Dissipation of small-scale primordial perturbations after neutrino decoupling cools relic neutrinos and reduces their abundance, enabling PTOLEMY to constrain the primordial curvature power spectrum to O(0.1) on scales k ≲ 3×10^5 Mpc^{-1}.
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The NANOGrav 15-year Data Set: Search for Signals from New Physics
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abstract
The 15-year pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) shows positive evidence for the presence of a low-frequency gravitational-wave (GW) background. In this paper, we investigate potential cosmological interpretations of this signal, specifically cosmic inflation, scalar-induced GWs, first-order phase transitions, cosmic strings, and domain walls. We find that, with the exception of stable cosmic strings of field theory origin, all these models can reproduce the observed signal. When compared to the standard interpretation in terms of inspiraling supermassive black hole binaries (SMBHBs), many cosmological models seem to provide a better fit resulting in Bayes factors in the range from 10 to 100. However, these results strongly depend on modeling assumptions about the cosmic SMBHB population and, at this stage, should not be regarded as evidence for new physics. Furthermore, we identify excluded parameter regions where the predicted GW signal from cosmological sources significantly exceeds the NANOGrav signal. These parameter constraints are independent of the origin of the NANOGrav signal and illustrate how pulsar timing data provide a new way to constrain the parameter space of these models. Finally, we search for deterministic signals produced by models of ultralight dark matter (ULDM) and dark matter substructures in the Milky Way. We find no evidence for either of these signals and thus report updated constraints on these models. In the case of ULDM, these constraints outperform torsion balance and atomic clock constraints for ULDM coupled to electrons, muons, or gluons.
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representative citing papers
Tensor-induced non-Gaussianity from primordial gravitational waves generates a unique scale-dependent halo bias correction that can reach order-one amplitude for rare high-redshift halos at z=7.
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.
Black holes in ultralight dark matter solitons undergo quasi-periodic stone-skipping orbits driven by soliton dipole excitations, modifying inspiral dynamics when the black hole is much lighter than the soliton.
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.
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.
Incorporating the general-relativity mass tail df_PBH/d ln M ∝ M^3.78 smooths PBH evaporation, suppresses the scalar-induced GW signal by orders of magnitude, and reopens the ultra-light PBH window for the hot Big Bang.
With a physically motivated z_min cutoff, higher-order moments of the SGWB from SMBH binaries depend on the mass function solely via <M^{10/3}>, giving a variance-to-mean ratio for <M^{10/3}>/<M^{5/3}> and a kurtosis-skewness consistency relation independent of redshift evolution.
Tensor perturbations from first-order phase transitions and domain wall annihilation induce curvature fluctuations at second order that form primordial black holes, allowing asteroid-mass PBHs to comprise all dark matter for specific parameter ranges with associated gravitational wave peaks in LISA,
Increasing the mass of a scalar field around a parity-symmetric beyond-Horndeski black hole strongly reduces the damping rate of quasinormal modes while suppressing low-frequency absorption and shifting efficient absorption to higher frequencies.
PTA statistical tests lose sensitivity to non-Gaussian GW features after decorrelation and cannot distinguish them model-agnostically.
Domain wall annihilation imprints a two-peaked spectrum on induced gravitational waves via an early matter-dominated phase and entropy dilution.
Spectral features imprinted by long-lived BSM particles on any primordial GWB directly determine the particles' mass and decay rate once the model and initial abundance are specified.
The gravitational wave background from supermassive black hole binaries has a universal heavy-tailed amplitude distribution with power-law index -4, causing divergent higher moments and dominance of the strongest signals by few loud sources.
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.
Finite populations of inspiralling supermassive black hole binaries plus finite observation windows introduce non-Gaussian statistics in the pulsar timing array signal that are absent from the Gaussian approximation used in current analyses.
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.
Analytical approximations for the ultra-high-frequency GW peak sourced by friction-era cosmic string loops, with expanded observable parameter space.
Positive tidal charge in this brane-world black hole lowers the effective potential barrier, pushes massive scalar quasinormal modes toward arbitrarily long lifetimes, and increases transmission and absorption.
Exact Hawking area law from black hole mergers restricts quantum gravity to singular Ricci-flat or specific regular black holes in Stelle and nonlocal theories, derives the standard entropy-area law, and realizes Barrow fractal black holes.
Massive scalar quasinormal modes in quasi-topological black holes become long-lived as scalar mass grows, while photon-sphere radius, shadow size, and ISCO exhibit moderate deviations from Schwarzschild.
citing papers explorer
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Probing the small-scale primordial power spectrum via relic neutrinos and acoustic reheating
Dissipation of small-scale primordial perturbations after neutrino decoupling cools relic neutrinos and reduces their abundance, enabling PTOLEMY to constrain the primordial curvature power spectrum to O(0.1) on scales k ≲ 3×10^5 Mpc^{-1}.
-
Tracing Primordial Gravitational Waves via non-Gaussian Signatures of Halo Bias
Tensor-induced non-Gaussianity from primordial gravitational waves generates a unique scale-dependent halo bias correction that can reach order-one amplitude for rare high-redshift halos at z=7.
-
Probing Supermassive Black Hole Mergers with Pulsar Timing Arrays
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.
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Detecting Chiral Gravitational Wave Background with a Dipole Pulsar Timing Array
A dipole pulsar timing array detects chiral nanohertz gravitational waves and extends PTA sensitivity into the microhertz regime.
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Stone Skipping Black Holes in Ultralight Dark Matter Solitons
Black holes in ultralight dark matter solitons undergo quasi-periodic stone-skipping orbits driven by soliton dipole excitations, modifying inspiral dynamics when the black hole is much lighter than the soliton.
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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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Gravitational waves from axion inflation in the gradient expansion formalism. Part I. Pure axion inflation
In pure axion inflation, detectable gravitational wave signals arise only in parameter regions with strong backreaction that violate the upper bound on ΔN_eff.
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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.
-
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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Opening the Window of Ultra-Light PBHs by Exorcising the Poltergeist
Incorporating the general-relativity mass tail df_PBH/d ln M ∝ M^3.78 smooths PBH evaporation, suppresses the scalar-induced GW signal by orders of magnitude, and reopens the ultra-light PBH window for the hot Big Bang.
-
Higher-order statistics of the stochastic gravitational wave background from supermassive black hole binaries
With a physically motivated z_min cutoff, higher-order moments of the SGWB from SMBH binaries depend on the mass function solely via <M^{10/3}>, giving a variance-to-mean ratio for <M^{10/3}>/<M^{5/3}> and a kurtosis-skewness consistency relation independent of redshift evolution.
-
Primordial Black Hole from Tensor-induced Density Fluctuation: First-order Phase Transitions and Domain Walls
Tensor perturbations from first-order phase transitions and domain wall annihilation induce curvature fluctuations at second order that form primordial black holes, allowing asteroid-mass PBHs to comprise all dark matter for specific parameter ranges with associated gravitational wave peaks in LISA,
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Massive Scalar Quasinormal Modes, Greybody Factors, and Absorption Cross Section of a Parity-Symmetric Beyond-Horndeski Black Hole
Increasing the mass of a scalar field around a parity-symmetric beyond-Horndeski black hole strongly reduces the damping rate of quasinormal modes while suppressing low-frequency absorption and shifting efficient absorption to higher frequencies.
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Are PTA measurements sensitive to gravitational wave non-Gaussianities?
PTA statistical tests lose sensitivity to non-Gaussian GW features after decorrelation and cannot distinguish them model-agnostically.
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Imprint of domain wall annihilation on induced gravitational waves
Domain wall annihilation imprints a two-peaked spectrum on induced gravitational waves via an early matter-dominated phase and entropy dilution.
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Irreducible Gravitational Wave Background as a Particle Detector
Spectral features imprinted by long-lived BSM particles on any primordial GWB directly determine the particles' mass and decay rate once the model and initial abundance are specified.
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The Heavy Tailed Non-Gaussianity of the Supermassive Black Hole Gravitational Wave Background
The gravitational wave background from supermassive black hole binaries has a universal heavy-tailed amplitude distribution with power-law index -4, causing divergent higher moments and dominance of the strongest signals by few loud sources.
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Two types of quasinormal modes of Casadio-Fabbri-Mazzacurati brane-world black holes
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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Finite Populations & Finite Time: The Non-Gaussianity of a Gravitational Wave Background
Finite populations of inspiralling supermassive black hole binaries plus finite observation windows introduce non-Gaussian statistics in the pulsar timing array signal that are absent from the Gaussian approximation used in current analyses.
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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 cosmic strings with friction: analytical approximations and parameter space
Analytical approximations for the ultra-high-frequency GW peak sourced by friction-era cosmic string loops, with expanded observable parameter space.
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Long-lived massive scalar modes, grey-body factors, and absorption cross sections of the Reissner--Nordstr\"om-like brane-world black hole
Positive tidal charge in this brane-world black hole lowers the effective potential barrier, pushes massive scalar quasinormal modes toward arbitrarily long lifetimes, and increases transmission and absorption.
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Hawking area law in quantum gravity
Exact Hawking area law from black hole mergers restricts quantum gravity to singular Ricci-flat or specific regular black holes in Stelle and nonlocal theories, derives the standard entropy-area law, and realizes Barrow fractal black holes.
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Long-lived quasinormal modes, shadows and particle motion in four-dimensional quasi-topological gravity
Massive scalar quasinormal modes in quasi-topological black holes become long-lived as scalar mass grows, while photon-sphere radius, shadow size, and ISCO exhibit moderate deviations from Schwarzschild.
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Dark QCD Origin of the NANOGrav Signal and Self-Interacting Dark Matter
A dark QCD model with a first-order phase transition at 5-6 MeV produces the NANOGrav SGWB amplitude while supplying self-interacting dark matter via a 40 GeV baryon and 20-50 MeV dilaton, linked by entropy dilution.
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LISA as a probe of pre-big-bang physics: a nested sampling analysis
Nested sampling analysis indicates LISA could constrain H1, m, sigma_i and beta in the pre-big-bang model to relative uncertainties of about 18 percent under favorable conditions when including foregrounds.
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Expectations for the first supermassive black-hole binary resolved by PTAs I: Model efficacy
Simulations of PTA data show that a full gravitational-wave signal template achieves the highest Bayes factors and most robust parameter estimation for individual supermassive black hole binaries compared to an Earth-term template and a novel Spike Pixel cross-correlation model.
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INTEGRAL, eROSITA and Voyager Constraints on Light Bosonic Dark Matter: ALPs, Dark Photons, Scalars, $B-L$ and $L_{i}-L_{j}$ Vectors
This work sets new upper limits on decay lifetimes and couplings for axion-like particles, dark photons, scalars, and B-L or L_i-L_j vector bosons using 511 keV line, X-ray continuum, and cosmic-ray flux observations.
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Thermodynamical uncertainties for primordial black holes from cosmological phase transitions
A state-of-the-art thermodynamic analysis of supercooled phase transitions yields a universal lower bound β/H_* ≃ 5 and shows that viable PBH dark-matter parameter space in classically conformal gauge-Higgs theories is severely limited by percolation and QCD constraints.
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TransitionListener v2.0 -- Robust gravitational wave predictions for cosmological phase transitions
TransitionListener v2.0 supplies an end-to-end pipeline from scalar potential to gravitational wave spectra with improved handling of transition dynamics and bubble separation.
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F-Term Hybrid Inflation with T-Model K\"ahler Geometry and Beyond
F-term hybrid inflation with SU(1,1)/U(1) or SU(2)/U(1) Kähler geometry in GUTs can be realized without inflationary extrema for broad parameters, matching ACT/SPT data via curvature and tadpole adjustments while predicting cosmic string gravitational waves.
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Metastable strings at PTAs: classical stability analysis
Classical instabilities in metastable strings from two-step symmetry breaking can restrict the viable parameter space for explaining the PTA gravitational wave signal.
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Constraints on Ultralight Scalar and Dark Photon Dark Matter from PPTA-DR3 and EPTA-DR2
Bayesian analysis of PPTA-DR3 and EPTA-DR2 finds no statistically significant ULDM signals and sets 95% CL upper limits on scalar and dark photon dark matter, improving prior bounds in most mass ranges.
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Massive scalar quasinormal modes of an asymptotically flat regular black hole supported by a phantom Dirac--Born--Infeld field
Massive scalar quasinormal modes in this DBI-supported regular black hole show higher oscillation frequencies and lower damping as field mass increases, with larger regularity scales producing softer and longer-lived ringing.
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Telling tails and quasi-resonances in the vicinity of Dymnikova regular black hole
Massive scalar perturbations on the Dymnikova regular black hole exhibit growing oscillation frequencies, reduced damping rates leading to quasi-resonances, power-law oscillatory tails, and mass-dependent suppression of grey-body factors.
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Sensitivity of Weak Lensing Surveys to Gravitational Waves from Inspiraling Supermassive Black Hole Binaries
Weak lensing surveys cannot detect nanohertz-microhertz gravitational waves from supermassive black hole binaries under realistic conditions; only unattainable idealized surveys could probe this band.
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Cosmic Strings as Dynamical Dark Energy: Novel Constraints
Cosmic string networks are constrained to less than ~1% of the energy density using CMB+BAO+SN data, with some models preferring mildly negative densities but no Bayesian evidence favoring them over LambdaCDM.