gr-qc — Pith

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gr-qc 2026-05-21 2 theorems

Modified gravity changes low-frequency gravitational-wave lensing

by Alice Garoffolo, Gianmassimo Tasinato

Wave-optics gravitational wave lensing in modified gravity

A curvature-coupled propagation equation prevents the amplification factor from reaching unity at zero frequency.

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We initiate the study of gravitational-wave lensing in the wave-optics regime within modified gravity. We consider a phenomenological setup in which the gravitational-wave amplitude obeys a curvature-coupled propagation equation. This framework reproduces the standard GR behaviour in the geometric-optics regime, while leading to qualitatively different infrared dynamics. In particular, the usual argument implying that the amplification factor approaches unity in the zero-frequency limit no longer applies. This is due to the persistence of curvature-induced interactions in the infrared, which modify the natural propagation basis itself. As a result, the standard Fresnel treatment ceases to be valid at sufficiently low frequency. The correct infrared regime is instead controlled by an interacting static Green function, with a finite-frequency completion provided by a partial-wave formulation. We show that this structure admits an equivalent distorted-wave interpretation, in which the curvature interaction is absorbed into a dressed reference propagation basis, while the residual lensing effect is encoded in finite-frequency phase shifts. We further demonstrate that these phenomena admit a natural interpretation in the language of scattering amplitudes. Wave-optics lensing can therefore probe propagation-level departures from GR that remain entirely invisible in geometric optics.

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Top Pith

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gr-qc 2026-05-18 2 theorems

Naked singularities stable under small Hölder perturbations

by Weihao Zheng

Nonlinear stability of continuously self-similar naked singularities for the Einstein-scalar field equations I: main results

Result for Christodoulou's family shows that weak cosmic censorship depends on the regularity class chosen for perturbations

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This is the first part of a series of papers proving the nonlinear stability of a one-parameter family of continuously self-similar $C^{1,\alpha}$ naked singularity solutions, with $0<\alpha\ll1$, to the spherically symmetric Einstein-scalar field equations. The stability holds for initial perturbations lying in a small open neighborhood of the data generating these naked singularity solutions, measured in a localized H\"older topology. These continuously self-similar naked singularity spacetimes were previously constructed by Christodoulou [D. Christodoulou, Examples of naked singularity formation in the gravitational collapse of a scalar field, Ann. of Math. 140 (1994), 607--653], who also proved their instability to black hole formation under sufficiently rough perturbations [D. Christodoulou, The instability of naked singularities in the gravitational collapse of a scalar field, Ann. of Math. 149 (1999), 183--217], thereby verifying weak cosmic censorship within a rough functional framework. In complete contrast, in this paper, we obtain the first nonlinear stability of these naked singularity spacetimes under general perturbations of the same regularity as the background. We rely on the linearized stability result established in the companion paper [J. Singh and W. Zheng, Nonlinear stability of continuously self-similar naked singularities for the Einstein--scalar field equations II: linearized stability]. Our result underscores the decisive role of the functional framework in formulating the Weak Cosmic Censorship conjecture.

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Top Pith

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gr-qc 2026-05-13 2 theorems

Black hole mergers calibrate gravitational wave detectors

by The LIGO Scientific Collaboration, the Virgo Collaboration +1839 more

GW240925 and GW250207: Astrophysical Calibration of Gravitational-wave Detectors

Two loud binary black hole events yield the first direct astrophysical constraints on LIGO and Virgo calibration uncertainties.

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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.

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gr-qc 2026-07-03

Small horizon persists through cosmological bounce

by Balkar Yildirim, Alan Albert Coley

Black Hole Persistence in Scalar Tensor Theories

Perturbative scalar-tensor solution finds an evolving horizon of size set by d0 that continues past the nonsingular transition without symme

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We construct a perturbative scalar-tensor solution describing a central inhomogeneity embedded in an evolving cosmological background, with the aim of studying black hole persistence through a nonsingular bounce. Scalar-tensor gravity provides a natural framework for realizing bouncing cosmologies, while the inclusion of a localized inhomogeneity makes the field equations substantially more difficult to solve. We therefore adopt a perturbative scheme, with perturbative parameter $\epsilon$, in which the leading-order equations are solved by a spatially flat bouncing FLRW spacetime sourced by a radiation perfect fluid. At next order, a central inhomogeneity is introduced through a generalized McVittie geometry, with the perturbations encoded in the corresponding first-order metric and scalar-field functions. We first allow an anisotropic fluid with radial and tangential pressures, whose diagonal components solve the diagonal field equations. The field equations are solved as a series expansion up to $\mathcal{O}(\eta^4)$ near the bounce at $\eta=0$. The resulting perfect fluid solution contains three arbitrary functions which are constrained by requiring the spacetime to asymptote to FLRW as $r\to\infty$. With suitable initial conditions preserving the parabolic structure of the bounce, the integration constant $d_0$ emerges as the true perturbative parameter: all perturbations vanish as $d_0\to0$. Finally, we find a small evolving horizon, $r_h\sim d_0$, which we interpret as the horizon of the central inhomogeneity. Its persistence through the bounce supports the interpretation of a black hole surviving the cosmological transition, and its evolution is not symmetric about $\eta=0$.

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gr-qc 2026-07-03

Direct wave does not probe black hole horizon

by Anuj Kankani, Sean T. McWilliams

The Direct Wave is Not a Meaningful Test of Horizon Properties

Numerical data shows its frequency matches the horizon only incidentally at one spin, producing false area law violations.

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Recently, a distinct non--quasinormal mode component of black hole binary merger radiation, named the direct wave, has been identified. The frequency and damping time of the direct wave have been associated with properties of the remnant horizon. This has led to direct-wave based analysis of GW250114, including a test of Hawking's area law. However, as we demonstrate here using numerical relativity strain data, the direct wave frequency is not correlated with the horizon frequency or surface gravity, other than an incidental crossing around $\chi_f \approx 0.7$ corresponding closely to the remnant spin of GW250114. We show that while the instantaneous frequency of the direct wave is quasi-stable, the damping time shows significant evolution and therefore a single damped sinusoid model, containing a fixed damping time, is not appropriate. We further show that an evolving frequency model based on horizon properties also does not model the direct wave component for systems with large remnant spins. We demonstrate that testing Hawking's area law with a horizon frequency based on the direct wave interpretation will lead to apparent violations of Hawking's area law when no violation actually occurs. Our results therefore indicate that the direct wave is not a reliable probe of the remnant horizon's properties.

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physics.hist-ph 2026-07-03

GRMHD models of Sgr A* carry problematic epistemic opacity

by Juliusz Doboszewski, Jamee Elder

Black Boxes in Black Hole Imaging

This signals limits in current model understanding and restricts machine learning uses in future observations.

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We investigate the epistemic opacity of computer simulations and machine learning methods in the context of black hole imaging. We argue that there are forms of opacity-including opacity resulting from the use of machine learning-which do not need to affect the reliability of an inference when it is seen as a part of a broader inferential framework. We propose conditions under which that can plausibly be the case, and discuss how opaque methods can be useful in the context of the (next generation) Event Horizon Telescope. However, we also argue that at least one problematic form of opacity is currently present in black hole imaging: GRMHD models of Sagittarius A* are opaque. This form of opacity signals the limitations of current understanding of the models of this source, and constrains the potential uses of ML models in future observations.

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hep-th 2026-07-03

Squeezed ultra-cold bosons enable graviton lasing

by Soham Sen, Vlatko Vedral

Towards graviton lasing from squeezed ultra-cold systems

Exponential growth depends on boson number and wave-packet squeezing, with a proposed lab setup for coherent gravitons.

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In our recent work, arXiv:2604.11474 [hep-th], we have shown that effective detection of gravitons is possible using an array of charged harmonic oscillators in a dynamical electromagnetic field. Using the interaction Hamiltonian of the identical model, we find out that a systematic way of population inversion of the gravitons is possible in ultra-cold atomic systems. We find out that the exponential growth depends strictly on the number of bosons in the system as well as their inherent squeezing of the matter wave packets. A coherent source of gravitons may lead directly to an unavoidable evidence on the existence of gravitons and based on this analysis we propose an experimental proposal for generating true graviton laser.

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astro-ph.HE 2026-07-03

SKA to test gravity with dozens of new pulsar binaries

by V. Venkatraman Krishnan, L. Shao +22 more

Testing Gravity with Binary Pulsars in the SKA Era

Better timing and fresh discoveries will probe strong-field effects and black-hole properties beyond current reach.

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Binary (and trinary) radio pulsars are natural laboratories in space for understanding gravity in the strong field regime, with many unique and precise tests carried out so far, including the most precise tests of the strong equivalence principle and of the radiative properties of gravity. The Square Kilometre Array (SKA) telescope, with its high sensitivity in the Southern Hemisphere, will vastly improve the timing precision of recycled pulsars, allowing for a deeper search of potential deviations from general relativity (GR) in currently known systems. A Galactic census of pulsars will, in addition, will yield the discovery of dozens of relativistic pulsar systems, including potentially pulsar -- black hole binaries, which can be used to test the cosmic censorship hypothesis and the ``no-hair'' theorem. Aspects of gravitation to be explored include tests of strong equivalence principles, gravitational dipole radiation, extra field components of gravitation, gravitomagnetism, and spacetime symmetries. In this chapter, we describe the kinds of gravity tests possible with binary pulsar and outline the features and abilities that SKA must possess to best contribute to this science.

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gr-qc 2026-07-03

Fermion correlations weaken with rising black hole temperature

by Yifei Xu, Yanjun Chen +2 more

Nonlocal correlations of fermionic entanglement in the spacetime of Einstein-Gauss-Bonnet black hole

In Einstein-Gauss-Bonnet spacetime both nonlocal advantage of coherence and Bell nonlocality decline steadily as Hawking radiation intensifi

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The investigation of nonclassical correlations in curved spacetimes offers key insights into the intersection of quantum information theory and gravitational physics. This paper studies two nonlocal correlation measures, non local advantage of quantum coherence (NAQC) and Bell nonlocality (BN) in a $d$-dimensional spherically symmetric Einstein-Gauss-Bonnet (EGB) black hole spacetime. We consider two observers (Alice and Rob) initially sharing a maximally entangled Bell state: Alice freely falls into the black hole (inertial Kruskal frame), while Rob accelerates outside the horizon (non-inertial Schwarzschild-like frame). The Unruh-Hawking effect modifies Rob's field modes, requiring Bogoliubov transformations to relate the two frames. We derive the mixed bipartite density matrix for fermionic fields and analytical expressions for NAQC and BN, which depend on Hawking temperature (itself governed by $\alpha$, $d$, and $r_h$). Our results show both correlations degrade monotonically with increasing Hawking temperature, confirm the NAQC-BN hierarchical relationship persists in EGB spacetime, and highlighting the impact of high curvature corrections on quantum resources.

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gr-qc 2026-07-03

Excited boson stars violate energy conditions in teleparallel gravity

by Long-Xing Huang, Ke Yang +1 more

Boson Stars in Teleparallel Gravity with a Nonminimally Coupled Field: The Violation of Energy Conditions and Gravitational Waveforms from EMRIs

Ground states obey them, yet EMRI signals from both lie in the LISA detection range.

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In this work, we investigate boson star models within the framework of teleparallel gravity with non-minimal coupling, and obtain static, spherically symmetric solutions for both the ground state and excited states. The results indicate that the energy density of the excited-state solutions can become negative. For these solutions, the four commonly used energy conditions are no longer satisfied. In contrast, for all the ground-state solutions we have studied, the energy density remains positive and all four energy conditions are consistently satisfied. Moreover, considering the importance of astrophysical observations, the gravitational-wave signals from Extreme-Mass-Ratio Inspirals (EMRIs) composed of these boson stars are investigated. Our results reveal that the frequency-domain characteristic strain of these waveforms falls within the detectability range of LISA, which can provide potential evidence for distinguishing compact astrophysical objects.

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gr-qc 2026-07-03

Scalar hair compacts neutron stars beyond GR predictions

by Hamza Boumaza, Christos Charmousis +2 more

Neutron stars with primary scalar hair

Positive charges increase compactness until a critical threshold triggers singularities, offering direct observational tests of DHOST parame

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We investigate static and spherically symmetric neutron star solutions endowed with primary scalar hair in a subfamily of Degenerate-Higher-Order-Scalar-Tensor (DHOST) theories of gravity. By solving the modified Tolman-Oppenheimer-Volkoff (TOV) equations, we construct equilibrium configurations for polytropic and realistic equations of state and analyse the impact of the scalar hair on the stellar structure. We examine the resulting metric and scalar field profiles as well as the mass-radius relation, showing deviations from the predictions of General Relativity (GR). Positive scalar charges lead to more compact stars than in GR and, above a critical threshold, to singularities. Observations could therefore put stringent constraints on the parameters characterising the beyond-GR effects in these theories and their potential scalar hair.

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gr-qc 2026-07-03

Lyapunov exponents track black hole phase transitions across frames

by Hocheol Lee, Bogeun Gwak

Phase Transitions with Lyapunov Exponents under Einstein and String Frames in Dilatonic Reissner--Nordstr\"om--AdS Black Holes

Values depend on the frame but critical cusps and points remain fixed, agreeing with thermodynamic calculations.

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We investigate Lyapunov exponents as dynamical probes of black hole phase transitions in dilatonic Reissner--Nordstr\"om--AdS black holes within Einstein--Maxwell--dilaton theory. The thermodynamic quantities and the Lyapunov exponent of charged probe particles were analyzed in both the Einstein and string frames, thus providing a direct comparison between the thermodynamic phase structure of the black hole and that captured by the Lyapunov exponent. Thermodynamic quantities, including the Hawking temperature and Wald entropy, remained constant under conformal frame transformations, yielding identical phase structures in the two frames. In contrast, the Lyapunov exponent exhibited non-trivial frame dependence for massive probe particles due to dilaton coupling, while no frame dependence was found in the massless limit. Numerical analysis revealed that the phase structure features captured by the Lyapunov exponent, including characteristic cusp behavior and transition points, were independent of the choice of frame, despite the Lyapunov exponent itself being frame-dependent. Therefore, the Lyapunov exponent exhibited frame-dependent values, while the critical structure it captures remained constant across conformal frames.

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gr-qc 2026-07-03

Anisotropic matter suppresses local chaos near black holes

by Khusan Alibekov, Hocheol Lee +5 more

Chaotic behaviors of particles around the black hole with an anisotropic matter immersed in a magnetic field

Magnetic field changes instead produce transitions between regular and chaotic orbits via Poincaré sections in the exact solution.

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We present an exact solution to the Einstein-Maxwell equations that describes a static black hole coexisting with anisotropic matter immersed in an external magnetic field, obtained via the Harrison transformation. Our findings reveal that an increase in the anisotropic matter parameter systematically suppresses the local chaotic behavior, as indicated by a reduction in the Lyapunov exponent. Conversely, variations in the external magnetic field lead to qualitative changes in global chaotic behavior. This is analyzed through Poincar\'e sections, which demonstrate transitions between regular and chaotic trajectories resulting from the nonlinear gravitational-magnetic interactions. These factors play distinct yet complementary roles in shaping chaotic particle dynamics around black holes. This study would offer a new theoretical framework for exploring non-integrable particle motion within magnetized black hole spacetimes and for probing a black hole at the galactic center, where magnetic fields may arise from plasma effects surrounding astrophysical black holes.

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gr-qc 2026-07-03

Kerr/CFT matches Komar entropy for Bumblebee black holes

by YU-Qi Chen, Jin-Yang Shen +1 more

Rotating Black Holes and the Kerr/CFT Correspondence in Einstein-Bumblebee Gravity

Microscopic count from near-horizon CFT agrees with Komar integrals but differs from Wald by the Bumblebee coupling factor.

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We constructed rotating black holes with equal angular momentum in five dimensional Einstein-Bumblebee gravity with and without cosmological constant. Their thermodynamic properties are examined via two distinct methods: the Wald formalism and the Komar integral. Notably, the conserved charges, including mass, angular momentum, and entropy, computed from these two approaches differ by a constant prefactor that is solely determined by the Bumblebee coupling. Subsequently, we apply the Kerr/CFT correspondence to derive the microscopic entropy of these black holes and find that it precisely reproduces the entropy in Komar-integral version, rather than the Wald entropy.

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hep-th 2026-07-03

Typicality bounds extend to Type II von Neumann factors

by Zhi-Wei Wang, Samuel L. Braunstein

Lubkin-Page typicality bounds for Type~II von~Neumann factors

Mutual information vanishes as O((dA dB/dE)^2) for Type II1 and gains entropy suppression for II∞ gravitational algebras.

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Typicality arguments for emergent spacetime rely on the Lubkin-Page bounds, which show that generic quantum states have vanishing correlations between subsystems. These bounds assume a tensor-product Hilbert space (a Type~I von~Neumann algebra), but the observable algebras in quantum field theory and quantum gravity are generically Type~II or Type~III, raising the question of whether the bounds survive. We prove that they do for all Type~II von~Neumann factors. For the hyperfinite Type~II$_1$ factor with a tripartite decomposition $R \cong A \otimes B \otimes E$, the mutual information between subsystems $A$ and $B$ vanishes as $O((d_A d_B / d_E)^2)$ in finite-dimensional approximations, provided $d_A d_B \leq d_E$ (Theorem~1). For Type~II$_\infty$ factors, including the gravitational algebras constructed via the crossed-product method by Witten and by Chandrasekaran, Longo, Penington, and Witten, the bound acquires an additional exponential suppression controlled by the Bekenstein-Hawking entropy (Theorem~2). We identify the obstructions to extending the result to Type~III factors and discuss the open question of whether the commutant of the observable algebra can serve as a natural thermal bath that tightens the bound further.

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astro-ph.HE 2026-07-03

Black hole spin alone sets near-horizon jet polarization

by Zhenyu Zhang, Yehui Hou +3 more

Polarization Architecture of Steady GRMHD Jets from the Horizon to Infinity

A semi-analytic model finds hierarchical convergence that separates spin effects from collimation and plasma loading across image scales.

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We develop a semi-analytic framework for stationary, axisymmetric GRMHD jets that efficiently generates resolved polarized images from the near-horizon region out to $\sim 10^5\,r_g$ across a broad parameter space, enabling rapid exploration of how gravity and magnetohydrodynamic flows imprint scale-dependent signatures on jet morphology and polarization. We identify a new scale-dependent separation in polarimetric diagnostics. Outside the photon ring, plasma loading strongly modifies the polarization-angle profile of the integrated jet-layer emission through inertia-driven winding of the magnetic field. At large image-plane radii, the polarization angle follows a power-law in radius, with an index determined by the jet collimation profile. Near the horizon, in contrast, jets converge to a universal polarization pattern controlled solely by black hole spin. This convergence is hierarchical: differences in velocity and magnetic-field structure are erased first, whereas collimation-dependent differences persist to smaller radii, thereby allowing these effects to be disentangled. These results establish a largely achromatic polarimetric diagnostic that connects GRMHD jet dynamics to resolved image structure, with direct implications for high-resolution polarimetry and for constraining black hole spin and jet formation.

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astro-ph.CO 2026-07-03

PBH mergers peak at 1.79 times ISCO frequency

by Ashu Kushwaha

Gravitational Waves from Primordial Black Holes: Connecting Low-Frequency Scalar-Induced Signatures to High-Frequency Binary Mergers

Monochromatic mass function creates direct, model-independent link between low-frequency scalar-induced waves and high-frequency merger sign

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Formation of primordial black holes (PBHs) requires a significant enhancement of curvature perturbations. This mechanism leaves a twofold gravitational-wave (GW) signature: a \emph{low-frequency} stochastic background of scalar-induced GWs (SIGWs) and a distinct \emph{high-frequency} signal from subsequent PBH binary mergers. We leverage this shared origin to establish a consistent, \emph{model-independent} connection between these two observables for a monochromatic PBH mass function. Using PBH abundance constraints on the primordial curvature power spectrum, we evaluate the stochastic SIGW background for spherical and ellipsoidal collapse models, demonstrating that the ellipsoidal scenario yields a significantly stronger signal. Furthermore, we analyze the GW signal from PBH binary mergers and find a direct correspondence between the SIGW frequency and the innermost stable circular orbit (ISCO) frequency of the binaries. Because GW emission is nearly maximal near the ISCO, we additionally show that the peak of the full merger GW spectrum relates to the ISCO frequency via $f_{\text{peak}} = 1.79 \, f_{\text{ISCO}}$, a relation that is independent of the binary masses. Remarkably, this unified framework connects these distinct GW channels, enabling the same primordial fluctuations to be probed across widely separated frequency bands.

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astro-ph.EP 2026-07-03

Lunar longitude alters clock frequency shifts by separation

by Hongbin Zhang, Yanyue Gao +1 more

The influence of lunar tidal potential on clock frequencies at different positions on Earth

Calculations in the geocentric frame show that clocks at the same latitude but different longitudes experience changing tidal offsets as the

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With the advancements in clock timing technology, increasingly smaller time differences can be distinguished. Therefore, it is critical to investigate the fractional frequency shift of clocks at different locations on Earth. In this paper, we study it systematically under the influence of a subtle lunar tidal potential based on a new method. Our calculations in the geocentric Fermi frame show that when two clocks are located at the same latitude, the longitude difference changes the fractional frequency shift between them. A similar phenomenon occurs when there is a difference in latitude between two clocks on the ground at the same longitude. Interestingly, when the Moon's longitude changes, the phase and amplitude of the lunar tidal fractional frequency shift between two clocks with the same longitude difference will change, while the change in the Moon's latitude only affects the amplitude of the fractional frequency shift of these two clocks. Our results provide useful information for the calibration and synchronization of clocks on Earth.

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gr-qc 2026-07-03

Quantum bounce erases stable attractors in dark energy models

by Mohd Shahalam, K. Yerzhanov +2 more

Classical and Loop Quantum Cosmology of Interacting Dark Energy: A Dynamical System Analysis with Superfluid Dark Matter and Dust Matter

Loop quantum cosmology leaves only saddle points for all interacting dark sector cases, unlike classical gravity where pressureless matter r

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We study the cosmological dynamics of interacting dark energy and dark matter in Classical Einstein Gravity and Loop Quantum Cosmology. Two dark matter scenarios are considered: superfluid dark matter described by a generalized cubic equation of state and the standard pressureless fluid. The dark energy component is modeled using both a generalized nonlinear equation of state and a constant equation of state. We examine two phenomenological interaction terms, $Q=\alpha\dot{\rho}_m$ and $Q=\beta\dot{\rho}_d$, which govern the energy transfer between the dark sectors. In classical gravity, the pressureless matter model exhibits stable late-time attractors, whereas the superfluid dark matter model admits only saddle and non-hyperbolic critical points. Extending the analysis to Loop Quantum Cosmology, quantum geometric corrections replace the Big Bang singularity with a nonsingular quantum bounce, and significantly modify the phase-space dynamics. As a result, the stable attractors of the classical pressureless matter model disappear, and all interacting models possess only saddle and non-hyperbolic critical points. These findings highlight the significant influence of both dark matter properties and quantum gravitational effects on the asymptotic evolution of interacting dark-sectors.

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gr-qc 2026-07-03

Kalb-Ramond black hole reproduces observed QPO pairs

by Faizuddin Ahmed, Ahmad Al-Badawi +3 more

Particle dynamics and quasi-periodic oscillations of a Reissner--Nordstr\"om-like black hole in Kalb--Ramond gravity under an external magnetic test field

MCMC fits show charge, Lorentz-violating parameter and magnetic coupling match data from three X-ray sources under the relativistic precessi

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We investigate the dynamics of charged test particles and quasi-periodic oscillations around a Reissner--Nordstr\"om-like black hole in Kalb--Ramond (KR) gravity in the presence of an external magnetic test field. The KR background introduces a Lorentz-violating parameter $\ell$, which modifies the spacetime geometry, horizon structure, circular orbits, and characteristic frequencies of particle motion. In contrast to the standard Wald-type prescription, the magnetic-field configuration is constructed from the source-free Maxwell equation on the charged KR background, allowing the magnetic profile to be consistently adapted to the modified geometry. We derive the equations of motion, the effective potential, the conditions for circular orbits, and the orbital and radial epicyclic frequencies of charged particles. The results show that the black-hole charge $Q/M$, the KR parameter $\ell$, the specific particle charge $\epsilon$, and the magnetic coupling $\beta=bM$ jointly affect the innermost stable circular orbit (ISCO) and the quasi-periodic oscillation (QPO) frequencies. We then apply the obtained frequencies to the relativistic precession model, where the upper QPO frequency is identified with the orbital frequency and the lower one with the periastron-precession frequency. Using the observed twin-peak QPO data of GRO J1655--40, XTE J1550--564, and M82 X-1, we perform a Markov chain Monte Carlo analysis to constrain the model parameters. The obtained posterior constraints indicate that the charged KR black-hole model with an external magnetic field can consistently reproduce the observed QPO pairs within the adopted parameter ranges. These findings suggest that QPO observations may serve as a useful phenomenological tool for probing Lorentz-violating black-hole geometries and electromagnetic effects in strong-gravity environments.

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gr-qc 2026-07-03

Gluing massless wormholes yields similar stability regions

by G. F. Akhtaryanova, R. Kh. Karimov +2 more

Stability regions of glued wormholes with massless Kim-Lee backreacted spacetimes as interior

Scalar and electric charge Kim-Lee interiors produce nearly identical stability domains when matched to Schwarzschild and Reissner-Nordstrom

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Asymptotic zero Arnowitt-Deser-Misner (ADM) mass wormholes, such as the zero-mass traversable Ellis-Bronnikov wormhole, are of great interest for astrophysical applications such as in the galactic microlensing. However, when considered individually, they are unstable to small perturbations. On the other hand, there is a possibility that they can be stable as an interior partner of a traversable glued wormhole obtained by suitably gluing the interior to the observationally relevant massive exterior spacetimes across spherically symmetric thin shells. Although the exterior spacetime has non-zero ADM mass, massless interior partner remains massless sharing the stability of the glued wormhole. The dynamics of the thin-shell then demarcates the stability regions of the glued wormhole that we wish to study here by employing the novel concepts of thin-shell "mass" and of "external force" constraints discovered by Garcia, Lobo and Visser. We shall consider two classes, where the zero ADM mass interior are Kim-Lee wormholes glued to the exterior Schwarzschild vacuum and Reissner-Nordstr\"{o}m spacetime respectively. It turns out that the stability regions in both cases are almost similar although the two interior Kim-Lee spacetimes are physically very different, one scalar charged and the other electrically charged. The conditions under which the stability of glued wormholes could be achieved are analyzed in detail.

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astro-ph.IM 2026-07-03

New splitting yields explicit high-order PN integrators

by Yujie Jiang, Lijie Mei

Efficient high-order explicit symplectic splitting methods for post-Newtonian Hamiltonian systems

Avoids order reduction for time steps below ε cubed and improves efficiency over implicit methods in binary simulations.

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The nonseparability of post-Newtonian (PN) Hamiltonian systems typically necessitates the use of computationally expensive implicit integrators. Recent research overcomes this limitation by embedding the dynamics into a doubled phase space, which enables the development of explicit symplectic methods. However, existing specially designed explicit integrators suffer from order reduction for high-order methods when the time stepsize is small, i.e., $h <\varepsilon^3$. In this paper, we propose a novel extension and splitting approach for the doubled Hamiltonian, under which specially designed explicit symplectic integrators can be constructed. It is shown that the proposed integrators achieve genuine high-order convergence without order reduction and take advantage of the small PN parameter $\varepsilon$. Numerical results from simulations with 2PN spinning binaries demonstrate superior long-term conservation of invariants and significantly higher computational efficiency compared to both implicit methods and existing explicit splitting techniques.

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astro-ph.HE 2026-07-02

MRI in solids needs strong shear to beat elasticity

by Arthur G. Suvorov, Thomas Celora +1 more

Magneto-rotational instabilities in solids: application to neutron-star crusts

Neutron-star crusts allow magnetic growth only above 300 Hz spin, or less if heated viscously.

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The magneto-rotational instability can generate strong, turbulent substructure within magnetised shear flows. The efficacy of the mechanism as a function of microphysical aspects of the fluid, such as stratification and diffusivity, has been explored extensively. One aspect that has not been studied thus far, however, is whether the instability can also operate in solids. Motivated by the possibility that solid regions within planets or degenerate stars may rotate differentially with respect to liquid or gaseous layers during some phase of their life, we examine the extent to which elasticity suppresses the instability. A simplified, plane-parallel analysis reveals that only in cases where the flow is strongly sheared, such that the magnetic tension that would result from the instability in a liquid exceeds the shear modulus of the elastic cavity, can magnetic growth occur. In the context of dynamical tides in binary neutron-star mergers, this implies that the magnetic field can be amplified in the crust prior to coalescence only if the star boasts a spin frequency of $\gtrsim 300$Hz. If viscous heating weakens the crystalline structure prior to resonance, the required spin frequency is reduced.

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gr-qc 2026-07-02

Vacuum Cherenkov radiation differs above critical magnetic field

by Daniel Gálvez-García, Nora Bretón

Vacuum Cherenkov radiation in supercritical magnetic fields

Euler-Heisenberg comparison shows distinct emission versus critical fields and versus synchrotron radiation.

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In the presence of very intense electromagnetic fields, the refractive index of vacuum is modified such that light velocity is less than $c$ and ultrarelativistic charged particles can be faster than light and can induce Cherenkov radiation. We present the comparison of the Cherenkov radiation produced by the Euler-Heisenberg theory for critical and supercritical magnetic fields. We also make the comparison between the Cherenkov and the synchrotron radiation produced by the charged particles.

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astro-ph.GA 2026-07-02

Variable dimension fits Milky Way curves without dark matter

by Gabriele U. Varieschi

Fractional-Dimension Gravity and the Milky Way Galaxy

A radially changing fractional space dimension matches Gaia DR3 velocities across the full observed range.

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In this work, we focus our analysis of Fractional-Dimension Gravity (FDG) on our home galaxy, the Milky Way (MW), by using the latest Gaia DR3 data as well as previous rotation curve (RC) data for this galaxy. FDG is an alternative gravitational model (previously known as Newtonian Fractional-Dimension Gravity - NFDG) which does not require the dark matter (DM) paradigm. The MW is studied here with the methods of FDG and its observed rotation curves are successfully reproduced by using a variable fractional dimension $D\left (R\right)$, following previous studies of several other galaxies which were analyzed with the same methodology. An alternative dimension function $D_{m}\left(R \right)$, based on the mass-dimension field equation, was also used and yielded less accurate fits to the experimental data. In addition, we also considered possible implications of the FDG metric, based on the presence of additional weights, on the structure of Special Relativity (SR) for spacetimes with fractional dimension. One notable outcome of this analysis is the possibility of an effective superluminal motion in galactic regions where the space dimension is $D<3$. Although this result is very speculative, it opens interesting new perspectives for possible interstellar travel in our galaxy.

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astro-ph.CO 2026-07-02

ALP dark matter produces Lyman-Werner photons via magnetic fields

by Abdias Aires, Robert Brandenberger +1 more

Secondary Production of Photons from ALP Dark Matter interacting with a Cosmological Magnetic Field

Chern-Simons interactions with cosmological B-fields yield sufficient flux without violating CMB or X-ray limits.

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Under the assumption that dark matter is a coherently oscillating pseudoscalar field coupled to electromagnetism by the usual Chern-Simons term, we study the production of secondary photons from dark matter fluctuations coupled to a pre-existing magnetic field, taking into account the spectral distribution of the magnetic field. Specifically, we apply the formalism to the case of a large-scale magnetic field generated previously via a parametric resonance instability due to the same Chern-Simons coupling. However, our analysis is applicable to any spectrum of cosmological scale magnetic field fluctuations present at the time of recombination. We show that obtaining a sufficiently large flux of photons in the Lyman-Werner frequency range is consistent with constraints from CMB and X-ray observations.

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hep-th 2026-07-02

Closed manifold data fixes unitary QFTs uniquely

by Jacob McNamara, Zhencheng Wang

Wormholes as red herrings: reflection positivity and the reconstruction of unitary quantum field theories

Reflection positivity turns the data into a full theory, showing factorization issues arise from missing charged states.

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As Coleman famously argued, the apparent breakdown of partition-function factorization in quantum gravity associated with Euclidean wormholes is a red herring, arising from a hidden average over an ensemble of theories. We present a direct analog of Coleman's argument for the apparent breakdown of Hilbert-space factorization associated with spatial wormholes, i.e., Einstein--Rosen bridges. Our main result is the following reconstruction theorem for quantum field theories: unitary QFTs are determined, up to unitary isomorphism, by their closed-manifold partition functions; every reflection-positive partition function arises from a unitary quantum field theory; and the states prepared by manifolds span the space of invariant states under the reconstructed theory's symmetry group. Interpreting the result gravitationally, we conclude that any apparent breakdown of Hilbert-space factorization is a red herring, arising from restricting to an incomplete spectrum of charged states.

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gr-qc 2026-07-02

LISA orbit errors limit response mismatches to below 10^{-7}

by Lorenzo Speri, Olaf Hartwig +6 more

Impact of Spacecraft Orbit Uncertainties and Velocity Mismodeling on the LISA Gravitational-Wave Response

Velocity mismodeling at 10^{-4} Hz produces 10^{-4} mismatches but keeps galactic binary biases under 1 sigma

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The Laser Interferometer Space Antenna (LISA) is a space-based gravitational wave observatory that consists of three spacecraft in a near-equilateral triangular formation. The spacecraft orbits are typically assumed to be perfectly known in LISA data analysis studies, but in reality, the orbit determination process introduces uncertainties in the spacecraft positions and velocities. In this work, we investigate how these uncertainties propagate into the LISA detector output and the impact of neglecting the spacecraft velocities. We quantify these errors in the knowledge of the LISA response using mismatches and discuss the implications for gravitational wave data analysis. We find that spacecraft orbit uncertainties impact the LISA response knowledge at high frequencies with worst mismatch below $10^{-7}$. The effect of neglecting the spacecraft velocities is largest at frequencies around $10^{-4}$ Hz with mismatches of order $10^{-4}$. For a galactic binary with frequency $10^{-4}$ Hz and SNR=200 observed for one year, we find that neglecting the spacecraft velocities in the response leads to less than 1-$\sigma$ biases in the parameter estimates. This work provides the first characterization of how errors in the LISA gravitational wave response propagate from gravitational wave strain through detector output to estimated parameters.

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hep-th 2026-07-02

Worldline quantization yields all-orders 3D gravity path integral

by Robert Bourne, Jackson R. Fliss +1 more

What's the Matter with 3D Gravity?

Geometric quantization on the matter phase space reproduces the one-loop result and conjectures the full thermal AdS3 partition function wit

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We revisit the problem of minimally coupling matter to Einstein gravity in three dimensions with negative cosmological constant. By working in the worldline formalism, we construct a classical phase space on an initial time surface $\Sigma$, which we quantize using geometric quantization. States in the Hilbert space correspond to Virasoro conformal blocks with operators of conformal weight $h<c/24$. As an application of our formalism, we compute the partition function on thermal $\text{AdS}_3$ through equivariant localization. Our answer reproduces the AdS$_3$ Wilson spool and agrees with the known one-loop result. It further serves as a conjecture for the value of the path integral of gravity minimally coupled to a massive scalar field in thermal $\text{AdS}_3$ to all orders in $G_N$.

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hep-ph 2026-07-02

No evidence for axions in 257 black hole spins

by Orion Ning, Benjamin R. Safdi +1 more

No Evidence for Superradiant Axions in LIGO-Virgo-KAGRA GWTC-5 Binary Black Hole Spins

LIGO-Virgo-KAGRA GWTC-5 data excludes masses 1.7e-14 to 3.3e-12 eV at 95 percent , one of the strongest robust bounds.

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The quantum chromodynamics (QCD) axion and axion-like particles may form bound clouds around spinning black holes (BHs) when their Compton wavelength is comparable to the BH gravitational radius, depleting the BH spin through what is known as a $\textit{superradiance}$ instability. Using binary BH (BBH) spin measurements obtained from the LIGO-Virgo-KAGRA GWTC-5 catalog, the most extensive public BBH catalog to date containing $N=257$ mergers with BH masses spanning roughly $5$-$135$ $M_\odot$, we perform a hierarchical Bayesian analysis in the context of a BH spin population model to constrain ultralight axions. The presence of axions at a given mass would imprint a unique signature in the observed mass-spin relation relative to the formation distribution. We find no evidence for axions across more than two decades in mass, excluding axion masses $1.7 \times 10^{-14} \, {\rm eV} \lesssim m_a \lesssim 3.3 \times 10^{-12} \, {\rm eV}$ at 95% confidence. Because prior superradiance bounds in this range derive from X-ray spin measurements with substantial modeling systematics, this result represents one of the strongest robust lower bounds on the QCD axion mass.

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hep-th 2026-07-02

BPS instanton Hessian factorizes as Q dagger Q

by Soo-Jong Rey

Type IIB Axion--Dilaton Wormholes and the BPS Limit Hessian

Reductions around E=0 saddle produce factorized operator, strengthening wormhole stability statements

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I revisit Type-IIB axion--dilaton Euclidean saddles in a specified axion charge sector. In that sector, the solution with $E=0$ is the BPS instanton, while $E>0$ gives non-BPS wormholes with a smooth throat. The two cases solve the same radial equations but define different fluctuation problems. For the $E=0$ instanton, the Hamiltonian constraint, gauge quotient, charge-sector boundary condition, and removal of collective zero modes reduce the quadratic action to a physical Hessian. This Hessian factorizes, $ {\cal H}_\nu={\mathcal Q}_\nu^\dagger{\mathcal Q}_\nu$. I interpret this as an endpoint theorem, beyond a stability theorem for the full $E>0$ wormhole. This puts Type IIB wormhole spectra on firmer grounds. I also separate the connected two-ended wormhole throat from its long-distance two-end multipole operator term. Once the coefficient matrix $C^{ij}$ is derived, the different-component and same-component placements of the two end insertions are terms in the same quadratic expression. Removing either term requires a genuine projection or cancellation.

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gr-qc 2026-07-02

Gauss-Bonnet corrections preserve oscillons but break EFT at large coupling

by Areef Waeming, Josu C. Aurrekoetxea +3 more

Preheating and oscillon formation in Einstein-scalar-Gauss-Bonnet gravity

Simulations show curvature in dense cores drives the leading-order description out of its validity range.

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Non-perturbative processes in the early universe may create overdense structures in scalar fields like the inflaton, called oscillons. In this work, we explore whether the leading order higher derivative contributions to the scalar-tensor theory change the formation and growth of these structures, and investigate the limits in which the effective field theory (EFT) description breaks down. We find that whilst the properties of the oscillons are not significantly modified, and black holes do not generically form, for large couplings the period of formation can result in the evolution leaving the regime of validity of the EFT, at which point predictivity is lost and the next order terms in the EFT should become relevant. If the oscillons survive their formation, they tend to be stable and the EFT corrections remain bounded. The EFT breakdown is triggered by large curvature terms in the metric in the densest regions of the oscillon, meaning that approximations of such modified theories that neglect the local backreaction and non-linear dynamics of the fields may miss important effects.

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astro-ph.HE 2026-07-02

High-spin black hole masses trace low-spin merger remnants

by Yin-Jie Li, Yuan-Zhu Wang +2 more

Smoking-gun evidence for hierarchical black-hole mergers

Peak-by-peak match in 259 events shows high-spin black holes form via successive mergers rather than isolated processes.

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How stellar-mass black holes grow after their birth is a central open question in astrophysics. Gravitational-wave observations have revealed a subpopulation of coalescing black holes with both high masses and high spins, but whether these properties arise from hierarchical mergers in dense stellar environments or from accretion onto isolated black holes has remained unresolved. Here, using a flexible mixture population model applied to the 259 binary black hole mergers in GWTC-5, we show that the mass function of the high-spin subpopulation traces, peak by peak, the predicted remnant-mass distribution of the low-spin, stellar-collapse-origin subpopulation up to $\sim80\,M_\odot$. This morphological match, quantified by a Bhattacharyya coefficient as high as $\sim0.95$, is naturally expected if the high-spin black holes are themselves the products of earlier mergers, whereas any alternative scenario would require fine-tuning, thereby providing smoking-gun evidence for hierarchical mergers. In addition, the sharp upper-mass cutoff of the low-spin subpopulation at $m_{\rm max,1}=54.2^{+7.7}_{-7.2}\,M_\odot$ yields an astrophysical $S$-factor of $S_{300}=151^{+30}_{-26}$~keV~b (68\% credible interval) for the $^{12}{\rm C}(\alpha,\gamma)^{16}{\rm O}$ reaction, in agreement with the benchmark theoretical value. These results establish that the entire observed black-hole population can be accounted for by stellar collapse followed by dynamical hierarchical assembly, without invoking primordial black holes.

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gr-qc 2026-07-02

Direct process supplies energy for analogue Hawking radiation

by Lorenzo M. Procopio, Raul Aguero-Santacruz +2 more

Backreaction of stimulated Hawking radiation in an optical analogue

Fibre experiment measures how emitted quanta deplete the pump field, replacing the assumed cascade with a single interaction.

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Hawking radiation - the emission of quantum particles at the event horizon of a black hole - connects gravity with quantum mechanics and thermodynamics; the Bekenstein-Hawking entropy has been the benchmark for potential quantum theories of gravity. But Hawking radiation has never been observed in astronomy, only in laboratory analogues and the chances of ever observing it in space are astronomically small. The energy of Hawking radiation must come from the gravitational field around the black hole, but how field quanta generate Hawking quanta has been unknown. Here we report on experimental and theoretical evidence for the process that generates Hawking radiation in a fibre-optical analogue of the event horizon. There, as in gravity, it has been believed that Hawking radiation comes from a complicated, cascaded process; here we have found a simple, direct process and measured its backreaction on the field. Our findings suggest an equally direct process for other laboratory analogues and perhaps also for gravitational fields, shedding light on how black holes might radiate.

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gr-qc 2026-07-02

Thick disks yield distinct black hole image features

by Bing-Bing Chen, Chen-Yu Yang +2 more

Horizon-scale intensity and polarization images of rotating Konoplya-Zhidenko black holes with thick accretion flows

Intensity and polarization patterns from deformed rotating black holes differ from thin-disk cases and can probe spacetime geometry.

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We investigate the shadow and polarization images of a Konoplya-Zhidenko rotating non-Kerr black hole surrounded by a geometrically thick and optically thin accretion flow. The accretion flow is described by an analytical ballistic approximation accretion flow model. The numerical results show that the shadow image exhibits two main features, an outer bright ring and an inner dark region. The former corresponds to higher order images, while the latter is produced by the black hole event horizon. Increasing the deformation parameter $\eta$ does not significantly change the overall shape of the higher order images, but it enlarges their size. Increasing the spin parameter $a$ and the observer inclination angle $\theta_o$ enhances the asymmetry of the higher order images and makes the intensity on the left side much larger than that on the right side. This behavior is associated with frame dragging and the relativistic Doppler effect. In the polarization images, the degree of linear polarization is much smaller in the higher-order image region than in other regions, and the polarization vectors extend over the whole image plane. These results indicate that the thick disk model produces features in both intensity and polarization images that differ markedly from those in thin disk models. Within the framework used in this work, the observed intensity and polarization signatures can serve as effective probes of the underlying spacetime geometry and near horizon accretion dynamics.

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hep-ph 2026-07-02

Entropy bound forces primordial black holes to explain dark matter and early galaxies

by Sidan A, Tom Banks +1 more

Can Primordial Black Holes Be Seeds for Early Galaxies in Models Satisfying the Covariant Entropy Bound?

Tiny early black holes decay to radiation while larger ones supply all dark matter and seed JWST galaxies.

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We argue that cosmological models obeying the Covariant Entropy Bound (CEB) mathematically favor states with no localized excitations or one large black hole containing all the energy in a constrained initial state. In order to get a long radiation-dominated era, one must postulate that at a very early time, most horizon volumes of the universe contained tiny black holes that decayed into radiation. A previous work by two of the authors showed that such a scenario could fit the data on the Cosmic Microwave Background (CMB). In order to account for dark matter, we also postulate some random black holes of at least horizon size at that time. A reasonable distribution of such primordial black holes can account for all of dark matter as well as the early galaxies seen by the James Webb Space Telescope. Some of the dark matter may also be in Planck-scale remnants of the decaying black holes. We describe our model both in terms of approximate solutions to General Relativity and a speculative quantum gravity model whose hydrodynamics matches the flat $p = \pm \rho$ FRW model that saturates the CEB.

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hep-th 2026-07-02

Horizon diffeomorphisms yield dissipative hydro actions

by Mike Blake, Arpit Das +1 more

Dissipative hydrodynamic actions and horizon symmetries in gravity

The action matches known Green's functions to first order for thermal stress tensor dynamics in AdS4 gravity.

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We give a prescription to compute a dissipative action describing the large-scale thermal stress tensor dynamics of a holographic quantum field theory dual to AdS$_4$ gravity, in the context of the Schwinger-Keldysh formalism. Our prescription is valid to quadratic order in perturbations about the thermal equilibrium state. The hydrodynamical degrees of freedom of this action are realised in gravity as relative diffeomorphisms between the black hole horizon and the two asymptotic boundaries of the Crossley-Glorioso-Liu contour. We explicitly compute the action to first order in derivatives, and confirm it correctly reproduces the known hydrodynamic Green's functions. Our prescription requires a choice of horizon boundary conditions for the metric. We study the horizon symmetries that preserve these, and their relation to conjectured hydrodynamic symmetries responsible for many-body quantum chaos.

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gr-qc 2026-07-02

LISA binary population stays compatible with vacuum GR

by Lorenzo Copparoni, Enrico Barausse

Environmental effects vs. modified gravity in the LISA massive black hole binary population

Hierarchical analysis finds environmental effects do not mimic modified gravity even at 50 percent active fraction.

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Gravitational-wave signals from massive black hole binaries observed by LISA can carry imprints of both the astrophysical environment of the source and possible deviations from general relativity. We investigate whether environmental effects leave a detectable imprint on the LISA binary population, and whether they can mimic modified-gravity effects with the same frequency dependence. As representative channels we adopt accretion and viscous migration in a circumbinary disk for the environmental sector, and a time-varying Newton constant $\dot G$ for the modified-gravity sector. All three effects enter the waveform at the same negative post-Newtonian order and are described, at leading order, by a common phase-deformation parameter, which makes them formally degenerate at the single-event level. Combining Fisher-matrix forecasts with a hierarchical nested-sampling analysis of synthetic catalogs from astrophysically motivated population models, we find that, even under extreme astrophysical assumptions -- an active fraction of $50\%$, together with a super-Eddington accretion tail -- the population-level posteriors remain fully compatible with vacuum. However, a hierarchical population-wide analysis may yield a non-trivial upper limit on the active fraction and a mild lower bound on the slope of the Eddington-ratio distribution. Environmental effects are therefore unlikely to bias LISA's tests of general relativity with massive black hole binaries in astrophysically realistic scenarios.

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gr-qc 2026-07-02

Dark matter halo enlarges black hole orbits and damps wave signals

by Bahromjon Shokirov, Arabboy Mirzakulov +2 more

Gravitational Wave Signatures of Schwarzschild Black Hole in a Generalized Dehnen-Type (1,4,γ) Dark Matter Halo

Periodic orbits grow and gravitational wave amplitudes drop as halo parameters increase, placing some EMRI peaks within reach of LISA and si

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In this paper, we investigate timelike geodesic motion, periodic orbits, and the associated gravitational-wave signals around a Schwarzschild-like black hole (BH) embedded in a generalized Dehnen-type dark matter (DM) halo. We show that the Dehnen-type $(1,4,\gamma)$ DM halo profile modifies test-particle dynamics, with increasing the parameter of density profile, $\gamma$, leading to larger marginally bound orbit (MBO) and innermost stable circular orbit (ISCO) radii and angular momenta, together with a higher ISCO energy. These findings provide further insight into the role of the DM distribution in modifying the orbital dynamics, energy, and angular momentum of timelike test particles near the BH. Furthermore, we investigate the gravitational-wave signals produced by a stellar-mass compact object moving along periodic orbits around a supermassive BH embedded in a generalized Dehnen-type DM halo. Using the numerical kludge approach, we calculate the orbital trajectories and the corresponding gravitational-wave polarizations. We find that increasing the halo parameters $\gamma$, $\rho_s$, and $r_s$ produces larger periodic orbits, longer orbital periods, and lower waveform amplitudes. The resulting spectra lie mainly in the millihertz frequency range, while several characteristic-strain peaks lie above the sensitivity curves of future space-based gravitational-wave detectors such as LISA, Taiji, and TianQin. These results suggest that the surrounding DM halo may leave observable imprints on extreme mass-ratio inspiral (EMRI) gravitational-wave signals.

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gr-qc 2026-07-02

Vacuum wave creates closed timelike curves from flat data

by Semin Xavier

Closed Timelike Curves from a Vacuum Traveling Wave

Exact solution evolves regular initial data into time loops while obeying all energy conditions.

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We construct an exact vacuum spacetime that develops closed timelike curves from regular, asymptotically flat initial data respecting the weak, dominant, and strong energy conditions. Einstein's equations fix the geometry through two functions, a harmonic transverse profile and a traveling-wave mode, whose evolution drives the closed curves of the time-machine core from spacelike to timelike. The chronology horizon admits a degenerate limit in which its generating closed null geodesic has vanishing boost and optical scalars, the conditions for a Killing spinor.

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gr-qc 2026-07-02

Anchored variational principle carves constrained GR sector

by Prasanta Sahoo

Hypersurface Anchored Variational Principle for General Relativity

Einstein-Hilbert action plus hypersurface term produces anchoring equation and standard bulk Einstein equations without new degrees of freed

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A hypersurface anchored variational extension of General Relativity is formulated in which the Einstein-Hilbert action is supplemented by a diffeomorphism invariant functional supported on an embedded spacelike hypersurface whose embedding is varied independently of the spacetime metric. The resulting Euler-Lagrange system consists of the Einstein equations with a localized distributional contribution together with an anchoring equation determining admissible embeddings. For the admissible class of hypersurface functionals considered here, the bulk field equations retain the standard second order principal structure away from the hypersurface and no additional propagating bulk gravitational degrees of freedom are introduced. Under ellipticity and invertibility assumptions, local persistence and linear stability of anchoring hypersurfaces follow from standard implicit function and elliptic estimates. The anchoring condition is generically inequivalent to local slicing gauge conditions and therefore defines a genuine variational restriction rather than a coordinate choice. In the canonical formulation, the momentum constraints retain their standard form, whereas the Hamiltonian constraint acquires a hypersurface supported term. The corresponding smeared generators close in the weak sense: the Dirac algebra is recovered in the bulk, with deviations confined to localized distributional surface contributions. The construction therefore defines a constrained sector of the classical solution space of General Relativity consisting of spacetimes that admit at least one embedded hypersurface satisfying the anchoring equation. In homogeneous cosmology, the localized term induces matching conditions across the anchoring surface, allowing finite transitions in the expansion rate while preserving standard evolution away from the transition hypersurface.

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gr-qc 2026-07-02

f(Q) black holes link thermodynamic degeneracy to ringdown shifts

by Wen-Xiang Chen

Thermodynamic-Geometric Phase Transition and Gravitational-Wave Quasinormal Modes of Schwarzschild Black Holes in f(Q) Gravity: An RVB-Residue Approach

The same residue fixing Hawking temperature also moves photon-sphere frequency and damping time when the thermodynamic Hessian degenerates.

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We construct a residue-based framework connecting the thermodynamic geometry of a Schwarzschild-type black hole in $f(Q)$ gravity with its gravitational-wave quasinormal-mode spectrum. The analysis is based on the symmetric teleparallel formulation of gravity, in which the gravitational field is encoded by the nonmetricity scalar $Q$ rather than by curvature or torsion. For the Schwarzschild branch, the Robson--Villari--Biancalana (RVB) method gives the Hawking temperature through the simple-pole residue of the inverse blackening function. We show explicitly that the same residue also controls the logarithmic monodromy of the tortoise coordinate near the event horizon, and therefore enters the ingoing quasinormal-mode boundary condition. In the strict general-relativistic Schwarzschild limit the heat capacity is negative and finite, the one-dimensional Ruppeiner geometry contains no intrinsic curvature singularity, and no genuine thermodynamic phase transition occurs. In the extended $f(Q)$ state space, however, the modified horizon function and the effective Wald entropy generate a non-trivial thermodynamic Hessian. Its degeneracy condition coincides with singular behavior of the thermodynamic curvature and is reflected in the quasinormal-mode spectrum through shifts of the photon-sphere frequency, Lyapunov exponent, damping time, and near-horizon monodromy. This gives a precise statement of the internal relation between thermodynamic-geometric phase structure and gravitational-wave ringdown: both are different projections of the same analytic structure of the corrected black-hole metric.

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gr-qc 2026-07-02

Torsion from fermion spins corrects light bending in stars

by Sagar Kumar Maity, Amitabha Lahiri

Spin-torsion interaction and geodesic bending

The additional deflection depends on density, chirality, and temperature and may reach detectable levels in neutron stars.

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The intrinsic spin of fermions induces torsion in spacetime, leading to an effective four-fermion interaction. This affects the bending of null and timelike geodesics inside a star with a spherically symmetric distribution of gravitationally dense fermionic matter of constant density. Our analysis shows an additional torsional contribution to the geodesic deflection, alongside the conventional curvature-induced effect. This change depends on the fermion number density, coupling constants of the different species of fermions with different chiralities, and the temperature of the matter distribution. We have shown that the torsion-induced corrections to null geodesic bending remains very small for both low- and high-mass white dwarfs, whereas significantly larger effects may arise in more compact astrophysical objects such as neutron stars.

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gr-qc 2026-07-02

Non-metricity alone encodes all of information geometry

by Tatsuaki Wada

Reframing of Information Geometry via Symmetric Teleparallel Gravity

By setting curvature and torsion to zero, the statistical manifold structure reduces to the non-metricity tensor and separates general from

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Information geometry has traditionally been formulated within the framework of Riemannian geometry and dual affine connections. In this work, we reframe this foundational structure by introducing the geometric machinery of symmetric teleparallel gravity. By requiring both curvature and torsion to vanish globally on the statistical manifold, we demonstrate that the fundamental properties of the information space can be entirely encoded into the non-metricity tensor. This approach allows us to distinguish the general $\xi$-parameterized space from the $\theta$- (or $\eta$-) parameterized space, mirroring the relationship between conventional general relativity and symmetric teleparallel gravity. Specifically, the $\theta$- or $\eta$-coordinates emerge as the special coordinates in the coincident gauge, where the connection coefficients vanish.

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hep-th 2026-07-02

Symplectic eigenvalues match for Wands-dual backgrounds

by Suddhasattwa Brahma, Jaime Calderon-Figueroa +2 more

Hidden quantum-informatic symmetries of quasi-de Sitter backgrounds

Covariance matrix entries differ but quantum measures of entanglement coincide in dual quasi-de Sitter histories.

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We investigate how degeneracies in quasi-de Sitter backgrounds, in the sense of Wands' duality, are reflected in real-space quantum correlations of primordial perturbations. Using the continuous-variable Gaussian formalism for coarse-grained scalar fluctuations, we construct the covariance matrix of a pair of spatially localized modes in inflationary spacetime, and extract the symplectic invariants of the system. For a generic Wands-dual pair of backgrounds, we find that while the individual entries of the covariance matrix are highly background-dependent, the symplectic eigenvalues -- and hence the entanglement entropy, mutual information, quantum discord and log-negativity -- all coincide for the two dual realizations. Our results unveil a new ''quantum-informatic symmetry'' of the de Sitter vacuum, according to which local linear entanglement witnesses constructed from coarse-grained fields cannot distinguish between Wands-dual inflationary histories, even though their background trajectories differ. We show that the special nature of the Wands-duality symmetry (of being local, scale-independent canonical transformations) is at the heart of this duality.

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gr-qc 2026-07-02

Modified gravity object relaxes without ringdown

by Gianmassimo Tasinato

Relaxation without ringdown for a compact object in modified gravity

Odd-parity perturbations follow one-way transport; black-hole limit erases the modes rather than creating them.

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Compact objects with black-hole-like exteriors may hide new strong-field physics in their interiors, making their dynamical response a sensitive probe of gravity beyond General Relativity. We present an analytically tractable, gravitationally bound compact object with a genuinely new dynamical signature: under a minimal passive boundary prescription, its exactly controlled odd-parity sector exhibits purely dissipative relaxation poles, rather than the oscillatory modes usually associated with black holes and exotic compact alternatives. The object we study is a regular, vector-supported compact solution of a vector--tensor theory, matched without any surface layer to an exterior Schwarzschild geometry. Owing to its anisotropic stress, it can violate the Buchdahl bound and be continuously connected to the black-hole compactness limit. Its unusual response follows from a hidden chiral symmetry, which turns the perturbation problem into one-way transport rather than ordinary wave propagation. The exterior region alone has no conventional quasinormal-mode spectrum; instead, the regular interior and the matching conditions break the symmetry and quantize the fluctuation spectrum. We analytically compute the retarded Green function and susceptibility, and derive an effective membrane response by integrating out the object's interior. In the black-hole limit, the relaxation times diverge, the poles collapse toward zero frequency, and finite-frequency exterior perturbations decouple from the interior. Black-hole behaviour is therefore approached through the disappearance of relaxation modes, not through the emergence of ringdown.

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gr-qc 2026-07-02

Boosts lock scalar amplitudes in five-dof gravitational waves

by Jie Zhu, Hao Li

Reference Frames and Gravitational-Wave Polarizations: Symmetry Classification and Preferred-Frame Phenomenology

Preferred-frame theories add vector-to-tensor conversion for moving observers

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Gravitational wave (GW) polarizations are traditionally classified in a fixed frame ($E(2)$ classification), which does not account for how polarization patterns change under Lorentz boosts. In this work, we derive the explicit transformation laws for all six GW polarizations under longitudinal and transverse boosts. For gravity theories devoid of preferred frames, we propose a symmetry-based classification of the GW polarizations they admit. Among our key findings, we demonstrate that a propagating mode with five degrees of freedom strictly locks its longitudinal and breathing scalar amplitudes via the universal relation $A_l/A_b = -2(1-k^2/\omega^2)$. For theories with a preferred frame, we analyze Bumblebee gravity and reveal that preferred-frame effects induce significant GW birefringence and observer-dependent polarization mixing. Crucially, we identify a novel vector-to-tensor polarization conversion mechanism, where vector modes in the preferred frame inevitably generate observable tensor polarizations for moving detectors, offering a new pathway to test Lorentz-violating gravity. Our framework provides a novel, observer-independent classification of GW polarizations and reveals previously unnoticed polarization mixing effects.

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gr-qc 2026-07-02

Spinning particles show rotation quenches charge chaos violations

by Deyou Chen, Chuang Yang +1 more

Probing the chaos bound via spinning particles in Kerr-Newman-AdS spacetime

In Kerr-Newman-AdS, prograde rotation stabilizes against charge while negative Lambda promotes chaos through particle spin coupling.

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In this paper, we employ spinning test particles as probes to investigate the regulatory effects of particle and black hole parameters on the violation of the chaos bound in Kerr-Newman-AdS spacetime. Our results demonstrate that the chaos bound violation is governed by the interplay of spacetime geometry, electromagnetic forces, and particle dynamics. The particle spin modulates the direction dependence and parameter thresholds of the violation through its coupling with the orbital angular momentum, which contributes to the total angular momentum. The negative cosmological constant acts as a potential well: a larger value enhances the chaotic behavior. A competitive coupling exists between the black hole rotation and charge -- its prograde rotation exerts a stabilizing effect that can suppress or even completely quench charge-driven violations, while the charge serves as a condition for triggering the violation, with its effect modulated by the spin stabilization. In the Kerr-AdS limit, the violation occurs only when the black hole rotates opposite to the $z$-axis with a sufficiently large rotation parameter and a sufficiently small cosmological constant. In the RN-AdS limit, the violation condition is jointly determined by the charge and the cosmological constant, with electromagnetic repulsion more readily inducing the violation than electromagnetic attraction.

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gr-qc 2026-07-02

Unified hoop conjecture holds for braneworld black holes

by A. Bhattacharya, R. N. Izmailov +1 more

Comments on the non-existence of unified hoop conjecture

Tidal charged 4D string theory solutions satisfy it for static and spinning cases using the same quasi-local mass.

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In a recent article, Hod [1] has concluded the non-existence, heretofore unnoticed, of a unified Thorne's hoop conjecture that holds for the quasi-local mass, $\mathcal{M}(r\leq R_{+})$ for static Reissner-Nordstr\H{o}m black hole, but does not hold for the spinning electrically charged Kerr-Newman black holes, when the same quasi-local mass is used. While the conclusion is correct and important, we wish to point out a curious exception for which the conjecture holds in a unified way for both the static and spinning \textit{tidal} charged $4d$ braneworld black holes of string theory, when the mass in the conjecture is the same quasi-local mass.

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gr-qc 2026-07-02

Wormholes mimic black hole accretion even at λ ~1

by R. M. Yusupova, R. Kh. Karimov +1 more

Bondi Accretion onto a Damour-Solodukhin Wormhole

Bondi profiles near the horizon match Schwarzschild cases for Damour-Solodukhin parameter values of order 1.

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The Damour-Solodukhin wormhole (hereinafter DSWH) is known to mimic Schwarzschild black hole (hereinafter SBH) horizon in some properties. To act as a mimicker, the DSWH parameter $\lambda$ by definition is required to be extremely tiny, i.e., $\lambda \sim 0$. Our comparative analyses show that such a requirement may be too restrictive at least as far as the Bondi accretion profiles of the two objects, the DSWH and SBH, are concerned. Intriguingly, it turns out that some profiles of DSWH mimic those for the SBH near the horizon even at values of $\lambda$ considerably higher, i.e., $\lambda \sim 1$.

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gr-qc 2026-07-01

Signature change produces geometric inflation

by Raghvendra Singh, Sergey Bondarenko

Inflation from Covariant Signature Change: A Geometric Mechanism

A covariant Euclidean-to-Lorentzian transition yields accelerated expansion via a localized effective source, with a model-independent end c

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We present a covariant mechanism in which a smooth change of metric signature, from a Euclidean to a Lorentzian regime, drives a finite interval of accelerated expansion. The transition, encoded by a scalar interpolator along a timelike congruence, occurs on a codimension-one hypersurface where the continued metric is degenerate but curvature invariants remain finite, so the surface is curvature-regular. Using this covariant continuation, we rewrite the Einstein tensor of the continued metric as a localized, interpolator-dependent effective source for the post-transition Lorentzian branch, yielding a purely geometric stress tensor supported near the crossing. In the Lorentzian regime, we derive a model-independent, local criterion for acceleration: inflation persists while the interpolator's slope exceeds a critical value fixed by the extrinsic curvature and the spatial Ricci curvature on the initial hypersurface, and ends when this inequality is first saturated. Standard smooth profiles (tanh, generalized logistic, and power-law/arctan) admit closed-form expressions for the proper-time duration of the accelerated epoch, showing that, for fixed geometric data, the profile shape controls this duration. The construction provides a non-singular, inflaton-free route from a regular Euclidean origin to an early Lorentzian phase of accelerated expansion, in a manner compatible with no--boundary--type boundary conditions.

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gr-qc 2026-07-01

f(T,B) gravity fits CC+PPS data better than ΛCDM

by Laxmipriya Pati, Santosh V. Lohakare +1 more

Cosmological implications of f(T, B) gravity: constraints from recent observations

Power-law model shows phantom crossing and moves H0 closer to local values in MCMC fits to chronometers and supernovae.

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In this work, we examine the theoretical framework of modified teleparallel gravity with the inclusion of the boundary term in the action and investigate its cosmological implications by considering the power-law model $f(T, B) = -T + \alpha (-B)^{\beta}$, with the aim of addressing the late-time accelerated expansion and the dark energy. In this context, $T$ denotes the torsion scalar and $B$ represents the boundary term, whose presence allows for departures from standard teleparallel dynamics and provides a unified description that connects torsion and curvature-based formulations, reproducing $f(T)$ and $f(R)$ gravity in appropriate limits. The viability of the model is assessed by confronting its theoretical predictions with observational data while constraining the cosmological and model parameters through a Markov Chain Monte Carlo (MCMC) analysis using cosmic chronometers (CC), the Pantheon Plus sample (PPS), and the DESI baryon acoustic oscillation (BAO) Data Release 2 (DR2) datasets, and comparing its performance with the standard $\Lambda$CDM model. The Akaike Information Criterion (AIC) analysis shows that the combined CC+PPS dataset strongly favors the $f(T, B)$ model, suggesting an improved phenomenological fit to late-time observations relative to $\Lambda$CDM. Our result further shows an alleviation of H0 tensions, although a dedicated analysis is required to establish its full statistical significance. Furthermore, the background cosmological quantities indicate that the model exhibits a dynamical phantom-divide crossing while remaining consistent with late-time observations and yielding a viable expansion history and characteristic dark energy evolution.

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gr-qc 2026-07-01

Bouncing coupled dark matter produces scale-invariant fluctuations

by Samuele Silveravalle, Andrea Lapi +2 more

Cosmology with a Non-minimally Coupled Dark Matter Fluid II. Cosmological Perturbations

Fluctuations generated in the pre-bounce contraction match observations without extra scalar fields or blue-tilted spectra.

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We extend our study of a cosmological scenario in which dark matter is non-minimally coupled to gravity at the fluid level. In previous work, we showed that this interaction can drive an early phase of accelerated expansion, addressing the horizon and flatness problems, and can also lead to a cosmological bounce in the presence of spatial curvature. Here we analyse the evolution of linear perturbations in this framework. We derive the equations governing scalar, vector and tensor perturbations, and obtain analytic solutions in the relevant cosmological regimes. We find that perturbations generated during the accelerated expansion phase produce a strongly blue scalar power spectrum and are therefore incompatible with observations. By contrast, in bouncing solutions primordial fluctuations can originate during the contracting phase before the bounce. In this case, the model yields an approximately scale-invariant scalar power spectrum while keeping the tensor-to-scalar ratio compatible with current bounds, without introducing additional scalar fields. Although our treatment relies on simplifying approximations that should be refined in future work, these results indicate that non-minimally coupled dark matter may provide a viable alternative mechanism for the generation of primordial cosmological perturbations.

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gr-qc 2026-07-01

Viable horizon entropies confined near standard area law

by Pranav Prasanthan (1), Hussain Gohar (1) +4 more

Modified Cosmology from Mass-to-Horizon Relation: Background Evolution

Background evolution rules out large deviations and keeps all surviving models LambdaCDM-like today

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We investigate the cosmological implications of the mass-to-horizon relation, which provides a unified framework for thermodynamically consistent generalized horizon-entropy functionals. Using the Cai-Kim formulation of the first law of thermodynamics, we derive the corresponding modified Friedmann equations and examine the resulting background evolution. We find that cosmological viability sharply restricts admissible deviations from the Bekenstein-Hawking area law: phenomenologically acceptable scenarios are confined to a narrow neighborhood of the standard entropy, while more pronounced deviations generically spoil the standard radiation-matter-dark-energy sequence. Power-law entanglement corrections can give rise to a moderate early-dark-energy component, but only within a tightly constrained region of parameter space, whereas quantum-gravity corrections are suppressed by the Planck scale and remain observationally irrelevant. Consequently, all viable models predict a $\Lambda$CDM-like cosmological background at the present epoch. These findings demonstrate that background cosmology alone imposes stringent constraints on thermodynamically consistent generalized entropy constructions of this class.

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hep-th 2026-07-01

Four-derivative theory stays unitary via hidden ghost parity

by Sam Bateman, Neil Turok

Escape from Ostrogradsky via Hidden Ghost Parity

Embedding the model in a two-field O(1,1) theory reveals a symmetry that keeps tree-level probabilities positive.

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We present a counterexample to Ostrogradsky's famous "no go" theorem as usually interpreted in quantum field theory (QFT), namely a four-derivative, UV-complete QFT with a consistent perturbative expansion which describes high energy scattering processes. We carefully quantize the theory on an $\textit{indefinite}$ space of states - a Krein space - using covariant methods which ensure perturbative causality and unitarity (in the form of the optical theorem) to all orders. We generalize the Born rule to Krein spaces and prove that all tree level transition probabilities are positive in spite of the presence of ghosts. A key role in the proof is played by a hidden "ghost parity" symmetry which becomes explicit when the theory is embedded in a two-derivative, two-field $O(1,1)$-symmetric perturbative field theory.

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astro-ph.HE 2026-07-01

Double polytrope fits neutron star data with max mass 2.45 solar masses

by Tian-Shun Chen, Xiao-Ding Zhou +1 more

An Analytical Toy Equation of State for Neutron Stars Consistent with Current Observations

Analytic models give 11.3 km radius and tidal deformability 485-512 while staying causal.

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Fast analytic and semi-analytic studies of neutron stars often require an equation of state that is convenient to evaluate while producing relativistic stellar sequences compatible with current multimessenger constraints. We construct such a benchmark by scanning a smooth double polytropic relation for the energy density as a function of pressure, $\hat\epsilon (\hat p)=a_1\hat p^{\Gamma_1}+a_2\hat p^{\Gamma_2}$. The parameters are selected with filters based on massive pulsars, tidal deformability from the binary-neutron-star event GW170817, and NICER mass-radius measurements. A single polytropic baseline scan finds no model passing all filters, whereas a double-polytrope scan identifies a viable region. A curve-integral score, evaluated against public NICER and GW170817 posterior data sets, is then used to choose benchmark equations of state within this region. The selected representatives support $M_{\max}=2.44$--$2.49\,M_\odot$, with $R_{1.4}\simeq 11.3$ km and $\Lambda_{1.4}=485$--$512$, and remain causal on the stable branch. This compact analytic family provides reference cases for relativistic stellar-structure tests at current observational scales.

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gr-qc 2026-07-01

Gravitational wave turns static charge field into electromagnetic radiator

by Vladimir Epp, Konstantin Osetrin +1 more

Electromagnetic radiation from a point-like charge in a weak gravitational wave: a Shapiro-delay-motivated approach

The initially Coulomb field becomes time-dependent and radiates with an angular pattern derived from first-order potentials for any polariza

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We investigate the field of a point-like electric charge freely falling in a gravitational wave. In the presence of a gravitational wave, the initially static Coulomb field of the charge becomes time-dependent and generates corresponding radiation. The gravitational wave is treated as a weak perturbation of the Minkowski metric. The electromagnetic four-potential of the charge is sought as a solution to Maxwell's equations in the gravitational wave metric, to first order in perturbation theory. The potentials of the point charge are found in quadratures throughout the space. To regularize the potentials, an approach motivated by the Shapiro effect for the time delay of radiation in a gravitational field is used. The potentials of the charge in the far zone are calculated explicitly for a monochromatic, arbitrarily polarized gravitational wave. The angular distribution of the electromagnetic radiation induced by the gravitational wave is obtained.

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astro-ph.CO 2026-07-01

LSS probes raise dark energy perturbation FoM by factor 2.69

by Neel Shah, Kazuya Koyama +2 more

Constraining dark energy with complementary probes of large-scale structure

DESI RSD, DES 3x2pt and ISW data tighten EFTofDE constraints on c_B and c_M when added to CMB+BAO+SNe.

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To observationally pin down the nature of dark energy, it is essential to consistently model cosmological perturbations in the presence of dark energy alongside the background expansion and constrain this joint theory space with a large array of complementary probes. Here, we achieve this by constraining a model in the Effective Field Theory of Dark Energy (EFTofDE) framework by supplementing probes of the expansion history with several probes of large-scale structure: redshift space distortions (RSD) from DESI DR1, $3\times2$pt measurements from DES Y3, and the Integrated Sachs-Wolfe effect from cross-correlating CMB temperature anisotropies with galaxy number counts or CMB lensing. We demonstrate the complementarity of different probes which leads to strong improvements on constraints on DE perturbations. For our most constraining dataset combination that supplements CMB+BAO+SNe probes with DESI DR1 RSD, DES Y3 $3\times2$pt and ISW cross-correlations between CMB temperature and galaxy counts, we find an improvement in the Figure of Merit (FoM) for the DE perturbation parameters $\{c_B, c_M\}$ by a factor of 2.69. We show the phenomenological implications of these constraints by mapping them to the present-day values of the phenomenological functions $\{\mu(z), \Sigma(z)\}$, where we see an FoM improvement by a factor of 3.37. We find a significant interdependence between the posteriors of $\{w_0, w_a\}$ and $\{c_B, c_M\}$, caused by the theoretical prior imposed by the gradient stability condition within the EFTofDE framework. Finally, we compute the significance of deviation from $\Lambda$CM for the EFTofDE model when constrained with CMB+BAO+SNe datasets, finding it to be at 2.9$\sigma$. This significance is nontrivially similar to the significance for the $w_0w_a$CDM model for the same dataset combination which we find to be 3.1$\sigma$.

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hep-ph 2026-07-01

Monopole scaling networks yield broad-mass primordial black holes

by Daiki Aburatani, Wakutaka Nakano +1 more

PBHs and GWs from Scaling Monopoles

Stochastic number fluctuations in Hubble patches drive overdensities when v exceeds 0.1 Planck mass, also producing correlated gravitational

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Monopoles with sufficiently weak gauge couplings, or from global symmetries, can form scaling networks in the early Universe whose average energy density tracks the cosmological background. In this work, we find, by performing classical lattice simulations to estimate the overdensities, that primordial black holes (PBHs) with a broad mass spectrum can be produced during this evolution if the Higgs expectation value $v$ satisfies $v\gtrsim 0.1 M_{\rm pl}$. The formation is driven by the stochastic realization of the monopole number in Hubble patches causing the overdensities. We also show that gravitational waves (GWs) generated by the scaling dynamics are produced at the same epoch, with spectra correlated with the PBH spectra and with amplitudes testable in future observations. Interestingly, if the scaling regime is terminated by the gauge boson mass for the gauged monopole, a non-negligible fraction of the PBHs can carry magnetic charge, and the resulting magnetic Coulomb force between such charged PBHs is predicted to be comparable to the gravitational force. Together with the PBH and GW signals, this provides a smoking-gun signature of the scenario. We also point out simple cosmological scenarios, which may also apply to PBH formation from scaling cosmic strings, that allow PBHs to constitute dominant dark matter.

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hep-th 2026-07-01

Matrix model singularities vanish beyond double scaling

by Sumit R. Das, Shaun D. Hampton +2 more

Fate of "Space-like singularities" in c=1 Matrix Model

Quenches retaining non-linear terms cause phase space folds to proliferate then relax to equilibrium with universal power law.

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A class of time dependent backgrounds in two dimensional String Theory leads to superluminal Liouville walls on the worldsheet. In the dual double scaled $c=1$ matrix model these backgrounds involve eigenvalues leaking out to infinity, and the collective field fluctuations become strongly coupled along space-like regions, resembling singularities. We realize these backgrounds as results of quantum quenches in the matrix model, retaining non-linear terms in the matrix potential, thus departing from a double scaling limit. Working in the fermion picture in a Thomas-Fermi approximation, we show that while the early time behavior of the phase space density near the maximum of the potential agrees with that obtained in the double scaled theory, at times of the order $(\log N)$ the effect of the IR wall becomes significant. At later times, with a characteristic winding time of order $(\log N)^2$, folds on the fermi surface proliferate and eventually cover the allowed region in phase space densely. Using action-angle variables, we show that the phase space density oscillates around a time independent and angle independent value rapidly at late times. A coarse-grained density in the angle space relaxes to a time independent equilibrium value as a power law with a universal exponent largely independent of the details of the initial state. Thus, the appearance of a space-like singularity is an artifact of the strict double scaling limit. We comment on the interpretation of the final state in String Theory.

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hep-th 2026-07-01

Exact black brane solution recovers conformal fluid in IR

by Sangheon Yun

Exact Planar Black Hole in AdS-Einstein-Scalar Gravity with IR Emergent Nearly Conformal Fluid

The dual three-dimensional QFT breaks scale symmetry at high energies through a marginally relevant operator but approaches conformal behavi

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We study an exact analytic solution describing a static plane-symmetric hairy black brane in four-dimensional Einstein gravity minimally coupled to a neutral scalar, arising as a consistent truncation of the type IIA supergravity whose low-energy limit captures the strongly coupled thermal dynamics of the ABJM theory. The solution is characterized by two independent parameters. We perform the thermodynamic description by treating the scalar hair parameter as an independent variable, deriving the generalized first law and verifying the Euler relation. The UV boundary theory is a three-dimensional QFT at finite temperature deformed by a marginally relevant scalar operator with logarithmic RG flow. The boundary theory exhibits explicit scale-symmetry breaking at high energies but recovers the behavior of a conformal fluid in the infrared thermal limit.

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hep-ph 2026-07-01

Particle physics explains the Universe's birth and evolution

by Venus Keus

Particle Cosmology

The early Universe functions as a natural laboratory revealing fundamental laws through observations like the CMB and theories such as infla

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Particle cosmology is the branch of science that seeks to understand the birth and evolution of the Universe by applying the principles of particle physics. It brings together the physics of the very small (fundamental particles and forces) with the physics of the very large (the structure and evolution of the cosmos). In many ways, the early Universe acts as a natural laboratory - one far more energetic than any collider we can build - offering unique insights into phenomena that may never be accessible on Earth. Cosmological observations such as the Cosmic Microwave Background, the distribution of galaxies, and the accelerating expansion of the Universe serve as windows into the fundamental laws of nature. At the same time, theoretical developments in particle physics have led to theories, such as inflation, baryogenesis, and Dark Matter, that help explain key features of the cosmos.

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astro-ph.HE 2026-07-01

Carbon-alpha rate shifts upper black hole mass gap edge by 30 solar masses

by Jeremy Sakstein, Djuna Croon

The location of the upper edge of the pair-instability supernovae black hole mass gap

Simulations identify the 12C(α,γ)16O reaction as the largest source of uncertainty in where pair-instability supernovae cut off black hole f

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Gravitational wave observations are beginning to probe the upper edge of the pair-instability supernova (PISN) black hole mass gap, a key prediction of stellar evolution. In this work, we quantify the sensitivity of this boundary to uncertainties in stellar evolution using a suite of simulations that vary inputs including nuclear reaction rates, mixing processes, and stellar winds. We find that the $^{12}{\rm C}(\alpha,\gamma)^{16}{\rm O}$ reaction rate is the dominant source of uncertainty, shifting the upper edge by $\Delta M\sim30\,{\rm M}_\odot$, with the triple-$\alpha$ rate producing a comparable shift of $\sim25\,{\rm M}_\odot$. Notably, $^{16}{\rm O}+^{16}{\rm O}$ reactions shift the upper edge by $\sim15\,{\rm M}_\odot$ while leaving the lower edge unchanged, implying they can widen or narrow the mass gap. Other processes affect the location at the $\lesssim10\,{\rm M}_\odot$ level. In contrast to the lower edge, we find that the upper edge is robust to variations in spatial and temporal resolution, indicating that it is reliably resolved in current simulations. Our results demonstrate that the upper edge carries substantial theoretical uncertainty and, while comparatively less affected by astrophysical contamination than the lower edge, provides a direct probe of the nuclear processes governing pair instability. We discuss the implications for interpreting high-mass black hole detections in gravitational wave data.

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gr-qc 2026-07-01

Photon sphere stays at Schwarzschild radius in regular DBI black holes

by Mardon Abdullaev, Gumisbek Allambergenov +3 more

Eikonal Ringing, Shadows, Lensing, Grey-Body Factors, and Binding Energy of Asymptotically Flat Regular Black Holes in Phantom Dirac-Born-Infeld Gravity

Eikonal QNMs, shadows, GBFs and lensing all collapse to one core-size function; ISCO binding efficiency falls with larger core

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We develop a geodesic-optics description of eikonal quasinormal ringing, blackhole shadows, strong lensing, grey-body factors (GBFs), and the binding energy of massive particles for the asymptotically flat regular black-hole geometry obtained in phantom Dirac-Born-Infeld (DBI) gravity. The null-orbit structure admits an especially compact analytic treatment. The unstable photon orbit remains at the Schwarzschild-like coordinate radius throughout the black-hole branch, while the orbital frequency and Lyapunov exponent coincide exactly. Consequently, eikonal quasinormal modes (QNMs), shadow radius, GBFs, and strong-deflection observables are all governed by a single dimensionless function of the core-size parameter. For timelike circular motion, we derive exact expressions for the specific energy and angular momentum, obtain the innermost stable circular orbit (ISCO) condition in closed implicit form, and show that the ISCO binding efficiency decreases as the regular core grows. We present illustrative plots for the exact geodesic invariants, the corresponding grey-body profiles, and the timelike binding-energy curves. The resulting construction provides an exact one-parameter bridge between the regular black-hole metric and its leading geodesic observables.

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quant-ph 2026-07-01

Frame dragging generates gravity-induced entanglement phase

by Eyuri Wakakuwa, Luciano Petruzziello +3 more

Relativistic Gravity-Induced Entanglement via Frame Dragging

Two independent calculations agree on a phase equal to proper-time difference and modified by retardation, extending tests to post-Newtonian

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Gravity-induced entanglement has been proposed as a method for testing the non-classical nature of gravity via tabletop experiments. While most existing proposals are restricted to the Newtonian limit, the frame dragging effect offers access to genuinely post-Newtonian features of the gravitational interaction and remains comparatively less explored. Here, we study gravity-induced entanglement generated by frame dragging in an interferometric setting and compute the entanglement phase between the rotational degrees of freedom of a source mass and the paths of a particle in two complementary ways: (i) via Schr\"odinger evolution with a quantized Lense-Thirring Hamiltonian in the large angular momentum limit, and (ii) via the on-shell action of linearized quantum gravity within the stationary phase approximation. Both approaches yield the same entanglement phase, consistent with the proper time difference between the interferometer arms. The path integral derivation further reveals how gravitational retardation modifies the entanglement phase, thereby making the local, relativistically causal linearized-gravity description explicit. Under the standard locality/mediator assumptions used in existing arguments, the resulting entanglement would witness non-classicality of the gravitational interaction.

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astro-ph.CO 2026-07-01

One percent PBHs change ULDM soliton participation by twenty percent

by Xing-Yu Yang

Ultralight dark matter mixed with primordial black holes

Continuum background effect dominates while discrete fluctuations take 10 billion years to act on galactic halos.

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Dark matter candidates span many orders of magnitude in mass, from ultralight bosonic fields to massive compact objects. In this work, we connect these two extremes by investigating ultralight dark matter (ULDM) mixed with primordial black holes (PBHs). We study mixed ULDM-PBH halos by separating the continuum PBH contribution from the shot-noise fluctuation generated by discrete PBHs. The continuum contribution enters the averaged Schr\"odinger-Poisson background, while the discreteness contribution is treated as a perturbation that induces ULDM eigenmode transitions and soliton heating. The two contributions have distinct parametric dependencies: continuum effects scale with PBH fraction, whereas discreteness-driven transition rates scale with the product of PBH fraction and individual PBH mass in the perturbative regime. For a fiducial mixed halo with ULDM particle mass $10^{-22}\,\mathrm{eV}$, virial mass of order $10^{10}\,M_{\odot}$, and PBH fraction $1\%$, the continuum PBH component modifies the background density, gravitational potential, and low-lying ULDM eigenvalues only at the sub-percent level. Nevertheless, this percent-level continuum PBH contribution produces a tens-of-percent response in the coherent soliton region, changing the radial mode participation by about $20\%$. For stellar-mass PBHs, the discrete shot-noise fluctuation induces extremely slow ULDM mode transitions, with the fastest low-lying multiplet transition having a timescale of order $10^9\,\mathrm{Gyr}$ for solar-mass PBHs. In this regime, the leading PBH effect is the continuum contribution, while discrete PBH shot noise is dynamically negligible on galactic timescales.

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hep-th 2026-07-01

Higher curvature raises KK graviton masses in warped models

by Abhirup Karmakar, Isika Mandal +1 more

Kaluza-Klein Gravitons in a Higher Curvature Warped Geometry : A New Perspective

Masses shift upward, virtual production cross sections drop, and dilepton plus diphoton decay widths grow compared with Einstein gravity alo

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Kaluza-Klein (KK) Gravitons are the direct collider imprints of the higher dimensional bulk physics in our four dimensional universe, arising from the compactification of an extra spatial dimension. In this work, we consider a two-brane warped geometry with a 5D $f(\mathcal R) = \mathcal R + \alpha\mathcal R^2$ gravity along with cosmological constant $\Lambda$. The warped spacetime provides an elegant resolution of the gauge-hierarchy problem without introducing any intermediate scale, while the Planck-scale curvature of the underlying $AdS_5$ bulk naturally motivates the inclusion of higher-curvature corrections. For small values of higher-curvature parameter ($\alpha$), we obtain the leading-order back-reacted warp factors perturbatively from the modified gravitational field equations. In the backdrop of a warped braneworld model, we have solved the Schr\"odinger-like equation governing the graviton fluctuations using a Euclidean path integral formalism, yielding the KK graviton spectrum and normalized wavefunctions directly from the corresponding quantum-mechanical propagator. Treating these results as the unperturbed background, we analytically determine the higher curvature corrections to KK graviton spectrum and their couplings to Standard Model (SM) matter fields. We find that there is an appreciable upward shift in the KK graviton masses while leaving the graviton-SM couplings only mildly modified as compared to a model with only Einstein gravity in the bulk. However the net cross-section of processes involving virtual gravitons appears to be suppressed whereas the dilepton and diphoton decay widths of the gravitons are significantly enhanced because of the higher curvature corrections. Overall, these effects lead to observable modifications to both the production and decay signatures of massive KK gravitons and may be probed in some future precision collider experiments.

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physics.hist-ph 2026-07-01

Quantum dynamics block spacetime emergence from non-spatiotemporal stuff

by Álvaro Mozota Frauca

The Dynamics of Quantum Gravity: the Missing Piece in the Spacetime Emergentist Account

Current theories leave their dynamical quantum aspects uninterpreted, so functionalism cannot reduce spacetime.

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Quantum gravity suggests that spacetime may not be fundamental, and it has been argued that we can understand a theory without a fundamental spacetime if we are able to claim that spacetime `emerges' from some non-spatiotemporal entities. In this sense, strategies like functionalism have been deployed to claim that this emergence is possible and plausible, both in principle and in practice for current approaches to quantum gravity. In this article I argue that this analysis is incomplete, as it tends to overlook the way the dynamics of these theories is `quantum' in a way that differs from standard quantum theory. The challenge for the emergentist (and for the quantum gravity theorist) is to give an interpretation not only to the kinematical and classical aspects of these theories, but to the dynamical and quantum ones, and to show how the spacetime roles can be fulfilled, if possible at all. Therefore, I argue that some current approaches to quantum gravity seem to fail to provide meaningful theories, that spacetime functionalism is of no help, and that the position of the spacetime emergentists is weakened, as they lack any example of a successful reduction of spacetime to some truly quantum non-spatiotemporal stuff.

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gr-qc 2026-07-01

Lensed GW signals recover globular cluster velocity dispersion

by Sreekanth Harikumar, Abbas Askar +4 more

Probing globular clusters parameters through gravitational wave lensing with stellar-mass black hole binaries

Wave-optics effects allow estimation of central velocity dispersion when the effective lensing mass is combined with sky localization data.

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Globular clusters (GCs) can act as gravitational lenses for gravitational waves(GWs) in the wave-optics regime, imprinting frequency-dependent signatures on the observed signal. We investigate whether such lensing effects can be used to probe intrinsic properties of GCs, in particular their central velocity dispersion. Modeling GCs as singular isothermal spheres, we simulate lensed GW150914-like signals and perform Bayesian parameter estimation using waveform templates that include both source and lens parameters. We show that the effective lensing mass can be recovered and, when combined with GW sky localization information and GC catalogs, allows for an estimate of the cluster velocity dispersion. For favorable source-lens alignments, the injected values are well recovered within credible intervals. Our results demonstrate that lensed GWs can provide a complementary probe of GC dynamics and motivate searches for such signatures in current and future observations.

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gr-qc 2026-07-01

Scale-invariant cosmologies require non-zero cosmological constant

by Chiara Cecchini, Massimiliano Rinaldi

The unavoidable de Sitter fate of a scale-invariant Universe

Unless the scalar field's quartic coupling vanishes exactly, a condition quantum effects do not protect.

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We consider a very general scale-invariant scalar-tensor theory of gravity and its flat cosmological solutions. We show that any stable configuration with non-degenerate gravitational dynamics carries a non-vanishing cosmological constant, unless the quartic self-coupling of the scalar field vanishes. Since this condition is not protected against radiative corrections, a residual cosmological constant is expected as a generic and robust prediction of this class of theories. This result suggests that dark energy may be a natural consequence of an early scale-invariant phase of the Universe.

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gr-qc 2026-07-01

GWTC-3 signals match black-hole compactness of 0.5

by Shrobana Ghosh, Charlie Hoy +2 more

Establishing Compactness as a Population Observable in Gravitational-Wave Astronomy

Hierarchical analysis of all high-significance events limits exotic low-compactness mergers to under 0.7 Gpc^{-3} yr^{-1}

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Classically, black holes (BHs) are the most compact objects predicted in nature with C=0.5 in the Schwarzschild limit; C is defined as the mass-to-radius ratio in geometric units. In this work we perform a novel measurement on the nature of putative BH mergers in the gravitational wave (GW) data by directly probing the binary's closest approach through an effective compactness parameter. We confidently show all such high-significance signals in GWTC-3 are consistent with the BH hypothesis for the first time. Our hierarchical analysis yields $C_{\rm eff} = 0.5^{+0.3}_{-0.1}$, and we further limit the merger rate of low-compactness exotic binaries to $< 0.7\,{\rm Gpc}^{-3}\,{\rm yr}^{-1}$. This work establishes compactness as a key observable in GW astronomy.

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astro-ph.CO 2026-07-01

EDE raises α_s, tightening tension for USR PBH models

by Miguel A. Sabogal, Antonio J. Iovino +1 more

Running into tension: primordial black holes from ultra-slow-roll inflation, spectral running, and the Hubble tension

Solutions to the Hubble tension that alter pre-recombination expansion also push the inferred spectral running upward, disfavoring negative-

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Single-field ultra-slow-roll (USR) inflation is among the most studied mechanisms for primordial black hole (PBH) formation. These models predict a negative spectral running ($\alpha_s<0$), whose magnitude increases with the PBH mass. This is in tension with recent hints for positive running from Atacama Cosmology Telescope (ACT) Cosmic Microwave Background (CMB) data. However, inflationary parameters inferred from CMB data are sensitive to the assumed pre-recombination expansion history, which is precisely where new physics motivated by the Hubble tension should operate. Focusing on axion-like early dark energy (EDE) as a benchmark, we investigate the effect of such pre-recombination new physics on $\alpha_s$, and hence on the viability of USR PBH models, in light of state-of-the-art CMB data from Planck, ACT, and the South Pole Telescope, together with Baryon Acoustic Oscillation data from DESI DR2. Our analysis therefore provides an updated set of constraints on $\alpha_s$ and the running of the running $\beta_s$. For most dataset combinations, moving from $\Lambda$CDM to EDE increases the inferred $\alpha_s$: once the acoustic angular scale $\theta_s$ is fixed, EDE increases the diffusion-to-acoustic angular scale ratio $\theta_d/\theta_s$, and the shift in $\alpha_s$ compensates this extra damping by increasing small-scale power. In this sense, tension calls for tension: taking the Hubble tension seriously as an indication for new physics strengthens the challenges faced by USR PBH models. More broadly, our analysis stresses that inflationary model selection using CMB-inferred inflationary parameters such as $n_s$ and $\alpha_s$ may be premature, especially until the Hubble tension, and more generally the pre-recombination expansion history, is understood.

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gr-qc 2026-07-01

GWTC-3 mergers match black hole model after noise check

by Shrobana Ghosh, Charlie Hoy +2 more

Compactness Inference in Gravitational-Wave Mergers with PhenomDECO: Catalog Benchmarks and Robustness Diagnostics

Compactness tests find all but one high-mass event consistent with standard BBH sources once low-frequency data are excluded.

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Several gravitational wave (GW) observations have been identified as binary black hole (BBH) mergers, including systems with component masses that challenge typical formation scenarios. These observations motivate broader tests of whether the detected sources are consistent with this interpretation. We address this question using~\deco~, an existing phenomenological extension of a BBH model that uses an effective compactness parameter to characterize departures from the expected merger morphology. Applying this model to all high-significance BBH events from GWTC-3, we establish~\deco~as a robust test of the nature of compact binaries. In preliminary analyses we identify three recurring posterior morphologies: (i) near-Gaussian peaks consistent with the BBH expectation $C\sim0.5$, seen in 60\% of events; (ii) posteriors with additional high-compactness support $(C\ge0.8)$; and (iii) dominant low-compactness modes near $C\sim0.15$ in $\sim 20\%$ of cases. For the latter, the low-compactness modes disappear when the data, especially from Livingston, are analyzed from a higher starting frequency, indicating sensitivity to low-frequency noise artefacts. We further use time--frequency residuals, computed after subtracting maximum-likelihood BBH and~\deco~waveforms from the strain data, to assess if the data is better described by a compactness-based deformation. With this analysis, we conclude that all of the GWTC-3 observations that we have considered are indeed consistent with BBH sources. The exception is the high-mass GW231123 signal, for which data from \emph{both} detectors must be analyzed above 50Hz to remove a low-compactness mode. This study shows that low-frequency data treatment is crucial before attributing apparent deviations from BBH expectations to exotic physics, and provides a benchmark for compactness-based tests of merger morphology in current and future GW detections.

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hep-th 2026-07-01

Ghost-free f(R) branes lack narrow tensor resonances

by Xin-Yi Pan, Heng Guo +2 more

Two-scalar-field f(R) Thick Branes, Gravitational Resonances and Quasinormal Modes

Spectra show only broad dissipative modes; real peaks require vanishing effective coupling

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In this paper, we investigate thick brane worlds in $f(R)$ gravity supported by two-scalar-field. The two-scalar sector provides an analytical warped background with tunable energy-density splitting, allowing us to test whether a Bloch-type internal structure can generate long-lived tensor perturbations resonances in the physically admissible region. We impose the positivity of $f_R\equiv df/dR$, the derivative of the gravitational Lagrangian with respect to the Ricci scalar, which plays the role of an effective gravitational coupling in $f(R)$ gravity. This separates the smooth ghost-free branch from a singular branch where this effective coupling vanishes. In the ghost-free branch, neither the relative-probability spectrum nor the phase-shift transmission spectrum shows narrow real-axis resonant peaks. These real-axis diagnostics indicate that the internal brane structure alone does not produce long-lived tensor resonances in the ghost-free region. Sharp quasi-localization peaks appear only in the singular branch, where the vanishing effective coupling induces divergent structures in the tensor potential; these peaks should therefore be interpreted as singular-boundary signals rather than ghost-free resonances of the smooth brane background. We then characterize the ghost-free massive Kaluza-Klein modes in the complex-frequency plane. Using the Asymptotic Iteration Method where applicable and time-domain evolutions with a supersymmetric partner potential as a zero-mode filtering tool, we extract the fundamental quasinormal frequencies. The modes have negative imaginary parts and quality factors $Q\simeq0.9-1.9$, showing that the ghost-free massive tensor excitations are broad, short-lived dissipative modes. Thus the QNM spectrum provides the appropriate complex-frequency description of the Kaluza-Klein dynamics when no narrow real-axis resonances are resolved.

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astro-ph.CO 2026-07-01

f(T) gravity branches ruled out by CMB and distance data

by Mahmoud Hashim, Eleonora Di Valentino +2 more

Cosmological Viability of Exponential Infrared f(T) Gravity

Phantom branch eases Hubble tension but loses to Lambda CDM; second branch fails when background fixes force bad CMB fits.

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We investigate the cosmological viability of exponential infrared $f(T)$ teleparallel gravity using current cosmological observations. This framework realizes late-time cosmic acceleration through torsional modifications of gravity without enlarging the six-parameter cosmological parameter space of spatially flat $\Lambda$CDM, and admits two distinct solution branches: a phantom-like model (Model I) and a model featuring a negative-to-positive transition in the effective torsional dark-energy density (Model II). We constrain both branches using CMB observations from Planck, ACT, and SPT together with DESI BAO and Pantheon+ Type Ia supernovae. We find that the principal branch (Model I) alleviates the Hubble tension relative to $\Lambda$CDM, but remains statistically disfavoured by the combined dataset. The secondary branch (Model II) is decisively ruled out. We show that the failure of Model II originates from the interplay between background and perturbation constraints: once late-time distance measurements constrain the expansion history, the model becomes overconstrained, forcing correlated shifts in $\Omega_{\rm m}h^2$, $A_s$, $n_s$, and $\tau_{\rm reio}$, degrading the fit to the CMB damping tail and driving the optical depth to unphysical values. Our results demonstrate that perturbation observables provide stringent and complementary tests of teleparallel gravity beyond the background expansion history.

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gr-qc 2026-07-01

Joint glitch model recovers true GW source parameters

by Charlie Hoy, Ruxandra Bondarescu +2 more

A parametric signal plus noise inference framework for short duration non-Gaussian noise transients

Adding a parametric description of short non-Gaussian transients to the inference allows unbiased recovery of signal properties where standa

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Gravitational waves are now routinely detected with ground-based observatories, and, through a process known as Bayesian inference, their source properties are inferred. However, terrestrial noise artifacts, often referred to as glitches, commonly overlap astrophysical signals. This invalidates a fundamental assumption of gravitational wave analyses: the noise is no longer stationary and Gaussian. As a result, traditional techniques can provide biased inferences in realistic data. One method for mitigating the effect of glitches is to jointly analyse both the signal and noise in a single framework. In this work, we introduce bilby-antiglitch to infer the astrophysical signal properties in non-Gaussian noise. By additionally including a quasi-physical glitch model to describe short duration non-Gaussian noise transients, we show that unlike traditional techniques, we infer the true source properties of simulated signals contaminated with loud glitches. We also show that bilby-antiglitch prevents false violation claims of General Relativity, and validates the exceptional nature of gravitational wave signals in spurious data.

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gr-qc 2026-07-01

Nonminimal coupling violates distance duality in teleparallel gravity

by Rocco D'Agostino

Distance duality relation in symmetric teleparallel gravity

The standard relation survives minimal coupling but breaks when the electromagnetic field interacts with the nonmetricity scalar, linking to

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In this work, we investigate the distance duality relation (DDR) in symmetric teleparallel theories, where gravity is mediated by nonmetricity. Starting from the general metric-affine formulation and adopting the geometrical optics approximation, we show that the standard Etherington reciprocity relation remains valid in the presence of nonmetricity when electromagnetism is minimally coupled and the photon number is conserved. We then extend the analysis to a class of $f(Q)$ theories with a nonminimal coupling between the electromagnetic field and the nonmetricity scalar. We demonstrate that such an interaction modifies the conservation of the photon number current, leading to a dynamical violation of the DDR. Focusing on a homogeneous and isotropic spacetime background in the coincident gauge, we derive a generalized DDR formula that directly relates observational distance measures to the Hubble expansion rate. Furthermore, we discuss the link between the deviations from Etherington's relation and variations of the effective fine-structure constant. Specific illustrative examples of the coupling function are also analyzed, showing that phenomenologically viable models predict only small deviations from the standard DDR. Our results provide a unified framework to distinguish between the geometric and dynamical origins of DDR violations, opening new avenues for testing non-Riemannian gravity with future high-precision astrophysical and cosmological observations.

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quant-ph 2026-07-01

Accelerated clock decay drops unphysical cross-wedge term

by Vladimir Toussaint

Comment on "Ideal clocks -- a convenient fiction" by K. Lorek et al

Corrected probability retains only thermal terms consistent with wedge separation.

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We correct a subtle oversight in Eq.(19) of K. Lorek et al. [Class. Quantum Grav. 32 175003 (2015)] concerning the decay probability of a uniformly accelerated quantum clock. The original expression included unphysical cross-wedge term ($|\bar{\gamma}_{K 1}|^2$) violating the spatial separation of Rindler wedges. We derive the corrected probability using the paper's Rindler conformal coordinates $(\tau, \xi)$, retaining only causally consistent thermal terms, and discuss implications for relativistic clock models.

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astro-ph.CO 2026-07-01

Fifth-order bias renormalization handles two-loop power spectrum UV issues

by Thomas Bakx, Mathias Garny +2 more

Galaxy bias renormalization: Two-loop Power Spectrum, One-loop Trispectrum and Bispectrum

Framework computes one-loop bispectrum and trispectrum consistently with gradient corrections and stochastic terms.

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We present a complete treatment of fifth-order renormalized galaxy bias at the one- and two-loop level in real space, including gradient corrections to deterministic bias operators at next-to-leading order. We then provide a complete computation of the two-loop power spectrum as well as the one-loop bispectrum and trispectrum of biased tracers, and demonstrate how to jointly model these statistics in a fully renormalized framework. These statistics also require stochastic renormalization of products of two, three or four operators at coincidence, which we include at leading order in gradients by means of an operator product expansion. We verify that all UV limits of loop integrals are absorbed by the counterterms we consider. Upon solving the resulting renormalization group equations, we find a pronounced scale-dependence of higher-gradient bias coefficients. Since our renormalization prescription is performed manifestly at the operator level, our results can also easily be extended to higher $N$-point functions, higher loop orders and field-level analyses.

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gr-qc 2026-07-01

Mimetic stealth solutions are perturbatively fragile

by Alireza Allahyari, Clarisse Donio +3 more

Fragility of stealth solutions in mimetic gravity

The screening limit where the multiplier vanishes imposes an infinite constraint hierarchy on fluctuations.

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We study a broad class of constrained mimetic-type extensions of general relativity with action $S=\int{\rm d}^4x\sqrt{-g}\,\bigl(R/2+\lambda\,C[g,\Psi]+{\cal L}_{\rm m}\bigr)$, where $R$ is the Ricci scalar, $\lambda$ is a Lagrange multiplier, $C[g,\Psi]$ is a scalar functional of the metric and generic field content $\Psi$ (possibly involving $\Psi$ and its covariant derivatives) and ${\cal L}_{\rm m}$ is the matter Lagrangian. The branch $\bar\lambda\to 0$, with the bar denoting a background value, provides a simple screening-like limit in which the constrained sector decouples, as in cosmological realizations where $\bar\lambda$ is typically nonzero on large scales while locally one expects $\bar\lambda\simeq 0$. On the exactly stealth branch $\bar{\lambda}=0$, the constrained sector drops out of the background dynamics, so, on domains where a background profile $\bar\Psi$ satisfying $\bar C=0$ exists, the theory admits the corresponding general relativity geometries as stealth solutions. As an explicit realization of this mechanism, we consider the scalar field case, where $C=g^{\mu\nu}\partial_\mu\phi\partial_\nu\phi\pm1=0$ becomes a Hamilton-Jacobi equation selecting geodesic congruences; in this setting, we study spherically symmetric solutions and construct a stealth Kerr profile using Carter separability. We then show, at the general level, that the $\bar{\lambda}=0$ branch is perturbatively degenerate with general relativity: the constrained sector contributes to the dynamics only through terms weighted by $\bar\lambda$, which vanish on the stealth branch, while still imposing an infinite hierarchy of constraints on the fluctuations. Consequently, the $\bar\lambda\to0$ limit is generically non-uniform, making the would-be screening perturbatively pathological.

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