Search

We present the first directed searches for long-transient and continuous gravitational waves from ultralight vector boson clouds around known black holes (BHs). We use LIGO data from the first part of the fourth LIGO-Virgo-KAGRA observing run. The searches target two distinct types of BHs and use two new semicoherent methods: hidden Markov model (HMM) tracking for the remnant BHs of the mergers GW230814_230901 and GW231123_135430 (referred to as GW230814 and GW231123 in this study) and a dedicated method using the Band Sampled Data (BSD) framework for the galactic BH in the Cygnus X-1 binary system. Without finding evidence of a signal from vector bosons in the data, we estimate the mass range that can be constrained. For the HMM searches targeting the remnants from GW231123 and GW230814, we disfavor vector boson masses in the ranges [0.94, 1.08] and $[2.75,3.28]\times {10}^{-13}\mathrm{eV}$, respectively, at 30% confidence, assuming a 1% false alarm probability. Although these searches are only marginally sensitive to signals from merger remnants at relatively large distances, future observations are expected to yield more stringent constraints with high confidence. For the BSD search targeting the BH in Cygnus X-1, we exclude vector boson masses in the range $[0.85,1.59]\times {10}^{-13}\mathrm{eV}$ at 95% confidence, assuming an initial BH spin larger than 0.5.

The study of electric quadrupole transitions from the ground state into symmetric states and into states of mixed symmetry in the deformed nucleus ${}_{}{}^{156}{}_{}{}^{}\mathrm{Gd}$ by inelastic electron scattering has been used to derive effective neutron and proton boson charges for the $E2\mathrm{}$ operator in the framework of the interacting-boson model. The values for $e_{\pi }$ and $e_{\nu }$ differ at most by 30% in the rotational limit.

The gravitational-wave signal GW250114 was observed by the two LIGO detectors with a network matched-filter signal-to-noise ratio of 80. The signal was emitted by the coalescence of two black holes with near-equal masses $m_1={33.6}_{-0.8}^{+1.2}{M}_{\odot }$ and $m_2={32.2}_{-1.3}^{+0.8}{M}_{\odot }$, and small spins ${\chi }_{1,2}\le 0.26$ (90% credibility) and negligible eccentricity $e\le 0.03$. Postmerger data excluding the peak region are consistent with the dominant quadrupolar $(\ell =|m|=2)$ mode of a Kerr black hole and its first overtone. We constrain the modes’ frequencies to $\pm 30\%$ of the Kerr spectrum, providing a test of the remnant’s Kerr nature. We also examine Hawking’s area law, also known as the second law of black hole mechanics, which states that the total area of the black hole event horizons cannot decrease with time. A range of analyses that exclude up to five of the strongest merger cycles confirm that the remnant area is larger than the sum of the initial areas to high credibility.

We present a search for short-duration gravitational-wave transients in data from the first eight months of Advanced LIGO-Virgo-KAGRA’s fourth observing run, denoted O4a. We use four analyses which are sensitive to a wide range of potential signals lasting up to a few seconds in the 16–4096 Hz band. Excluding binary black hole merger candidates that were already identified by low-latency analyses, we find no statistically significant evidence for other gravitational-wave transients. We measure the sensitivity of the search for representative signals, including sine-Gaussians, Gaussian pulses, and white-noise bursts with different frequencies and durations, adopting a false alarm rate of 1 per 100 years as detection threshold. Depending on signal type, we find improvements over previous searches by factors of 2 to 10 in terms of sensitivity to strain amplitude and of 90% confidence upper limit on the rate density of sources. We also evaluate a variety of core-collapse supernova models and find that, for some models, the search could have detected gravitational waves from stellar core-collapse throughout the Milky Way. Finally, we consider neutron star $f$-modes associated with pulsar glitches and find that, assuming a source similar to the Vela Pulsar, the search could have detected a gravitational-wave signal from a glitch with fractional frequency change as small as $\sim 2$ to $6\times {10}^{-5}$ depending on the neutron star mass.

The binary black hole signal GW250114, the loudest gravitational wave detected to date, offers a unique opportunity to test Einstein’s general relativity (GR) in the high-velocity, strong-gravity regime and probe whether the remnant conforms to the Kerr metric. Upon perturbation, black holes emit a spectrum of damped sinusoids with specific, complex frequencies. Our analysis of the postmerger signal shows that at least two quasinormal modes are required to explain the data, with the most damped remaining statistically significant for about one cycle. We probe the remnant’s Kerr nature by constraining the spectroscopic pattern of the dominant quadrupolar ($\ell =m=2$) mode and its first overtone to match the Kerr prediction to tens of percent at multiple postpeak times. The measured mode amplitudes and phases agree with a numerical-relativity simulation having parameters close to GW250114. By fitting a parametrized waveform that incorporates the full inspiral-merger-ringdown sequence, we constrain the fundamental $(\ell =m=4)$ mode to tens of percent and bound the quadrupolar frequency to within a few percent of the GR prediction. We perform a suite of tests—spanning inspiral, merger, and ringdown—finding constraints that are comparable to, and in some cases 2–3 times more stringent than those obtained by combining dozens of events in the fourth Gravitational-Wave Transient Catalog. These results constitute the most stringent single-event verification of GR and the Kerr nature of black holes to date, and outline the power of black-hole spectroscopy for future gravitational-wave observations.

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.

A Landau theory for wetting in systems with an internal defect plane is proposed and solved exactly. The systems can undergo a phase transition in which an interface depins from the defect plane (or a phase transition from partial to complete wetting of the defect plane), when the bulk critical point $T_c$ is approached. This phenomenon of critical-point wetting occurs if the defect plane remains ordered at $T_c$ (extraordinary transition) but is absent if the defect plane disorders at $T_c$ (ordinary and special transitions). This latter possibility has previously been found in Ising models with defect bonds and in lattice-gas models with a grain boundary between binary-alloy crystals.

In the present article, we study systematically the influence of different types of perturbations on the ${\mathrm{SU}}^{\mathrm{*}}$(3) dynamical symmetry. Both a Majorana perturbation, a d-boson energy perturbation, and the ${\mathrm{SU}}^{\mathrm{*}}$(3)→O(6) and ${\mathrm{SU}}^{\mathrm{*}}$(3)→SU(3) transitions are considered. In all cases, we study the variation of the ground and gamma bands as well as some important electromagnetic transitions, in particular the B(M${1;1}_1^{+}$→$0_1^{+}$) value. Even if the present calculations start from a simple Hamiltonian (a consistent Q Hamiltonian), the results can be of interest for the study of the Xe, Ba A≃130 mass region, the Ru, Pd A≃100 mass region, and the Pt, Os A≃190 mass region.

The angular distribution of gravitational-wave power from persistent sources may exhibit anisotropies arising from the large-scale structure of the Universe. This motivates directional searches for astrophysical and cosmological gravitational-wave backgrounds, as well as continuous-wave emitters. We present results of such a search using data from the first observing run through the first portion of the fourth observing run of the LIGO-Virgo-KAGRA Collaborations. We apply gravitational-wave radiometer techniques to generate skymaps and search for both narrowband and broadband persistent gravitational-wave sources. Additionally, we use spherical harmonic decomposition to probe spatially extended sources. No evidence of persistent gravitational-wave signals is found, and we set the most stringent constraints to date on such emissions. For narrowband point sources, our sensitivity estimate to effective strain amplitude lies in the range $(0.03–8.4)\times {10}^{-24}$ across all-sky and frequency range ($20-160$) Hz. For targeted sources—Scorpius X-1, SN 1987A, the Galactic Center, Terzan 5, and NGC 6397—we constrain the strain amplitude with best limits ranging from $\sim 1.1\times {10}^{-25}$ to $6.5\times {10}^{-24}$. For persistent broadband sources, we constrain the gravitational-wave flux $F_{\alpha ,\widehat{n}}^{95\%,\mathrm{UL}}(25\mathrm{Hz})<(0.008–5.5)\times {10}^{-8}\mathrm{erg}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{Hz}}^{-1}$, depending on the sky direction $\widehat{n}$ and spectral index $\alpha =0,2/3$, 3. Finally, for extended sources, we place upper limits on the angular power spectrum $C_{\ell }^{1/2}<(0.63–17)\times {10}^{-10}{\mathrm{sr}}^{-1}$.

We present a search for gravitational waves from inspiraling, planetary-mass ultracompact binaries using data from the first part of the fourth observing run of LIGO, Virgo, and KAGRA. Finding no evidence of such systems, we determine the maximum distance reach for such objects and their merger rate densities. Then, we identify classes of primordial black hole mass distributions for which these rate limits can be translated into relevant constraints on the mass distribution of primordial black holes, assuming that they are all composed of dark matter, in the mass range $[{10}^{-6},{10}^{-3}]M_{\odot }$. Our constraints for the class of primordial black hole mass distribution functions $f(m)$ we consider reach down to $f(m)\sim 0.1$. They are consistent with existing microlensing results in the planetary-mass range, provide a complementary probe to subsolar mass objects, and are publicly available [1].

We extend our previous theory of the gauging of classical quadratically nonlinear algebras without a central charge but with a coset structure to the quantum level. Inserting the minimal anomalies into the classical transformation rules of the currents introduces further quantum corrections to the classical transformation rules of the gauge fields and currents which additively renormalize the structure constants. The corresponding Ward identities are the $c\to \infty$ limit of the full quantum Ward identities, and reveal that the $c\to \infty$ limit of the quantum gauge algebra closes on fields and currents. Two examples are given.

In the present article, we discuss the Xe and Ba nuclei in the A≃130 mass region. This mass region has been shown to constitute a new region of O(6)-like nuclei. A number of deviations, however, from a pure O(6) dynamical symmetry are experimentally observed, in particular the energy staggering in the gamma band. Here, we study the influence of triaxial perturbations, i.e., introducing terms in the Hamiltonian that are of ${\mathrm{SU}}^{\mathrm{*}}$(3) type, on the energy spectra of the ${}_{}{}^{124\mathrm{-}130}{}_{}{}^{}\mathrm{Xe}$ and of the ${}_{}{}^{128\mathrm{-}134}{}_{}{}^{}\mathrm{Ba}$ nuclei. We also address the problem of B(E2) transitions, connecting the $2_{\gamma }^{+}$, $3_{\gamma }^{+}$, $4_{\gamma }^{+}$, $5_{\gamma }^{+}$, and $0_3^{+}$ levels to the ground state and the gamma band.

GW240925 and GW250207 are two loud gravitational-wave signals from binary black hole coalescences observed with network signal-to-noise ratios $\sim 32$ and $\sim 69$, respectively, by the LIGO Hanford-LIGO Livingston-Virgo network. Gravitational-wave signals from coalescing binaries have characteristic phase and amplitude evolution predicted by general relativity. These signal waveforms, together with measured instrumental calibration uncertainties, are used to infer source parameters. However, for sufficiently loud detections, it is possible to constrain the calibration of the detectors directly using the signals themselves. We present the first informative astrophysical measurements of gravitational-wave detector calibration. For GW240925, we verify the inference of Hanford calibration from the astrophysical signal through cross-checks with known calibration errors obtained from in situ measurements. At the time of GW250207, the Hanford detector was not fully stabilized, leading to elevated calibration uncertainties; thus, astrophysical calibration is essential to obtain accurate data and to enable source localization. These well-localized, high signal-to-noise observations have the potential to offer precise measurements of source properties, stringent tests of general relativity, and informative dark siren measurements, provided that calibration uncertainties are properly incorporated. As detector sensitivity improves, astrophysical calibration will become an increasingly valuable complement to in situ calibration measurements. Obtaining accurate calibration will be essential for precision gravitational-wave science.

We present a novel baryogenesis mechanism in which the asymmetry is sourced from heavy particles which either gain their mass or are created during bubble expansion in a strong first order phase transition. These particles then decay in a $CP$ and baryon number violating way inside the bubble. The particles are inherently out of equilibrium and sufficiently dilute after wall crossing so the third Sakharov condition is easily met. Washout is avoided provided the reheat temperature is sufficiently below the scale of the heavy particles. The mechanism relies on moderate supercooling and relativistic walls which—in contrast to electroweak baryogenesis—generically leads to a sizable gravitational wave signal, although in the simplest realizations at frequencies beyond upcoming detectors. We present a simple example model and discuss the restrictions on the parameter space for the mechanism to be successful. We find that high reheat temperatures $T_{\mathrm{RH}}\gtrsim {10}^{10}\mathrm{GeV}$ are generally preferred, whereas stronger supercooling allows for temperatures as low as $T_{\mathrm{RH}}\sim {10}^6\mathrm{GeV}$, provided the vacuum energy density is sufficiently suppressed. We briefly comment on using resonantly enhanced $CP$ violation to achieve even lower scales.

The Yang-Mills (YM) equation in three spacetime dimensions (3D) can be modified to include a novel parity-preserving interaction term, with an inverse mass parameter, in addition to a possible topological mass term. The novelty is that the modified YM equation is not the Euler-Lagrange equation of any gauge-invariant local action for the YM gauge potential alone. Instead, consistency is achieved in the “third way” exploited by 3D minimal massive gravity. We relate our results to the “novel Higgs mechanism” for Chern-Simons gauge theories.

We investigate the reach of the LIGO/Virgo/KAGRA detectors in the search for signatures of first-order phase transitions in the early Universe. Utilizing data from the first three observing runs, we derive constraints on the parameters of the underlying gravitational-wave background, focusing on transitions characterized by strong supercooling. As an application of our analysis, we determine bounds on the parameter space of two representative particle physics models. We also comment on the expected reach of third-generation detectors in probing supercooled phase transitions.

The effective actions for $d=2\mathrm{}$, $N=3, 4$ chiral supergravities with a linear and a nonlinear gauge algebra are related to each other by a quantum reduction; the latter is obtained from the former by putting quantum currents equal to zero. This implies that the renormalization factors for the quantum actions are identical.

A large class of noncritical string theories with extended world sheet gauge symmetry are described by two coupled, gauged Wess-Zumino-Witten models. We give a detailed analysis of the gauge-invariant action and in particular the gauge-fixing procedure and the resulting BRST symmetries. The results are applied to the example of ${\mathit{scrW}}_3$ strings.