3D simulations in an expanding background show cosmic expansion drives nonlinear growth that amplifies gravitational-wave spectra from slow phase transitions by factors of 10 to 100.
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The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background
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We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15-year pulsar-timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings-Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law-spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of $10^{14}$, and this same model is favored over an uncorrelated common power-law-spectrum model with Bayes factors of 200-1000, depending on spectral modeling choices. We have built a statistical background distribution for these latter Bayes factors using a method that removes inter-pulsar correlations from our data set, finding $p = 10^{-3}$ (approx. $3\sigma$) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of inter-pulsar correlations yields $p = 5 \times 10^{-5} - 1.9 \times 10^{-4}$ (approx. $3.5 - 4\sigma$). Assuming a fiducial $f^{-2/3}$ characteristic-strain spectrum, as appropriate for an ensemble of binary supermassive black-hole inspirals, the strain amplitude is $2.4^{+0.7}_{-0.6} \times 10^{-15}$ (median + 90% credible interval) at a reference frequency of 1/(1 yr). The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black-hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. The observation of Hellings-Downs correlations points to the gravitational-wave origin of this signal.
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- abstract We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15-year pulsar-timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings-Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law-spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of $10^{14}$, and this same model is favored over an uncorrelated common power-law-spectrum model with Baye
- background sient catalogs GWTC-1 through GWTC-3 [2-4]. These observations have transformed gravitational-wave astron- omy into a precision discipline, enabling detailed tests of strong-field gravity and compact-object population stud- ies. In parallel, pulsar timing arrays, including NANOGrav, have recently reported evidence for a stochastic nanohertz gravitational-wave background [5], opening a complementary low-frequency window onto su- permassive black hole binaries and possible cosmological sources. Ev
- background (PTAs) has provided strong evidence for a stochastic GW background [5-11]. With the fourth LIGO-Virgo- KAGRA observing run in progress and the continued PTA campaign [5, 7, 12, 13], more and more observa- tional data and, thus, scientific insight can be expected. While Earth-based detectors utilize interferometry to detect GWs, PTAs, including NANOGrav [7], the Euro- pean Pulsar Timing Array [8, 14], the Parkes Pulsar Tim- ing Array [9, 10, 12], the Chinese Pulsar Timing Array [11], and the Meer
- background ch § dschmitt@itp.uni-frankfurt.de [1] B. P. Abbott et al. (LIGO Scientific, Virgo), Phys. Rev. Lett. 116, 061102 (2016), arXiv:1602.03837 [gr-qc]. [2] G. Agazie et al. (NANOGrav), Astrophys. J. Lett. 951, L10 (2023), arXiv:2306.16218 [astro-ph.HE]. [3] G. Agazie et al. (NANOGrav), Astrophys. J. Lett. 951, L8 (2023), arXiv:2306.16213 [astro-ph.HE]. [4] G. Agazie et al. (NANOGrav), Astrophys. J. Lett. 951, L9 (2023), arXiv:2306.16217 [astro-ph.HE]. [5] G. Agazie et al. (NANOGrav), (2023), arXiv:2
- background Ever since the first detection of a gravitational wave event by LIGO [183], several large observatories are projected, e.g., LISA [184], Taiji [185], TianQin [185] and the Einstein Telescope [186]. In addi- tion to the detection of singular events, the gravitational wave background has also been recently detected by Pulsar Timing Array collaborations (e.g., NANOGrav, [187], CPTA [188], EPTA, [189]). Regarding FRBs, current radio observatories regularly detect these events, compiling ever-growing
- background be the detection of a stochastic primordial gravitational wave background, and the future gravitational wave experiments will operate in frequency bands that will probe the inflationary gravitational waves [6-14]. NANOGrav already verified a stochastic gravitational wave background back in 2023 [15], but inflation itself cannot generate such a signal [16, 17]. Thus the next ten years will be extremely important for modern theoretical physics. Recently, the Atacama Cosmology Telescope (ACT) [18,
- background turbation equations in certain higher-dimensional scenar - ios due to the influence of the bulk on the brane [55, 56]. Secondly, massive gravitons, either in explicit massive gravity theories or as effective degrees of freedom, have been argued to contribute to very long-wavelength grav- itational signals [57], which are currently being probed by Pulsar Timing Array experiments [58, 59]. Thirdly, massive fields may support arbitrarily long-lived QNMs for particular values of the field mass, leading
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representative citing papers
Future microhertz detections combined with nanohertz pulsar terms can serve as gravity echoes to measure supermassive black hole binary inspiral rates from hundreds to thousands of years in the past.
First search for high-frequency gravitational waves via inverse Gertsenshtein conversion in Earth's magnetic field with VLA and ALMA sets new upper limits h_c ≲ 10^{-18} from 1 GHz to 1 THz.
Self-consistently heated and cooled thin circumbinary disks still drive massive black hole binaries into long-lived non-accreting phases, producing X-ray-weak, optically variable sources that LSST and Roman could find.
A warped 5D geometry with hidden-sector accretion produces growing Schwarzschild/Vaidya black-hole seeds on our brane via a common horizon intersection.
Implements full-Stokes SGWB map-making for ground-based networks, applies to LVK O3 data, and constrains polarized angular spectra while showing intensity-only models can be biased.
Hardening binaries experience deterministic self-acceleration of their center of mass, induced precession, and plane rotation in uniform isotropic media, driving outward spiraling and eccentricity growth in all cases rather than circularization.
A full-covariance formalism for PTA-astrometry ORF estimators forecasts graviton-mass upper limits of 4.41e-24 eV/c2 for current-like setups and 0.48e-24 eV/c2 for SKA/Theia-like future setups, with astrometry adding significant power in the latter case.
Pulsar timing arrays can probe supermassive black hole binaries that merged prior to observations via the pulsar term, with SKA potentially detecting a few such zombie binaries at SNR > 3.
A dipole pulsar timing array detects chiral nanohertz gravitational waves and extends PTA sensitivity into the microhertz regime.
A general relativistic derivation of gravitational wave response in an optically levitated cavity sensor reveals position-dependent strain sensitivity and suppressed input-mirror noise coupling.
Stupendously large black holes cast shadows on the CMB that rule out masses above 10^17 solar masses within the last scattering surface and limit their density parameter to below 10^-5 for masses 10^15 to 10^18 solar masses.
Bubble collisions in a seesaw model produce right-handed neutrinos that source novel gravitational waves detectable by LISA, ET, and LVK while allowing the lightest RHN to explain dark matter or enable leptogenesis.
Cross-correlating pulsar timing and polarimetry isolates the circular polarization of isotropic stochastic GW backgrounds and shares the Hellings-Downs angular pattern.
In pure axion inflation, detectable gravitational wave signals arise only in parameter regions with strong backreaction that violate the upper bound on ΔN_eff.
Scalar metric perturbations after inflation break conformal invariance and induce quantum production of gravitons, generating a GW spectrum that peaks near GHz frequencies for standard primordial scalar power spectra.
First astrometric constraints on parity-violating SGWB amplitude are reported as h70²ΩV = -0.020 ± 0.025 (Gaia) and -0.004 ± 0.010 (VLBA) at 2σ, consistent with zero, over 4.2e-18 Hz to 1.1e-8 Hz.
Proposes APTA with 6 satellites and 10^{-18} relative clock uncertainty at 1s averaging to achieve sensitivity for observing 10^3-10^4 solar-mass black hole mergers in the decihertz band.
A hierarchical Bayesian inference framework combining free-spectrum reconstruction with population-level likelihoods distinguishes finite SMBHB populations from Gaussian primordial GWB using mock PTA data.
Stochastic inflationary fluctuations cannot supply the large dark-Higgs displacement required for broad parametric resonance production of vector dark matter, but a classically sourced Hubble-induced minimum can, with distinct relic scaling and consistency conditions.
Scaling monopoles generate PBHs via stochastic overdensities and GWs with correlated spectra, potentially with magnetically charged PBHs as a signature if the scaling ends via gauge boson mass.
Periodic warm inflation imprints one log-periodic feature on the curvature spectrum that saturates asteroid-mass PBHs, generates dual-band GW backgrounds, and offsets the bispectrum phase by a quarter cycle fixed by spectral running.
PPO reinforcement learning accelerates identification of gravitational wave signals from supercooled phase transitions in a minimal dark U(1)_x sector compared to Monte Carlo sampling.
Scalar-induced tensor modes inherit anomalous coherence from a decohered two-mode Gaussian scalar state, generating nonzero tensor discord and connected power covariance as probes of primordial quantum memory.
citing papers explorer
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Nonlinear growth and amplification of phase-transition gravitational waves induced by cosmic expansion
3D simulations in an expanding background show cosmic expansion drives nonlinear growth that amplifies gravitational-wave spectra from slow phase transitions by factors of 10 to 100.
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Gravity Echoes from Supermassive Black Hole Binaries
Future microhertz detections combined with nanohertz pulsar terms can serve as gravity echoes to measure supermassive black hole binary inspiral rates from hundreds to thousands of years in the past.
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Search for High-Frequency Gravitational Waves via Geomagnetic Conversion with Radio Telescopes
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Detecting Chiral Gravitational Wave Background with a Dipole Pulsar Timing Array
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Shadows of Giants: Constraints on Stupendously Large Black Holes from Negative Sources against the Cosmic Microwave Background
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Cosmic Collider Gravitational Waves sourced by Right-handed Neutrino production from Bubbles: Testing Seesaw, Leptogenesis and Dark Matter
Bubble collisions in a seesaw model produce right-handed neutrinos that source novel gravitational waves detectable by LISA, ET, and LVK while allowing the lightest RHN to explain dark matter or enable leptogenesis.
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Detecting Parity-Violating Gravitational Wave Backgrounds with Pulsar Polarization Arrays
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Quantum production of gravitational waves after inflation
Scalar metric perturbations after inflation break conformal invariance and induce quantum production of gravitons, generating a GW spectrum that peaks near GHz frequencies for standard primordial scalar power spectra.
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First astrometric constraints on parity-violation in the gravitational wave background
First astrometric constraints on parity-violating SGWB amplitude are reported as h70²ΩV = -0.020 ± 0.025 (Gaia) and -0.004 ± 0.010 (VLBA) at 2σ, consistent with zero, over 4.2e-18 Hz to 1.1e-8 Hz.
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Parametric Resonance of Higgsed Vector Dark Matter: Inflationary Initial Conditions and Sourced Displacements
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PBHs and GWs from Scaling Monopoles
Scaling monopoles generate PBHs via stochastic overdensities and GWs with correlated spectra, potentially with magnetically charged PBHs as a signature if the scaling ends via gauge boson mass.
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One Feature, Three Clocks: Phase-Locked Gravitational Waves, Primordial Black Holes, and Non-Gaussianity from Periodic Warm Inflation
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Higher-order statistics of the stochastic gravitational wave background from supermassive black hole binaries
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Conservative and dissipative sectors in a nonlinear scalar model for the gravitational self-force problem
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Phase-resolved field-space distance criteria in ekpyrotic, bouncing and cyclic cosmologies
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Testing General Relativity with Individual Supermassive Black Hole Binaries
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Are PTA measurements sensitive to gravitational wave non-Gaussianities?
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High-Power AM-CW Lunar Laser Ranging as a $\mu$Hz SGWB Detector
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Gravitational Waves from a Black Hole Falling Radially into a Thin-Shell Traversable Wormhole
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Imprint of domain wall annihilation on induced gravitational waves
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Spectral Butterfly Effect and Resilient Ringdown in Thick Braneworlds
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Irreducible Gravitational Wave Background as a Particle Detector
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The Heavy Tailed Non-Gaussianity of the Supermassive Black Hole Gravitational Wave Background
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Stone Skipping Black Holes in Ultralight Dark Matter Solitons
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Quasinormal modes of massive scalars in CFM brane-world black holes split into two types, with modes disappearing at critical masses where real or imaginary frequency parts reach zero.
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Reaching diffraction-limited localization with coherent PTAs
Coherent map-making with pulsar distances in PTAs reaches diffraction-limited angular resolution of ~2 arcmin for GW sources at SNR=10 using roughly 9 pulsars.
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Stochastic gravitational-wave background search using data from five pulsar timing arrays
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Finite Populations & Finite Time: The Non-Gaussianity of a Gravitational Wave Background
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Addressing prior dependence in hierarchical Bayesian modeling for PTA data analysis II: Noise and SGWB inference through parameter decorrelation
A reparametrized hierarchical Bayesian approach using normalizing flows and orthogonal projection of hyperparameters yields tighter noise constraints and partially breaks the red-noise-SGWB degeneracy in a minimal 3-pulsar PTA analysis.
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Finding Supermassive Black Hole Binary Mergers in Pulsar Timing Array Data
A complete SMBHB waveform model enables unified PTA searches for mergers and memory signals, with parameter recovery shown on simulated data for 10^8-10^10 solar mass systems.
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Gravitational waves from axion inflation in the gradient expansion formalism. Part II. Fermionic axion inflation
Schwinger fermion production in axion inflation damps gauge fields, enabling observable primordial gravitational waves in LISA/ET bands while satisfying ΔN_eff limits and identifying a new damped-oscillation backreaction regime.