Search

An innovative biepitaxial technique for the fabrication of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ artificial grain-boundary Josephson junctions is proposed. The structure was specifically designed to analyze the effects of anisotropy, both in the order parameter and in the crystallographic structure of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta },$ on the Josephson current crossing the artificial grain boundary. Samples are grown on vicinal (110) oriented ${\mathrm{SrTiO}}_3$ substrates, and a ${\mathrm{CeO}}_2$ film is employed as a seed layer. Crystallography and morphology of the samples are analyzed, thus allowing us to infer the nature of the grain boundary. Our measurements show that the obtained grain boundary, besides possessing a unique and complex structure, exhibits very peculiar Josephson and tunnel-like properties. The intrinsic flexibility of the biepitaxial technique is employed to modify the in-plane angle of the grain-boundary interface, allowing for the realization of symmetrical, asymmetrical, and intermediate configurations on the same substrate. Accordingly, junctions exhibiting different kinds of magnetic field dependence of the Josephson current are obtained on the same chip. Evidence of d-wave-induced effects and of a dielectric character of the barrier is obtained by the transport measurements.

We report results of a wideband search for periodic gravitational waves from isolated neutron stars within the Orion spur towards both the inner and outer regions of our Galaxy. As gravitational waves interact very weakly with matter, the search is unimpeded by dust and concentrations of stars. One search disk (A) is 6.87° in diameter and centered on $20^{\mathrm{h}}10^{\mathrm{m}}54.71^{\mathrm{s}}+33°33^{\prime }25.29^{\prime \prime }$, and the other (B) is 7.45° in diameter and centered on $8^{\mathrm{h}}35^{\mathrm{m}}20.61^{\mathrm{s}}-46°49^{\prime }25.151^{\prime \prime }$. We explored the frequency range of 50–1500 Hz and frequency derivative from 0 to $-5\times {10}^{-9}\mathrm{Hz}/\mathrm{s}$. A multistage, loosely coherent search program allowed probing more deeply than before in these two regions, while increasing coherence length with every stage. Rigorous follow-up parameters have winnowed the initial coincidence set to only 70 candidates, to be examined manually. None of those 70 candidates proved to be consistent with an isolated gravitational-wave emitter, and 95% confidence level upper limits were placed on continuous-wave strain amplitudes. Near 169 Hz we achieve our lowest 95% C.L. upper limit on the worst-case linearly polarized strain amplitude $h_0$ of $6.3\times {10}^{-25}$, while at the high end of our frequency range we achieve a worst-case upper limit of $3.4\times {10}^{-24}$ for all polarizations and sky locations.

Structural and morphological properties of $[{\mathrm{BaCuO}}_{2+x}{]}_2/[{\mathrm{CaCuO}}_2{]}_3$ superlattices with different thicknesses, grown on specially prepared vicinal (001) ${\mathrm{SrTiO}}_3$ substrates, are investigated. Using undulator radiation from a third-generation synchrotron we have performed x-ray-diffraction and diffuse scattering measurements, both in conventional and grazing-incidence geometries. We obtain detailed information about the role of the miscut of the substrate on the growth process of these superlattices. The critical thickness for pseudomorphic growth is found to depend on the miscut angle and, to a lesser extent on the film thickness. Thus the miscut of the substrate surprisingly influences the phase transition from the pseudomorphic, pseudotetragonal state to the orthorhombic state. Our results show that the interface morphology depends on the specific miscut of the substrate. Isotropic ripples, anisotropic ripples, and a fractal structure are formed upon slightly increasing the miscut angle from about 0.15° up to angles less than 1°. The ripples accompany the two-dimensional, layer-by-layer growth mode, which prevails for thin layers of the superlattices on well-oriented surfaces.

We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range $100–450{\mathrm{M}}_{\odot }$ and with the component mass ratios between $1:1$ and $4:1$. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on $88+88{\mathrm{M}}_{\odot }$, for nonspinning sources, the rate density upper limit is 0.13 per ${\mathrm{Mpc}}^3$ per Myr at the 90% confidence level.

The gravitational-wave (GW) sky may include nearby pointlike sources as well as stochastic backgrounds. We perform two directional searches for persistent GWs using data from the LIGO S5 science run: one optimized for pointlike sources and one for arbitrary extended sources. Finding no evidence to support the detection of GWs, we present 90% confidence level (C.L.) upper-limit maps of GW strain power with typical values between $2-20\times {10}^{-50}{\mathrm{strain}}^2{\mathrm{Hz}}^{-1}$ and $5-35\times {10}^{-49}{\mathrm{strain}}^2{\mathrm{Hz}}^{-1}{\mathrm{sr}}^{-1}$ for pointlike and extended sources, respectively. The latter result is the first of its kind. We also set 90% C.L. limits on the narrow-band root-mean-square GW strain from interesting targets including Sco X-1, SN 1987A and the Galactic center as low as $\approx 7\times {10}^{-25}$ in the most sensitive frequency range near 160 Hz.

Compact binary systems with neutron stars or black holes are one of the most promising sources for ground-based gravitational-wave detectors. Gravitational radiation encodes rich information about source physics; thus parameter estimation and model selection are crucial analysis steps for any detection candidate events. Detailed models of the anticipated waveforms enable inference on several parameters, such as component masses, spins, sky location and distance, that are essential for new astrophysical studies of these sources. However, accurate measurements of these parameters and discrimination of models describing the underlying physics are complicated by artifacts in the data, uncertainties in the waveform models and in the calibration of the detectors. Here we report such measurements on a selection of simulated signals added either in hardware or software to the data collected by the two LIGO instruments and the Virgo detector during their most recent joint science run, including a “blind injection” where the signal was not initially revealed to the collaboration. We exemplify the ability to extract information about the source physics on signals that cover the neutron-star and black-hole binary parameter space over the component mass range $1{\mathrm{M}}_{\odot }–25{\mathrm{M}}_{\odot }$ and the full range of spin parameters. The cases reported in this study provide a snapshot of the status of parameter estimation in preparation for the operation of advanced detectors.

Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signal-to-noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO’s first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far.

We perform an unmodeled search for persistent, directional gravitational wave (GW) sources using data from the first and second observing runs of Advanced LIGO. We do not find evidence for any GW signals. We place limits on the broadband GW flux emitted at 25 Hz from point sources with a power law spectrum at $F_{\alpha ,\mathrm{\Theta }}<(0.05–25)\times {10}^{-8}\mathrm{erg}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{Hz}}^{-1}$ and the (normalized) energy density spectrum in GWs at 25 Hz from extended sources at ${\mathrm{\Omega }}_{\alpha }(\mathrm{\Theta })<(0.19–2.89)\times {10}^{-8}{\mathrm{sr}}^{-1}$ where $\alpha$ is the spectral index of the energy density spectrum. These represent improvements of $2.5–3\times$ over previous limits. We also consider point sources emitting GWs at a single frequency, targeting the directions of Sco X-1, SN 1987A, and the Galactic center. The best upper limits on the strain amplitude of a potential source in these three directions range from $h_0<(3.6–4.7)\times {10}^{-25}$, $1.5\times$ better than previous limits set with the same analysis method. We also report on a marginally significant outlier at 36.06 Hz. This outlier is not consistent with a persistent gravitational-wave source as its significance diminishes when combining all of the available data.

We present the results from an all-sky search for short-duration gravitational waves in the data of the first run of the Advanced LIGO detectors between September 2015 and January 2016. The search algorithms use minimal assumptions on the signal morphology, so they are sensitive to a wide range of sources emitting gravitational waves. The analyses target transient signals with duration ranging from milliseconds to seconds over the frequency band of 32 to 4096 Hz. The first observed gravitational-wave event, GW150914, has been detected with high confidence in this search; the other known gravitational-wave event, GW151226, falls below the search’s sensitivity. Besides GW150914, all of the search results are consistent with the expected rate of accidental noise coincidences. Finally, we estimate rate-density limits for a broad range of non-binary-black-hole transient gravitational-wave sources as a function of their gravitational radiation emission energy and their characteristic frequency. These rate-density upper limits are stricter than those previously published by an order of magnitude.

During their first observational run, the two Advanced LIGO detectors attained an unprecedented sensitivity, resulting in the first direct detections of gravitational-wave signals produced by stellar-mass binary black hole systems. This paper reports on an all-sky search for gravitational waves (GWs) from merging intermediate mass black hole binaries (IMBHBs). The combined results from two independent search techniques were used in this study: the first employs a matched-filter algorithm that uses a bank of filters covering the GW signal parameter space, while the second is a generic search for GW transients (bursts). No GWs from IMBHBs were detected; therefore, we constrain the rate of several classes of IMBHB mergers. The most stringent limit is obtained for black holes of individual mass $100M_{\odot }$, with spins aligned with the binary orbital angular momentum. For such systems, the merger rate is constrained to be less than $0.93{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$ in comoving units at the 90% confidence level, an improvement of nearly 2 orders of magnitude over previous upper limits.

We present results from a semicoherent search for continuous gravitational waves from the low-mass x-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the $\mathcal{J}$-statistic, and by analyzing data from Advanced LIGO’s second observing run. In the frequency range searched, from 60 to 650 Hz, we find no evidence of gravitational radiation. At 194.6 Hz, the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95% confidence) of $h_0^{95\%}=3.47\times {10}^{-25}$ when marginalizing over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering.

Isolated spinning neutron stars, asymmetric with respect to their rotation axis, are expected to be sources of continuous gravitational waves. The most sensitive searches for these sources are based on accurate matched filtering techniques that assume the continuous wave to be phase locked with the pulsar beamed emission. While matched filtering maximizes the search sensitivity, a significant signal-to-noise ratio loss will happen in the case of a mismatch between the assumed and the true signal phase evolution. Narrow-band algorithms allow for a small mismatch in the frequency and spin-down values of the pulsar while coherently integrating the entire dataset. In this paper, we describe a narrow-band search using LIGO O2 data for the continuous wave emission of 33 pulsars. No evidence of a continuous wave signal is found, and upper limits on the gravitational wave amplitude over the analyzed frequency and spin-down ranges are computed for each of the targets. In this search, we surpass the spin-down limit, namely, the maximum rotational energy loss due to gravitational waves emission for some of the pulsars already present in the LIGO O1 narrow-band search, such as $\mathrm{J}1400-6325$, $\mathrm{J}1813-1246$, $\mathrm{J}1833-1034$, $\mathrm{J}1952+3252$, and for new targets such as $\mathrm{J}0940-5428$ and $\mathrm{J}1747-2809$. For $\mathrm{J}1400-6325$, $\mathrm{J}1833-1034$, and $\mathrm{J}1747-2809$, this is the first time the spin-down limit is surpassed.

We present results of an all-sky search for continuous gravitational waves (CWs), which can be produced by fast spinning neutron stars with an asymmetry around their rotation axis, using data from the second observing run of the Advanced LIGO detectors. Three different semicoherent methods are used to search in a gravitational-wave frequency band from 20 to 1922 Hz and a first frequency derivative from $-1\times {10}^{-8}$ to $2\times {10}^{-9}\mathrm{Hz}/\mathrm{s}$. None of these searches has found clear evidence for a CW signal, so upper limits on the gravitational-wave strain amplitude are calculated, which for this broad range in parameter space are the most sensitive ever achieved.

We report the observation of gravitational waves from a binary-black-hole coalescence during the first two weeks of LIGO’s and Virgo’s third observing run. The signal was recorded on April 12, 2019 at 05∶30∶44 UTC with a network signal-to-noise ratio of 19. The binary is different from observations during the first two observing runs most notably due to its asymmetric masses: a $\sim 30M_{\odot }$ black hole merged with a $\sim 8M_{\odot }$ black hole companion. The more massive black hole rotated with a dimensionless spin magnitude between 0.22 and 0.60 (90% probability). Asymmetric systems are predicted to emit gravitational waves with stronger contributions from higher multipoles, and indeed we find strong evidence for gravitational radiation beyond the leading quadrupolar order in the observed signal. A suite of tests performed on GW190412 indicates consistency with Einstein’s general theory of relativity. While the mass ratio of this system differs from all previous detections, we show that it is consistent with the population model of stellar binary black holes inferred from the first two observing runs.

We present the results from a search for gravitational-wave transients associated with core-collapse supernovae observed within a source distance of approximately 20 Mpc during the first and second observing runs of Advanced LIGO and Advanced Virgo. No significant gravitational-wave candidate was detected. We report the detection efficiencies as a function of the distance for waveforms derived from multidimensional numerical simulations and phenomenological extreme emission models. The sources with neutrino-driven explosions are detectable at the distances approaching 5 kpc, and for magnetorotationally driven explosions the distances are up to 54 kpc. However, waveforms for extreme emission models are detectable up to 28 Mpc. For the first time, the gravitational-wave data enabled us to exclude part of the parameter spaces of two extreme emission models with confidence up to 83%, limited by coincident data coverage. Besides, using ad hoc harmonic signals windowed with Gaussian envelopes, we constrained the gravitational-wave energy emitted during core collapse at the levels of $4.27\times {10}^{-4}{M}_{\odot }{c}^2$ and $1.28\times {10}^{-1}{M}_{\odot }{c}^2$ for emissions at 235 and 1304 Hz, respectively. These constraints are 2 orders of magnitude more stringent than previously derived in the corresponding analysis using initial LIGO, initial Virgo, and GEO 600 data.

We present results from the search for an isotropic gravitational-wave background using Advanced LIGO and Advanced Virgo data from O1 through O4a, the first part of the fourth observing run. This background is the accumulated signal from unresolved sources throughout cosmic history and encodes information about the merger history of compact binaries throughout the Universe, as well as exotic physics and potentially primordial processes from the early cosmos. Our cross-correlation analysis reveals no statistically significant background signal, enabling us to constrain several theoretical scenarios. For compact binary coalescences which approximately follow a $2/3$ power-law spectrum, we constrain the fractional energy density to ${\mathrm{\Omega }}_{\mathrm{GW}}(25\mathrm{Hz})\le 2.0\times {10}^{-9}$ (95% credibility), a factor of 1.7 improvement over previous results. Scale-invariant backgrounds are constrained to ${\mathrm{\Omega }}_{\mathrm{GW}}(25\mathrm{Hz})\le 2.8\times {10}^{-9}$, representing a $2.1\times$ sensitivity gain. We also place new limits on alternative gravity theories predicting nonstandard polarization modes and confirm that terrestrial magnetic noise sources remain below our detection threshold. Combining these spectral limits with population models for Gravitational-Wave Transient Catalog (GWTC)-4, the latest gravitational-wave event catalog, we find our constraints remain above predicted merger backgrounds but are approaching detectability. The joint analysis combining the background limits shown here with GWTC-4 enables improved inference of the binary black hole merger rate evolution across cosmic time. Furthermore, employing GWTC-4 inference results and standard modeling choices, we estimate that the total background arising from compact binary coalescences is ${\mathrm{\Omega }}_{\mathrm{CBC}}(25\mathrm{Hz})={0.9}_{-0.5}^{+1.1}\times {10}^{-9}$ at 90% confidence, where the largest contribution is due to binary black holes only, ${\mathrm{\Omega }}_{\mathrm{BBH}}(25\mathrm{Hz})={0.8}_{-0.5}^{+1.1}\times {10}^{-9}$.

We present a search of data from the first part of the fourth observing run of LIGO-Virgo-KAGRA for three kinds of dark matter—dilatons (spin-0), dark photons (spin-1), and tensor bosons (spin-2)—using three independent methods, each extended to search for all three candidates. Each dark matter candidate could interact with different standard-model particles in the instruments, causing unique differential strains on the interferometers. While we do not find any evidence for a signal, we place the most stringent upper limits to date on the couplings of each dark matter model to the interferometers. For scalars with masses between $[4\times {10}^{-14},1.5\times {10}^{-13}]\mathrm{eV}$ that couple to photons or electrons, our constraints on the scalar-to-electron or photon coupling improve upon those from the third observing run by 1 order of magnitude, with the tightest limit of $\sim {10}^{-20}{\mathrm{GeV}}^{-1}$ at a mass of $\sim 2\times {10}^{-13}\mathrm{eV}$. For vectors with masses between $[7\times {10}^{-13},8.47\times {10}^{-12}]\mathrm{eV}$ that couple to baryons, our constraints on the dark-photon or baryon coupling supersede those from MICROSCOPE and Eöt-Wash by 1 to 2 orders of magnitude, reaching a minimum of $\sim 5\times {10}^{-24}$ at a mass of $\sim {10}^{-12}\mathrm{eV}$. For tensors with masses of $[4\times {10}^{-14},8.47\times {10}^{-12}]\mathrm{eV}$ (the full mass range analyzed) that couple via a Yukawa interaction, our constraints, which are the first obtained from gravitational-wave interferometers, surpass those from fifth-force experiments by 4 to 5 orders of magnitude, achieving a limit as low as $\sim 8\times {10}^{-9}$ at $\sim 2\times {10}^{-13}\mathrm{eV}$. Our results show that each method has substantially different sensitivity to each dark matter candidate, highlighting the importance of a multimethod approach to search for new physics. Moreover, they demonstrate that gravitational-wave interferometers can simultaneously probe multiple ultralight dark matter models and place unprecedented constraints on tensor fields arising in a broad range of modified-gravity theories.

We present an all-sky search for long-duration gravitational waves (GWs) from the first part of the LIGO-Virgo-KAGRA fourth observing run (O4), called O4a and comprising data taken between May 24, 2023, and January 16, 2024. The GW signals targeted by this search are the so-called “long-duration” ($\gtrsim 1\mathrm{s}$) transients expected from a variety of astrophysical processes, including nonaxisymmetric deformations in magnetars or eccentric binary coalescences. We make minimal assumptions on the emitted GW waveforms in terms of morphologies and durations. Overall, our search targets signals with durations of $\sim 1–1000\mathrm{s}$ and frequency content in the range 16–2048 Hz. In the absence of significant detections, we report the sensitivity limits of our search in terms of root-sum-square signal amplitude ($h_{\mathrm{rss}}$) of reference waveforms. These limits improve upon the results from the third LIGO-Virgo-KAGRA observing run (O3) by about 30% on average. Moreover, this analysis demonstrates substantial progress in our ability to search for long-duration GW signals owing to enhancements in pipeline detection efficiencies. As detector sensitivities continue to advance and observational runs grow longer, unmodeled long-duration searches will increasingly be able to explore a range of compelling astrophysical scenarios involving neutron stars and black holes.