Gravitational electric-magnetic duality at the light ring organizes and preserves quasinormal mode isospectrality in GR and selects duality-invariant higher-derivative corrections in effective field theories.
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Testing General Relativity with Present and Future Astrophysical Observations
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abstract
One century after its formulation, Einstein's general relativity has made remarkable predictions and turned out to be compatible with all experimental tests. Most of these tests probe the theory in the weak-field regime, and there are theoretical and experimental reasons to believe that general relativity should be modified when gravitational fields are strong and spacetime curvature is large. The best astrophysical laboratories to probe strong-field gravity are black holes and neutron stars, whether isolated or in binary systems. We review the motivations to consider extensions of general relativity. We present a (necessarily incomplete) catalog of modified theories of gravity for which strong-field predictions have been computed and contrasted to Einstein's theory, and we summarize our current understanding of the structure and dynamics of compact objects in these theories. We discuss current bounds on modified gravity from binary pulsar and cosmological observations, and we highlight the potential of future gravitational wave measurements to inform us on the behavior of gravity in the strong-field regime.
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representative citing papers
A reduction scheme transforms arbitrary N-term scalar and matrix recurrence relations from black hole perturbations in modified gravity into three-term relations solvable by continued fractions.
Polynomial models for the (2,2) post-merger waveform amplitudes of eccentric non-spinning binary black holes are constructed from numerical-relativity data as functions of symmetric mass ratio and two merger-time dynamical parameters.
GreyRing model based on greybody factors reproduces numerical relativity ringdown signals with mismatches of order 10^{-6} and enables a new post-merger consistency test of general relativity applied to GW250114.
Exact non-singular black holes from the phantom DBI field evaporate to gram-mass relics, opening a new mass window for primordial black holes as dark matter.
Self-force theory is extended to compute merger and ringdown waveforms in beyond-GR black hole binaries under the extreme mass-ratio approximation, with first calculations of self-force corrections to the merger waveform.
Stable neutron-star configurations denser than black holes exist in quasi-topological gravity and may produce detectable gravitational-wave echoes.
A mixture-model framework for combining gravitational-wave tests of General Relativity yields Bayes factors of 10-20 favoring GR, substantially lower than existing methods that assume uniform deviations across events.
Numerical relativity in the decoupling limit reveals dynamical scalarization and spin-induced (de)scalarization during hyperbolic black hole encounters for both signs of the coupling.
Constructs charged distorted black hole metric via Harrison transformation and analyzes thermodynamics, geodesics, shadow, and quasinormal modes.
The Breitenlohner-Freedman bound restricts Gauss-Bonnet scalarization of RN-AdS black holes to a single fundamental branch for 0<η<2.25, with a separate single branch for η<0.
X-ray timing and spectral analysis of ASKAP J174508.9-505149 detects matching periodicity and features consistent with an accreting magnetic CV.
Neutron stars in quasi-topological gravity can be more compact than black holes and radially stable across several equations of state.
In massive Hellings-Nordtvedt theory, a nonzero vector vacuum asymptotically forbids both curvature-vector couplings at once, and the A²R sector yields Schwarzschild-like black holes plus neutron stars that can deviate from general relativity.
Ghostly quantum systems can have discrete non-dense energy spectra under classical stability conditions, providing counterexamples to spectral denseness.
Jordan-frame multi-scalar-tensor gravity admits an Eckart-like first-order thermodynamic description whose heat flux and residual gradient sector are not generically reducible to a single KT-type quantity.
A glitch-robust amortized inference framework combining normalizing flows, time-frequency multimodal fusion, and contrastive learning outperforms MCMC for Taiji massive black hole binary parameter estimation under noise contamination.
The LQG parameter ξ enlarges equatorial bound orbit energy ranges, confines off-equatorial trajectories, and produces larger deviations from Kerr waveforms in EMRI models for two rotating LQG black holes, though signals fall below detector sensitivities.
KiDS-Legacy weak lensing plus CMB data yields a 3 sigma deviation in light deflection from GR in a Lambda CDM background, with the signal driven by large-scale CMB lensing amplitudes.
Nonlinear tails of massive scalar fields around black holes decay at the same rate as linear tails during intermediate times, independent of sources or initial conditions.
Quadratic gravity with Weyl-squared and Ricci-squared terms produces PPN parameters that equal their GR values except for exponentially decaying corrections, with gamma identically 1 when the two mode masses are equal, yielding solar-system lower bounds m_R, m_W greater than or equal to 23 per AU.
Higher-curvature terms deform the near-horizon potential of spherically symmetric black holes, producing progressively larger shifts in overtone quasinormal frequencies that remain detectable in ringdown waveforms when the fundamental mode stays close to its GR value.
Excitation factors of long-lived quasinormal modes in horizonless compact objects scale with their small imaginary frequency, suppressing early contributions and producing a hierarchy where prompt ringdown uses ordinary modes and late echoes use cavity modes.
GW250114 data confirm the remnant is consistent with a Kerr black hole and bound the dominant quadrupolar mode frequency to within a few percent of the GR prediction, with constraints tighter than prior multi-event catalogs.
citing papers explorer
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Gravitational electric-magnetic duality at the light ring and quasinormal mode isospectrality in effective field theories
Gravitational electric-magnetic duality at the light ring organizes and preserves quasinormal mode isospectrality in GR and selects duality-invariant higher-derivative corrections in effective field theories.
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Beyond Three Terms: Continued Fractions for Rotating Black Holes in Modified Gravity
A reduction scheme transforms arbitrary N-term scalar and matrix recurrence relations from black hole perturbations in modified gravity into three-term relations solvable by continued fractions.
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Highly eccentric non-spinning binary black hole mergers: quadrupolar post-merger waveforms
Polynomial models for the (2,2) post-merger waveform amplitudes of eccentric non-spinning binary black holes are constructed from numerical-relativity data as functions of symmetric mass ratio and two merger-time dynamical parameters.
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Novel ringdown tests of general relativity with black hole greybody factors
GreyRing model based on greybody factors reproduces numerical relativity ringdown signals with mismatches of order 10^{-6} and enables a new post-merger consistency test of general relativity applied to GW250114.
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Exact, non-singular black holes from a phantom DBI Field as primordial dark matter
Exact non-singular black holes from the phantom DBI field evaporate to gram-mass relics, opening a new mass window for primordial black holes as dark matter.
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Black hole mergers beyond general relativity: a self-force approach
Self-force theory is extended to compute merger and ringdown waveforms in beyond-GR black hole binaries under the extreme mass-ratio approximation, with first calculations of self-force corrections to the merger waveform.
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Neutron stars more compact than black holes as a probe of strong-field gravity
Stable neutron-star configurations denser than black holes exist in quasi-topological gravity and may produce detectable gravitational-wave echoes.
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Testing General Relativity with GWTC-4.0 through mixture models
A mixture-model framework for combining gravitational-wave tests of General Relativity yields Bayes factors of 10-20 favoring GR, substantially lower than existing methods that assume uniform deviations across events.
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Scalarization and descalarization in hyperbolic encounters of black holes
Numerical relativity in the decoupling limit reveals dynamical scalarization and spin-induced (de)scalarization during hyperbolic black hole encounters for both signs of the coupling.
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Electrically Charged Distorted Black Holes: Thermodynamics, Particle Dynamics, and Quasinormal Signatures
Constructs charged distorted black hole metric via Harrison transformation and analyzes thermodynamics, geodesics, shadow, and quasinormal modes.
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Curvature-induced scalarization of charged AdS black holes
The Breitenlohner-Freedman bound restricts Gauss-Bonnet scalarization of RN-AdS black holes to a single fundamental branch for 0<η<2.25, with a separate single branch for η<0.
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The X-ray emission of the long-period transient and accreting cataclysmic variable ASKAP J174508.9-505149
X-ray timing and spectral analysis of ASKAP J174508.9-505149 detects matching periodicity and features consistent with an accreting magnetic CV.
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Neutron stars more compact than black holes in quasi-topological gravity: Equilibrium configurations and radial stability
Neutron stars in quasi-topological gravity can be more compact than black holes and radially stable across several equations of state.
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Black holes and neutron stars in massive Hellings-Nordtvedt theory
In massive Hellings-Nordtvedt theory, a nonzero vector vacuum asymptotically forbids both curvature-vector couplings at once, and the A²R sector yields Schwarzschild-like black holes plus neutron stars that can deviate from general relativity.
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Quantum mechanics with a ghost: Counterexamples to spectral denseness
Ghostly quantum systems can have discrete non-dense energy spectra under classical stability conditions, providing counterexamples to spectral denseness.
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First-order thermodynamics of multi-scalar-tensor gravity
Jordan-frame multi-scalar-tensor gravity admits an Eckart-like first-order thermodynamic description whose heat flux and residual gradient sector are not generically reducible to a single KT-type quantity.
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Robust parameter inference for Taiji via time-frequency contrastive learning and normalizing flows
A glitch-robust amortized inference framework combining normalizing flows, time-frequency multimodal fusion, and contrastive learning outperforms MCMC for Taiji massive black hole binary parameter estimation under noise contamination.
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Particle motions and gravitational waveforms in rotating black hole spacetimes of loop quantum gravity
The LQG parameter ξ enlarges equatorial bound orbit energy ranges, confines off-equatorial trajectories, and produces larger deviations from Kerr waveforms in EMRI models for two rotating LQG black holes, though signals fall below detector sensitivities.
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Evidence for deviation in gravitational light deflection from general relativity at cosmological scales with KiDS-Legacy and CMB lensing
KiDS-Legacy weak lensing plus CMB data yields a 3 sigma deviation in light deflection from GR in a Lambda CDM background, with the signal driven by large-scale CMB lensing amplitudes.
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Nonlinear tails of massive scalar fields around a black hole
Nonlinear tails of massive scalar fields around black holes decay at the same rate as linear tails during intermediate times, independent of sources or initial conditions.
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Parameterized Post-Newtonian Analysis of Quadratic Gravity and Solar System Constraints
Quadratic gravity with Weyl-squared and Ricci-squared terms produces PPN parameters that equal their GR values except for exponentially decaying corrections, with gamma identically 1 when the two mode masses are equal, yielding solar-system lower bounds m_R, m_W greater than or equal to 23 per AU.
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Probing higher curvature gravity via ringdown with overtones
Higher-curvature terms deform the near-horizon potential of spherically symmetric black holes, producing progressively larger shifts in overtone quasinormal frequencies that remain detectable in ringdown waveforms when the fundamental mode stays close to its GR value.
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Excitation factors for horizonless compact objects: long-lived modes, echoes, and greybody factors
Excitation factors of long-lived quasinormal modes in horizonless compact objects scale with their small imaginary frequency, suppressing early contributions and producing a hierarchy where prompt ringdown uses ordinary modes and late echoes use cavity modes.
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Black Hole Spectroscopy and Tests of General Relativity with GW250114
GW250114 data confirm the remnant is consistent with a Kerr black hole and bound the dominant quadrupolar mode frequency to within a few percent of the GR prediction, with constraints tighter than prior multi-event catalogs.
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Tracing Signatures of Modified Gravity in Redshift-Space Galaxy Bispectrum Multipoles: Prospects for Euclid
In Hu-Sawicki f(R) gravity the redshift-space bispectrum monopole and quadrupole show 2-8% deviations from GR at z=0.7 and k~0.3 h/Mpc with forecasted SNR of 30 and 15 for Euclid.
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On the universality of late-time ringdown tail
Analytical proof establishes universality of late-time ringdown tails for any effective potential decaying as 1/r², with different power-law behavior for 1/r^α (1<α<2), covering charged black holes, Kerr, exotic objects, modified gravity, and environmental matter distributions.
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Testing the no-hair theorem with GW150914
Ringdown analysis of GW150914 with overtones measures remnant mass and spin consistent with a Kerr black hole, supporting the no-hair theorem at the 10% level.
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Modeling Uncertainties in Modified Gravity Predictions for the Stochastic Gravitational-Wave Background
Third-generation gravitational-wave detectors can constrain frequency-dependent beyond-GR waveform modifications in the stochastic background, but modified propagation effects remain degenerate with astrophysical population parameters.
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Distance duality relation in symmetric teleparallel gravity
In symmetric teleparallel f(Q) gravity with nonminimal EM-nonmetricity coupling, the distance duality relation is dynamically violated, yielding a generalized formula relating observational distances to the Hubble rate.
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Massive scalar fields in eccentric regime: Detectability and constraints from LISA observations of extreme mass-ratio inspirals
Computes scalar and tensor fluxes for eccentric EMRIs with massive scalars, quantifies dephasing, and shows via Fisher matrix that LISA can constrain scalar charge and mass.
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QPO-like Signatures and Hydrodynamical Variability in Accretion around a JNW-type Compact Spacetime in Freund-Nambu Scalar-Tensor Gravity
New FNST scalar-tensor generalization of JNW spacetime is used in GR hydrodynamic simulations of BHL accretion, yielding hydrodynamically generated QPO-like frequencies overlapping observed ranges in stellar-mass compact object systems.
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Another Look at the Weak-Field Limit of Generalized Hybrid Metric-Palatini Gravity
Generalized hybrid metric-Palatini gravity propagates a massless spin-2 mode and two massive scalars in the weak field; stability requires algebraic conditions on f derivatives at flat space, and planetary data constrain the scalar masses in a hierarchical regime.
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The Impact of Spin Priors on Parameterized Tests of General Relativity
Spin prior choices propagate into tests of GR via the 1.5PN deviation parameter δφ̂3 in a non-trivial, event-dependent way, with stronger effects for short-inspiral events and partial degeneracy with χ_eff when the deviation is included.
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A note on methods for computing the critical curve of Kerr-like black holes
Bardeen's definition of black hole critical curves deviates from de Vries and Grenzebach definitions in homogeneous plasma by contracting with increasing density, contrary to prior expectations.
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Hawking area law in quantum gravity
If Hawking's area law is taken as exact, nonlocal and Stelle quantum-gravity theories are forced to drop R^2 and (Riemann)^2 terms (or use singular Ricci-flat black holes), and the standard entropy-area law follows as a consequence.
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Scalarizations of magnetized Reissner-Nordstr\"om black holes induced by parity-violating and parity-preserving interactions
Magnetic fields lower the scalarization threshold for electromagnetic and gravitational Chern-Simons couplings but produce opposite trends on the two Gauss-Bonnet branches, with nonlinear terms converting exponential growth into bounded oscillations.
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Observational constraints on nonlocal black holes via gravitational lensing
Nonlocal black holes remain consistent with general relativity at the 1.13-sigma level after joint lensing and quasinormal-mode constraints.
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Black Hole-Boson Star Binaries: Gravitational Wave Signals and Tidal Disruption
Numerical simulations of black hole-boson star binaries show that scalar self-interactions can suppress tidal disruption while radiative efficiency depends on the chosen potential.
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Are Black Holes Fuzzballs? Probing Horizon-Scale Structure with LISA
LISA can constrain non-axisymmetric mass quadrupole deformations at the 10^{-3} level and axisymmetric mass octupole deformations at the 10^{-2} level in EMRI signals to test fuzzball proposals.
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Three dimensional black bounces in $f(R)$ gravity
Black bounce geometries exist in 2+1D f(R) gravity with scalar-nonlinear electrodynamics matter, including vanishing scalar curvature solutions whose viability is checked via scalaron mass and energy conditions.
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Confronting eikonal and post-Kerr methods with numerical evolution of scalar field perturbations in spacetimes beyond Kerr
Numerical simulations benchmark the eikonal and post-Kerr approximations for quasinormal modes in deformed Kerr spacetimes, quantifying their errors relative to expected observational precision.
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Revisiting black holes and their thermodynamics in Einstein-Kalb-Ramond gravity
Exact black hole solutions with topological horizons are found in EKR gravity and their thermodynamics are analyzed using the Wald formalism for mass and entropy.
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Greybody factors, reflectionless scattering modes, and echoes of ultracompact horizonless objects
High-frequency quasi-reflectionless scattering modes in the greybody factors of ultracompact horizonless objects are responsible for echoes in the time-domain response.
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Nonlinear Stability of Kerr-Sen Black Holes in Merging Binaries
Head-on binary black hole simulations in EMDA theory show dilaton and axion fields persist through merger, indicating nonlinear stability of Kerr-Sen black holes and scalarization of initially unscalarized solutions.
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Equatorial Periodic Orbits and Gravitational Wave Phenomenology around Spherically-symmetric vacuum solution in Freund-Nambu scalar-tensor gravity
Scalar couplings in Freund-Nambu gravity shift ISCO inward and produce detectable temporal dephasing in EMRI gravitational wave bursts while preserving orbit topology.
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Equivalence Principle violation in metric-affine gravity and finite-temperature effects
Metric-affine gravity formulates equivalence principle violations via non-metricity that parallel finite-temperature mass-ratio shifts, and a generalized Fermi-Walker derivative shows no orthonormal tetrad propagates along observer worldlines.
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Probing Gravitational Wave Signatures from Periodic Orbits of Regular Black Holes in Asymptotically Safe Gravity
The quantum parameter ξ in an asymptotically safe regular black hole shifts the innermost stable orbit, enhances whirl behavior in periodic geodesics, and produces amplitude-modulated millihertz gravitational-wave strains whose peak amplitude grows with ξ, placing them inside the sensitivity bands预计
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Can wormholes have vanishing Love numbers?
The paper claims the ℓ=2 magnetic tidal Love number of the Dadhich–Kar–Mukherji–Visser R=0 wormhole vanishes to first order in the regularization parameter p, based on a throat-regularity condition that removes the 1/r² response term.
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Scalar-Electromagnetic Couplings as Source of Deformed Black Hole: From Shadows to Thermodynamic Topology
A scalar-NED coupled black hole metric is reconstructed from an effective geometry, yielding EHT bounds on magnetic charge, Hawking-Page transition, and topological equivalence to the Reissner-Nordström solution.
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Constraints on Einstein-aether gravity from the precision timing of PSR J1738+0333
Precision timing of PSR J1738+0333 from EPTA and NANOGrav data yields the tightest strong-field constraints on Einstein-aether parameters from any single binary pulsar.