Preprints in GR/QC

Jahed Abedi

Published: 2026-10-29

Categories: gr-qc

When a static, spherically symmetric configuration is brought close to a marginal-trapping threshold, it develops a long throat. As the nondegenerate minimum of $F=1-2m/r$ approaches zero, $F\simeqΔ+β(r-R_M)^2$, the proper length across the throat grows as $-\lnΔ/\sqrtβ$, even though the local curvature stays finite. We study how axial gravitational waves propagate in an effective model of this throat, in which the lapse is parametrized as $N\propto F^{s/2}$. For $s>0$ the throat acts as a cavity behind the angular-momentum barrier, and waves come back out as echoes spaced by $T_{\rm echo}\simeq2Λ+δ\proptoΔ^{-s/2}$, where $Λ$ is the optical length of the throat and $δ$ does not depend on $Δ$. We study four-dimensional, matter-supported quasi-black holes in which a regular centre caps the near-AdS$_2$ throat. These configurations provide a simplified model for investigating capped throats in horizonless microstate geometries. The echo delay in this model is controlled by the inverse redshift near the bottom of the throat, as in capped microstate geometries. This differs from thin-shell gravastars and wormholes, where the delay grows only logarithmically with the distance to the would-be horizon. Time-domain evolutions confirm the $Δ^{-s/2}$ scaling over three decades in $Δ$; for $s=0$ the throat becomes part of the barrier and no distinct echo appears. The barrier also imposes a greybody cutoff on the reflected spectrum, $1-Γ\simeq e^{-(ω-f)/T}$, where $T$ is fixed by the curvature of the barrier and does not depend on the surface gravity of any horizon behind it. In this model, the prompt signal is the same whether the interior contains a horizon or a reflecting throat. In the horizonless case, however, the transmitted wave returns as echoes, restoring the high-frequency part of the full reflected spectrum.

Manthos Karydas, Murat Kologlu, Allic Sivaramakrishnan

Published: 2026-10-29

Categories: hep-th

Measures of geometry like distance and time are staples of classical gravity. While geometric quantities arise broadly in quantum gravity, their graviton corrections are less explored. In this paper, we study geometric observables in perturbative quantum gravity. We form distance and time observables that model measurements, including in the presence of spacetime fluctuations. Gravitational dressing ensures these constructions are coordinate invariant. Then we show how these finite-distance observables become memory and Shapiro time delay operators upon taking asymptotic limits. We compute leading graviton effects in correlators of geometric observables throughout. Altogether, our results identify a class of geometric observables that link experiments and operations on the celestial sphere.

Kun Zhou, Jin Li

Published: 2026-10-29

Categories: gr-qc

We establish a unified analytic framework for anisotropic overlap reduction functions (ORFs) of arbitrary finite-delay time-delay interferometry (TDI) channels in a static, reciprocal, equal-arm equilateral constellation. The construction combines the polynomial constraints for laser-noise cancellation, constellation symmetries, and directional-projection integration. A free basis of the admissible channel module separates channel generation from angular integration; two families of elementary angular kernels then generate all channel-pair intensity ORFs. The channel algebra is independent of gravitational-wave polarization, and the intensity-kernel reduction applies to tensor, vector, breathing, and longitudinal sectors. Tensor multipoles illustrate the framework here. Complete propagation effects are retained at arbitrary fixed finite angular order, with explicit examples through $\ell=5$. Prepared frequency batches, shared multiprecision expressions, and local expansions at removable delay points provide stable evaluation. In the prepared-batch benchmark, the analytic implementation is approximately 50 to 5000 times faster than optimized sky quadrature at matched error tolerances. Independent multiprecision sky integrations also validate prescribed mixed error targets down to $10^{-100}$ in the tested cases. The resulting kernels and generation rules supply reusable inputs for anisotropic multichannel background models.

Philippe G. LeFloch

Published: 2026-10-29

Categories: math.DG

We generalize a method first introduced by Li, Yau, Simon, and Topping (for closed surfaces immersed in the flat Euclidean space), and we establish a global-in-nature estimate, with an explicit cut-locus contribution, on the Willmore energy of closed surfaces that are immersed in a complete Riemannian three-manifold and need not be embedded. Our estimate applies to ambient spaces whose sectional curvature is bounded above and whose injectivity radius may be finite. For positive upper curvature bounds, the global weighted estimates require an explicit radius restriction. The Willmore energy is bounded below by a functional involving the self-intersection number of the surface and the injectivity radius of the ambient space. Furthermore, by investigating in what sense our inequalities are optimal and realized by geodesic spheres in constant curvature spaces, we are led to introduce a weighted version of the Willmore functional, which is adapted to geodesic spheres in the model spaces and takes the sectional curvature of the ambient space into account. As a corollary, we obtain sufficient conditions for an immersed surface in a curved space to be embedded.

Jacob M. Krebs

Published: 2026-10-29

Categories: gr-qc

Gravitational observations can leave material properties undetermined in two different ways: distinct states can have the same total source, and distinct spacetime histories can have the same retained observations. We organize these inverse problems in general relativity through a property-level identifiability criterion, with applications to stars and black hole candidates. Two ideal massless gases illustrate equal-source ambiguity: their temperatures differ by a factor of $(8/29)^{1/4}$ and their entropies differ while their stress-energy tensors agree. A separate causal-fluid example starts with identical sources and geometric data but different constitutive responses; the two models' curvature histories separate at linear order in proper time and their scale factors at cubic order. For black hole candidates, the relevant distinction is between stationary exterior parameters, perturbing fluxes and constituent history. The framework provides a test for whether retained data identify a material property, separating instantaneous source equality, history-wide source equality and observational projection.

Zhengwen Liu, Xing-Bo Yuan

Published: 2026-10-29

Categories: hep-th

Newton's law of universal gravitation describes the attraction between two masses through an inverse-distance potential. In Einstein's theory gravity gravitates: each mass reshapes the spacetime geometry through which the other acts. More than a century later, extracting the two-body interaction from this coupled geometry remains a fundamental analytical challenge. Even without motion or radiation, the static sector of the interaction harbours an infinite hierarchy of field couplings: the purest laboratory for gravitational non-linearity. Here we determine the static interaction from ninth to twelfth order in Newton's constant for arbitrary mass ratios, and derive a closed expression for the first backreaction beyond the Schwarzschild test-body limit to all orders in the gravitational coupling. We achieve both advances by formulating the problem around the stationary interaction energy. An exact one-body background resums one source's self-interaction, stationarity reduces the fields required from the other, and integrated response identities reveal cancellations across the coupled modes. Complementary expansions then resolve the complete mass dependence at finite order. Together, these results bridge the gap between an infinitesimal probe and comparable masses, exposing hidden analytical simplicity within Einstein's theory and providing essential building blocks for modelling orbital dynamics and gravitational-wave generation.

Matteo Fadel, Giulia Gubitosi

Published: 2026-10-29

Categories: quant-ph

Quantum reference frame (QRF) transformations relate the description of a physical system to different quantum observers, but their connection to concrete experimental phenomena remains largely unclear. Here we show that the trajectory-sharpening effect obtained by correlating a probed system with an effective negative-mass reference admits a natural interpretation as a QRF transformation to the frame of a negative-mass system. Using a minimal toy model of free particles with signed masses, we identify the Einstein-Podolsky-Rosen-type observables responsible for this effect with a pair of commuting relational observables that, under the instantaneous QRF transformation, are mapped to operators local to distinct subsystems. We then show that the corresponding relational trajectory is reproduced by the dynamical QRF transformation, where the transformed relational position acquires an explicit time dependence. We introduce QRF-invariant sharpness measures for relational trajectories and derive monogamy relations showing that a trajectory cannot be made simultaneously arbitrarily sharp with respect to two distinct negative-mass frames. We further show that trajectory sharpness can instead reside in a collective reference mode encoded across two physical systems, even when neither constituent alone provides an arbitrarily sharp reference, so that sharpness can be distributed rather than localized in a single constituent frame. These results provide an operational, experimentally relevant interpretation of QRF transformations for continuous-variable systems.

Chen-Hsu Chien

Published: 2026-10-29

Categories: math-ph

Twinor theory is formulated as a spacetime-based counterpart to twistor theory using holomorphic reductive Cartan geometry modelled on complexified $(A)dS_4$. The fundamental spin-tractor bundle defines Dirac twinors, its symmetric powers define ladder twinors, and their extremal Lorentz components define chiral twinors. The general \textit{twinor field equation} is $D\mathbf Y=\mathbf J$. Its adjacent contractions and mixed divergence are constrained by source relations; no additional equation is imposed on its completely symmetric projection. On a flat torsion-free Lorentzian background, the adjacent equations with the mass-normalization source and vanishing additional contracted sources, together with vanishing mixed divergence, reproduce the massive \textit{Dirac--Fierz--Pauli system}; the massless chiral realization gives the zero-rest-mass equations. Within the fixed mass normalization, the reality condition yielding a positive real mass squared is the \textit{anti-de Sitter reality condition} on the particle scale, independently of the cosmological scale and background curvature. The mass-coupling phase is therefore present in the classical connection before quantization. Nonlinear gravity is formulated through the full adjoint curvature, with energy--momentum and spin currents specifying Einstein--Cartan dynamics without requiring an action. The adjoint Bianchi identity constrains source compatibility, while a BGG-type sequence organizes torsion-free infinitesimal deformations. Matter interactions enter through the coupled connection and contracted source relations, with curvature compatibility recorded by $D\mathbf J=\mathcal F_D\mathbf Y$. Both chiralities are retained, and the additional consistency requirements for interacting higher-spin fields are distinguished from the underlying bundle construction.

Andreas Belaey, Thomas G. Mertens, Lorenzo Russo, Alex Tarana

Published: 2026-10-29

Categories: hep-th

We formulate JT gravity with finite-cutoff boundaries and end-of-the-world branes in the first-order BF formulation. We dynamically reduce the BF model into a one-dimensional system living at the boundaries, generalizing earlier constructions. We obtain in particular a geometrical understanding of the phase space degrees of freedom associated to each of these boundaries. We leverage these results to probe bulk locality and the underlying structure of spacetime. Within our framework, we are able to derive a closed-form expression for the holographic Schwarzian description of JT gravity at finite-cutoff in phase space. The resulting degrees of freedom describe the embedding of the finite-cutoff curve in AdS$_2$. A quantization of these systems is presented in a companion paper.

Siqing Yu

Published: 2026-10-29

Categories: hep-th

The Abelian Higgs model in AdS$_5$, in the probe limit, is a standard holographic model of a strongly coupled superfluid, usually solved numerically. When the scalar mass saturates the Breitenlohner-Freedman bound and the quartic coupling takes the Bogomolny value, its condensed phase can be found in closed form on every static, uncharged AdS$_5$ background with maximally symmetric spatial sections. We prove that it is linearly stable, as is any nodeless probe-limit condensate in the standard quantization with a nonnegative quartic coupling and no superflow. On each slicing it answers a different question about the dual conformal field theory. On the planar black brane it is the superfluid at all temperatures below $T_c$: the superfluid fraction follows the Gorter-Casimir two-fluid law exactly, and the speed and the attenuation of sound are found in closed form. In global AdS$_5$ it describes a state of charge $Q$ on $\mathbb{R}\times S^3$, arguably the lowest-energy one, and gives its scaling dimension in closed form at all $Q$, classically in the bulk. Its excitations include towers that the superfluid effective theory does not describe; they come from an infrared fixed point of the probe sector. The hyperbolic slicing gives in closed form a homogeneous hairy phase of the black holes that compute the charged Rényi entropies of a ball. Its condensate does not vanish at the entangling surface. When sourced by operators inserted there, the phase sets in at Rényi index exactly one at zero chemical potential, as found for a neutral scalar.

Kyriakos Destounis

Published: 2026-10-29

Categories: gr-qc

Exceptional points (EPs), at which two quasinormal frequencies and their eigenvectors coalesce, can strongly enhance the spectral instability of black hole quasinormal modes. We investigate this behavior in Kerr--Newman spacetimes through pseudospectra and condition numbers for neutral massless scalar fields and coupled gravitoelectromagnetic (GE) perturbations. For the scalar field, we follow the $(\ell,m)=(1,1)$ spheroidal branch and derive the energy norm from the stress-energy tensor. For GE perturbations, we use a coupled four-field system equipped with a positive radiative energy. At the selected near-EP backgrounds, the condition numbers of both modes in the close pair exceed those of the two more-damped modes shown for comparison at the same background. Along a matched GE parameter path, the frequency splitting follows a square-root law and the condition numbers grow as the inverse square root of the distance to the EP. The pseudospectral contours resolve the transition from individual-mode sensitivity to the collective response of the pair. Within the discretized problems and energy norms considered here, these results quantify the amplification of spectral instability near EPs and provide a basis for studying their contribution to black-hole ringdown.

Y Bisabr

Published: 2026-10-29

Categories: gr-qc

Interactions between a cosmological scalar field and radiation can modify the pre-recombination expansion history and leave observable signatures in cosmic microwave background (CMB) anisotropies. We investigate an effective scalar-photon-fluid coupling, deriving the coupled background and linear perturbation equations and leading-order adiabatic initial conditions for a canonical scalar field with an exponential potential. Starting from a radiation-era scaling solution, we implement the dynamical interaction in CLASS and compute the resulting recombination history, CMB anisotropies, and linear matter power spectrum. Photon thermodynamics and collisions are treated phenomenologically, assuming preservation of a Planckian spectrum. We assess observational compatibility using conditional Planck 2018 temperature, polarization, and lensing likelihoods, holding the six standard cosmological parameters fixed while profiling the calibration parameter $A_{\rm Planck}$. The interaction produces scale-dependent modifications to CMB and matter spectra, but the conditional likelihood remains shallow at weak coupling. The best sampled interacting point, $(ε_i,σ)=(4\times10^{-5},0.10)$, is slightly disfavored relative to the matched interaction-off $Λ$CDM reference ($Δχ^2\simeq+0.30$). These results establish phenomenological cosmological signatures without demonstrating an observational preference for the interaction. Definitive constraints require further validation of photon thermalization, collision dynamics, and photon-density normalization.

Arad Nasiri, Murali Saravanan, Caio B. de S. Nascimento

Published: 2026-10-29

Categories: astro-ph.CO

Linear Boltzmann solvers typically evolve the perturbations of noncold relics, such as massive neutrinos or hot subcomponents of the dark matter, on a momentum grid, often switching to a fluid approximation on small scales for efficiency. We implement in CLASS the Dispersive Fluid Approximation (DFA), a fluid scheme that captures the scale-dependent sound speed of these species. Within the standard ncdm module, the DFA significantly outperforms the default CLASS fluid approximation in the cross and neutrino power spectra, and reduces errors in the cold dark matter power spectrum by up to an order of magnitude, while adding only 1-4% to the total runtime. We also present the first open-source implementation of the Generalized Boltzmann Hierarchy (GBH), which simplifies the implementation of noncold relics by integrating out the momentum dependence of their perturbations altogether. Combined with the DFA and tested on massive neutrinos, the GBH reproduces the matter power spectrum to better than permille accuracy and cosmological parameter constraints to better than 0.05 sigma, at a computational cost comparable to that of the standard implementation. We argue that the GBH is particularly well suited to non-thermal relics whose distribution function varies with time or across parameter space. Our implementation of both the DFA and the GBH in CLASS is publicly available at https://github.com/aradn97/class_GBH.

Michele Mancarella, Viola De Renzis, Alessandro Agapito

Published: 2026-10-29

Categories: astro-ph.IM

We present posterior-landscape, a Python framework to identify and characterize morphological features in two-dimensional probability densities. The framework combines concepts from topological data analysis, statistical density-ridge estimation, and scale-space image analysis. It extracts localized concentrations, valleys, ridges, and changes of slope; for Bayesian reconstructions, it propagates uncertainty in feature recovery, geometry, and correspondence across posteriors. The framework also connects two-dimensional structures to features in one-dimensional marginals, and quantifies their correlation with other inferred parameters. We validate the method on controlled densities, and demonstrate its use on gravitational-wave population reconstructions, where it provides a systematic way to identify and interpret population features and assess which ones carry information relevant for cosmology. The resulting catalogues also offer a common morphological representation for future comparisons between predictions and population reconstructions.

Yunliang Ren, Xiaofeng Yang, Xuwei Zhang, Shuangnan Chen, Yangjun Shi, Hoernisa Iminniyaza

Published: 2026-10-29

Categories: astro-ph.CO

Recent DESI DR2 results suggest that dark energy may evolve with time, which motivates a re-examination of entropic cosmology. In this work, we study three representative entropic models, denoted as Models A, B, and C, corresponding to the driving terms $H^2$, $H^2+\dot H$, and $H^2+\dot H+H^4$, respectively. We establish a general framework for entropic cosmology and examine these models through early universe consistency, the Trans-Planckian Censorship Conjecture (TCC), and the realization of Quintom-B crossing. We constrain these models using the Pantheon+ sample, DESI DR2 BAO measurements, and Planck 2018 CMB distance priors, and compare their fits to the data. For Model C, we adopt a first-order perturbative treatment in the full data analysis to maintain numerical stability in the presence of the higher-order term. We find that Model A is the simplest among the three models, but it is difficult to make it compatible with both early universe consistency and the TCC condition. Model B, which includes a derivative correction term, shows a small difference in the fit to observational data compared to Model A, and is more consistent with the theoretical constraints. Model C includes more correction terms, but does not provide a better fit to the data. The parameter region favored by observations does not fully overlap with that preferred by theoretical consistency, which suggests that entropic cosmology may require further development to achieve a self-consistent description across different cosmic epochs.

Marco Refuto, Giampiero Esposito

Published: 2026-10-29

Categories: gr-qc

Gravitational waves as one approaches Schwarzschild null infinity are the core of our investigation, treated as the spin-weighted generalisation of a massless scalar field. In particular, we compute their full spectrum, consistent with observations coming from LIGO and VIRGO experiments. This paper continues recent work by the authors, where the Poincaré asymptotic expansion was exploited in black hole perturbation theory. The mathematical formalism we developed is now intimately connected with gravitational wave phenomenology, providing new mathematical tools to investigate their features.

Shengjun Guo, Guangzai Ye, Peng Liu

Published: 2026-10-29

Categories: gr-qc

A charged black hole has a ceiling: extremality bounds the charge that a given mass and spin can support. Vector hair has so far only lowered it. In the Einstein--Maxwell--Vector (EMV) model, where a massless vector field couples nonminimally to the electromagnetic invariant, the spherically symmetric vectorized Reissner--Nordström black holes are strictly undercharged: vector hair is paid for in charge. Whether this ceiling is a property of the vector field or merely of spherical symmetry has remained open, because spherical symmetry hides the hair's mass as well: its Komar mass vanishes identically and the exact identity $M_V=2Ω_HJ_V$ degenerates to $0=0$. Rotation lifts both degeneracies at once. We construct the rotating solutions of the model, the first in this setting, and find that the hair's mass is not a free parameter but a second-order invariant of the rotational response, fixed by $M_V=2Ω_HJ_V$. Above a coupling threshold the ceiling gives way: the domain of existence crosses the extremal Kerr--Newman bound, reaching $q=Q/M>1$ with $q^2+χ^2$ up to $1.84$, while at $α=5$ the maximum charge stays below it. The shadow is where the hair becomes visible. At $(q,χ)=(0.9947,0.10)$, near the extremal bound, the hair contributes an ellipticity of $8.30\%$, against $0.44\%$ from the charge and $0.06\%$ from rotation --- a factor of $19$ that charging a Kerr black hole cannot mimic; at the overcharged solution $(q,χ)=(1.2527,0.10)$ the total ellipticity reaches $25.6\%$. Whether the branch is ghost-free remains open, but the existing no-go criteria do not settle it: they assume a background and a dispersion relation that do not hold here.

Zhi-Peng Peng, Shi-Chao Zhang, Xiao-Pei Xu, Ruan-Jing Zhang, Xiao-Min Zhang, Xi-Bin Li

Published: 2026-10-29

Categories: gr-qc

We investigate a noncanonical warm inflationary model with a nonminimal coupling between the inflaton field and scalar curvature. Within the Jordan frame, we derive the modified background equations and establish the slow-roll conditions through a linear stability analysis. We find that the nonminimal coupling enhances the effective damping and modifies the potential gradient, facilitating slow-roll evolution even for relatively steep potentials. Using the stochastic approach, we derive the Langevin equation for inflaton fluctuations and obtain the primordial scalar and tensor power spectra. Our results show that the scalar spectrum is nearly scale-invariant, while the combined effects of nonminimal coupling, noncanonical dynamics, and thermal dissipation can further suppress the tensor-to-scalar ratio. Moreover, the model can sustain warm inflation even in the weak-dissipation regime and accommodate sub-Planckian field excursions in suitable parameter regions. These findings highlight the potential of this framework as a viable extension of conventional warm inflation.

N. Emil J. Bjerrum-Bohr, Gang Chen, Konstantinos Papadimos, Nabha Shah, Chenliang Su

Published: 2026-10-29

Categories: hep-th

We develop a new method to construct the tree-level Compton amplitude for gravitational-wave scattering off a Kerr black hole in post-Minkowskian effective field theory. Building on previous computations that required physical consistency of the amplitude, the method uses wave scattering functions from black hole perturbation theory to uniquely determine additional contact terms. We illustrate the iterative procedure by deriving explicit expressions up to sixth order in spin, including previously unknown sectors at the fifth and sixth orders in spin. The amplitude features complex transcendental structures and a leading dissipative contact term at sixth order in spin. We verify our result against known results in the literature and reproduce the one-loop tail result from black hole perturbation theory.

Patricia McMillin, Giuseppe Ficarra, Carlos O. Lousto, Richard O'Shaughnessy

Published: 2026-10-29

Categories: gr-qc

We use the more than 2000 full numerical-relativity simulations included in the fifth release of the RIT binary-black-hole waveform catalog to perform Bayesian parameter estimation, via the rapid iterative fitting algorithm (RIFT), for the gravitational-wave events GW190521 and GW231123. We revisit GW190521, which has previously been identified as potentially possessing large eccentricity upon entering the detector band at $20~\mathrm{Hz}$, and confirm this finding: the highest likelihood is obtained from waveforms that are simultaneously eccentric and spin-precessing, yielding $e_{20} =0.207_{-0.147}^{+0.192}$ and $χ_{1,\perp}=0.717_{-0.406}^{+0.194}$. Applying the same simulation pool to GW231123, we likewise find a preference for spin precession where at 20 Hz $χ_{1,\perp}=0.678_{-0.462}^{+0.218}$, but in this case with negligible eccentricity at both $10~\mathrm{Hz}$ and $20~\mathrm{Hz}$, with $e_{10}=0.097_{-0.073}^{+0.124}$ and $e_{20}=0.056_{-0.045}^{+0.059}$. For comparison, both events are also analyzed using exclusively non-precessing (eccentric and quasi-circular) simulations, which yield lower likelihoods in each case. These results indicate that our approach is capable of discriminating between the effects of eccentricity and spin precession in current gravitational-wave signals. The singled out top peak likelihood NR simulations give estimates of the recoil velocities of the merged final holes of 3965km/s for GW190521, and of 2059km/s for GW231123.

Amrillokhon Mamatkhonov, Javokhir Sharipov, Tursunali Xamidov, Chen Zhou, Sanjar Shaymatov, Chengxun Yuan

Published: 2026-10-29

Categories: gr-qc

We investigate the optical properties of a five-dimensional charged anti-de Sitter (AdS) black hole. Using the null geodesic equations, we determine the event horizon and photon sphere radii and the critical impact parameter, showing that all decrease with increasing charge, while the photon sphere radius remains independent of the AdS radius. To avoid dependence on the mass scale and the observer-dependent apparent size of the shadow in an AdS spacetime, we introduce two mass-independent geometric observables: the subring exponent $γ$ and the ratio of the critical impact parameter to that of the direct image of the innermost stable circular orbit (ISCO). We derive $γ$ in closed form and show that it is independent of the AdS radius and satisfies $2π/\sqrt{3}<γ\leqπ\sqrt{2}$, above the values for four-dimensional Schwarzschild and Reissner--Nordström black holes. Using a Markov chain Monte Carlo (MCMC) forecast based on noiseless mock data with illustrative fractional uncertainties of $5\%$, we find that the dimensionless AdS radius can be constrained with a relative uncertainty of $16$--$19\%$, whereas the charge can be distinguished from zero only for the near-extremal fiducial model considered. Under these assumptions, the subring exponent provides a Gaussian separation of $3.4$--$5.9σ$ from the four-dimensional Schwarzschild black hole.

Fu-Guo Yang

Published: 2026-10-29

Categories: gr-qc

We identify the mechanisms and range of validity of two scaling laws reported in charged black-hole interiors. In spherical evolutions with a neutral massless scalar, mass inflation produces a large internal mass $m$, followed by a plateau. Small scalar and electric corrections give $K\simeq48m^2/r^6$, where $r$ is the areal radius and $K$ the Kretschmann scalar. The local exponent is near six when the mass and relative curvature correction also vary slowly with radius. The exact bound $K\geq28q^4/(5r^8)$, with $q$ the charge, excludes a finite-coefficient $r^{-6}$ asymptote, while a large plateau mass delays electric corrections to $r\sim q^2/m$. For sufficiently large plateau mass, this classical regime can reach Planckian curvature before electric corrections become significant. At fixed coordinates and initial gauge, a linear response of $ρ=r^2$ to the initial scalar amplitude $A$ gives the half-power radius law near a simple zero. Where both mechanisms apply, $K/m^2\propto(A_*-A)^{-3}$, with $A_*$ the area zero. Full evolutions confirm the electric correction, support the half-power law at several observation times, and test the joint inverse-cube law.

Rajendra Prasad Bhatt, Rudraksh Verma, R. Prasad, Sudipta Sarkar

Published: 2026-10-29

Categories: gr-qc

The inverse Gertsenshteǐn-Zel'dovich effect describes the conversion of gravitational waves into electromagnetic waves in the presence of a background electromagnetic field. This effect has primarily been studied for constant background electromagnetic fields. In this work, we develop a general formalism for calculating the components of the electric and magnetic fields induced by the passage of a gravitational wave through a spatially varying, time-independent background electromagnetic field. The formalism accommodates all six possible polarization modes of gravitational waves. We illustrate its applicability through several examples, including gravitational waves propagating through constant and spatially varying electromagnetic fields. We further investigate the electromagnetic signals generated by the passage of gravitational waves through astrophysical magnetic fields, particularly those associated with neutron stars and magnetars. By connecting gravitational waves and electromagnetic waves--two essential messengers of multi-messenger astronomy--the inverse Gertsenshteǐn-Zel'dovich effect offers a promising framework for both gravitational-wave detection and astrophysical observations. The formalism developed here may therefore find applications in the design of high-frequency gravitational-wave detectors and in the investigation of high-energy astrophysical electromagnetic signals.

Anastasios Avgoustidis, Edmund J. Copeland, Adam Moss, Juhan Raidal, Filippo Revello, Gonzalo Villa

Published: 2026-10-29

Categories: astro-ph.CO

Cosmic strings and cosmic superstrings could have formed in the early universe. In a particular class of models, the tension associated with these defects is time dependent, either because the strings themselves are composed of evolving moduli fields, or because they are directly coupled to evolving scalar fields leading to an effective time dependence in the string tension. Here we take seriously the possibility of this time dependence and investigate the phenomenological consequences of such an evolution, comparing the results to the more traditional case of a fixed time independent tension. In particular, for five different time varying models, motivated by different possible forms of evolution of the string tension, we evaluate their Gravitational Wave (GW) contributions as well as their impact on the Cosmic Microwave Background (CMB). Performing an MCMC analysis of the models we find there are indeed interesting spectral signatures in the GW emission at frequencies between the current PTA and interferometer data, but the signatures are not unique to these strings, making them hard to pin down using current data. However, we do find cosmic strings with evolving tension fit the GW data as well as other favoured models.

Pierre Auclair, Chams Gharib, Danièle Steer

Published: 2026-10-29

Categories: gr-qc

We carry an in-depth analysis of the gravitational wave (GW) emission of cosmic string cusps, going beyond the seminal work of Damour and Vilenkin. We identify two features that, to the best of our knowledge, have not been described in the literature: first the GWs emission from a cusp, at any given frequency, is not concentrated inside a cone but instead draws a diamond-like shape in the sky. Second, the emission is not maximal in the direction of the cusp velocity, but in two slightly offset directions. We explain these effects in detail, and illustrate them with simplified examples. Then, we study two limiting cases for which the overall radiated power is enhanced: when the diamond is stretched in a particular direction, and when higher order derivatives vanish at the cusp. We statistically estimate the importance of these effects in a population of odd-harmonic loops.

Maria-Catalina Isfan, Laurentiu-Ioan Caramete, Ana Caramete

Published: 2026-10-29

Categories: astro-ph.CO

Machine learning (ML) techniques are increasingly explored to analyse gravitational wave (GW) data expected from the Laser Interferometer Space Antenna (LISA). At the same time, advances in quantum computing have stimulated interest in quantum machine learning as a potential alternative to conventional approaches. We investigate the applicability of quantum, hybrid quantum-classical, and classical ML models to two tasks relevant for LISA observations of massive black hole binaries: GW signal detection and merger prediction. Using the Sangria dataset from the LISA Data Challenge, we benchmark several quantum architectures, including variational quantum classifiers (VQCs), post VQC hybrid models, quantum kernel methods, data reuploading classifiers, and quantum long short-term memory (QLSTM) networks, against classical support vector machines, multilayer perceptrons, recurrent neural networks, and LSTM networks. The models are trained on labelled data derived from the Sangria training dataset and evaluated on the corresponding blind dataset. For signal detection, several quantum models match or outperform classical baselines. In particular, the best performing hybrid post VQC architecture correctly identifies all signal samples in the blind dataset, while the standard VQC and data reuploading classifier achieve competitive detection rates. For merger detection and coalescence time estimation, however, the standard VQC emerges as the most reliable model, successfully localising all detected merger events with the lowest localisation errors. We further analyse the trade-offs between predictive performance, model complexity, and quantum circuit resources. Our results indicate that, although no universal quantum advantage is observed, selected quantum models can provide practical benefits for specific GW analysis tasks and represent promising candidates for future LISA data analysis pipelines.

Furqan Nazeer, Tooba Feroze

Published: 2026-10-29

Categories: gr-qc

Analytic compact-star models in modified gravity usually borrow the junction conditions of general relativity and fix their constants with radii derived for a particular stellar model. Here we avoid both. We study $\mathcal{F}(\mathcal{R})=\mathcal{R}+α\mathcal{R}^{2}$ gravity with a Durgapal-Bannerji interior of embedding class one (Karmarkar condition) and a Hayward exterior. Without Birkhoff's theorem, the exterior is an assumption, and we measure its effect with the Hayward metric, which deforms Schwarzschild by a length $\ell$. The junction conditions of quadratic $\mathcal{F}(\mathcal{R})$ gravity fix all constants in closed form in terms of $M$, $R$ and $\ell$. The condition $p_r(R)=0$ is replaced by continuity of the trace of the extrinsic curvature. The Ricci scalar jumps at the surface, so there is a thin shell with negative surface energy density for $α>0$, a gravitational double layer, and a small radial stress. For this stress to be below 1% of the central pressure we need $α\lesssim0.2$ km$^{2}$ and $\ell\lesssim0.3M$. The interior behaves as a self-bound star. A single surface energy density, $ρ_s=(1.37\pm0.16)ρ_0$, reproduces PSR J0740+6620, J0437-4715, J0030+0451 and J0614-3329, and for $α=0.1$ km$^{2}$ the model predicts $R_{1.4}=11.5$ km and a maximum mass of $2.9 M_\odot$. Because $\ell$ enters surface observables only at order $(\ell/M)^{2}(M/R)^{3}$, the results carry over to a Schwarzschild exterior. Calibrating instead with strange-star radii of eclipsing X-ray pulsars gives $R_{1.4}\approx9$ km, which current data rule out.

Diego Blas

Published: 2026-10-29

Categories: gr-qc

`Adding colour'' to the gravitational-wave sky by probing unexplored frequency bands has the potential to unveil new and unexpected phenomena in the Universe. The microhertz band, between pulsar timing arrays and LISA, is a particularly attractive target: it should host the extension of the signal recently found by pulsar timing arrays (if it is generated by a family of sources of gravitational waves), and it may harbour signals from the early Universe, primordial black holes or dark matter. In these proceedings, we review how the orbits of gravitationally bound systems act as resonant detectors of microhertz gravitational waves and ultra-light dark matter. We then describe GUEST (Gravitational Universe Exploration with Satellite Tracking), a mission concept recently proposed to the ESA F-class call, consisting of two dense passive spheres covered with retroreflectors, placed in highly eccentric Earth orbits and tracked by a global laser-ranging network.

Rahime Matur, Beyhan Karakas, Ian Hawke, Nils Andersson

Published: 2026-10-29

Categories: astro-ph.HE

Binary neutron star (BNS) and black hole--neutron star mergers are among the most important multimessenger sources. Observations of these events could provide valuable insights into several unresolved phenomena, ranging from the efficiency of magnetic field amplification during and after mergers to the formation of magnetars and jets. Understanding these phenomena requires accurate modelling of magnetic field evolution, which remains a challenge for state-of-the-art general relativistic magnetohydrodynamics (GRMHD) simulations. In this work, we present \texttt{RAKI} (Relativistic Astrophysics Code Implementation of the Alternative Finite Difference Approach for GRMHD), the first GRMHD code to simulate BNS mergers using high-order alternative finite-difference methods with adaptive-order WENO (AFD-WENO-AO) reconstruction and a fully non-staggered, node-centred vector-potential formulation. The code achieves up to ninth-order convergence in smooth test problems while accurately capturing discontinuities. In magnetised Tolman--Oppenheimer--Volkoff (TOV) star tests, \texttt{RAKI} retains $99.2$ per cent of the initial maximum magnetic field strength over ${\sim}2$ ms, exhibiting an order of magnitude less magnetic field loss than a reference GRMHD code at the same resolution. In BNS merger simulations, fifth-order AFD-WENO-AO reconstruction yields approximately third-order convergence of the gravitational-wave phase in both magnetised and unmagnetised models. The discrete no-monopole constraint is preserved to machine precision without staggered grids, even during BNS mergers with moving refinement regions. These results establish \texttt{RAKI} as a high-order, non-staggered GRMHD framework for accurate modelling of magnetic field evolution in neutron star mergers and its implications for multimessenger astrophysics.

Alexandre Sébastien Göttel

Published: 2026-10-29

Categories: astro-ph.IM

The field of gravitational-wave data analysis heavily relies on Bayes factors to make statements about astrophysical effects in events detected by the LIGO-Virgo-KAGRA collaboration. This is true on an event level, for example when discussing the potential detection of precession or eccentricity, as well as on a population level. For the latter, perhaps the main limiting factor is the reliance on the output from event-level nested sampling analyses, which is known to introduce growing uncertainties and biases as the number of detections increases. In both cases, while Bayes factors are useful when comparing different models, because the underlying distribution of Bayes factors in noise is unknown, it is often not possible to use them to make quantifiable statistical statements. Their statistical meaning is also questionable in the at least $20\%$ of gravitational-wave events that contain transient noise artifacts. This paper shows that it is possible to use evidence networks, which can infer Bayes factors after learning the distinguishability between datasets, to solve all of the aforementioned problems. By being able to calculate up to $10^5$ Bayes factors per second, we can construct background distributions of Bayes factors under different signal assumptions to estimate significance. We show that the high precision achieved allows us to scale the results from up to $10^4$ events with no discernable bias on population-level quantities, while laying the foundations for a likelihood-free method that does not rely on the assumption of Gaussian and stationary noise.

Ashfaque Ahmad, Sudhir Kumar Gupta, Abbas Ali

Published: 2026-10-29

Categories: gr-qc

We extend the horizon wave-function (HWF) formalism to a spherically symmetric, charged, spinless quantum source in $\mathcal{D} + 1$ dimensional spacetime geometry and construct the HWFs associated with inner- as well as outer-horizons of the Tangherlini--Reissner--Nordström (TRN) black hole. The corresponding black hole formation probabilities, $P_{\rm BH}^{\pm}$, are also calculated and their sensitivities due to various source parameters including charge, mass, and $\mathcal{D}$ are analysed as well. Our analysis reveals that the ratio of inner- to outer-horizon probabilities, $P_{\rm BH}^{-}/P_{\rm BH}^{+}$, changes drastically from being unity as the source departs away from being in the extremal limit defined by $α$ ($\to 1$ for extremal case). Furthermore, black hole formation probabilities are found to be highly suppressed for higher values of $\mathcal{D}$, particularly for the source mass, $m \lesssim Λ_{\mathcal{D}}$, e.g., for $α= 0.5$, the ratio, $P_{\rm BH}^{+}(\mathcal{D} = 5)/P_{\rm BH}^{+}(\mathcal{D}=10)$ turn out to be approximately associated with $\mathcal{D}$ spatial-dimensions.

Sreeshma A, Md Sabir Ali, C. L. Ahmed Rizwan

Published: 2026-10-29

Categories: gr-qc

The interplay between black hole thermodynamics and topology provides a strong, coordinate-independent framework for discovering the underlying structure of black hole phase transitions as well as their universal features. We explore the thermodynamic topology of the anisotropic Kerr-Newman-AdS black hole using Duan's $φ$-mapping theory and a complex residue approach. By creating the generalized off-shell free energy, we propose a thermodynamic vector field in the parameter space with zero points corresponding to equilibrium black hole states. The winding numbers associated with these defects are utilized to calculate the black hole's global topological number. We begin with an analysis of the entire anisotropic Kerr-Newman-AdS black hole, followed by two limiting examples. Setting the anisotropic parameter $K = 0$ produces the Kerr-Newman-AdS black hole, while eliminating the AdS contribution produces the Kerr-Newman black hole. The anisotropic Kerr-Newman-AdS and Kerr-Newman-AdS black holes have a single thermodynamic defect with winding number $+1$, which results in $W = +1$. In contrast, the Kerr-Newman black hole has two defects with winding numbers $+1$ and $-1$, which result in a vanishing global topological number, $W = 0$. These findings show that the AdS contribution alters the global topological classification, but the anisotropic matter studied here preserves the topological class of the Kerr-Newman-AdS black hole. As an analogous limiting instance, we further study a Kiselev-type black hole, analyzing the circumstances in which its metric reduces to a charged black-hole geometry and how the thermodynamic topology reflects this reduction. Finally, we use the complex residue approach on the anisotropic Kerr-Newman-AdS black hole.

Brennen Black

Published: 2026-10-29

Categories: gr-qc

The horizon shear of a near-extremal Kerr black hole perturbed by an eccentric extreme mass ratio inspiral shows low amplitude, high frequency oscillations (''wiggles") after periapsis passage. Previous works are unable to tie the frequency of the wiggles to the orbit, and argue they cannot be quasinormal modes (QNMs). We show that they are Kerr QNMs belonging to the damped-mode branch --- that is, modes whose decay rate stays finite as the spin approaches extremality. For an equatorial prograde orbit with $p = 3M$ and $e = 0.85$ and spins ranging from $a/M = 0.999$ to $a/M = 0.99999$, fits to the time-domain shear identify the fundamental $(\ell,m) = (2,1)$ and $(3,2)$ modes as the dominant and first subdominant excitations. Fitting each multipole separately gives frequencies to within two standard deviations of the Kerr values and provides evidence for the excitation of the fundamental $(3,1)$, $(4,1)$ and $(4,2)$ modes, though these are not resolvable in the full signal. We further argue that the same wiggles must be present in the tidal field that drives the shear. For $\ell \leq 4$ we find no evidence of QNM excitation in the $m = 0$ or the $m = \ell$ multipoles.

Yu-Song Cao, Nick Houston, YanXia Liu, QingZheng Lv, She-Sheng Xue

Published: 2026-10-29

Categories: hep-ph

Axion like particles (ALPs) are particularly well motivated candidates for dark matter, and physics beyond the Standard Model more generally. However, direct detection remains extremely challenging due to the weakness of their interactions. In this work, we propose to employ space-based optical lattice clock networks (SOLCN), originally targeted to probe the stochastic gravitational wave background (SGWB), to detect axion dark matter through cosmic birefringence via minor modifications to their laser links. Searching for cross-correlated signals then provides significant sensitivity to low mass ALPs as a result of their large correlation lengths. In this work we focus on ALPs in the mass range $10^{-18.55}\text{eV}-10^{-14}\text{eV}$, For ALPs mass region $10^{-18}-10^{-14}\text{eV}$, finding that we can probe down to $g_{aγ}\geq 10^{-12}\,\text{GeV}^{-1}$. Moreover, we find that the SOLCN sensitivity to the ALP-photon coupling depends crucially on the frequency of the network link. With an $8$ GHz frequency link, we then have the potential to reach $g_{aγ}\geq10^{-16}\,\text{GeV}^{-1}$ in this region.

S. W. Zhou, W. Su, S. Y. Zhou, C. F. Li, J. X Zhang

Published: 2026-10-29

Categories: astro-ph.SR

TianQin, a space-borne gravitational wave observatory, is designed to detect gravitational-wave signals via laser interferometry. As the inhomogeneous space plasma surrounds the inter-satellite laser links, the propagation of the laser in space plasma can introduce pointing error noise. In this work, we quantitatively assess the effect of plasma on the pointing accuracy of TQ's inter-satellite laser links. We employ a magnetohydrodynamic model to simulate the plasma distribution around the TQ orbit for different orbital orientations. Using the fourth-order Runge-Kutta method to conduct the ray-tracing calculations over a TQ orbital cycle under a solar wind dynamic pressure close to the 23-year average, we find that the plasma-induced laser deflection angle and pointing eccentricity are on the order of $10^{-20} \ \mathrm{rad}$ and picometers, respectively. These values are significantly lower than TQ's requirements. Our results demonstrate that the impact of space plasma on TQ's pointing error is negligible in moderate space weather conditions, indicating a positive outlook for the TQ mission.

Xing-Hui Feng, Bo Wang

Published: 2026-10-29

Categories: gr-qc

We investigate axial quasinormal modes of black holes embedded in Hernquist halos, using an established analytic static geometry with an inner vacuum cavity extending to $4M_{\mathrm{BH}}$ and solving for frame dragging to first order in rotation. We compute the fundamental and first overtone branches for mass ratios $ε\equiv M_{\mathrm{BH}}/M_{\mathrm{halo}}$ of $0.1$ and $0.01$, and halo compactness $\mathcal C\equiv M_{\mathrm{halo}}/a_0$ in the range $10^{-4}\leq\mathcal C\leq0.3$. The cavity geometry gives a local Kerr estimate in which redshift rescales the vacuum frequencies, horizon angular momentum sets the rotational splitting, and uniform frame dragging adds a real frequency shift. At zero spin, the cavity redshift reproduces the complex $\ell=2$ frequencies with relative residuals below $0.04\%$ for the fundamental and $0.31\%$ for the first overtone. Its leading weak compactness behavior, $1-\mathcal C$, explains the weak mass ratio dependence in dilute halos; at larger compactness, the exact redshift accounts for most of the separation between the two mass ratio sequences. At fixed total angular momentum, halos with vanishing local angular momentum and those with vanishing coordinate angular velocity exhibit opposite compactness trends in the real spin coefficient. At $\mathcal C=0.3$, their real fundamental mode spin coefficients differ by approximately $38\%$ and $54\%$ for the two mass ratios. Fixing the horizon angular momentum reduces these differences below $1\%$ for both overtones, showing that angular momentum partition accounts for most of the configuration dependence.

Mariam Campbell, Eduardo Bittencourt, Peter K. S. Dunsby

Published: 2026-10-29

Categories: gr-qc

We formulate the static, spherically symmetric vacuum equations of power-law metric $f(R)$ gravity as a covariant autonomous system using the $(1+1+2)$ formalism. The finite critical sets include the scale-invariant Clifton--Barrow solution, a Minkowski endpoint shared by the Schwarzschild family, and degenerate boundaries of the normalized chart. The Clifton--Barrow equilibrium is an outward-radial attractor over a positive interval of the power-law parameter, whereas the Schwarzschild endpoint is a saddle of the polynomially extended system. Poincaré compactification, supplemented by secondary and weighted charts, resolves several asymptotic regimes. In particular, normally attracting sheets at large normalized curvature occur in the positive-curvature sector and are separated from the negative-curvature Clifton--Barrow equilibrium. Metric reconstruction also identifies a selected scalar-flat family with a regular throat, one asymptotically flat end, and a curvature-singular end. These results organize the regular reduced chart and the boundary regimes resolved here; they do not constitute a complete classification of static spherical vacua. All stability statements concern the static radial flow.

Hao-Kang Chen, Pan-Pan Wang, Cheng-Gang Shao

Published: 2026-10-29

Categories: gr-qc

Space-based gravitational-wave detectors compare laser phases exchanged between distant spacecraft. Offset phase locking keeps beatnotes in the phasemeter band, while time-delay interferometry suppresses laser frequency noise. A disturbance of one reference can degrade the functions that depend on it, making robustness an additional criterion for choosing a phase-reference architecture. We introduce a quantitative comparison based on established cascade equations and percolation measures, with directed reference graphs and Erdős--Rényi support layers. Under uniform disturbances, the robustness score is determined by the reference-depth distribution. Under nonuniform disturbances and partial dependence, the connected-support criterion can select a different configuration from both the published depth and local-lock criteria and a reference-path baseline. The phase-locking comparisons favor configurations that limit accumulated degradation and supply downstream lasers from references retaining greater connected support. Paired finite-network calculations support these differences in preference. In a separate comparison of optical-input support for time-delay interferometry, requiring connected support on all spacecraft gives a different preference from requiring it on at least one spacecraft. These findings identify disturbance location, reference dependence and the required extent of support as factors that can change architecture selection. Within the stated statistical model, robustness rankings can complement phase-locking feasibility and interferometric performance when prioritizing configurations for space-based gravitational-wave detectors.

Probit J Kalita, Subha Mitra, Bharat Kumar

Published: 2026-10-29

Categories: hep-th

Axion-like particles (ALPs) that couple to protons are produced in a core-collapse supernova, and the slow ones remain bound to the new neutron star. Bose, Ganguly, Kumar, and Raj [arXiv:2610.30255] proposed that the photons from the decay of this bound cloud reheat old neutron stars, and they derived strong limits on the ALP-photon coupling. They neglected the absorption of the ALPs by the star, but a bound ALP on an orbit that enters the star and reaches 50 km crosses it about $6\times 10^{18}$ times over the 333 Myr age of PSR J2144$-$3933. We show that inverse nucleon bremsstrahlung in the cold star absorbs every ALP whose orbit enters it within minutes, long before it decays, so only ALPs born outside the final star on nearly circular orbits survive; they carry $9\times 10^{-9} - 6\times 10^{-5}$ of the heating. We compute the protoneutron-star evolution, the production, the general-relativistic orbits and the absorption ourselves, for twelve protoneutron-star evolutions, three nucleon-bremsstrahlung rates normalized to the same supernova energy loss of light ALPs, and equations of state with and without $Δ(1232)$ isobars. PSR J2144$-$3933 still excludes a window at $m_a\simeq 7.7-196$\ MeV, with a lower edge in the photon coupling $280-700$ times higher than without absorption. Pion conversion and the $Δ(1232)$ resonance, which raise the production of surviving ALPs more than their absorption, widen this window to $m_a\simeq$ $7.7-260$\ MeV. The window depends at similar levels on the bremsstrahlung rate and on the radius of the final star. It requires a direct photon coupling that cancels the one induced by ALP-pion mixing, and existing supernova gamma-ray limits may already cover it.

Wen-Xiang Chen, M. Zeeshan Gul

Published: 2026-10-29

Categories: gr-qc

We extend the analysis of local horizon remnants in quadratic non-metricity gravity to a specific matter trace theory with the functional form f(Q) = Q + alpha Q^2 + 16 pi lambda T. Here, the matter trace is defined by contracting the energy-momentum tensor with the metric from the original matter action. In the absence of explicit lambda-corrections, the theory inherits the vacuum logarithmic-connection hairy branch. To obtain a non-zero trace, we introduce polynomial non-linear electrodynamics and construct an exact magnetic branch in coincident Cartesian Kerr-Schild coordinates. The non-metricity scalar of this branch vanishes, while its matter trace is proportional to the inverse eighth power of the distance. Its metric component function is given by 1 - 2M/r + q^2/r^2 + C/r^6, where the correction term C equals xi(1 - 4 lambda)q^4 / 10. Consequently, the quadratic non-metricity coupling is sterile on this branch. We derive the metric and matter equations, the Euclidean temperature, the single-horizon remnant, the master scalar equation, and the first-order gauge shift. The logarithmic derivative of the matter trace imparts a winding number of -8 on a closed contour enclosing the central singularity, but a winding number of zero on a sufficiently small horizon contour. Nevertheless, the temperature and scalar propagation still vary continuously with the correction coefficient. Therefore, the trace winding number classifies divisor data rather than superseding the matter trace or determining its backreaction. This analysis also demonstrates a degeneracy between the trace coupling coefficient and the non-linear electromagnetic coefficient. These results are specific to this particular branch; this paper does not expound upon the full coupled gravity spectrum, nor does it claim priority for this magnetic metric.

Antonino Flachi

Published: 2026-10-29

Categories: gr-qc

We build an acoustic black hole in a lattice model: a draining vortex evolved by the local collide-and-stream rule of a lattice-Boltzmann model, with no acoustic metric imposed, the geometry being measured from the steady state. A horizon emerges, first located from the measured Mach profile and then confirmed by phonon ray tracing on the measured metric, and the ringdown after a perturbation follows approximately the quasinormal frequencies of the draining bathtub. The residual departures are traced to the cell-scale structure of the horizon, which is not an ideal absorber. We model it in two ways: as a reflective horizon on the ideal bathtub, with two free parameters (the modulus and phase of the reflectivity), and as the sonic point of the realised flow absorbing in its own frame, with no adjustable parameter. The second describes the horizon and the non-rotating spectrum best. Superradiance has two ingredients: the emergent geometry, which amplifies in a loss-free calculation on the measured metric, and the horizon, whose absorption frame sets the width and strength of the amplified band but leaves no trace in the ringdown. Both models are used to examine superradiance, which has not been observed in the present toy model: whether the lattice hole superradiates dynamically remains open. The lattice leaves its own imprint as well: a fourfold anisotropy of the sonic surface and a surface gravity set by the cell-scale structure of the horizon.

D. Santana, C. Usca, J. Andrade, J. O. Cedeño

Published: 2026-10-29

Categories: gr-qc

We construct anisotropic self-bound stellar configurations through gravitational decoupling in the minimal geometric deformation framework and investigate their stability against linear radial perturbations. Retaining the Tolman IV temporal potential, we impose the generalized linear equation of state $P_r=η(ρ-ρ_s)$ on the complete matter distribution. Central regularity and Schwarzschild matching determine the radial geometry and relate the surface density to the compactness and stellar radius. Closed-form solutions are obtained for $η=1,1/2,1/3,1/4$, including the MIT bag radial relation when $η=1/3$ and $ρ_s=4B$. Since the equilibrium anisotropy does not determine its dynamical response, we introduce two material prescriptions that preserve either the anisotropy of each fluid layer or its ratio to $ρ+P_r$. Including metric perturbations, we compute the fundamental mode and three overtones for twelve equilibrium configurations under both prescriptions. All 24 background response combinations have positive fundamental squared frequencies, establishing linear radial stability within the adopted closures. The fundamental eigenvalue decreases with compactness within each sampled family, while changing the anisotropic response produces shifts whose direction depends on the background. Tangential tensions in several configurations and the failed tangential profile diagnostic of the maximally stiff family limit their physical interpretation. These results provide analytically tractable self-bound backgrounds and demonstrate that identical equilibrium configurations can support distinct radial spectra depending on their anisotropic material response.

Bruno Le Floch, Philippe G. LeFloch

Published: 2026-10-29

Categories: gr-qc

We construct complete vacuum initial data sets with prescribed asymptotically flat exterior geometry, including the gluing of two Schwarzschild exterior regions with small masses (which need not be positive). The construction allows for arbitrarily slow leading decay and nonzero second fundamental form. For leading terms with a fixed radial power, we first construct localized seed data sets whose constraint errors decay to any prescribed finite order, then apply the projection and stability theorems of our companion papers. The resulting vacuum data sets differ from seeds by harmonic terms controlled by Hamiltonian and momentum silhouettes, and by super-harmonic corrections. This difference of harmonic terms is measured by a relative notion of ADM energy-momentum, which is defined even for slowly-decaying data sets that do not admit an ADM energy-momentum. Upon adjusting seed data sets by either harmonic-decaying terms or compact transverse-traceless terms, we freely control this relative ADM charge and, when it exists, the total ADM charge. In particular, when gluing Schwarzschild metrics the total ADM mass can be specified independently of the Schwarzschild mass parameters. Together with our companion papers, these results establish a constructive theory of optimal localization beyond harmonic decay.

Jia-Xi Feng, Yang Yu, Yan-Heng Yu, Xian Gao, Qing-Guo Huang

Published: 2026-10-29

Categories: gr-qc

We study scalar-induced gravitational waves (SIGWs) in a spatially covariant gravity model with two tensorial degrees of freedom, minimally coupled to a $k$-essence scalar field. For the parameter choice considered during radiation domination, the quadratic tensor action coincides with that of general relativity (GR). We derive the scalar transfer functions at finite $σ\equiv C_2\bar N$ and in the large-$|σ|$ limit. We then construct the source function of SIGWs. We further examine a cubic extrinsic-curvature interaction that modifies the source function of SIGWs without affecting the background or quadratic actions. We calculate the fractional energy density of SIGWs for monochromatic and log-normal primordial curvature power spectra. We find that, for the positive values of $σ$ studied, finite-$σ$ effects suppress the spectrum over a broad range of scales relative to the result in the $σ\rightarrow \infty$ limit. In this limit, the cubic interaction suppresses the spectrum at small wavenumbers and enhances it at larger wavenumbers. These results show that modified scalar dynamics and non-linear interactions can alter the fractional energy density of SIGWs even when the quadratic tensor action is identical to that of GR.

Lin-Lin Yang, Hao Yu, Pan-Pan Wang, Jin Li, Cheng-Gang Shao

Published: 2026-10-29

Categories: gr-qc

This paper investigates the energy-flux noise induced by imperfections of the Gaussian beam (GB) in the Li-Baker high-frequency gravitational wave (HFGW) detector. Modeling these imperfections with higher-order Laguerre-Gaussian (LG) beams, we analytically derive the resulting noise-to-signal ratio for both co- and cross-polarized $\mathrm{LG}_{nl}$ modes. It is found that higher-order co-polarized LG beams generate no tangential energy-flux noise at the optimal detection plane ($φ=π/2$ or $3π/2$), whereas higher-order cross-polarized LG beams introduce non-negligible noise. Specifically, for an individual higher-order cross-polarized $\mathrm{LG}_{nl}$ mode under our representative parameters, maintaining the noise-to-signal ratio below unity typically requires the power fraction to satisfy $σ_{nl}<10^{-46}$, with the $\mathrm{LG}_{01}$ mode imposing the most stringent constraint of $σ_{01}<6.0\times10^{-49}$. Monte Carlo simulations suggest that the total power fraction $σ_{\mathrm{total}}$ of multiple higher-order cross-polarized $\mathrm{LG}_{nl}$ modes needs to remain below $10^{-49}$. Consequently, we propose employing a polarization filter to retain only the co-polarized component of the GB adopted in the practical experiment, thereby suppressing the noise while preserving signal integrity. These results provide theoretical guidance for noise control in the Li-Baker HFGW detector.

Jian-hua He

Published: 2026-10-29

Categories: gr-qc

We simulate the gravitational lensing of gravitational waves (GWs) by a Kerr black hole using a $(1+1)$-dimensional time-domain mode-sum approach. To enable efficient explicit time evolution, we implement a localized hyperboloidal foliation combined with a static field redefinition, ensuring bounded characteristic speeds across an extended, uniform tortoise-coordinate grid. Incident GW initial data are constructed by projecting a plane-wave Weyl tensor onto the Kinnersley tetrad. Through local spin-dyad rotations and Wigner $D$-matrix transformations, our framework accommodates both idealized wave packets and realistic binary coalescence signals at arbitrary incidence and polarization angles. To accurately resolve the lensed waveforms, we evolve over $68,000$ coupled $(j,m)$ modes. Our results reveal that a Kerr black hole acts as a diffraction-limited thick lens, focusing GWs into a forward beam. For idealized wave packets, the primary prompt pulse exhibits a spin-independent transverse Gaussian profile, whereas the subsequent lensing coda is sensitive to the black hole's spin. For binary coalescence signals, strong-field lensing substantially modifies the post-merger ringdown. However, the lensed inspiral and merger phases in Kerr and Schwarzschild backgrounds are virtually identical, yielding waveform mismatches below $2.2\times10^{-5}$ across various inclinations and polarizations. These findings demonstrate that non-spinning Schwarzschild models provide an accurate and computationally economical surrogate to search for strong-field lensing signatures with current ground-based detectors.

Changkai Chen, Xiaohua Zhang, Zhoujian Cao, Jiliang Jing

Published: 2026-10-29

Categories: gr-qc

We develop a double-confluent Heun (HeunD) method that extends our construction of complete quasinormal-mode (QNM) spectra to extremal Kerr black holes. Matching the horizon-ingoing and infinity-outgoing radial solutions together with angular regularity yields the frequencies directly at extremality, without extrapolation from nonextremal spins. For gravitational perturbations, we obtain an expanded spectrum on both conventional and unconventional Riemann sheets, including additional QNMs revealed by analytic continuation across frequency branch cuts. Continuation in spin connects the extremal modes to our complete Schwarzschild spectrum, including its unconventional branches. We show for the first time that unconventional Class I sequences with $m<0$, continued from unconventional Schwarzschild modes, approach negative superradiant bounds with vanishing damping in the extremal limit. We also identify finite-damping modes interspersed among sequences approaching zero damping, showing that a single overtone cutoff cannot describe the transition to extremality. Independent scattering-amplitude calculations verify representative frequencies and their sheet assignments, while a contour count establishes spectral completeness within a bounded frequency domain. Uniform matching near the superradiant bound further distinguishes critical accumulation from isolated extremal QNMs and resolves the associated Riemann-sheet structure. These results bring extremal Kerr into our unified treatment of black-hole QNM spectra and reveal how the Schwarzschild mode families reorganize in the extremal limit.

Ansh Gupta, Naritaka Oshita

Published: 2026-10-28

Categories: gr-qc

Black hole ringdowns are modelled as a superposition of quasinormal modes (QNMs), although the branch cut of the Green's function produces a nonoscillatory tail that may contaminate early-time ringdown analyses. Within linear perturbation theory, we quantify this branch-cut contribution for the scattering of localised Gaussian wave packets by a Kerr black hole with mass $M$. Defining the onset of ringdown as the earliest time at which the QNM and branch-cut contributions reconstruct the waveform, we evaluate the branch-cut amplitude relative to the QNM amplitude. For wave packets with a characteristic frequency $ω_0\sim 1/M$, the branch-cut amplitude is typically of order $10\%$ of the QNM amplitude at ringdown onset with only a mild dependence on spin. We further find that the tail waveform before convolving with a source is almost independent of spin. The spin dependence of the relative amplitude therefore resides primarily in the excitation of the QNMs. Our results suggest that the branch-cut contribution may affect the accuracy of black hole spectroscopy, particularly near the onset of ringdown.

Zachary J. Hoelscher

Published: 2026-10-28

Categories: hep-th

It has recently been argued that cosmological horizon thermodynamics and black hole thermodynamics are generically inequivalent in any consistent, UV complete theory of quantum gravity, where it was suggested that this could be falsified by the identification of a counterexample. This conjecture was motivated in part by noting that cosmological horizons do not incorporate many of the convenient features found in the black holes described by string theory. In this work, we consider as a toy model a universe with a single non-rotating black hole and a positive cosmological constant. We work in the Nariai limit where the mass of the black hole is taken to its maximum possible value, and where we also assert that the quantum field theory living on this background is strictly parity invariant. In the semi-classical regime where we neglect instability of the exact Nariai equilibrium under quantum fluctuations, we find that the observer cannot readily distinguish the physics in the neighborhood of the black hole horizon from the physics in the neighborhood of the cosmological horizon. This does not prove that the two are generically equivalent in any universe, though it does suggest that they cannot be entirely unrelated in general. We propose that any consistent theory of quantum gravity that aims to describe black holes in a universe with a positive cosmological constant should provide a related microscopic origin for the leading semiclassical cosmological entropy and black hole entropy in the neighborhood of the particular limit considered here.

A. Racioppi, M. Vijar

Published: 2026-10-28

Categories: astro-ph.CO

We revisit single-field slow-roll inflation driven by a running cosmological constant, i.e. a cosmological constant receiving a logarithmic radiative correction, in light of the latest CMB-BAO data. The relative radiative correction $δ$ is treated as a free parameter of the model and allowed to be positive or negative. For positive $δ$, the predictions interpolate between a logarithmic regime and a linear inflation one. Compatibility with CMB-only data is confined to a narrow stripe near the $2σ$ border where $δ$ is relatively large. On the other hand, the predictions fit easily within the constraints including BAO data in a wide range of parameters. For negative $δ$, the slow-roll approximation breaks down at small field values and the predictions are excluded by data. However, once the effective mass contribution inside the logarithmic correction is taken into account, the negative $δ$ potential develops a local maximum and behaves like a hilltop model, achieving compatibility with CMB-only data, while agreement with CMB-BAO data is possible only at $2σ$.

Sk Md Adil Imam, Macarena Lagos

Published: 2026-10-28

Categories: gr-qc

Gravitational-wave observations of compact binaries offer a direct way to test whether gravity admits polarizations beyond the two tensor modes of general relativity. We perform a forecast to assess how well future multi-messenger events will constrain the presence of scalar polarizations in gravitational waves. Performing binary neutron star injections, we forecast next-generation constraints on three modified gravity parameters in the PPE formalism: $α$ (tensor amplitude), $α_B$ (scalar amplitude) and $β$ (tensor and scalar phase). Cosmic Explorer (CE) and Einstein Telescope (ET) each tighten every parameter by 1--2 orders of magnitude over an O5 LIGO-Virgo network, with ET's triangular geometry giving a persistent $\approx2\times$ improvement over 2$\times$CE on the scalar-mode amplitude $α_B$ in both a GW170817-like and a second, representative BNS. We show that, if the sky position and luminosity distance are known from EM observations, adding an EM-based prior on the orbital inclination $ι$ narrows the $α_B$ constraint by $\approx56\times$ relative to an isotropic inclination prior, for a GW170817-like event. We also assess how EM inclination priors as well as assumptions on the neutron star equation of state may affect the inference on the scalar amplitude $α_B$. Overall, these results indicate that detector geometry and the availability of well-placed EM external information are both important levers --- alongside raw network sensitivity --- for next decade scalar-polarization tests.

David A. Lowe, Yiru Wang, Juanyi Yang

Published: 2026-10-28

Categories: hep-th

We reconstruct linearized gravitational perturbations in $AdS_{4}$ from a conserved, traceless stress tensor on a fixed conformally flat boundary metric, extending our earlier real Lorentzian construction. For admissible data with no spacelike Fourier support in a flat conformal frame, the physical response reduces to an integral over boundary light-cone cuts. Boundary improvements restore Fefferman--Graham (FG) gauge while preserving normalizability and the linearized Weyl tensor. We then reconstruct perturbations with general spacelike boundary momentum, including nonzero frequency and its zero-frequency limit, using explicit position-space generalized functions on real stress data. Boundary kernels are constructed for normalizable perturbations and sufficient conditions are derived for the reconstruction to converge. The results motivate controlled flat-space limits relevant to Bondi--Metzner--Sachs symmetries and celestial holography.

Konstantin Beyer, Niklas E. Önne, Shimon Kolkowitz, Dolev Bluvstein, Mikhail Lukin, Jun Ye, Igor Pikovski

Published: 2026-10-28

Categories: quant-ph

Atomic clocks achieve extraordinary precision through quantum control over large ensembles of atoms, with precision increasing and atom number advancing steadily. Emerging nuclear clock technology encodes clock states in nuclear rather than electronic transitions, offering a new frontier for precision measurement. Here we study whether a large ensemble of such clock nuclei could be used to observe their mutual gravitational interaction. We investigate the gravitational redshift induced by neighboring atoms, including nuclear energy superpositions as sources of gravity, giving rise to a genuinely quantum gravitational interaction between pairs of nuclei. We find that the resulting clock frequency shift due to mutual gravity may become non-negligible for a macroscopic number of nuclei, for instance in a solid-state thorium clock, and we propose approaches to mitigate electromagnetic field effects by exploiting spatial symmetry and high-precision spectroscopy. We further discuss how energy-induced mass superpositions could be directly probed using external gravitational field sensors. By contrast, observing gravity-induced entanglement involving clocks would require substantially greater experimental advances due to decoherence from spontaneous emission. Taken together, our results suggest that nuclear clocks, either alone or in combination with complementary sensors such as optomechanical systems, may offer a future route toward probing gravity at short distances and testing gravitating quantum source masses beyond the Newtonian limit.

Francisco Tello-Ortiz

Published: 2026-10-28

Categories: gr-qc

Black-hole interiors with an inner (Cauchy) horizon are unstable through the Poisson-Israel-Ori mass-inflation mechanism, governed by the Dray-'t Hooft-Redmount relation and widely regarded as a dynamical realization of strong cosmic censorship. We show that static, spherically symmetric anisotropic interiors supported by a marginally divergent but integrable density $ρ\sim A/r^2$, with $A>1/(8π)$ and mild screening at finite radius, are incompatible with this mechanism. The compactness $q=m/r$ decreases monotonically from a super-critical central value to $1/2$ at the unique event horizon, producing a strictly positive compactness gap throughout the trapped region and excluding any second zero of the lapse. This gap enters the dynamics quantitatively. (i) Under the null energy condition and a dynamical screening condition, $2m/r$ is non-decreasing along both future null directions of a trapped domain, so the gap propagates under nonlinear spherically symmetric evolution. (ii) For ingoing radiation (generalized Vaidya), the gap bounds the blueshift: the advanced time spent in the gapped region is finite, whereas it diverges at a Cauchy horizon. (iii) For counter-streaming null dust, the radiative part $μ$ of the Misner-Sharp mass obeys exactly $\partial_u\partial_vμ=2\,\partial_uμ\,\partial_vμ/(r|f|)$, of which the DTR relation is the thin-shell form; the in-out coupling $2/(r|f|)$ is uniformly bounded on the interior precisely when the gap is positive. This yields an a priori mass bound and, in the Ori thin-shell model, an e-folding rate bounded by the influx luminosity instead of tending to the inner-horizon surface gravity. Integrable-singularity interiors thus realize a class of sources for which the Poisson-Israel-Ori amplification channel is structurally inoperative in the models in which mass inflation was originally established.

Gianluca Calcagni, Iván Salvador-García

Published: 2026-10-28

Categories: hep-th

Fractional field theory is a promising framework wherein to quantize the gravitational interaction but the presence of nonlocal operators can make its handling difficult. With the purpose of easing this problem, we recast the theory as a local dual in two ways. First, we generalize the Caffarelli--Silvestre extension theorem to self-adjoint fractional field theories with multi-scale kinetic terms and nonlocal interactions, taking the example of a scalar field. The latter is reinterpreted as a nonlocal boundary degree of freedom holographically dual to a local theory of two scalars living in a higher-dimensional bulk. However, inclusion of a local non-linear potential is not straightforward. We therefore propose an alternative picture where the nonlocal theory is not extended to a higher-dimensional space but is localized at the price of introducing a continuum of masses. This \emph{spectral localization} allows for a natural implementation of the fakeon prescription and the related classicization procedure, already employed in local theories with higher-derivative and complex ghosts. Applications to fractional quantum gravity and its comparison with quadratic quantum gravity are discussed.

Philippe G. LeFloch, Yue Ma

Published: 2026-10-28

Categories: gr-qc

We establish the general-relativistic limit of f(R) gravity coupled to a massless scalar field for small, asymptotically Euclidean, well-prepared Cauchy data near Minkowski spacetime. We prove global existence and future causal geodesic completeness, with uniform estimates for the metric, matter, and rescaled effective field as an admissible family of modified Lagrangians f(R) approaches the Einstein-Hilbert Lagrangian R. The physical and conformal metrics and the matter field converge to the limiting Einstein-massless-scalar development, uniformly on the entire future spacetime, together with finitely many space and time derivatives. The effective field, defined by a nonlinear reparametrization of the physical scalar curvature, converges to the scalar curvature of the limiting Einstein development. The main analytical difficulty is that the effective-field mass tends to infinity, while its evolution equation becomes an algebraic trace relation. Small field amplitudes may coexist with high-frequency oscillations and comparatively large derivatives, whose quadratic contributions must be controlled uniformly. Using the Euclidean-hyperboloidal foliation method and adapted wave coordinates, we analyze a quasilinear wave-Klein-Gordon system whose nonlinearities do not satisfy the classical null condition. We combine oscillatory estimates, weighted interior and exterior energies, and propagation estimates for the discrepancy from the Einstein trace relation. Quantitative convergence on compact regions and uniform spacetime decay yield global convergence.

Tore Boybeyi, Vuk Mandic, Joseph Romano

Published: 2026-10-28

Categories: gr-qc

Over the past decade, the Advanced LIGO, Advanced Virgo, and KAGRA detectors have detected nearly 400 compact binary mergers, most of which are stellar-mass binary black-hole (BBH) mergers. Nevertheless, most mergers in the Universe are too weak to be individually detected at current sensitivity levels. Since a BBH merger in band is much shorter than the average time between successive mergers, the population of these subthreshold events gives rise to an intermittent background of gravitational waves (GWs). This GW background is guaranteed to exist, but it has not yet been detected with current stochastic or deterministic searches. Here we propose a fast and accurate likelihood-based search for this background, which unifies the standard model-agnostic cross-correlation search and a fully deterministic, template-based search in a single likelihood. Our search is based on a truncated likelihood ratio, which is fully marginalized over the extrinsic parameters of the individual mergers, and which represents the data in two detectors as an expansion in terms of approximate sufficient statistics. These statistics are higher-order cross-moments of the data, weighted by geometrical factors that generalize the standard overlap reduction function (ORF) used in cross-correlation searches. We show that almost all the Bayesian evidence and information on the BBH merger population comes from correlations between frequency bins induced by individual mergers and is captured in the higher-order generalized ORFs. Consequently, any likelihood function that does not take these inter-frequency correlations into account is necessarily suboptimal. We validate our search on one year of simulated Advanced LIGO data, and find that a catalog-informed analysis, which uses information from both the detected and unresolved mergers, can infer the peak of the redshift distribution of the population of BBH mergers.

Tore Boybeyi, Vuk Mandic, Joseph Romano

Published: 2026-10-28

Categories: gr-qc

The stochastic gravitational-wave background from stellar-mass compact binaries is non-Gaussian since it is made up of a finite number of individual mergers. Over the years, several methods have been developed to search for this background beyond the standard cross-correlation statistic. We reformulate the data analysis problem for such astrophysical backgrounds in terms of the characteristic function of the data in multiple detectors, and show that the existing searches arise as different limiting cases. We also show that new searches can be constructed through different approximations of the characteristic function, which gives a concrete way to engineer suitable approximate sufficient statistics. To illustrate this framework in the context of a simple example, we use the formalism proposed here to analyze an exactly solvable toy model.

Jorge Castelo Mourelle, Saeed Fakhry, Néstor Ortiz

Published: 2026-10-28

Categories: gr-qc

In the massless Damour-Esposito-Farèse scalar-tensor theory of gravity, we numerically construct static, spherically symmetric star models composed of a mixture of fermionic and bosonic matter, interacting purely gravitationally. The fermionic sector is modeled as a perfect fluid, while the bosonic sector is described by a massive, free, complex scalar field. We demonstrate that mixed fermion-boson stars can undergo spontaneous scalarization, and we systematically investigate the role played by the bosonic field across different regimes of bosonic mass, central fermionic pressure, and central bosonic amplitude. Our analysis reveals a complex interplay among the parameters, giving rise to a variety of scalarized configurations, ranging from fermionic matter embedded within extended bosonic halos to bosonic cores confined within fermionic matter. We examine sequences of solutions, in particular mass-radius surfaces, and we determine the critical coupling parameter for the onset of scalarization.

Jorge Castelo Mourelle, Saeed Fakhry, Néstor Ortiz

Published: 2026-10-28

Categories: gr-qc

We examine the observational viability of scalarized fermion-boson stars (FBSs) in massless Damour-Esposito-Farèse gravity, using the MPA1 nuclear equation of state and a self-interacting complex scalar field playing the role of an ultralight bosonic dark matter model. Constraining stellar models within a multi-messenger-motivated mass-radius window, we obtain three main results: First, bosonic dark matter acts as a catalyst for spontaneous scalarization. Second, energetically favored configurations are scalarized FBSs featuring bosonic dark matter cores that reconcile strongly coupled regimes with radius bounds. Third, dark matter cores tend to suppress scalar charges, which mimics the effect of a massive gravitational scalar field and could contribute to evade observational constraints. Additionally, the exclusive prediction of scalarized FBSs at high masses suggests a way to test this theoretical scenario.

Abhishek Rout

Published: 2026-10-28

Categories: gr-qc

We study odd-parity perturbations of Reissner-Nordström black holes in dynamical Chern-Simons gravity. The dCS action is parity invariant because $\vartheta\,{}^{*}RR$ is the product of two pseudoscalars; nevertheless, the pseudoscalar perturbation has odd parity and enters only the axial sector at linear order and so lifts the axial--polar isospectrality of general relativity. We derive the finite-charge couplings between the pseudoscalar and the axial gravitational and electromagnetic perturbations directly from the linearized field equations. Both directions are governed by the radial kernel $(Mr-Q^2)Δ/r^8$, and at nonzero charge the pseudoscalar couples to $Ψ+χΨ_e$, with $χ=2Q/[r\sqrt{(l-1)(l+2)}]$. After diagonalizing the Einstein--Maxwell sector, we compute branch-resolved quasinormal-mode shifts with exterior complex scaling for the photon-sphere modes and Frobenius shooting for the near-extremal zero-damping modes. For the Schwarzschild $l=2$ fundamental mode we obtain $β\,δω=-0.7733-0.3946\,i$ (units $M=α=1$). Off resonance, the gravitational-led shift scales as $ζ\,l^3$ at $Q=0$ but as $ζ\,l^2/Q$ at fixed nonzero charge and large $l$. The electromagnetic-led branch becomes exactly degenerate with the pseudoscalar mode at $Q_c=2M\sqrt{l(l+1)+1}/[l(l+1)+2]$, where the pseudoscalar potential coincides with the polar partner of the electromagnetic-led potential; there the breaking is $\mathcal{O}(\sqrtζ)$, $M|Δω|\simeq2.4\sqrtζ$ for $l=2$, and the shift reverses sign across $Q_c$. Near extremality the photon-sphere shifts remain finite, whereas the non-degenerate fundamental gravitational-led zero-damping mode is suppressed, $δω/ω\simeq6.0\times10^{3}\,ζ\,(1-Q^2/M^2)$ for $l=2$.

Nikodem Popławski

Published: 2026-10-28

Categories: gr-qc

The conservation law for the orbital plus spin angular momentum of a free Dirac particle in curved spacetime requires that the affine connection has the antisymmetric part: the torsion tensor, which extends general relativity to the Einstein$-$Cartan theory of gravity. In spacetime with torsion, the Dirac equation becomes a nonlinear, cubic equation in the spinor wave function. Under charge conjugation, the nonlinear term changes sign relative to the mass term. A Dirac spinor and its charge conjugate therefore satisfy different field equations. We use the spinor connection formalism to derive the Dirac equation for a spherical spinor in its centrally symmetric gravitational field with torsion. We determine the energy$-$momentum tensor for this spinor and show that the energy contribution from torsion is negative for matter particles and positive for antimatter particles. Consequently, the ground state of a fermion has a lower energy than the ground state of the corresponding antifermion. We also derive the Einstein$-$Cartan$-$Dirac equations for this spinor; they indicate the existence of particle-like soliton solutions exhibiting matter$-$antimatter energy asymmetry.

Jackson R. Fliss, Andrew Rolph

Published: 2026-10-28

Categories: hep-th

We revisit bounds on energy and entropy in semiclassical gravity, aiming to strengthen and unify established bounds, in particular the quantum focussing conjecture (QFC) and the smeared null energy condition (SNEC). Both the QFC and SNEC have important applications and are the strongest in their respective hierarchies; however, neither implies the other, nor reduces to the null energy condition (NEC) in the classical limit. To that end, we define a new class of bounds dubbed gravitational energy-entropy conditions (GEECs) that imply both the QFC and SNEC, and reduce to the NEC classically. We construct an explicit family of GEECs by imposing the defining criteria on a broad set of stress tensor bounds, and constrain its remaining parameter space through test cases, in an effective field theory-inspired approach. Our GEECs are powerful candidate bounds on energy and entropy in semiclassical gravity.

Mahmoud Hashim, Jackson Levi Said, Waleed El Hanafy, Eleonora Di Valentino

Published: 2026-10-28

Categories: astro-ph.CO

We place cosmological constraints on an extended exponential infrared (EExpIR) $f(T)$ teleparallel gravity model using current observational datasets. The extension is characterized by an additional parameter, $b$, which governs the late-time cosmological dynamics. Owing to the existence of two solution branches, phase-space analysis is employed to select the cosmological branch and to establish an appropriate prior range for the new parameter. In this framework, the torsion sector acts as an effective dark-energy component, exhibiting a smooth evolution from a quintessence-like phase to a phantom regime, while recovering the standard cosmological behavior at early times. To constrain the model parameters, we combine early-Universe observations from Planck, ACT, and SPT measurements of the CMB with late-time probes from DESI BAO and PantheonPlus Type Ia supernovae. Using the full dataset, including the SH0ES calibration, we obtain $b=0.573^{+0.016}_{-0.060}$ and $H_0=70.67^{+0.31}_{-0.35}~{\rm km\,s^{-1}\,Mpc^{-1}}$ at 68\% CL. Model comparison based on Bayesian evidence reveals that the EExpIR $f(T)$ and the $Λ$CDM models are statistically indistinguishable when only CMB data are considered, whereas the inclusion of the full cosmological dataset with SH0ES leads to a weak preference in favor of $Λ$CDM.

Shani Avitan, Ram Brustein

Published: 2026-10-28

Categories: gr-qc

General Relativity predicts that black holes lack an internal structure and that their tidal Love numbers vanish. However, if astrophysical black holes were instead ultra-compact objects (UCOs) with internal structure, their tidal Love numbers would no longer vanish. Then, during a binary inspiral, their tidal deformation could transfer orbital energy to the UCO, increasing the orbital period and leaving an observable imprint on the phase of the emitted gravitational waves. As we discussed previously, the effect is enhanced if one binary companion is resonantly excited. Here we use the point-particle effective field theory framework to calculate this enhancement. We consider circular orbits and focus on excitations of the internal electric quadrupole, modelling the UCO spectrum as a harmonic oscillator spectrum. However, our methods could be straightforwardly extended to more complicated situations. Integrating out the internal quadrupole induces a series of time-dependent finite-size operators with specific numerical coefficients, which we calculate. We find that the static electric quadrupole Love number $k_2$ is negative, and that all finite-size terms are proportional to $k_2$. We further show that resonant excitation induces a leading 2.5 Post-Newtonian term, compared with the 5 Post-Newtonian term in the time-independent case. Our results confirm the expectation that resonant excitation during a binary inspiral offers one of the best ways to detect whether astrophysical black holes can undergo tidal deformation and, if they do, learn about their internal excitation spectrum.

Jose Luis Blázquez-Salcedo, Luis Manuel González-Romero, Fech Scen Khoo, Burkhard Kleihaus, Jutta Kunz, Pablo Navarro Moreno

Published: 2026-10-28

Categories: gr-qc

We give an independent closed-form construction of rotating five-dimensional Ellis--Bronnikov wormholes with equal angular momenta and analyze the radial instability of the reflection-symmetric family. The nontrivial coupled metric equations reduce exactly to an open $A_2$ Toda system. The general two-ended solution is expressed in terms of elementary Toda tau functions; the symmetric subclass reduces to a particularly simple one-parameter family interpolating between the static wormhole and the extremal equal-spin Myers--Perry geometry. On this exact background we revisit the cohomogeneity-one perturbation problem. Besides the ordinary unstable mode of the static wormhole, rotation renders the descendant of its non-normalizable zero mode normalizable. The two purely imaginary unstable frequencies coalesce at $|J|/A=0.100628$, where their eigenvectors coalesce as well, identifying a second-order exceptional point. Beyond it the pair continues as $ω_\pm=\pmω_R+\mathrm iω_I$ with $ω_I>0$: the apparent loss of the radial instability found in the original real-eigenvalue treatment is therefore not stabilization, but a transition to an oscillatory instability. We follow this branch deep into the rapidly rotating regime, where its growth rate becomes strongly suppressed.

Eduard Kim, Oleg Kondrashov, Emin Nugaev, Yakov Shnir

Published: 2026-10-28

Categories: hep-th

We investigate the non-relativistic limit of spherically symmetric boson stars in (4+1)-dimensional general relativity (GR). In this limit, the resulting Newtonian theory exhibits an exact scale invariance, leading to a critical boson star configuration with a fixed global U(1) charge and vanishing binding energy. We identify the origin of these properties in the restored scale symmetry and analyze how relativistic and gravitational corrections break this symmetry. By comparing the full (4+1)-dimensional Einstein-Klein-Gordon system with the Wick-Cutkosky model, we quantify the effects of these corrections on the energy-charge relation and the kinematic stability of the configurations. Our results demonstrate how weak violation of scale invariance lifts the degeneracy of the non-relativistic solutions and determines the behavior of boson stars away from the critical limit.

Wen-Di Guo, Wentao Liu, Yu-Xiao Liu

Published: 2026-10-28

Categories: gr-qc

Quasinormal modes (QNMs) provide a powerful probe of strong-field gravity. We study fundamental scalar quasinormal modes of an asymptotically flat rotating black hole in the low-energy sector of Hořava gravity, whose exact scalar equation is nonseparable due to rotation-induced Lorentz violation. We develop two complementary approximations that both preserve the exact Kerr sector: Method I applies a slow-rotation approximation only to the nonseparable Lorentz-violating part, whereas Method II employs a small-$η$ biorthogonal spheroidal projection, with $η$ the Lorentz-violating parameter. Using residual-controlled continuation and symmetric finite differences, validated by a Kerr continued-fraction benchmark and an independent radial spectral method, we compute the linear frequency response. Axisymmetric modes provide an exact Kerr null test. For the corotating modes studied, the real-frequency response is positive and increases with spin. At $a/M=0.9$, the two methods reveal a roughly $2\%$ angular correction to the real response, while the imaginary response is nonmonotonic and highly sensitive to angular projection due to internal cancellation. These results highlight the distinct rotational signatures of Lorentz violation in black-hole ringdown.

Omid Yahyayi Monem, Hosein Mohammadzadeh

Published: 2026-10-28

Categories: quant-ph

A uniformly accelerated observer perceives the Minkowski vacuum as a thermal bath, so acceleration acts as a noise channel on correlations shared with an inertial partner. For a Dirac field in the standard treatment, the resulting map is a one-sided amplitude-damping channel, and entanglement and quantum discord survive at infinite acceleration. We introduce a symmetric Unruh-like map in which the vacuum and the one-particle state both exchange amplitude with the inaccessible Rindler region; for a Bell state it yields a bit-flip channel whose flip probability is the Fermi-Dirac occupation at the Unruh temperature. Using negativity, mutual information, and all six pairwise quantum discords, we find that the entanglement and discord between the inertial observer and the accessible mode vanish together at infinite acceleration, leaving only one bit of classical correlation. These results show that the fate of quantum correlations in noninertial frames depends on the structure of the Minkowski-Rindler map.

Chen-Yi Sia, Tee-How Loo, Avik De

Published: 2026-10-28

Categories: gr-qc

We present a systematic Hamiltonian analysis of the five-parameter class of theories known as Newer General Relativity. Quadratic nonmetricity theories of this type can be divided into nine types according to the structure of their primary constraints. After reviewing the framework of symmetric teleparallel gravity, we derive the ADM formulation of Newer General Relativity, discuss the existing classification and perform the Hamiltonian formulation of the theory. For each type, we compute the conjugate momenta, identify the primary constraints, and construct both the canonical and primary Hamiltonians. We then determine the constraint structure and analyze the resulting physical degrees of freedom in each type.

Safiqul Islam, Ayan Banerjee, Javlon Rayimbaev, Safyan Mukhtar

Published: 2026-10-28

Categories: gr-qc

We investigate how a fixed, spatially uniform axion angle modifies the rotational and static tidal properties of self-bound quark stars in general relativity, using an axion-extended Polyakov-loop Nambu--Jona-Lasinio equation of state. We vary $θ$ from $0$ to $π$ while holding the remaining model parameters fixed, and compute the leading-order moment of inertia and the second-order spin-induced quadrupole moment and mass shift. The calculation includes finite-surface-density contributions to the rotational mass shift and static tidal response. Across this range, the static maximum mass increases from $1.68$ to $1.95\,M_\odot$, remaining below the lower edge of the quoted $1σ$ timing interval for PSR~J0740+6620. At $M=1.338\,M_\odot$, the moment of inertia increases by $13\%$ and the dimensionless tidal deformability rises from $342$ to $547$. Over the common mass range examined, the differences in the moment of inertia between adjacent sampled angles exceed the tested interpolation and table-resolution sensitivities. Despite these changes, joint fits to the five sequences describe the $\bar I$--$C$ and I-Love-Q relations with maximum departures of $2.7\%$ and $0.4\%$, respectively, over the fitted domains. The predicted binary tidal-deformability curves lie within the estimated 90\% credible region of the adopted GW170817 posterior over the mass-ratio ranges examined. Within this EOS family, stellar properties vary appreciably with $θ$, while the normalized quantities admit accurate joint fits across the five sequences.

Tao Li, Hai-Bing Fu, Lei-Hua Liu

Published: 2026-10-28

Categories: hep-th

We study the circuit complexity of coupled curvature and entropy perturbations in two-field inflation. We start from the quadratic action and derive the full Hamiltonian. The Hamiltonian includes all diagonal and off-diagonal quadratic terms. We then obtain three coupled equations for the pair amplitudes of the four-mode squeezed state. From these amplitudes, we calculate the two principal squeezing strengths. We use them to determine the Nielsen circuit complexity. For an equal-weight Gaussian circuit, the complexity takes the form $\mathcal{C}_{2,k}=\sqrt{2(r_{1k}^{2}+r_{2k}^{2})}$. It depends on the squeezing strengths but not explicitly on the squeezing angles. Our numerical results show that the complexity grows after horizon crossing in both coupled and uncoupled models. Interfield coupling changes the pair amplitudes and the four-mode squeezed state. However, its effect on the circuit complexity is small for the parameters considered. This result shows that different four-mode pair-amplitude matrices can yield similar values of the chosen equal-weight circuit complexity. The present calculation provides a reference for studying Gaussian circuit complexity in more general two-field inflationary models.

Ian B Whittingham

Published: 2026-10-28

Categories: gr-qc

The present study investigates the feasibility of gravitational baryogenesis in a Gauss-Bonnet (GB) modified Randall-Sundrum (RS) type II braneworld cosmology. The modified expansion rate of the Universe in this scenario evolves through three distinct expansion regimes, the GB regime at early times where the expansion rate $H \sim ρ^{1/3}$ falls more slowly than the standard expansion law $H\sim ρ^{1/2}$ of GR, then the RS type era with an enhanced expansion $H \sim ρ$, before finally reducing to the standard expansion law in the low energy limit. Gravitational baryogenesis depends on $\dot{R}$ and requires $\dot{R} <0$. This condition is satisfied for the GB and GR regimes. However, $\dot{R}>0$ for the RS regime and successful baryogenesis requires either that the decoupling temperature occurs during the GB regime or that the Universe makes a direct transition from the GB regime to the GR regime. The GB baryon asymmetry $η(T)$ is proportional to $μ(1+w)(1-w)(1+1/β)$, where $μ$ is the energy scale $μ\equiv 1/l$ associated with the bulk curvature scale $l$, $β\equiv 4 αμ^{2}$, where $α$ is the GB coupling, and $w$ is the equation of state parameter $p=w ρ$. Studies of inflation in GB-braneworld cosmology place constraints on the allowed ranges of the parameters $μ$ and $β$. Guided by these, the asymmetry has been calculated for ranges of $(μ, β, w)$ and it is found that the observed values can be obtained for a value of $β$ within the range $(10^{-2} - 10^{-3})$ for $μ=10^{12}$ GeV, and within the range $(10^{-1}- 10^{-2})$ for $μ=10^{13}$ GeV. All values of $η$ for $μ=10^{14}$ are too high. In contrast to GR where $η$ is zero for a radiation dominated Universe ($w=1/3$), it is non-zero in GB braneworld cosmology.

Alex Koek

Published: 2026-10-27

Categories: gr-qc

General relativity, a theory that is already over a century old, is still the best theory that we have to describe the universe at energy scales where only the gravitational force is important. It has stood tall to any observational tests thrown at it since its inception, and it has remarkable predictive power when it is utilized to study and model astrophysical problems. It also continues to surprise us with its ability to generate new problems and insights that render themselves useful in the study of modern physics. This is especially highlighted by the transition of modern observational astronomy away from an electromagnetic radiation epoch, and into a new gravitational wave epoch. This thesis devotes its study to phenomena that can be analyzed within the framework of classical general relativity, but whose results may contain interesting implications for cosmological and black hole observations. (Full abstract can be found in document).

Yasuyuki Hatsuda

Published: 2026-10-27

Categories: gr-qc

We develop a systematic method to compute the high overtone expansion of Kerr quasinormal modes on normal angular branches to arbitrary order. We first obtain the expansion of the angular eigenvalue at large frequencies by a simple polynomial recursion. Using this result in an alternative form of the radial Teukolsky equation, we find that all the WKB corrections are defined on a fixed genus-one spectral curve, and that the quantum periods at the second and higher orders are expressed in terms of only two elliptic periods. This allows us to determine the expansion coefficients order by order. We confirm that the truncated expansions reproduce quasinormal frequencies obtained by solving the angular and radial equations directly, for scalar, electromagnetic and gravitational fields. We also compare the scalar results with the exact WKB analysis of extremal Kerr black holes.

Aleyna Akyüz, Keisi Kacanja, Rahul Dhurkunde, Alexander H. Nitz

Published: 2026-10-27

Categories: astro-ph.HE

The observation of orbital eccentricity in compact binary coalescences would provide a direct signature of dynamical formation environments. Previous matched-filter searches for eccentric neutron star-black hole (NSBH) binaries have been severely limited by computational constraints, necessitating the use of simplified waveform models that capture secular dephasing but omit apsidal precession and inter-orbit harmonics. Including these physical features increases the sensitive search volume for systems with $0.2 \le e_{20} \le 0.28$ by $\sim 25\%$ to $30\%$. We present a rapid matched-filter search methodology that makes the direct use of time-domain effective-one-body waveforms computationally feasible. By multibanding and high-frequency ratio-filtering, our pipeline achieves a $\sim 20\times$ reduction in computational cost. This allows a bank of 88.6 million effective-one-body templates, fifteen times larger than prior eccentric analyses, to search O4a and O4b Advanced LIGO data. We recover the known low-mass mergers GW230518_125908 and GW230529_181500 with parameters consistent with zero eccentricity. Finding no new gravitational-wave events with orbital eccentricity ($e_{20} \ge 0.05$), we place $90\%$ credible upper limits on the local merger rate density of eccentric NSBH systems across the search space of $\mathcal{R}_{90\%} \le 7.5\text{-}57\ \mathrm{Gpc}^{-3}\ \mathrm{yr}^{-1}$, up to a factor of $\sim 4$ improvement over previous observational bounds. At the parameters of GW200105_162426, this non-detection establishes an upper limit of $\mathcal{R}_{90\%} \le 12.1\ \mathrm{Gpc}^{-3}\ \mathrm{yr}^{-1}$. Alternatively, if GW200105_162426 is treated as an eccentric detection, the lack of subsequent detections in O4 updates the inferred local merger rate density of this population to $\mathcal{R} = 6.6^{+6.3}_{-3.8}\ \mathrm{Gpc}^{-3}\ \mathrm{yr}^{-1}$.

Federico Elizondo Lopez, Ivan Booth

Published: 2026-10-27

Categories: gr-qc

Five years ago Pook-Kolb, Hennigar and Booth published a series of three papers exploring the evolution of apparent horizons and other marginally outer trapped surfaces during a black hole merger. This was seen to be much more intricate than the well-known "pair-of-pants" merger associated with event horizons. In this paper we show that parameter evolutions of Brill-Lindquist-deSitter initial data mimic many of the features of that evolution. Hence, this analytic intial data is a useful testing ground for ideas about marginally outer trapped surface evolution and spacetime geometry during mergers.

Asma Tahar Taiba, Abdelaali Boudjemaa

Published: 2026-10-27

Categories: gr-qc

We study the thermodynamics of quadrupolar Bose-Einstein condensates in the realm of the generalized uncertainty principle (GUP) for the quest of understanding and testing quantum gravity (QG). Using both quadratic GUP (QGUP) and linear-quadratic GUP (LQGUP) which incorporate modified density of states, we calculate corrections to the condensed fraction, critical temperature, equation of state and other thermodynamic quantities. We find that the intriguing interplay of quadrupole-quadrupole interactions (QQIs) and the GUP may strongly modify the finite-temperature properties of the condensate, with the LQGUP generally predicting larger corrections than the QGUP, although their relative magnitudes depend on the chosen parameters and the validity of the perturbative expansion. We further estimate the sensitivity of the critical temperature to GUP-induced effects by imposing an assumed fractional temperature resolution which provides projected upper bounds on the GUP deformation parameters. Our findings demonstrate that quadrupole-quadrupole interacting Bose gases provide a promising platform for testing GUP-induced deviations from standard quantum mechanics and for probing QG phenomenology through measurements of finite-temperature many-body observables. They also motivate future studies using realistic system-specific parameters.

Kazufumi Takahashi, Yuki Watanabe

Published: 2026-10-27

Categories: gr-qc

We develop an inverse-design approach to the effective field theory (EFT) of perturbations in scalar-tensor gravity around static and spherically symmetric backgrounds with a timelike scalar-field gradient, taking the odd-parity effective potential as input and reconstructing compatible background and EFT data. As analytically tractable examples, we construct explicit realizations of the Pöschl-Teller potential, for which the quasinormal-mode spectrum can be obtained in closed form. We then study the Regge-Wheeler potential of general relativity and its parametrized deformations, showing how both can be realized within the scalar-tensor EFT. In particular, the latter realizations provide a route to interpreting phenomenological constraints on potential deformations from black hole ringdown observations in terms of the underlying EFT data.

Shawn Ray, Keefe Mitman, Vera Delfavero, Emily McPike, Jake Postiglione, Harrison E. Cook, Kaila Nathaniel, Nicolas Posner, Barry McKernan, K. E. Saavik Ford, Richard O'Shaughnessy

Published: 2026-10-27

Categories: astro-ph.HE

Binary black hole mergers (BBH) are currently observed by the gravitational-wave detectors LIGO, Virgo, and KAGRA (LVK). A fraction of these mergers are likely to originate in active galactic nuclei (AGN), but the details of the dynamical processes driving AGN channel mergers remain poorly understood. Monte Carlo For AGN Channel Testing and Simulation (McFACTS) is an open-source, public software used to simulate AGN channel BBH formation and evolution with configurable options for exploring various AGN and Nuclear Star Cluster (NSC) parameter options. Within McFACTS, BBH mergers evolve through gas drag and dynamical interactions, ignoring relativistic effects which can influence merger remnant properties. Here we demonstrate in McFACTS the effect of handing off inspiralling BBH to a numerical relativity (NR) surrogate model, which more accurately predicts the masses, spins, and kick velocities of merger remnants. Compared to a simple analytic approach to calculating merger and remnant properties the NR surrogate model is significantly more accurate at predicting remnant spins, which improve $χ_{eff}$ and $χ_{p}$ calculations, and recoil kicks, parameters especially important for higher generation BBH mergers. Our findings show the NR surrogate significantly changes distributions of remnant spins and kick velocities, as well as showing that alternative methods should be used cautiously in future studies. We also outline some simple models which are computationally efficient and can reproduce much of the NR surrogate model results.

Mah Noor Jamil, Parampreet Singh

Published: 2026-10-27

Categories: gr-qc

We compute the primordial tensor power spectrum in standard loop quantum cosmology and in the modified models mLQC-I and mLQC-II, evolving the tensor perturbations across the bounce in the hybrid and dressed metric prescriptions with a Starobinsky potential. In mLQC-I, the emergent de Sitter contracting branch requires the use of dedicated initial states. We use de Sitter mode function in the dressed metric approach and a Hankel-function solution in the hybrid approach. For inflationary e-foldings $N_e = 60$ and $65$, the pivot-scale tensor-to-scalar ratio agrees with the value of standard inflation with this potential. The scale-dependent ratio $r(k)=\mathcal{P}_T/\mathcal{P}_S$ cancels effects common to the two sectors and separates features that are independent of the initial state from those that depend on it. It varies slowly in the scale-invariant regime and oscillates around $r_\star$ at smaller $k$. The oscillations next to the scale-invariant regime do not depend on the adiabatic order, unlike the peaks and spikes at lower $k$. For a given initial state, the regularization dependence survives in the infrared, where long-wavelength modes retain a record of the bounce and of the pre-bounce branch. We propagate the normalized spectra to the CMB $B$-mode spectrum and discuss observational prospects.

Nicole Marcelina Gountanis, David H. Weinberg, Andrés N. Salcedo, Claire Lamman

Published: 2026-10-27

Categories: astro-ph.CO

Testing General Relativity (GR) on cosmological scales requires probes that are directly sensitive to gravitational dynamics. We present a Fisher matrix forecast of how well the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey (BGS) can constrain departures from GR through the cluster infall velocity field, using the redshift-space cluster-galaxy cross-correlation function $ξ^{\rm s}_{\rm cg}(r_p, r_π)$ as the primary observable. We construct mock catalogs from the AbacusSummit N-body simulations, using a Halo Occupation Distribution (HOD) model for galaxies and a log-normal mass-observable relation for cluster selection. We parameterize departures from GR with a single multiplicative factor $F_{\rm G}$ that rescales halo infall velocities relative to the GR prediction. Marginalizing over the HOD, mass-observable, and cosmological parameters, we find that DESI BGS can constrain $F_{\rm G}$ to $σ(F_{\rm G}) = 0.033$ at $z \sim 0.3$. This precision is sufficient to distinguish representative $f(R)$ and Galileon gravity models from GR at $\gtrsim 4σ$. The strongest limitation is a degeneracy between $F_{\rm G}$ and the scatter in the cluster mass-observable relation, while the constraint shows no strong degeneracy with any individual HOD parameter. Perfect knowledge of the galaxy-halo connection would improve the constraint to $σ(F_{\rm G}) \approx 0.015$, and including the galaxy autocorrelation function in the data vector could recover part of this improvement. The same data vector yields tight constraints on the cosmological parameters, $σ(Ω_m) = 0.010$ and $σ(σ_8) = 0.010$, only moderately correlated with $F_{\rm G}$. These results demonstrate the potential of DESI BGS cluster-galaxy correlations to test gravity on quasi-linear scales, complementary to existing modified gravity probes and to weak-lensing cluster mass profiles.

Vsevolod Chistiakov, Artur Mingaleev

Published: 2026-10-27

Categories: gr-qc

We consider a quadratic gravity model supplemented by the terms $\nabla_μR\nabla^μR$ and $(\nabla^{2}R)^2$. For specific relations among the coupling constants, the action takes a perfect-square form. In the spatially flat FLRW model, we perform a reduction to a dynamical variable invariant under time reparameterizations. We construct a nonlinear change of variable that transforms the reduced action into the Gaussian action associated with the Wiener measure. An analysis of the transformation Jacobian within a time discretization singles out the case of $7+1$-dimensional spacetime, in which the Jacobian of the discrete transformation under consideration is independent of the dynamical variable. On this basis, we propose a formal representation of expectation values of observables in the reduced model as integrals with respect to the Wiener measure.

Pau Amaro Seoane, Qimin Song, Shao-Dong Zhao, Kostas Tzanavaris, Reinhard Genzel, Frank Eisenhauer, Thomas Ott, Stefan Gillessen, Guillaume Bourdarot, Diogo C. Ribeiro, Matteo Sadun Bordoni, Simran Joharle, Felix Mang, Andreas Burkert, Jorge Cuadra, Diego Calderón, Re'em Sari

Published: 2026-10-27

Categories: astro-ph.HE

The Galactic Center is expected to host a population of extremely large mass-ratio inspirals (X-MRIs) migrating toward the supermassive black hole. We propose an observational approach utilizing the secular gravitational torque exerted by X-MRIs on the highly eccentric S-star S301. This approach is intrinsically limited by the stochastic nature of the surrounding stellar-mass black hole cusp. As S301 propagates through this granular medium, it experiences discrete gravitational encounters. Standard orbital fitting procedures inherently assume a smooth background potential; applying them to stochastic trajectories averages these discrete velocity discontinuities into a continuous secular drift. This introduces a systematic bias that mimics the X-MRI precession signal, invalidating traditional mass estimation techniques. To resolve this degeneracy, we implement a methodology based on the Wavelet Transform Modulus Maxima method to characterize the local Hölder regularity of the orbital motion. This model isolates the singular discontinuities induced by stellar-mass black hole encounters from the continuous torque of the X-MRI distribution, allowing for detection even when instantaneous accelerations are below the instrumental noise threshold. We demonstrate analytically that S301 is highly sensitive to the interior X-MRI population while remaining dynamically decoupled from the secular influence of the exterior cusp. Combining precision astrometry and radial velocity projections, we establish that a minimal population of two X-MRIs is detectable within a five to nine-year timeframe, allowing us to constrain the presence of an unseen orbiter population prior to the launch of space-based gravitational wave detectors.

Ludovic Varrin

Published: 2026-10-27

Categories: hep-th

In the extended phase space of Donnelly and Freidel, the edge modes of a Schwarzschild black hole are dynamical reference frames whose phase space is the cotangent bundle of $\mathrm{SL}(2,\mathbb{R})$. Gluing the two exterior regions at the bifurcation point leaves a single canonical pair. Within the extended phase space, this pair can be described either by Kuchař's mass and difference of asymptotic times or by the area and the relative rapidity of the two frames, which are two gauge choices of the same system. The latter is the pair of Carlip and Teitelboim, and the relative rapidity is the time shift of the crossed product construction. We quantize the frames in this gauge and construct the gravitational entangling product of the two exteriors. Requiring the frames to be causal restricts them to the semigroup $\mathrm{SL}^+(2,\mathbb{R})$, whose Plancherel measure yields the Bekenstein--Hawking entropy as the entanglement entropy between the two exteriors, together with a logarithmic correction, both independent of the ultraviolet cutoff.

Avipsa Chakrabarti, Avik Chakraborty, Martín Molina, Ayan Mukhopadhyay, Salomón Romero

Published: 2026-10-27

Categories: hep-th

The singularity theorems and the past incompleteness of inflationary spacetimes suggest that the beginning of the Universe lies beyond the domain of semiclassical gravity. We show that the creation of the Universe can nevertheless be understood within Lorentzian gravity by allowing gravitational junctions, so that the full spacetime need not be a smooth manifold. We construct rotationally invariant cosmic creation gates joining any finite number $n\geq2$ of locally de Sitter regions in $D\geq3$ spacetime dimensions at a timelike perfect-fluid junction with $P=wρ$. For $w>-(D-3)/(D-2)$, they are geodesically complete in both temporal directions. The total spatial volume approaches finite, positive limits in the infinite past and future on the global-time foliation adapted to the junction fluid. We also construct exact deformed cosmic creation gates through nonlinear homogeneous backreaction that retain the initial volume while the future volume grows without bound. In these solutions, the junction fluid always expands, cooling for $w>0$ and heating for allowed $w<0$. Keeping the bulk regions locally de Sitter, we determine the linearized perturbations: in three dimensions, the generic inhomogeneous sector contains one hybrid sound mode and $n-1$ relative transverse modes; in four and higher dimensions, only the homogeneous hybrid sound mode survives. A finite-volume beginning requires fine-tuned homogeneous and inhomogeneous initial data, while causal response generically leads to unbounded future spatial volume. We also discuss a broader creation criterion allowing bounded past-volume oscillations. The gravitational equations determine conditioned admissible histories. We discuss implications for cosmology.

Rodrigo Vicente, Francisco Duque, Theophanes K. Karydas, Gianfranco Bertone

Published: 2026-10-27

Categories: gr-qc

It is commonly assumed that the mass of dark matter particles cannot be determined from their gravitational effects when dark matter behaves as collisionless matter. Here we show that extreme-mass-ratio inspirals observable by millihertz gravitational-wave observatories such as the Laser Interferometer Space Antenna (LISA) could measure the mass of ultralight dark matter particles in sufficiently dense dark matter spikes. The separation of scales between the two black holes allows ultralight dark matter to form a collisionless density spike around the massive primary while retaining wave effects in its interaction with the stellar-mass companion. We incorporate wave-dependent accretion and dynamical friction into relativistic inspiral waveforms and jointly infer the dark matter particle mass, spike normalisation and binary parameters from simulated LISA signals. For massive black holes at the low-mass end of the LISA population ($M\sim 10^5 M_\odot$), our forecasts show that particle masses spanning $10^{-14}-10^{-11}\,\mathrm{eV}$ could be measured to within an order of magnitude.

Ignacio Magaña Hernandez, Antonella Palmese

Published: 2026-10-27

Categories: astro-ph.HE

The high-mass black hole population inferred from ground-based observations can substantially affect the number of binaries detectable by the Laser Interferometer Space Antenna (LISA). We use population constraints based on data from the latest LIGO/Virgo/KAGRA Gravitational-Wave Transient Catalog (GWTC-5.0), as well as constraints from the O3 search for intermediate-mass black hole binaries, to forecast the number and masses of binary black holes detectable by LISA. Using the released GWTC-5.0 population posterior, we obtain $6.6^{+5.5}_{-2.2}$ expected detections with signal-to-noise ratio $>8$ in 4 years (median and $90\%$ credible interval). The alternative population models we consider use a broken power law with two or three Gaussian peaks for either the primary-mass distribution or a common mass distribution for both black holes. For the three-peak model with the common mass distribution, extrapolating from $300$ to $1000M_\odot$ roughly doubles the median expected number of LISA detections to $\sim14$. The upper end of its $90\%$ credible interval rises from tens to thousands of expected detections, although approximations may limit the reliability of the most extreme counts. For the reference GWTC-5.0 population, $39^{+22}_{-11}\%$ of the binaries detectable by LISA merge during the mission or within $10$ years after its end and are potential multiband sources. Essentially all of these mergers would be detectable by a reference Cosmic Explorer configuration if it is operating at merger. Ground-based measurements of the high-mass population can therefore inform both LISA forecasts and the prospects for observing the same binaries through inspiral and merger.

Mirzabek Alloqulov, Sanjar Shaymatov, Bobomurat Ahmedov, Chengxun Yuan

Published: 2026-10-27

Categories: gr-qc

We investigate how deviations from the Schwarzschild geometry affect the motion of massive test particles and the gravitational radiation associated with their periodic trajectories around a new improved Schwarzschild black hole. Periodic configurations are determined by examining the commensurability of the radial and azimuthal orbital frequencies. For representative trajectories, we numerically reconstruct the particle motion and calculate corresponding gravitational wave polarizations using the symmetric trace-free mass-quadrupole approach. By comparing these signals with their Schwarzschild counterparts, we assess how the modified spacetime geometry is encoded in the radiation. Our analysis shows that the parameters $ξ$ and $γ$ produce modest changes in the orbital configurations and their associated waveforms, providing a means of investigating the dynamical signatures of this BH model.

Dongjun Li, Jierui Hu, Nicolás Yunes

Published: 2026-10-27

Categories: gr-qc

Rotating black holes offer powerful probes of gravity, but constructing their geometries beyond vacuum general relativity remains challenging. Here we develop a unified framework for constructing stationary, axisymmetric deformations of Kerr from their tidal curvature and physical sources. As a demonstration, we obtain closed-form solutions for six higher-curvature interactions at leading order in the couplings and for generic subextremal spin, without slow-rotation expansions, numerical fitting, or mode decomposition. The solutions pass stringent checks against the field equations, previous mode-by-mode constructions, and known analytic predictions for horizon quantities. We find that the chirality of the interactions organizes the analytic structure of these solutions, a pattern that likely extends to a large class of purely metric higher-curvature theories. Our framework opens a systematic route to black-hole geometries in beyond-Einstein theories and perturbative astrophysical environments. These geometries provide a foundation for strong-field tests with gravitational waves and other observational channels, such as black-hole images and X-ray spectroscopy, as well as theoretical studies of near-extremal black holes.

Semra Gurtas Dogan, Hassan Hassanabadi, Abdullah Guvendi

Published: 2026-10-27

Categories: gr-qc

We study scalar and electromagnetic perturbations of a Schwarzschild black hole (BH) surrounded by a dark matter halo described by the King density profile. The lapse function can be expressed as $1-2[M+M_{\rm DM}(r)]/r$, where $M_{\rm DM}(r)$ is the halo mass enclosed within radius $r$; thus, the halo affects the geometry through its enclosed-mass function. We compute the quasinormal frequencies using the sixth-order WKB method and its Padé-improved version. Rewriting the lapse function in terms of the inverse hyperbolic sine avoids the severe numerical cancellations that arise when evaluating its high-order derivatives. For the configurations examined, the fundamental frequencies agree with those extracted from time-domain evolution to within $0.2\%$.The halo lowers both the oscillation frequency and the damping rate. The change of the real part is almost entirely accounted for by the halo mass enclosed by the photon sphere, and the additional decrease of the damping rate follows the ratio of the Lyapunov exponent to the angular frequency of the circular null orbit. Since part of the halo lies inside the horizon in this metric, we also place the halo outside the BH by means of an Einstein cluster. The frequencies then decrease by a similar amount, but the real part follows the Schwarzschild value multiplied by the gravitational redshift factor of the halo. A jump in the density at the inner edge of the halo scatters the waves and changes the damping rate by up to about $9\%$. For a continuous density profile, deviations from the redshift relation remain below about $1.5\%$ for $r_{\rm in}=3M$ and below about $0.5\%$ for the cases with $r_{\rm in}\geq4M$. No unstable modes are found within the perturbation sectors and parameter configurations examined.

Alejandro Corichi

Published: 2026-10-27

Categories: quant-ph

Exact normalizable solutions of quantum constraints form a symplectic submanifold of the space of rays, whereas classical first-class constraints define a surface on which the symplectic form is degenerate. We ask how the degenerate directions can be recovered when quantum theory is regarded as fundamental and the constraints are imposed through a single positive master operator. For a nonnegative master function whose zero set is a Morse--Bott critical manifold, the image of the linearized Hamiltonian vector field is the symplectic orthogonal of the zero set, and coisotropy is equivalent to this linearization having square zero. The image is fixed by the zero set, but the theorem identifies it with the response of the master dynamics, which makes it accessible to quantum states. Three realizations follow. The exact quantum physical space is the opposite, rotational case of the same dichotomy. For quadratic masters, the bottom of the spectrum is $(\hbar/2)\Tr_+L$, so first-class zero sets carry no offset of order $\hbar$; within the harmonic approximation this explains the $\hbar$ versus $\hbar^2$ offsets observed in tests of the master-constraint programme. Finally, the second time derivative of the limiting covariance of a semiclassical packet, which can be determined by bounded probes, has the gauge distribution as its image. Two oscillators at fixed total energy give exact master evolution, an exact realization of this covariance shear, and the reduced symplectic limit. For the non-Abelian SL(2,$\R$) model we compute the coherent and Weyl master symbols, prove essential self-adjointness and a finite-time propagation estimate, and derive the spectral bottom $\hbar^2/2$.

P. S. Koliogiannis, N. Paar

Published: 2026-10-27

Categories: astro-ph.HE

The nuclear equation of state shapes both the structure of rapidly rotating neutron stars and the orbital motion in their surrounding spacetime. Its uncertainty affects the mass and radius at which the innermost stable circular orbit reaches the stellar surface, a condition that defines the transition between disks whose inner edge is set by the surface and those truncated by orbital instability. We quantify how measurements of the electric dipole polarizability of neutron-rich nuclei reduce the uncertainty in this transition and in the orbital properties at the disk inner edge. We compute uniformly rotating neutron stars in general relativity for a family of equations of state that systematically vary the symmetry energy, derived from relativistic energy density functionals with density-dependent point-coupling interactions. We compare the results for the full family with those for the subset consistent with the measured dipole polarizabilities of finite nuclei. The dipole polarizability constraint reduces the spread in transition mass and equatorial radius by factors of about seven to ten across the spin frequencies considered. Along this transition, it also confines the orbital frequency at the disk inner edge to a band narrower than $20$~Hz at each spin. Combined with a measured neutron-star spin, a kilohertz quasi-periodic oscillation interpreted as disk orbital motion further restricts the mass--radius region, allowing an independent mass estimate to probe the symmetry-energy constraint. The dipole response of finite nuclei thus informs both the structure of rotating neutron stars and the orbital properties of their inner accretion disks.

Qing-Yang Wang, Jing-Zhi Zhou, Fei-Yu Chen, Zhi-Chao Li

Published: 2026-10-27

Categories: astro-ph.CO

We investigate single-field inflation models that can produce large curvature perturbations at sub-Mpc scales while remaining consistent with cosmological observations across multiple regimes. We highlight the tension between generating enhanced small-scale perturbations and maintaining agreement with the scalar spectral index $n_s$ measured by ACT and SPT, which disfavors several conventional single-field inflation models. To address this issue, we propose three viable classes of inflationary potentials: bump/dip-modified, step-like, and double-inflection-point. Each can sufficiently amplify primordial perturbations while predicting $n_s$ that lie within the $2σ$ range of current observational bounds. In addition, we examine the primordial power spectra predicted by these models and constrain their parameter spaces using cosmological observations at different scales, including CMB, BAO, PBH, PTA, and CMB-distortion. Our results show that some of the models considered can simultaneously satisfy the ACT/SPT constraints and account for the current PTA observations, although doing so while respecting the constraints on the PBH abundance remains challenging.

G. Alencar, Micael S. Oliveira, Diego Sáez-Chillón Gómez, Marcos V. de S. Silva

Published: 2026-10-27

Categories: gr-qc

In this work, we investigate the geodesic dynamics and tidal force effects in neutral and electrically charged regular spacetimes inspired by T-duality. We first analyze the geometric properties of these solutions, including their regular central structure and horizon configurations, and show how the interplay between the T-duality scale $\ell_0$ and the electric charge $Q$ determines the transition between black hole and horizonless geometries. We then study the motion of massive and massless particles through the corresponding effective potentials, examining the existence and stability of circular orbits and the behavior of their characteristic radii. We further investigate the tidal forces experienced by observers in radial free fall, focusing on the behavior of the radial and angular components, their extrema and sign changes, and the location of these characteristic points relative to the horizon structure of the geometry. We show that the T-duality regularization renders the tidal forces finite in the central region and gives rise to different stretching and compression regimes, including a region of simultaneous compression in both the radial and angular directions, while the electric charge modifies the strength and location of these tidal features. Finally, we analyze the evolution of the geodesic deviation vector for two sets of initial conditions. We find that both the T-duality scale and the electric charge tend to suppress the accumulated radial stretching, whereas the angular deformation is considerably less sensitive to the charge. These results show how the quantum regularization induced by T-duality and the presence of electric charge modify the orbital dynamics and tidal response of these geometries in the strong-field regime. Furthermore, we demonstrate that the corresponding classical limits are recovered appropriately.

Antonio Gómez-Bañón, Pantelis Pnigouras, José A. Pons

Published: 2026-10-27

Categories: hep-ph

In light QCD axion models, finite-density corrections to the axion potential can source a nonvanishing axion field inside neutron stars. Extending our previous analysis of radial oscillations, we study the nonradial ($l=2$) oscillation spectrum of such axion condensed neutron stars in the relativistic Cowling approximation, keeping the fluid and axion perturbations fully coupled and dynamical. The condensate modifies the fluid spectrum in two ways: the altered equilibrium structure raises the $f$- and $p$-mode frequencies by up to $\sim20\%$, while the dynamical coupling to the axion field partially compensates this shift, almost entirely for the $f$-mode. Fluid modes with frequencies above the axion mass acquire a new damping channel through axion emission. The $f$-mode remains below this threshold for all configurations supporting a condensate, whereas the $p$-modes are damped on timescales that can be as short as $\sim10$ ms, shorter than their gravitational-wave damping times, except for certain axion masses where the outgoing axion amplitude nearly vanishes. The spectrum also contains a family of strongly damped axion-dominated quasinormal modes, with imaginary parts of order kHz, and a sequence of gravitationally bound axion states analogous to gravitational atom levels. Below the propagation threshold, the bound $p$-modes undergo avoided crossings with these levels, exchanging their fluid- and axion-dominated character.

Lorenzo Di Giacomo, Daniele Pranzetti

Published: 2026-10-27

Categories: hep-th

Central extensions of asymptotic symmetry algebras are traditionally determined through an explicit computation of the algebra of conserved charges. We show that, within an ambiguity-free covariant phase space formalism based on the Noetherian split, they instead arise as intrinsic quantities completely determined by the Lagrangian through the geometry of the associated covariant phase space. We prove two general Charge Representation Theorems describing the canonical realization of diffeomorphism symmetries in the presence of field-dependent vector fields and Lagrangian anomalies, corresponding respectively to vanishing and integrable Noetherian flux. In both cases, we derive explicit expressions for the associated central extensions and establish the corresponding cocycle identities. This provides a constructive algorithm for determining central charges directly from the Lagrangian formulation of the theory, without requiring an explicit computation of the charge algebra. As a non-trivial application, we consider asymptotically locally AdS$_3$ spacetimes with Penrose--Brown--Henneaux boundary conditions. We recover the corresponding centrally extended asymptotic symmetry algebra, providing an explicit realization of the Charge Representation Theorems.

Bo-Qiang Lu

Published: 2026-10-27

Categories: hep-ph

KM3NeT has reported KM3-230213A, a $220$\,PeV neutrino with no source identified. If it comes from a cosmic-string network, energy conservation makes the event a calorimeter. The flux measures the power the network has spent, not how it emits, and a cusp at critical current can supply that power at unit efficiency. The event gives $Gμε_p=(2.8\text{--}4.3)\times10^{-11}$ for $f_ν=0.1$. Pulsar timing already reaches $10^{-10}$, so one event competes with the arrays. For the branch that still radiates gravitationally, flux and timing together require a third of the network's energy in particles, a share that further events above $100$\,PeV would measure.

Amin Rezaei Akbarieh, Yusuf Kucukakca

Published: 2026-10-27

Categories: gr-qc

We study a canonical scalar field coupled to isotropic triplets of Abelian one-forms and two-forms through scalar-dependent kinetic functions and a constant topological $BF$ interaction. By retaining the lapse in the homogeneous reduction, we recover the Friedmann constraint and identify a sufficient domain in which all twelve physical modes have positive kinetic terms and luminal high-frequency propagation. A separate exponential model admits an accelerating mixed solution with $a\propto t^2$, nonzero asymptotic form fractions, and bounded normalized linear perturbations. For the Noether analysis, we choose a quadratic effective potential in flat minisuperspace coordinates and solve the zero-boundary determining equations. The canonical scalar potential is hyperbolic-squared or exponential, rather than a power law in the scalar field. The causal character of the potential coordinate separates three branches: Branch I admits a de Sitter limit, Branch II cannot sustain acceleration on regular future-complete expanding trajectories, and Branch III gives an exact solution with both form sectors active and late expansion $a\propto t^{4/3}$. Comparisons with consistent uncoupled and reduced-field limits separate the form contributions from the scalar-driven acceleration. The $BF$ term changes the finite-time exchange between the form sectors but supplies no direct negative-pressure source.

Qi-Quan Li, Yu Zhang, Hoernisa Iminniyaz

Published: 2026-10-27

Categories: gr-qc

We use the modified Newman--Janis algorithm to obtain the rotating ``mother'' black hole solution of the rotating Hayward-AdS black hole. We further derive the fundamental thermodynamic quantities of the ``mother'' black hole in the full unconstrained phase space $(S,J,q,α,P)$, and impose the regularity condition $M_1=q^3/α$ to obtain the thermodynamic quantities of the rotating Hayward-AdS regular black hole. This order of operations gives a Hawking temperature identical to the surface gravity temperature and produces the correct response functions of the regular black hole. For $P<P_c$, the Hawking temperature $T_2$ possesses a local maximum and a local minimum, which divides the black hole into small, intermediate, and large black hole branches, and the $P$--$V$ isotherms display oscillatory behavior characteristic of a liquid/gas phase transition. The small and large black hole branches are locally stable, whereas the intermediate black hole branch has negative heat capacity and is locally unstable. Increasing the rotation parameter $a$, magnetic charge $q$, or pressure $P$ reduces the region of the intermediate branch. The $G_2$--$T_2$ diagram shows that the phase structure, in contrast to the standard swallowtail of the Reissner--Nordström-AdS and Kerr--Newman-AdS black holes, is 8-shaped or C-shaped. These two shapes are divided by the characteristic pressure $P_z$. For $P<P_z$, the curve is 8-shaped, corresponding to a first-order small/large black hole transition. For $P_z<P<P_c$, the curve is C-shaped, corresponding to a zeroth-order transition. These results show that the 8-shaped/C-shaped phase structure characteristic of regular AdS black holes persists under rotation, indicating that it stems from the restructuring of the thermodynamic phase space by the regularity condition rather than from spherical symmetry.