution of the binary systems. The stellar history of a galaxy, meanwhile, depends on the cosmological evolution of the galaxy through time, and is tied to the growth of structure in the universe. We study the hosts of BNS mergers in the context of structure formation by populating the UniverseMachine simulations with gravitational wave (GW) events, based on a simple time-delay model. We find that different time-delay distributions predict different properties of the associated host galaxies, including the distributions of stellar mass, star formation rate, halo mass, and local and large-scale clustering of hosts. Moreover, BNSs merging today with short delay times occur preferentially in hosts with high star formation rates, while those with long delay times live in dense regions within massive halos that have low star formation. Here, we show that with ${ \mathcal O }(10)$ events from current GW detector networks, it is possible to make preliminary distinctions between formation channels which trace stellar mass, halo mass, or star formation rate. We also find that strategies to follow-up GW events with electromagnetic telescopes can be significantly optimized using the clustering properties of their hosts.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Gravitational waves from fully general relativistic oscillon preheating

As long-lived quasisolitons from the fragmentation of a scalar condensate, oscillons may dominate the preheating era after inflation. During this period, stochastic gravitational waves can also be generated. Here we quantify the gravitational-wave production in this period with simulations accounting for full general relativity to capture all possible nonperturbative effects. We compute the gravitational-wave spectra across a range of choices of the oscillon preheating models and compare our results to a conventional perturbative approach on a Friedmann-Lemaître-Robertson-Walker (FLRW) background. We clarify the gauge ambiguities in computing induced gravitational waves from scenarios where dense nonperturbative objects such as oscillons are being formed. In particular, we find that the synchronous gauge tends to contain large artificial enhancements in the gravitational-wave spectrum due to gauge modes if gravity plays an important role in the formation of the oscillons, while other gauge choices, such as the radiation gauge or a suitably chosen “1+log” gauge, can efficiently reduce the contributions of gauge modes. The full general-relativistic simulations indicate that gravitational-wave spectra obtained from the perturbative approach on the FLRW background are fairly accurate, except when oscillon formation induces strong gravitational effects, for which case there can be an order unity enhancement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Dark matter clumps as sources of gravitational-wave glitches in LIGO-Virgo-KAGRA data

We consider the hypothetical possibility that nonstationary glitch features in the noise of ground-based gravitational-wave detectors could be produced by small dark matter clumps that pass through the earth in the vicinity of gravitational-wave detectors. Here, we first derive the gravitational-wave strain that would be generated by the passage of such a dark matter clump. We find that the strain is primarily sourced by the Newtonian gravitational acceleration of the mirrors toward the clump and by the Shapiro time delay of the photons in the laser beams as they pass through the gravitational potential created by the dark matter clump. We also find that the Newtonian acceleration effect dominates the gravitational-wave strain for both ground and space-based interferometers. We then compare our dark matter clump, gravitational-wave strain model to 84 Koi-Fish glitches detected during the second observing run of the LIGO/Virgo/KAGRA Collaboration through a Markov chain Monte Carlo Bayesian analysis. We find that all glitches but nine can be confidently rejected as having originated from dark matter clumps. For the remaining glitches, the dark matter hypothesis cannot be excluded, and the maximum a posteriori parameters yield minimum densities of about 10 −7 g⁡/cm 3 , within the model. These results allow us to place the first direct upper limits with gravitational-wave detectors on the local over-density of dark matter in the form of clumps in the local neighborhood of Earth, namely 𝜌 DM ⁢clumps ≲ 10 −15 g⁡/cm −3 .

Astronomy and AstroPhysics↗
DOE OSTI2021

Multimessenger cosmology: Correlating cosmic microwave background and stochastic gravitational wave background measurements

Characterizing the physical properties of the stochastic gravitational wave background (SGWB) is a key step towards identifying the nature of its possible origin. We focus our analysis on SGWB anisotropies. The existence of a nontrivial primordial scalar-tensor-tensor (STT) correlation in the squeezed configuration may be inferred from the effect that a long wavelength scalar mode has on the gravitational wave power spectrum: an anisotropic contribution. Crucially, such a contribution is correlated with temperature anisotropies in the cosmic microwave background (CMB). This paper shows that, for inflationary models that generate suitably large STT non-Gaussianities, cross correlating the CMB with the stochastic background of gravitational waves is a very effective probe of early universe physics. The resulting signal can be a smoking gun for primordial SGWB anisotropies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Chimera D-Series Gravitational Wave Emission Sourced from Matter

Gravitational wave data sourced from the the time-dependent fluid quadrupole motion, in the Chimera D-Series three-dimensional core collapse supernova simulations. Data from three models initiated from three different progenitors are presented: D9.6-3D, D15-3D, and D25-3D. Please see the README for more information about the data structure and progenitors.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Modeling the Galactic Neutron Star Population for Use in Continuous Gravitational-wave Searches

Searches for continuous gravitational waves (GW) from unknown Galactic neutron stars provide limits on the shapes of neutron stars. A rotating neutron star will produce GW if asymmetric deformations exist in its structure that are characterized by the star's ellipticity. Here, in this study, we use a simple model of the spatial and spin distribution of Galactic neutron stars to estimate the total number of neutron stars probed, using GW, to a given upper limit on the ellipticity. This may help optimize future searches with improved sensitivity. The improved sensitivity of third-generation GW detectors may increase the number of neutron stars probed, to a given ellipticity, by factors of 100 to 1000.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Constraining Axion Inflation with Gravitational Waves across 29 Decades in Frequency

We demonstrate that gravitational waves generated by efficient gauge preheating after axion inflation generically contribute significantly to the effective number of relativistic degrees of freedom $N_{\text{eff}}$. In this work we show that, with existing Planck limits, gravitational waves from preheating already place the strongest constraints on the inflaton’s possible axial coupling to Abelian gauge fields. We demonstrate that gauge preheating can completely reheat the Universe regardless of the inflationary potential. Further, we quantify the variation of the efficiency of gravitational wave production from model to model and show that it is correlated with the tensor-to-scalar ratio. In particular, when combined with constraints on models whose tensor-to-scalar ratios would be detected by next-generation cosmic microwave background experiments, $\textit{r}$ ≳ 10 –3 , constraints from $N_{\text{eff}}$ will probe or rule out the entire coupling regime for which gauge preheating is efficient.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO and Advanced Virgo O3 data

We present results of an all-sky search for continuous gravitational waves which can be produced by spinning neutron stars with an asymmetry around their rotation axis, using data from the third observing run of the Advanced LIGO and Advanced Virgo detectors. Four different analysis methods are used to search in a gravitational-wave frequency band from 10 to 2048 Hz and a first frequency derivative from -10 -8 to 10 -9 Hz/s. No statistically significant periodic gravitational-wave signal is observed by any of the four searches. As a result, upper limits on the gravitational-wave strain amplitude ℎ 0 are calculated. The best upper limits are obtained in the frequency range of 100 to 200 Hz and they are ~1.1 ×10 -25 at 95% confidence level. The minimum upper limit of 1.10 ×10 -25 is achieved at a frequency 111.5 Hz. In conclusion, we also place constraints on the rates and abundances of nearby planetary- and asteroid-mass primordial black holes that could give rise to continuous gravitational-wave signals.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Search for continuous gravitational wave signals from luminous dark photon superradiance clouds with LVK O3 observations

Superradiance clouds of kinetically mixed dark photons around spinning black holes can produce observable multimessenger electromagnetic and gravitational wave signals. The cloud generates electric fields of up to a teravolt-per-meter, which leads to a cascade production of charged particles, yielding a turbulent quasiequilibrium plasma around the black hole, and resulting in electromagnetic fluxes ranging from supernova to pulsar-like luminosities. For stellar mass black holes, such systems resemble millisecond pulsars and are expected to emit pulsating radio waves and continuous gravitational waves (CWs) within the LIGO-Virgo-KAGRA (LVK) sensitivity band. We select 44 sources with approximately coincident frequencies or positive frequency drifts from existing pulsar catalogs as potential candidates of long-lasting superradiance clouds around old Galactic black holes. For a subset of 34 sources that are well measured and have not been previously targeted, we perform the first search for CW emission in LVK data from the third observing run. We find no evidence of a CW signal and place 95% confidence level upper limits on the emitted strain amplitude. We interpret these results, together with limits from previous searches, in terms of the underlying dark photon theory by performing an analysis of the expected signals from superradiance clouds from Galactic black holes. Finally, we find that, even for moderately spinning black holes, the absence of an observed CW signal disfavors a discrete set of dark photon masses between about 10 −13 and 10 −12 eV/c 2 and kinetic mixing couplings in the range of 10 −9 –10 −7 , subject to assumptions about the properties of the black hole population and the cloud’s electromagnetic emission.

astronomical black holes↗
DOE OSTI2025

$\mathrm{SageNet}$: Fast Neural Network Emulation of the Stiff-amplified Gravitational Waves from Inflation

Accurate modeling of the inflationary gravitational waves (GWs) requires time-consuming, iterative numerical integrations of differential equations to take into account their backreaction on the expansion history. To improve computational efficiency while preserving accuracy, we present the Stiff-amplified Gravitational-wave Emulator Network (SageNet), a deep learning framework designed to replace conventional numerical solvers (code available at https://github.com/YifangLuo/SageNet). SageNet employs a long short-term memory architecture to emulate the present-day energy density spectrum of the inflationary GWs with possible stiff amplification, Ω GW (f). Trained on a data set of 25,689 numerically generated solutions, SageNet allows accurate reconstructions of Ω GW (f) and generalizes well to a wide range of cosmological parameters; 90.9% of the test emulations with randomly distributed parameters exhibit errors of under 4%. In addition, SageNet demonstrates its ability to learn and reproduce the artificial, adaptive sampling patterns in numerical calculations, which implement denser sampling of frequencies around changes in spectral indices in Ω GW (f). The dual capability of learning both physical and artificial features of the numerical GW spectra establishes SageNet as a robust alternative to exact numerical methods. Finally, our benchmark tests show that SageNet reduces the computation time from tens of seconds to milliseconds, achieving a speedup of ∼10 4 times over standard CPU-based numerical solvers with the potential for further acceleration on GPU hardware. These capabilities make SageNet a powerful tool for accelerating Bayesian inference procedures for extended cosmological models. In a broad sense, the SageNet framework offers a fast, accurate, and generalizable solution to modeling cosmological observables whose theoretical predictions demand costly differential equation solvers.

Astronomy data modeling↗
DOE OSTI2025

Binary systems as gravitational wave detectors

``Adding colour'' to the gravitational-wave sky by probing unexplored frequency bands has the potential to unveil new and unexpected phenomena in the Universe. In these proceedings, we summarise current efforts to probe gravitational waves with $μ$Hz frequencies through their resonant impact on binary systems. We also discuss how these binaries can explore uncharted regions of parameter space in the hunt for dark matter.

Blas, Diego [Barcelona, IFAE]↗
DOE OSTI2024

Gravitational waves from primordial black hole evaporation with large extra dimensions

Abstract The spectra of gravitational waves from black hole evaporation generically peak at frequencies of order the Hawking temperature, making this signal ultra-high frequency for primordial black holes evaporating in the early universe. This motivates us to consider small black holes in theories with large extra dimensions, for which the peak frequency can be lowered substantially, since the true bulk Planck scaleM * can be much smaller than the effectiveM Pl . We study the emission of brane-localized gravitons during the Hawking evaporation of ultra-light primordial black holes in the context of theories with large extra dimensions, with the ultimate goal of computing the contribution to the stochastic gravitational wave background. To accurately model black hole evolution, we compute greybody factors for particles of spin-0, 1/2, 1, and 2 emitted on the brane and in the bulk, presuming the majority of emission proceeds during the Schwarzschild phase. We then compute the power spectrum and present day spectral density parameter for brane-localized gravitons contributing to a gravitational wave signal. We find that for an optimal choice of parameters, the peak frequency plateaus in the sub-MHz regime, within range of planned high-frequency gravitational wave detectors, making this scenario a target for detection once their sensitivity exceeds ΔN eff bounds.

Astronomy & Astrophysics↗
DOE OSTI2026

AT2025ulz and S250818k: Leveraging DESI Spectroscopy in the Hunt for a Kilonova Associated with a Subsolar-mass Gravitational-wave Candidate

On 2025 August 18, the LIGO–Virgo–KAGRA collaboration reported a subthreshold gravitational-wave candidate detection consistent with a subsolar-mass neutron star merger, denoted S250818k. An optical transient, AT2025ulz, was discovered within the localization region. AT2025ulz initially appeared to meet the expected behavior of kilonova emission, the telltale signature of a binary neutron star merger. The transient subsequently rebrightened after ∼5 days and was classified as a Type IIb supernova. In this work, we analyze the observations of its host galaxy obtained by the Dark Energy Spectroscopic Instrument (DESI). From the DESI spectrum, we obtain a secure redshift of z = 0.084840 ± 0.000006. If S250818k has an astrophysical origin, this places the transient within 2σ of the gravitational-wave distance and results in an integral overlap between the gravitational-wave alert and the transient location of log 10 $\mathcal{I} ≈ 3.9 - 4.2$. Our analysis of the host galaxy’s spectral energy distribution reveals a star-forming, dusty galaxy with stellar mass ∼10 10 M ⊙ , broadly consistent with the population of both short gamma-ray bursts and core-collapse supernova host galaxies. We also present our follow-up of DESI-selected candidate host galaxies using the Fraunhofer Telescope at the Wendelstein Observatory, and show the promise of DESI for associating or rejecting candidate electromagnetic counterparts to gravitational-wave alerts. These results emphasize the value of DESI’s extensive spectroscopic dataset in rapidly characterizing host galaxies, enabling spectroscopic host subtraction, and guiding targeted follow-up.

Hall, Xander J. [Carnegie Mellon University, Pitts↗
DOE OSTI2022

GUTs, hybrid topological defects, and gravitational waves

The symmetry breaking of grand unified gauge groups in the early Universe often leaves behind relic topological defects such as cosmic strings, domain walls, or monopoles. For some symmetry breaking chains, hybrid defects can form where cosmic strings attach to domain walls or monopoles attach to strings. In general, such hybrid defects are unstable, with one defect "eating" the other via the conversion of its rest mass into the other's kinetic energy and, subsequently, decaying via gravitational waves. In this work, we determine the gravitational wave spectrum from 1) the destruction of a cosmic string network by the nucleation of monopoles which cut up and "eat" the strings, 2) the collapse and decay of a monopole-string network by strings that eat the monopoles, 3) the destruction of a domain wall network by the nucleation of string-bounded holes on the wall that expand and eat the wall, and 4) the collapse and decay of a string-bounded wall network by walls that eat the strings. We call the gravitational wave signals produced from the eating of one topological defect by another "gravitational wave gastronomy." We find that the four gravitational wave gastronomy signals considered yield unique spectra that can be used to narrow down the SO (10) symmetry breaking chain to the Standard Model and the scales of symmetry breaking associated with the consumed topological defects. Moreover, the systems we consider are unlikely to have a residual monopole or domain wall problem.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Resonant interaction between dispersive gravitational waves and scalar massive particles

The Klein-Gordon equation is solved in the curved background spacetime created by a dispersive gravitational wave. Unlike solutions of perturbed Einstein equations in vacuum, dispersive gravitational waves do not travel exactly at the speed of light. Consequently, the gravitational wave can resonantly exchange energy with scalar massive particles. Some details of the resonant interaction are displayed in a calculation demonstrating how relativistic particles (modeled by the Klein-Gordon equation), feeding on such gravitational waves, may be driven to extreme energies.

79 ASTRONOMY AND ASTROPHYSICS↗