Preprints in GR/QC

Mu-Chun Chen, Yan Cao

Published: 2025-10-09

Categories: gr-qc

The final-parsec problem has long posed a central challenge in understanding the merger of supermassive black hole binaries. In this paper, we investigate a scenario in which a dark scalar or vector field is sourced by eccentric binaries, leading to accelerated mergers through additional dipole radiation, and thereby extending the range of masses for which the binary merges within a Hubble time. The radiation fluxes from an eccentric charged Keplerian binary are derived using general results for localized periodic sources in flat spacetime. We find that dipole radiation, although insufficient to fully resolve the final-parsec problem, can alter the low-frequency spectrum of the stochastic gravitational-wave background from supermassive black hole binary inspirals. We construct a simplified model for the spectrum and perform a Bayesian analysis using the current pulsar timing array data.

E. C. Valadão, Felipe Sobrero, Santiago Esteban Perez Bergliaffa

Published: 2025-10-09

Categories: gr-qc

The Lyra geometry provides an interesting approach to develop purely geometrical scalar-tensor theories due to the natural presence of the Lyra scale function. This paper explores further the scale function source term to construct a theory on Lyra manifolds which contains proper generalizations of both Brans-Dicke gravity and the Einstein-Gauss-Bonnet scalar-tensor theory. It is shown that the symmetry group of gravitational theories on the Lyra geometry comprises not only coordinate transformations but also local transformations of length units, so that the Lyra function is the conformal factor which locally fixes the unit of length. By performing a Lyra transformation to a frame in which the unit of length is globally fixed, it is shown that General Relativity is obtained from the Lyra Scalar-Tensor Theory (LyST). Through the same procedure, even in the presence of matter fields, it is found that Brans-Dicke gravity and the Einstein-Gauss-Bonnet scalar-tensor theory are obtained from their Lyra counterparts. It is argued that this approach is consistent with the Mach-Dicke principle, since the strength of gravity in Brans-Dicke-Lyra is controlled by the scale function. It might be possible that any known scalar-tensor theory can be naturally geometrized by considering a particular Lyra frame, for which the scalar field is the function which locally controls the unit of length. The Jordan-Einstein frame conundrum is also assessed from the perspective of Lyra transformations, it is shown that the Lyra geometry makes explicit that the two frames are only different representations of the same theory, so that in the Einstein frame the unit of length varies locally. The Lyra formalism is then shown to be better suited for exploring scalar-tensor gravity, since in its well-defined structure the conservation of the energy-momentum tensor and geodesic motion are assured in the Einstein frame.

Sebastian Schuster, Jessica Santiago, Justin Feng, Matt Visser

Published: 2025-10-09

Categories: gr-qc

Limits on the dark matter fraction of small mass primordial black holes from Hawking radiation are predominantly derived from the assumption of a Schwarzschild black hole evaporating. However, astrophysical black holes are usually much more realistically modelled by the rotating Kerr black hole solution. Meanwhile, electromagnetically charged black holes are astrophysically of little importance due to their fast neutralisation in the present universe. Dark matter is not just a possible solution to issues of astrophysics and cosmology, but also to issues of the standard model of particle physics. Extensions of this model thus can lead to charges present in the early universe which remain preserved in the charge of primordial black holes - even when the corresponding particles have disappeared from the particle content of the present epoch of the universe. Here, we report on a thorough proof-of-concept that such charges can greatly change evaporation limits for primordial black hole dark matter. Special emphasis is placed on (near-)extremal black holes, for which this effect is especially pronounced.

Himanshu Chaudhary, Vipin Kumar Sharma, Salvatore Capozziello, G. Mustafa

Published: 2025-10-09

Categories: astro-ph.CO

Observational data play a pivotal role in identifying cosmological models that are both theoretically consistent and empirically viable. In this work, we investigate whether the standard $\Lambda$CDM model exhibits significant departure with current late time datasets, including Cosmic Chronometers, Baryon Acoustic Oscillations from DESI DR2, and various Type Ia supernova compilations (Pantheon$^+$, DES-SN5Y, Union3). We analyze several dynamical dark energy models, including $\omega$CDM, o$\omega$CDM, $\omega_0\omega_a$CDM, Logarithmic, Exponential, JBP, BA, and GEDE. While CC + DESI DR2 data show mild deviations from $\Lambda$CDM ($\lesssim 2\sigma$), adding supernova samples (DES-SN5Y or Union3) increases deviations, with BA, JBP, and Logarithmic models reaching $3-3.5\sigma$, and CC + DESI DR2 + DES-SN5Y producing the largest deviations. We find consistent evidence for $\omega_0 > -1$ and $\omega_a < 0$ in all dark energy models, indicating that the cosmological constant faces a potential crisis and that dynamical dark energy models could provide a possible solution, characterized by a Quintom-B type scenario. The $\Lambda$CDM model has long served as the cornerstone of modern cosmology, successfully shaping our understanding of the Universe from its earliest epochs to the present day. However, in light of DESI DR2 and other recent measurements, emerging cracks in this paradigm suggest that a complete understanding of the cosmos may require moving beyond the cosmological constant and exploring new physics governing the dark sector.

Rafael L. S. Costa, Marcos L. W. Basso, Jonas Maziero, Lucas C. Céleri

Published: 2025-10-09

Categories: quant-ph

We investigate the formulation of work distributions for quantum scalar fields in static curved spacetimes by extending the Ramsey interferometric protocol originally developed in previous works for flat spacetimes. The use of Unruh-DeWitt particle detectors provides a causally consistent framework to define and measure work statistics, avoiding the limitations of the two-time projective measurement scheme in relativistic quantum field theory. We derive a non-perturbative expression for the characteristic function of the quantum field and apply it to thermal Kubo-Martin-Schwinger (KMS) states, showing that the resulting work distributions satisfy both the Crooks fluctuation theorem and the Jarzynski equality. Furthermore, we analyse the case of a pointlike detector, obtaining compact expressions for the first two moments of the work distribution, allowing us to recover the standard fluctuation-dissipation relation in the high-temperature limit. Our results demonstrate that fluctuation theorems hold for quantum fields interacting with Unruh-DeWitt particle detectors in static curved spacetimes.

Will Barker, Dražen Glavan

Published: 2025-10-09

Categories: gr-qc

We perform a full Hamiltonian constraint analysis of pure Ricci-scalar-squared ($R^2$) gravity to clarify recent controversies regarding its particle spectrum. While it is well established that the full theory consistently propagates three degrees of freedom, we confirm that its linearised spectrum around Minkowski spacetime is empty. moreover, we show that this is not a feature unique to Minkowski spacetime, but a generic property of all traceless-Ricci spacetimes that have a vanishing Ricci scalar, such as the Schwarzschild and Kerr black hole spacetimes. The mechanism for this phenomenon is a change in the nature of the constraints upon linearisation: ten second-class constraints of the full theory become first-class, while the three momentum constraints degenerate into a single constraint. Furthermore, we show that higher order perturbation theory around these singular backgrounds reveals no degrees of freedom at any order. This is in conflict with the general analysis and points to the fact that such backgrounds are surfaces of strong coupling in field space, where the dynamics of perturbations becomes nonperturbative. We further show via a cosmological phase-space analysis that the evolving universe is able to penetrate through the singular $R=0$ surface.

Nikola Herceg, Tajron Jurić, A. Naveena Kumara, Andjelo Samsarov, Ivica Smolić

Published: 2025-10-09

Categories: gr-qc

We study the gravitational perturbation theory of black holes in noncommutative spacetimes with noncommutativity of the type $[t\stackrel{\star}{,} r] = i a \alpha A(r)$ and $[\varphi \stackrel{\star}{,} r] = i a \beta A(r)$ for arbitrary $A(r)$, which includes several Moyal-type spaces and also the $\kappa$-Minkowski space. The main result of this paper is an analytical expression for the effective potential of the axial perturbation modes, valid to all orders in the noncommutativity parameter. This is achieved by evaluating the $\star$-products using translations in the radial direction, i.e., Bopp shift. We comment on various regimes, such as Planck-scale black holes, where the noncommutativity length scale is of the same order of magnitude as the black hole horizon.

Hao Wang, Bin Liu, Yuan-Chuan Zou, Qing-Wen Wu

Published: 2025-10-09

Categories: gr-qc

In studies of binary black hole (BBH) mergers in eccentric orbits, the mean anomaly, traditionally regarded as less significant than eccentricity, has been thought to encode only the orbital phase, leading to the assumption that it exerts minimal influence on the dynamics of eccentric mergers. In a previous investigation, we identified consistent oscillations in dynamical quantities peak luminosity $L_{\text{peak}}$, remnant mass $M_{\text{rem}}$, spin $\alpha_{\text{rem}}$, and recoil velocity $V_{\text{rem}}$ in relation to the initial eccentricity $e_0$. These oscillations are associated with integer orbital cycles within a phenomenological framework. In this paper, we aim to explore the underlying physical nature of these oscillations through gravitational waveforms. Our examination of remnant mass and spin reveals that while the initial ADM mass $M_{\mathrm{ADM}}$ and orbital angular momentum $L_0$ exhibit gradual variations with $e_0$, the radiated energy $E_{\text{rad}}$ and angular momentum $L_{\text{rad}}$ display oscillatory patterns akin to those observed in $M_{\text{rem}}$ and $\alpha_{\text{rem}}$. By decomposing the waveforms into three distinct phases inspiral, late inspiral to merger, and ringdown, we demonstrate that these oscillations persist across all phases, suggesting a common origin. Through a comparative analysis of $E_{\text{rad}}$ and $L_{\text{rad}}$ derived from numerical relativity (NR), post-Newtonian (PN) waveforms, and orbital-averaged PN fluxes during the inspiral phase, we identify the initial mean anomaly $l_0$ as the source of the observed oscillations. ...

Lina Zhang, De-Cheng Zou, Yun Soo Myung

Published: 2025-10-09

Categories: gr-qc

Th spontaneous scalarization of the Einstein-Euler-Heisenberg (EEH) black hole is performed in the EEH-scalar theory by introducing an exponential scalar coupling (with $\alpha$ coupling constant) to the Maxwell term.Here, the EEH black hole as a blad black hole is described by mass $M$ and magnetic charge $q$ with an action parameter $\mu$. A choice of $\mu=0.3$ gurantees a single horizon with unrestricted magnetic charge $q$. The onset scalarization of this black hole appears for a positive coupling $\alpha$ with an unlimited magnetic charge $q$. However, there exists a difference between $q\le1$ and $q>1$ onset scalarizations. We notify the presence of infinite branches labeled by the number of $n=0,1,2,\cdots$ of scalarized charged black holes by taking into account the scalar seeds around the EEH black hole. We find that the $n=0$ fundamental branch of all scalarized black holes is stable against the radial perturbations, while the $n=1$ excited branch is unstable.

Yu-Kun Zhang, Shao-Wen Wei

Published: 2025-10-09

Categories: gr-qc

In this paper, we study the kinematic effects of spinning test particles orbiting the Kerr-Bertotti-Robinson black hole. Employing with the Mathisson-Papapetrou-Dixon equations, we explore the dynamics of precessing orbits and distinct orbital types, including circular orbits and innermost stable circular orbits. Our results reveal the substantial impact of the magnetic field on the trajectories of spinning particles, particularly in regions characterized by significant radial distances. More importantly, our study shows that an augmented magnetic field necessitates an increased orbital angular momentum to uphold spinning particles within their characteristic orbits at equivalent radial distances. Our result contributes valuable insights to the understanding of the spinning celestial object motion around black holes endowed with magnetic fields.

Miguel Bermudez

Published: 2025-10-09

Categories: gr-qc

A simple covariant model is presented where the signature of the metric is a dynamical field. Degenerate minima of a curvature-minimizing potential correspond to Euclidean, Lorentzian or mixed phases of geometry. The Lorentzian phase emerges as the only stable configuration supporting causal propagation.

Wenlin Li, Chengsong Zhao, Najmeh Eshaqi-Sani, Zhiyu Jiang, Xingli Li

Published: 2025-10-09

Categories: quant-ph

A tenet of contemporary physics is that novel physics beyond the Standard Model lurks at a scale related to the Planck length. The development and validation of a unified framework that merges general relativity and quantum physics is contingent upon the observation of Planck-scale physics. Here, we present a fully quantum model for measuring the nonstationary dynamics of a ng-mass mechanical resonator, which will slightly deviate from the predictions of standard quantum mechanics induced by modified commutation relations associated with quantum gravity effects at low-energy scalar. The deformed commutator is quantified by the oscillation frequency deviation, which is amplified by the nonlinear mechanism of the detection field. The measurement resolution is optimized to a precision level that is $15$ orders of magnitude below the electroweak scale.

Tianzhe Zhou, Chun Huang

Published: 2025-10-09

Categories: astro-ph.HE

Pulse-profile modeling (PPM) of thermal X-ray emission from rotation-powered millisecond pulsars enables simultaneous constraints on the mass $M$, radius $R$, and hence the equation of state of cold, dense matter. However, Bayesian PPM has faced a hard accuracy-speed bottleneck: current production resolutions used to keep inference tractable can under-resolve extreme hotspot geometries and bias the waveform computation, whereas the higher resolutions that remove this bias push forward models to minutes per evaluation, making inference impractical. We break this trade-off with, to our knowledge, the first public GPU-accelerated X-ray PPM framework that matches established benchmarks to within $\sim10^{-3}$ relative accuracy even for extreme geometries, while collapsing minutes-long high-fidelity computations to $2$--$5$ ms on an RTX 4080 ($10^{3}$--$10^{4}\times$ speedups), enabling posterior exploration at resolutions and complexities previously out of reach. We further uncover a bias near the interpolation boundaries of atmosphere lookup tables, demonstrate it with two diagnostic tests, and counter it with a mixed-order interpolator. Together, these advances enlarge the feasible hotspot model space and reduce key systematics in PPM, strengthening inferences for current and future X-ray missions.

Roman Berens, Trevor Gravely, Alexandru Lupsasca

Published: 2025-10-09

Categories: gr-qc

In this second paper of our series started with \cite{Berens2024}, we investigate linearized gravitational perturbations of a rotating Kerr black hole in a non-asymptotically flat spacetime with (anti-)de Sitter boundary conditions. Here, we explicitly write down the metric components (in both ingoing and outgoing radiation gauge) of the perturbations that correspond to a given mode of either Weyl scalar. We provide formulas involving Hertz potentials (intermediate quantities with a holographic interpretation) as well as some that involve only the separated radial and angular modes. We expect these analytic results to prove useful in numerical studies of black hole perturbation theory in the context of the holographic correspondence.

Hussain Gohar

Published: 2025-10-08

Categories: gr-qc

We introduce a generalized mass-horizon relation applicable to cosmological horizons. This formulation provides a unified framework for deriving a broad class of Bekenstein entropy extensions motivated by statistical mechanics, quantum gravity, and phenomenological considerations, through the application of the Clausius relation together with the Hawking temperature. We further introduce this notion as a foundational framework for constructing generalized entropy forms that remain consistent with thermodynamic laws and the holographic principle.

Guillem Domènech, Apostolos Tsabodimos, Nathaniel Sherrill, Alexander Ganz, Fiona Kirk

Published: 2025-10-08

Categories: hep-ph

We study the impact of general disformal metric transformations on fermions, which shift the gravitational metric by an additional rank-2 tensor. This tensor can in principle be constructed from scalar-field gradients, vector fields, or field-strength contractions. We show this transformation results in the conventional Dirac action being modified by additional kinetic and axial-current couplings that are quadratic in the shifted field. When the field sourcing the metric shift takes on a non-trivial background value, apparent Lorentz-violating effects can result, which we identify as terms in an effective field theory. Assuming the well-motivated cases of scalar and vector ultralight dark matter, we demonstrate that experimental tests of rotation and boost violation imply constraints on the additional kinetic coupling. Even under conservative assumptions, the constraints for vector ultralight dark matter are extremely stringent.

Abraao J. S. Capistrano, Antonio C. Gutierrez-Pineres, Carlos H. Coimbra-Araujo

Published: 2025-10-08

Categories: gr-qc

We investigate a rotating black hole embedded in a five-dimensional flat bulk by extending the Kerr metric through the Gurses-Gursey line element. Employing Boyer-Lindquist coordinates, we reinterpret the black hole as a charged-like object in five dimensions and analyze its horizon structure and shadow morphology. Our results reveal that the shadow is shaped by an axially symmetric gravitational field modulated by an extrinsic curvature term arising from the higher-dimensional embedding. Simulations demonstrate that the visibility amplitude and shadow profile of the Gurses-Gursey black hole align with Event Horizon Telescope observations of M87 in the Kerr limit, while also allowing measurable deviations that could be probed by future high-resolution experiments.

Nils Siemonsen

Published: 2025-10-08

Categories: gr-qc

Ultracompact spinning horizonless spacetimes with ergoregions are subject to the ergoregion instability. We systematically investigate the instability of a massless scalar field in a variety of rapidly spinning Proca stars and boson stars using WKB-, frequency-, and time-domain methods. We find universal features in the mode structure: the onset of the instability is signaled by a zero-mode, the mode frequencies and growth rates are related by a simple scaling relation in the small-frequency limit (as found for Kerr-like objects), the mode frequencies approach the orbital frequency of counter-rotating stably trapped null geodesics in the eikonal limit, and for each unstable azimuthal mode only a finite number of overtones and polar modes are exponentially growing. The e-folding times are as short as $\tau\sim 10^4 M$ (in terms of the spacetime's ADM mass $M$). Interestingly, we find a near universal relationship between the frequencies and growth rates across all bosonic stars and also compared with Kerr-like objects. Furthermore, we show that weakly nonlinear backreaction of the instability induces a shift in growth rates as well as emission of gravitational waves; we find evidence that these effects lead to an amplification of the unstable process. This suggests that strongly nonlinear interactions are important during the gravitational saturation of the instability.

Nils Siemonsen

Published: 2025-10-08

Categories: gr-qc

We perform time-domain evolutions of the ergoregion instability on a horizonless spinning ultracompact spacetime in scalar theories with potential-type and derivative self-interactions mimicking the nonlinear structure of the Einstein equations. We find that the instability saturates by triggering a weakly turbulent direct cascade, which transfers energy from the most unstable and large-scale modes to small scales. The cascade's nonlinear timescales of each mode are orders of magnitude shorter than the corresponding linear e-folding times. Through this mechanism, the counter-rotating stable light ring is filled with a spectrum of higher-order azimuthal modes forming a ring-like shape. Thereby we demonstrate that turbulent processes are likely also important during the fully gravitational saturation of the instability, leaving imprints in the gravitational wave emission.

Maxime Van de Moortel

Published: 2025-10-08

Categories: gr-qc

In our recent work [Van de Moortel, The coexistence of null and spacelike singularities inside spherically symmetric black holes], we analyzed the transition between null and spacelike singularities in spherically symmetric dynamical black holes and demonstrated that the spacelike portion is described by a Kasner metric with positive varying exponents that degenerate to $(1,0,0)$ near the null-spacelike transition. In the present paper, we provide examples of global spacetimes satisfying the assumptions of this previous result and apply its analysis to obtain a large class of asymptotically flat (spherically symmetric) black hole spacetimes that exhibit coexisting null and spacelike singularities. Our main results include: _The construction of one-ended asymptotically flat black hole spacetimes solving the Einstein-Maxwell-charged-scalar-field equations. The proof relies on a new spacelike-characteristic gluing method between any uncharged spherically symmetric solution and the event horizon of a charged dynamical black hole. _The construction of a large class of two-ended asymptotically flat black hole spacetimes solving the Einstein-Maxwell-(uncharged)-scalar-field equations. In both cases, we show that the terminal boundary in the black hole interior only has two distinct components: a weakly singular (null) Cauchy horizon $\mathcal{CH}_{i^+}$ where curvature blows up and a strong singularity $\mathcal{S}=\{r=0\}$. Our construction provides the first examples of black holes with coexisting null and spacelike singularities. These examples hold particular significance in the one-ended case as a model of gravitational collapse, where this phenomenon is conjecturally generic for the Einstein-scalar-field model, even beyond spherical symmetry.

Guillem Domènech, Alexander Ganz, Apostolos Tsabodimos

Published: 2025-10-08

Categories: hep-th

Disformal couplings to fermions lead to a unique derivative coupling to the axial fermionic current, which contains higher derivatives in general. We derive general conditions on consistent disformal couplings by requiring the absence of higher time derivatives, as they typically lead to ghost degrees of freedom. For a two-scalar field disformal transformation, we show that the consistent disformal coupling must have a degenerate field space metric. This allows us to explore consistent, new two-scalar field modified gravity models. We show that the transformation of the Einstein-Hilbert action leads to two-field Horndeski or two-field DHOST theories. Our formalism also applies to disformal transformations with higher derivatives. We derive the consistent subclasses of disformal transformations that include second derivatives of a scalar field and first derivatives of a vector field that lead to generalized U-DHOST and degenerate beyond generalized Proca theories.

L. Filipe O. Costa, José Natário

Published: 2025-10-08

Categories: gr-qc

We show that, contrary to some recent claims, relativistic effects cannot mimic dark matter in the galactic rotation curves and gravitational lensing.

L. Filipe O. Costa, Francisco Frutos-Alfaro, José Natário, Michael Soffel

Published: 2025-10-08

Categories: gr-qc

In a recent paper we discussed when it is possible to define reference frames nonrotating with respect to distant inertial reference objects (extension of the IAU reference systems to exact general relativity), and how to construct them. We briefly review the construction, illustrating it with further examples, and caution against the recent misuse of zero angular momentum observers (ZAMOs).

Arpan Bhattacharyya, Saptaswa Ghosh, Ankit Mishra, Sounak Pal

Published: 2025-10-08

Categories: hep-th

We study classical scattering of charged black holes in Einstein-Maxwell-Dilaton (EMD) theory. Working in the classical (Post-Minkowskian) regime, we extract the conservative two-body potential by expanding the one loop amplitudes in the soft regime. We show explicitly that, as in GR, the relevant soft amplitudes are infrared (IR) finite once the long-range interactions are consistently treated via Lippmann-Schwinger equation and the associated IR subtraction. The scattering angle is then obtained from the eikonal exponentiation of the soft amplitude. Our results track the separate roles of electromagnetic and dilatonic charges in both the conservative dynamics and the eikonal phase, and they reduce smoothly to the GR limit when the charges and dilaton coupling are switched off. Where applicable, we compare with existing results in the literature and find agreement. These findings provide amplitude-based benchmarks for compact-object dynamics in EMD and furnish building blocks for waveform modeling in beyond-GR scenarios.

Oscar J. C. Dias, Jorge E. Santos

Published: 2025-10-08

Categories: hep-th

We analyze the recently discovered localized and non-uniform phases of the Banks-Fischler-Shenker-Susskind (BFSS) matrix quantum mechanics. Building on [1], we provide first-principles derivations of their properties and extend the results with new analytic and numerical insights. We show that strongly coupled BFSS dynamics emerge from a specific Carrollian transformation of 11-dimensional supergravity, which we justify in detail. In this framework, the uniform BFSS phase corresponds to a black string in a $pp$-wave background. We demonstrate that this background is unstable to a Gregory-Laflamme instability and, for the first time, compute the associated growth rate. The instability gives rise to non-uniform and localized phases that dominate the microcanonical ensemble in certain low-energy regimes, with the localized phase also prevailing in the canonical ensemble at low temperatures. We identify the corresponding first- and second-order phase transitions and derive analytic formulas for the thermodynamics of the localized phase, accurate to better than $0.3\%$ against numerical results.

Andrei Galiautdinov

Published: 2025-10-08

Categories: gr-qc

We introduce a coordinate system that complements the Kruskal--Szekeres extension. Like the standard construction, it covers the maximally extended Schwarzschild manifold in its entirety, while offering an additional advantage of expressing the areal radius as an explicit function of the new coordinates. Its main limitation, however, is that radial null geodesics are no longer represented as 45-degree lines in the Kruskal plane, making the causal structure more difficult to interpret. Nevertheless, the new system offers a compelling aesthetic trade-off: among all known maximally extended systems - including those of Kruskal-Szekeres, Israel, Fronsdal, Novikov, and Synge - it exhibits the highest degree of symmetry with respect to Schwarzschild's original r- and t-coordinate lines. It trades the regular pattern of Kruskal's light cones for a symmetric nesting arrangement of the two-dimensional spheres. The proposed extension sheds new light on the closely related Fronsdal's six-dimensional embedding construction, and clarifies the deep connection that exists between the most important implicit (Kruskal-Szekeres) and explicit (Israel's) procedures for maximal extension of the Schwarzschild geometry that is well known to those working in the field but rarely presented in textbooks on general relativity.

Bijan Bagchi, Sauvik Sen

Published: 2025-10-08

Categories: gr-qc

We investigate the implications provided by the modified Painlev\'{e}-Gullstrand coordinates in the context of quintessence for the Kiselev black hole. In this regard, we set up a fully static line element in terms of lapse and shift functions, apart from including the deformation parameter signaling deviation from the standard Painlev\'{e}-Gullstrand metric. We address two specific issues pertaining to the problems of radiation and dust furnished by the corresponding barotropic index parameter and study the related consequences by performing a range of analyses to explore the influence imposed by quintessence. We also discuss the thermodynamical consequences by evaluating the expressions of the Hawking temperature and the entropy function in closed forms.

M. Sharif, Tayyab Naseer, Hira Shadab

Published: 2025-10-08

Categories: gr-qc

Two distinct non-singular interior models that describe anisotropic spherical configurations are presented in this work. We develop the Einstein field equations and the associated mass function in accordance with a static spherical spacetime. We then discuss certain requirements that must be satisfied for compact models to be physically validated. Two distinct limitations are taken into account to solve the field equations, including different forms of the radial geometric component and anisotropy, which ultimately leads to a couple of relativistic models. In both cases, solving the differential equations result in the appearance of integration constants. By equating the Schwarzschild exterior metric and spherical interior line element on the interface, these constants are explicitly obtained. The disappearance of the radial pressure on the hypersurface is also used in this context. We further use estimated radii and masses of six different stars to graphically visualize the physical properties of new solutions. Both of our models are deduced to be well-aligned with all physical requirements, indicating the superiority of the presence of anisotropy in compact stellar interiors over the perfect isotropic fluid content.

Arshad Ali, Yang Lei, Mudassar Sabir

Published: 2025-10-08

Categories: gr-qc

We analytically study the gauge dependence of scalar-induced gravitational waves (SIGWs) sourced by primordial isocurvature perturbations during radiation domination (RD), working across nine gauges. Through analytical integrations of the kernels supported by graphical comparison we identify a clear dichotomy. We find that in some gauges viz. the uniform-density (UD), total-matter (TM), uniform-curvature (UC), comoving-orthogonal (CO) and transverse-traceless (TT) gauges the energy density grows polynomially in conformal time $\eta^n$, where $n$ varies from $2$ to $8$. While in rest of the gauges viz. the longitudinal (Long.), uniform-expansion (UE), Newtonian-motion (Nm), and N-body (Nb) gauges the late-time energy spectrum converges, and SIGWs behave as radiation. For subhorizon modes ($ k\eta \gg 1 $), the divergence becomes severe, showing that SIGWs are gauge-dependent observables in this regime. We resolve it through a kernel projection that isolates the luminal, freely propagating gravitational wave components (oscillating as $\sin(k\eta)$ and $\cos(k\eta)$), eliminating spurious contributions. The resulting kernel decays as $ (k\eta)^{-1} $ and yields a finite, gauge-independent late-time spectrum, confirming that only luminal modes represent physical SIGWs.

Sercan Kaya, Bayram Tekin

Published: 2025-10-08

Categories: gr-qc

We investigate whether fractional calculus, with its intrinsic long-tailed memory and nonlocal features, can provide a viable model for gravitational-wave memory effects. We consider two toy constructions: ($i$) a fractional modification of the linearized Einstein field equations using a sequential Caputo operator, and ($ii$) a fractionalized quadrupole formula where the source moment is acted upon by the same operator. Both constructions yield history-dependent responses with small memory-like offsets. However, in all cases, the signal decays to zero at late times, failing to reproduce the permanent displacement predicted by GR. Our results, therefore, constitute a no-go demonstration: naive fractionalization is insufficient to model nonlinear gravitational memory. We argue that any successful model must incorporate fractional kernels directly into the hereditary flux-balance integral of General Relativity, while preserving gauge invariance and dimensional consistency. We also discuss possible connections to modified gravity and the absence of memory in the spacetime with dimensions $D>4$.

Anarya Ray, Sharan Banagiri, Eric Thrane, Paul D. Lasky

Published: 2025-10-08

Categories: gr-qc

The recently reported binary black hole merger, GW231123, has unusual properties that make it hard to explain astrophysically. Parameter estimation studies are consistent with maximally spinning black holes and the dimensionless spin of the more massive component is constrained to be $\chi_1\gtrsim 0.8$. Analysis of data also revealed potential systematics that could not be fully replicated with simulated studies. We explore the possibility that these measurements are biased due to unmodeled non-Gaussian noise in the detectors, and that the actual black hole spins are more modest. We present evidence for a population of \textit{microglitches} in LIGO gravitational-wave strain data that can lead to biases in the parameter estimation of short-duration signals such as GW231123. Using simulated data of a massive event like GW231123, we demonstrate how microglitches can bias our measurements of black hole spins toward $\chi\approx1$ with negligible posterior support for the true value of $\chi\approx0.7$. We develop a noise model to account for microglitches and show that this model successfully reduces biases in the recovery of signal parameters. We characterize the microglitch population in real interferometer data surrounding GW231123 and find a single detector glitch duty cycle of $0.57_{-0.19}^{+0.21}$, which implies nearly a $100\%$ probability that at least one event through the fourth gravitational wave transient catalog coincides with microglitches in two detectors. We argue that further investigations are required before we can have a confident picture of the astrophysical properties of GW231123.

Francisco Fernández-Álvarez, José M. M. Senovilla

Published: 2025-10-08

Categories: gr-qc

The existence or absence of gravitational radiation escaping from the spacetime at $\mathscr{J}$ is characterized in the presence of a cosmological constant $\Lambda$ of any sign. To that end, the properties of the asymptotic super-momentum are used. When $\Lambda=0$, the characterization is equivalent to that based on the News tensor. For $\Lambda\neq 0$, it provides the first reliable definition of existence of radiation at $\mathscr{J}$, and it gives fully satisfactory results in known exact solutions.

Nihal Jalal Pullisseri, Sanil Unnikrishnan

Published: 2025-10-08

Categories: gr-qc

We consider a model of non-canonical scalar-tensor theory in which the kinetic term in the Brans-Dicke action is replaced by a non-canonical scalar field Lagrangian $\mathcal{L}(X, \phi)= \lambda X^\alpha \phi^\beta - V(\phi)$ where $X = (1/2) \partial_{\mu} \phi \partial^{\mu} \phi$ and $\alpha$, $\beta$ and $\lambda$ are parameters of the model. This can be considered as a simple non-canonical generalization of the Brans-Dicke theory with a potential term which corresponds to a special case of this model with the values of the parameter $\alpha = 1$, $\beta = -1$ and $\lambda = 2w_{_{BD}}$ where $w_{_{BD}}$ is the Brans-Dicke parameter. Considering a spatially flat Friedmann-Robertson-Walker Universe with scale factor $a(t)$, it is shown that, in the matter free Universe, the kinetic term $\lambda X^\alpha \phi^\beta$ can lead to a power law solution $a(t)\propto t^{n}$ but the maximum possible value of $n$ turns out to be $(1+\sqrt{3})/4 \approx 0.683$. When $\alpha \geq 18$, this model can lead to a solution $a(t)\propto t^{2/3}$, thereby mimicking the evolution of scale factor in a cold dark matter dominated epoch with Einstein's General Relativity (GR). With the addition of a linear potential term $V(\phi) = V_{0}\phi$, it is shown that this model mimics the standard $\Lambda$CDM model type evolution of the Universe. The larger the value of $\alpha$, the closer the evolution of $a(t)$ in this model to that in the $\Lambda$CDM model based on Einstein's GR. The purpose of this paper is to demonstrate that this model with a linear potential can mimic the GR based $\Lambda$CDM model. However, with an appropriate choice of the potential $V(\phi)$, this model can provide a unified description of both dark matter and dynamical dark energy, as if it were based on Einstein's GR.

Lorenzo Copparoni, Rohit S. Chandramouli, Enrico Barausse

Published: 2025-10-08

Categories: gr-qc

Gravitational-wave signals are typically interpreted under the vacuum hypothesis, i.e. assuming negligible influence from the astrophysical environment. This assumption is expected to break down for low-frequency sources such as extreme mass ratio inspirals (EMRIs), which are prime targets for the Laser Interferometer Space Antenna (LISA) and are expected to form, at least in part, in dense environments such as Active Galactic Nuclei or dark-matter spikes/cores. Modeling environmental effects parametrically is challenging due to the large uncertainties in their underlying physics. We propose a non-parametric test for environmental effects in EMRIs, based on assessing the self-consistency of vacuum parameter posteriors inferred from different portions of the signal. Our results demonstrate that this approach can reveal the presence of astrophysical environments, or even deviations from General Relativity, without introducing additional parameters or assumptions about the underlying physics.

Ivan Arraut, Abhishek Kumar Mehta

Published: 2025-10-08

Categories: hep-th

We show that black-hole remnant scenario naturally arises in the original computations of Hawking without extra assumptions.

Giorgio Di Russo, Anna Tokareva

Published: 2025-10-08

Categories: hep-th

Microscopic charged black holes can provide possibilities to test the consistency of the effective field theory (EFT) corrections to Einstein-Maxwell theory. A particularly interesting result is fixing the sign of a certain combination of EFT couplings from the requirement that all charged black holes should be able to evaporate (Weak Gravity Conjecture). In our work, we analysed the EFT corrections to a set of zero-damping quasinormal modes (QNMs) of the scalar wave probe in a nearly extremal Reissner-Nordstr\"om black hole. We review the duality of this setup to the problem of the quantum Seiberg-Witten curve of $N=2$ Super-Yang-Mills theory with three flavors. We provide an analytic result for the EFT corrections to the QNMs obtained from the quantization condition imposed on the Seiberg-Witten cycle. Our main result is that the causality requirement of the gravitational theory formulated for the QNMs translates to the same condition on EFT couplings as the one appearing in the Weak Gravity Conjecture.

I. V. Fomin

Published: 2025-10-08

Categories: gr-qc

The correspondence of single-field cosmological models based on Einstein gravity to modern observational data is considered. A method is proposed to determine possible types of dynamics based on extreme values of the scalar field. It is shown that within the framework of this approach, it is possible to obtain a limited class of known inflationary models at early times. It is also shown that on large times the proposed approach leads to the $\Lambda$CDM--model in order to describe the dynamics of the second accelerated expansion of the universe. An interpretation of the considered models is presented as a starting point for constructing verifiable cosmological models based on modified gravity theories.

Zainab Malik

Published: 2025-10-08

Categories: gr-qc

We study quasinormal modes of a massive scalar field in the background of the regular, quantum-corrected Bonanno-Reuter black hole, which arises from the renormalization group improvement of the Schwarzschild solution within the framework of asymptotically safe gravity. The analysis is performed in both the time and frequency domains. We find that increasing the mass of the field leads to a strong suppression of the damping rate, and extrapolation to larger masses indicates the emergence of arbitrarily long-lived oscillations, or quasi-resonances. In the time domain, the late-time decay follows an asymptotic behavior that differs from the power-law tails of the classical Schwarzschild case. Furthermore, we compute the grey-body factors and absorption cross-sections for the massive scalar field and show that the grey-body factors decrease as the field mass increases, effectively shifting the emitted radiation spectrum toward higher frequencies.

Babak Vakili

Published: 2025-10-08

Categories: gr-qc

We study the dynamics of the Bianchi~I cosmological model in the presence of both polymer quantization effects and an exponential deformation of the Poisson algebra. Starting from the Hamiltonian formulation, we derive the polymer-deformed equations of motion and analyze their solutions for the contracting branch of the model. In contrast with the undeformed classical dynamics, the exponential deformation with suitable values of deformation parameters, produces a noticeably slower evolution of the volume variable and leads to a stabilization of the anisotropy parameters, which remain bounded throughout the evolution. No removal of the initial singularity is observed; however, the deformation significantly modifies the asymptotic behavior, offering a mechanism to suppress anisotropic shear near the singularity. Our results are illustrated through analytic solutions, highlighting the qualitative differences between the standard and the polymer--deformed Bianchi~I cosmology.

Fynn Otto, Refik Mansuroglu, Norbert Schuch, Otfried Gühne, Hanno Sahlmann

Published: 2025-10-08

Categories: quant-ph

We study the existence and limitations for hyperinvariant tensor networks incorporating a local SU(2) symmetry. As discrete implementations of the anti de-Sitter/conformal field theory (AdS/CFT) correspondence, such networks have created bridges between the fields of quantum information theory and quantum gravity. Adding SU(2) symmetry to the tensor network allows a direct connection to spin network states, a basis of the kinematic Hilbert space of loop quantum gravity (LQG). We consider a particular situation where the states can be interpreted as kinematic quantum states for three-dimensional quantum gravity. We show that important aspects of the AdS/CFT correspondence are realized in certain quantum states of the gravitational field in LQG, thus justifying, from first principles, a class of models introduced by [F. Pastawski et al., JHEP 06, 149 (2015)]. We provide examples of hyperinvariant tensor networks, but also prove constraints on their existence in the form of no-go theorems that exclude absolutely maximally entangled states as well as general holographic codes from local SU(2)-invariance. We calculate surface areas as expectation values of the LQG area operator and discuss further possible constraints as a consequence of a decay of correlations on the boundary.

S. N. Sajadi, Supakchai Ponglertsakul

Published: 2025-10-08

Categories: hep-th

To satisfy the Cardy formula for Warped AdS$_3$ (WAdS$_{3}$) solutions in a quadratic ensemble, a specific set of boundary conditions has been proposed in \cite{Aggarwal:2020igb}. In this paper, these boundary conditions have been investigated in the three-dimensional new massive gravity (NMG) framework. The associated solution space, asymptotic symmetries, and charge algebra have been extracted. It has been shown that the surface charges are finite, but not integrable, and the integrability of the charges is obtained after restricting to a sub-sector of the original solution space. Finally, we have proved that the Cardy formula reproduces the thermodynamic entropy of a warped BTZ black hole.

Masato Nozawa, Takashi Torii

Published: 2025-10-08

Categories: gr-qc

The Benenti-Francaviglia (BF) family of metrics provides the most general form of a spacetime metric that admits two mutually commuting Killing vectors and an irreducible Killing tensor. The geodesic equations for the BF family are thus completely integrable by separation of variables. Within this broad class, we explore the Kerr-Schild transformation of a degenerate subclass distinguished by the existence of a shear-free null geodesic congruence. By requiring the deformed metric to preserve the Killing symmetry and circularity, we demonstrate that the deformed metric again falls into the degenerate BF family, modulo the replacement of a single structure function. We apply the present algorithm to ${\cal N}=2$ gauged supergravity and obtain a dyonic generalization of the Chong-Cveti\v{c}-L\"u-Pope rotating black hole solution, by taking the background metric to be a solution of the Einstein-scalar gravity. The present prescription extends to five dimensions, provided that the constant of geodesic motion associated with the extra Killing direction vanishes. The same reasoning applies to the case where the background degenerate BF metric is distorted in a (non)conformal manner. Our formalism offers a unified perspective on the relation between seed and deformed metrics in the Kerr-Schild construction.

M. C. Rodriguez, José C. Jiménez, Ignacio F. Ranea-Sandoval

Published: 2025-10-07

Categories: hep-ph

We investigate the behavior of the non-radial gravity-pulsation discontinuity mode ($g$-mode) in hybrid compact stars with a strong first-order phase transition, which can give rise to twin-star configurations in some cases. These modes are of utmost relevance since they can be potentially excited in isolated as well as binary neutron star systems in the inspiral phase, thus allowing us to indirectly detect the presence of a deconfinement transition. In order to do this, we consider four categories of twin stars that present distinctive features in their equations of state. We employ the constant speed of sound parametrization, which accounts for a sharp phase transition between confined hadronic matter and deconfined quark matter. Then, working within the relativistic Cowling approximation to obtain the frequencies of non-radial oscillations, we find that, depending on the twin star category, the relations between $g$-mode frequencies and masses as well as tidal deformabilities display a highly distinct behavior across the diverse twin star categories that appear in the slow hadron-quark conversion regime. This distinct phenomenology provides smoking-gun evidence to clearly distinguish and further classify hybrid stars with a strong transition from purely hadronic stars using upcoming gravitational-wave data. In addition, we present for each of the categories studied the relation between the $g$-mode frequency and the normalized energy density jump. Finally, we present a novel universal relationship for the discontinuity $g$-mode able to encompass the four categories including long branches of slow stable twin stars and address its asteroseismological capability.

Bernardo Araneda, Maciej Dunajski

Published: 2025-10-07

Categories: gr-qc

We explicitly construct a three--parameter family of asymptotically flat Einstein--Maxwell instantons. These solutions are toric, regular, and free of conical and orbifold singularities on the manifold $M=\CP^2\setminus S^1$. They are counterexamples to the Euclidean Einstein--Maxwell Black Hole Uniqueness Conjecture. In the case of vanishing charge these instantons reduce to the Chen--Teo Ricci flat instantons.

Eren Erberk Erkul

Published: 2025-10-07

Categories: gr-qc

We propose that black holes are \emph{soliton-esque} objects, where gravitational collapse is balanced by quantum vacuum dispersion, modeled via \(R+\alpha R^{2}\) gravity. Classical singularities are replaced by oscillating, finite-radius cores, thereby evading static no-go theorems. The event horizon is replaced by the \textit{Lamarina}, a surface of maximum redshift whose surface geometry yields Hawking-like radiation with corrections. The Raychaudhuri equations impose a Dyson-type ceiling on the maximum radiated power \((P_{\infty} \lesssim c^{5}/G)\), while effective field theory matching dictates a universal minimum Lamarina radius set by the dispersion scale.

Ollie Burke, Martina Muratore, Graham Woan

Published: 2025-10-07

Categories: gr-qc

We investigate the impact of missing input data on the construction of second-generation Time Delay Interferometry (TDI) variables, which enable data analysis for the Laser Interferometer Space Antenna (LISA). TDI relies on the introduction of precise time delays into the raw interferometric data streams before they are combined to suppress otherwise dominant laser phase noise. We show that a single missing sample, corresponding to 0.25 s of data, will result in an effective data gap of approximately 90 s in the second-generation TDI output if further measures are not taken. This additional gap is largely independent of the initial gap duration, but increases linearly with the order of the fractional-delay filter used for the computations. For a realistic gap scenario, incorporating both planned and unplanned data interruptions consistent with a target duty cycle of ~84%, we find that frequent, short-duration gaps (e.g., a total of 1000 per year, each of which have short durations ~ 100 s) could result in an additional loss in the TDI variables of about one day per year corresponding to a ~0.3% reduction in duty cycle. This amounts to a loss of approximately one day of LISA data suitable for the global-fit per year.

Taylor Knapp, Katerina Chatziioannou, Keefe Mitman, Mark A. Scheel, Michael Boyle, Lawrence E. Kidder, Harald Pfeiffer

Published: 2025-10-07

Categories: gr-qc

Numerical relativity simulations provide a full description of the dynamics of binary systems, including gravitational radiation. The waveforms produced by these simulations have a number of applications in gravitational-wave detection and inference. In this work, we revisit the accuracy of the waveforms produced by the Spectral Einstein Code. Motivated by the wide range of waveform applications, we propose and explore three accuracy metrics between simulation resolutions: (i) the generalized frequency-weighted mismatch, (ii) the relative amplitude difference, and (iii) the phase difference at different times. We find that numerical errors accumulate over the binary evolution, but the error is not intrinsically larger during the latest, more dynamical stages. Studying errors across the parameter space, we identify a positive correlation between both the mismatch and the phase difference with precessing spin, but little correlation with aligned spin or eccentricity. Lastly, amplitude and phases differences are symmetric upon exchanging resolutions across the catalog, suggesting that there is no systematic error.

G. Pérez Cuéllar, M. Sabido

Published: 2025-10-07

Categories: gr-qc

In previous works, entropic gravity and ungravity have been considered as possible solutions to the dark energy and dark matter problems. To test the viability of these models, modifications to planetary orbits are calculated for ungravity and different models of entropic gravity. Using the gravitational sector of unparticles, an equation for the contribution to the effect of orbital precession is obtained. We conclude that the estimated values for the ungravity parameters from planetary orbits are inconsistent with the values needed for the cosmological constant. The same ideas are explored for entropic gravity arising from a modified entropy--area relationship.

Luca Brunelli, Michele Cicoli, Francisco Gil Pedro

Published: 2025-10-07

Categories: hep-th

We exploit the techniques of dynamical systems to study the cosmological evolution of cosmic fundamental strings and effective strings arising from branes wrapped on internal cycles. We also include the whole potential of the volume modulus characterised by an early time run-away towards a late time minimum. We analyse the overshoot problem with and without radiation, and find that the presence of an initial population of strings arising from NS5-branes wrapped around 4-cycles is enough to ensure that the modulus stabilises in its late time minimum, even in the absence of radiation. The reason is the transfer of energy between the modulus and the effective strings caused by the fact that their tension depends on the volume modulus. Interestingly, we find that the energy density of cosmic superstrings is generically very large when the modulus is oscillating around its minimum, opening up the possibility of a detectable gravitational wave signal. We also find no evidence of an efficient resonant enhancement of cosmic superstrings due to an oscillating tension in the late time minimum.

Isaac C. F. Wong, Francesco Cireddu, Milan Wils, Tom Colemont, Harsh Narola, Chris Van Den Broeck, Tjonnie G. F. Li

Published: 2025-10-07

Categories: gr-qc

We introduce a Bayesian null-stream method to constrain calibration errors in closed-geometry gravitational-wave (GW) detector networks. Unlike prior methods requiring electromagnetic counterparts or waveform models, this method uses sky-independent null streams to calibrate the detectors with any GW signals, independent of general relativity or waveform assumptions. We show a proof-of-concept study to demonstrate the feasibility of the method. We discuss prospects for next-generation detectors like Einstein Telescope, Cosmic Explorer, and LISA, where enhanced calibration accuracy will advance low-frequency GW science.

Manuel Piarulli, Sylvain Marsat, Elise M. Sänger, Alessandra Buonanno, Jan Steinhoff, Nicola Tamanini

Published: 2025-10-07

Categories: gr-qc

Laser Interferometer Space Antenna (LISA) observations of massive black hole binaries (MBHBs) will provide long duration inspiral signals with high signal-to-noise ratio (SNR) data, ideal for testing general relativity (GR) in the strong-field and high-velocity regime. We present an extension of the Flexible Theory-Independent (FTI) framework, adapted to gravitational waves (GWs) from MBHBs observed with LISA, to perform parametrized inspiral tests of GR. This approach introduces generic deviations to the post-Newtonian (PN) coefficients of the frequency-domain GW phase while accounting for the time- and frequency-dependent instrument response, thus effectively identifying potential deviations from GR by constraining modifications to the PN phasing formula. Complementary analyses using Fisher matrix and full Bayesian approaches confirm that LISA observations could improve constraints on deviations from GR by at least two orders of magnitude compared to the most recent LIGO-Virgo-KAGRA measurements. Since LISA`s sensitivity to different GW phases -- inspiral, merger, and ringdown -- varies across the MBHB parameter space with masses between $10^4$ and $10^7M_{\odot}$, the optimal regime for testing deviations is not known a priori. Our results illustrate how the strength of these constraints depends significantly on both the total mass and the SNR, reflecting the trade-off between inspiral and merger-ringdown contributions to the observed signal. We also investigate the interplay between inspiral-only versus inspiral-merger-ringdown analyses in constraining these inspiral deviation parameters. This work contributes to the development of robust tests of GR with LISA, enhancing our ability to probe the nature of gravity and BHs with GW observations.

Vijay Balasubramanian, William KL Chan, Chitraang Murdia

Published: 2025-10-07

Categories: hep-th

We demonstrate that the Euclidean two-point function of an appropriately chosen probe operator can detect the microstate of an asymptotically AdS black hole. This detection, which requires a tuned, state-dependent choice of probe, is the result of a new gravitational saddle, which dominates over the usual saddles. The gravitational result can be explicitly reproduced in the dual boundary CFT if we assume the eigenstate thermalization hypothesis. We also discuss a binary search protocol to detect the black hole microstate from a candidate list.

Noah E. Wolfe, Matthew Mould, Jack Heinzel, Salvatore Vitale

Published: 2025-10-07

Categories: gr-qc

From catalogs of gravitational-wave transients, the population-level properties of their sources and the formation channels of merging compact binaries can be constrained. However, astrophysical conclusions can be biased by misspecification or misestimation of the population likelihood. Despite detection thresholds on the false-alarm rate (FAR) or signal-to-noise ratio (SNR), the current catalog is likely contaminated by noise transients. Further, computing the population likelihood becomes less accurate as the catalog grows. Current methods to address these challenges often scale poorly with the number of events and potentially become infeasible for future catalogs. Here, we evaluate a simple remedy: increasing the significance threshold for including events in population analyses. To determine the efficacy of this approach, we analyze simulated catalogs of up to 1600 gravitational-wave signals from black-hole mergers using full Bayesian parameter estimation with current detector sensitivities. We show that the growth in statistical uncertainty about the black-hole population, as we analyze fewer events but with higher SNR, depends on the source parameters of interest. When the SNR threshold is raised from 11 to 15 -- reducing our catalog size by two--thirds -- we find that statistical uncertainties on the mass distribution only grow by a few 10% and constraints on the spin distribution are essentially unchanged; meanwhile, uncertainties on the high-redshift cosmic merger rate more than double. Simultaneously, numerical uncertainty in the estimate of the population likelihood more than halves, allowing us to ensure unbiased inference without additional computational expense. Our results demonstrate that focusing on higher-significance events is an effective way to facilitate robust astrophysical inference with growing gravitational-wave catalogs.

Alexander Reeves, Simone Ferraro, Andrina Nicola, Alexandre Refregier

Published: 2025-10-07

Categories: astro-ph.CO

We perform a multiprobe analysis combining cosmic microwave background (CMB) data from Planck and the Atacama Cosmology Telescope (ACT), ACT CMB lensing, and large-scale structure (LSS) measurements from the Dark Energy Spectroscopic Instrument (DESI), including DESI Legacy Imaging Survey (LS) galaxies and baryon acoustic oscillations (BAOs). We present the first $5\times2$pt analysis of ACT DR6 lensing, DESI LS, and Planck ISW. Within $\Lambda$CDM, this yields $S_8 = \sigma_8(\Omega_m/0.3)^{0.5} = 0.819 \pm 0.016$, in good agreement with primary CMB inferences and provides a sound-horizon-free Hubble constant constraint of $H_0 = 70.0 \pm 4.4$ km s$^{-1}$ Mpc$^{-1}$. Then, combining with CMB primary and BAO, we reconfirm a CMB-BAO discrepancy in the $\Omega_m$-$\frac{D_v}{r_d}$ plane, which is heightened when combining BAO with the $5\times2$pt data vector. We explore two dark-energy extensions that may reconcile this: an early-time modification, early dark energy (EDE), and late-time dynamical dark energy (DDE) parameterized by $w_0w_a$. For CMB primary+BAO+$5\times2$pt, we find a $3.3\sigma$ preference for DDE over $\Lambda$CDM, while EDE is modestly favoured at $2.3\sigma$. The models address different shortcomings of $\Lambda$CDM: DDE relaxes the neutrino mass bound ($M_\nu<0.17$eV vs. $<0.050$eV under $\Lambda$CDM), making it compatible with neutrino oscillation measurements, while EDE raises the Hubble constant to $H_0=70.5\pm1.2\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$, easing the discrepancy with SH0ES. However, neither model resolves both issues simultaneously. Our analysis indicates that both DDE and EDE remain viable extensions of $\Lambda$CDM within current uncertainties and demonstrates the capacity of combined probes to place increasingly stringent constraints on cosmological parameters.

S. K. Maurya, Abdul Aziz, Ksh. Newton Singh, G. Mustafa, Y. Sekhmani, Saibal Ray

Published: 2025-10-07

Categories: gr-qc

In this investigation we examine the astrophysical consequences of the influence of pressure anisotropy on the physical properties of observed pulsars within the background of $f(Q,T)$ gravity by choosing a specific form $f(Q, T)=\psi_1\, Q + \psi_2 T$, where $\psi_1$ and $\psi_2$ are the model parameters. Initially, we solve the modified field equations for anisotropic stellar configurations by assuming the physically valid metric potential along with anisotropic function for the distribution of the interior matter. We test the derived gravitational model subject to various stability conditions to confirm physically existence of compact stars within the $f(Q,T)$ gravity context. We analyze thoroughly the influence of anisotropy on the effective density, pressure and mass-radius relation of the stars. The present inspection of the model implies that the current gravitational models are non-singular and able to justify for the occurrence of observed pulsars with masses exceeding 2 $M_{\odot}$ as well as masses fall in the {\em mass gap} regime, in particular merger events like GW190814. The predicted radii for the observed stars of different masses fall within the range \{10.5 km, 14.5 km\} for $\psi_1\leq 1.05$ whereas the radius of PSR J074+6620 is predicted to fall within \{13.09 km, 14.66 km\} which is in agreement with the predicted radii range \{11.79 km, 15.01 km\} as can be found in the recent literature.

Michele Benaco, Dimitrios Karamitros, Sami Nurmi, Kimmo Tuominen

Published: 2025-10-07

Categories: astro-ph.CO

We investigate scalar-induced stochastic gravitational waves from adiabatic curvature perturbations sourced by a spectator field via the modulated reheating mechanism. We consider a spectator scalar with Higgs-like couplings and inflaton decay via shift symmetric dimension-five operators. The spectator is assumed to be in the Sitter vacuum and it sources blue-tilted, strongly non-Gaussian curvature perturbations which can dominate the spectrum on small scales $k \gg \rm{Mpc}^{-1}$. We find that the setup could generate a gravitational wave signal testable by surveys like BBO and DECIGO but only for large coupling values not expected in low-energy particle physics setups that can be perturbatively extrapolated up to the inflationary scale.

R. A. Konoplya, D. Ovchinnikov, J. Schee

Published: 2025-10-07

Categories: gr-qc

We study the optical properties of black holes endowed with primary Proca hair, focusing on the distinctive double-peak structure generated in the effective potential by the massive vector field. This novel feature drastically modifies the geodesic motion of both photons and massive particles, leading to qualitatively new dynamical and observational signatures. We derive and analyze the effective potentials, classify time-like and null geodesics, and identify the conditions for multiple circular orbits. Particular attention is devoted to the photon sphere structure, the associated shadows, and lensing phenomena. Our analysis reveals that, for a broad range of parameters, the black-hole shadow can acquire a two-boundary structure and exhibit additional inner rings, unlike the standard Schwarzschild case. These modifications provide potentially observable imprints of Proca hair in electromagnetic spectra, highlighting the relevance of double-barrier optical phenomena for current and future observations of strong-gravity environments.

Bruce Allen, Arian L. von Blanckenburg, Ken D. Olum

Published: 2025-10-07

Categories: gr-qc

We use Legendre polynomials (previously discussed in this context by Pitrou and Cusin [1]) to model signals in pulsar timing arrays (PTA). These replace the (Fourier mode) basis of trigonometric functions normally used for data analysis. The Legendre basis makes it simpler to incorporate pulsar modeling effects, which remove constant-, linear-, and quadratic-in-time terms from pulsar timing residuals. In the Legendre basis, this zeroes the amplitudes of the the first three Legendre polynomials. We use this basis to construct an optimal quadratic cross-correlation estimator $\widehat{\mu}$ of the Hellings and Downs (HD) correlation and compute its variance $\sigma^2_{\widehat{\mu}}$ in the way described by Allen and Romano [2]. Remarkably, if the gravitational-wave background (GWB) and pulsar noise power spectra are (sums of) power laws in frequency, then in this basis one obtains analytic closed forms for many quantities of interest.

Maria Chiara de Simone, Manuela Campanelli, Lorenzo Ennoggi, Carlos O. Lousto, Yosef Zlochower

Published: 2025-10-07

Categories: astro-ph.GA

We report the first 3D general relativistic magnetohydrodynamic (GRMHD) simulation that captures the full, self-consistent evolution from the late inspiral through merger and subsequent recoil of a supermassive binary black hole (SMBBH) with misaligned spins embedded in an equilibrated circumbinary disk (CBD). Our full numerical simulation follows the final 40 orbits of the inspiral and merger of the binary, following an initial phase of 165 orbits of CBD evolution toward equilibrium. We find that the jets, launched from the minidisks surrounding each black hole, are tilted toward the black hole spin direction close to the individual black holes, but align with the binary's total angular momentum at larger distances. Following the merger, the remnant black hole receives a recoil kick exceeding 1000 km/s. Remarkably, it retains its gravitationally bound CBD as if it were ejected from a galactic nucleus. Furthermore, the jet launched by the recoiling remnant black hole preserves the large-scale orientation established during the late inspiral. We demonstrate that the majority of the luminosity emerges from a region in close proximity to the black hole, suggesting that the accretion disk surrounding the recoiling remnant would remain the most luminous feature postmerger, persisting for long enough to be observable by modern telescopes (hours in the case of LISA sources). These findings introduce a direct, first-principles model for the recoil of supermassive black holes (SMBH) in active galactic nuclei (AGNs), offering a comprehensive theoretical basis to support and elucidate both ongoing and future observational efforts.

Jureeporn Yuennan, Farruh Atamurotov, Phongpichit Channuie

Published: 2025-10-07

Categories: astro-ph.CO

Recent measurements from the Atacama Cosmology Telescope (ACT), particularly when combined with DESI baryon acoustic oscillation data, have reported a scalar spectral index $n_s$ slightly higher than that inferred by {\it Planck}~2018, suggesting a mild tension with the predictions of standard inflationary attractor models. In this work, we revisit the quantum-corrected Higgs inflation scenario within the framework of a non-minimally coupled scalar field theory. Starting from the one-loop effective action, we incorporate radiative corrections through the anomalous scaling parameter ${\bf A_I}$ and derive analytic expressions for the inflationary observables $n_s$ and $r$ in the Einstein frame. Our analysis demonstrates that quantum corrections naturally shift $n_s$ toward higher values while keeping the tensor-to-scalar ratio $r$ suppressed. For ${\cal N} = 60$, the model predicts $n_s \simeq 0.9743$ and $r \simeq 5.4\times10^{-3}$, in excellent agreement with the latest ACT+DESI (P-ACT-LB) data and fully consistent with the \textit{Planck}~2018 limit $r < 0.036$. The derived constraint $4.36\times10^{-10} < \lambda/\xi^{2} < 10.77\times10^{-10}$ confirms the robustness of the quantum-corrected Higgs framework and indicates that near-future CMB polarization experiments such as CORE, AliCPT, LiteBIRD, and CMB-S4 will be able to probe the predicted parameter space with high precision.

Reinosuke Kusano, Miguel Yulo Asuncion, Keith Horne

Published: 2025-10-07

Categories: gr-qc

We present a parametric study of the spacetime structures in the dyonic Reissner-Nordstr\"{o}m solution in Weyl's conformal theory of gravity. We derive expressions for photon sphere radii and horizons for this metric in terms of the conformal gravity parameters, from which we then obtain analytic formulae for extremal limits and Hawking temperatures. Due to the surprising lack of the inverse quadratic $1/r^2$ term in this fourth-order metric, there is no guarantee for the innermost horizon of a black hole spacetime to be a Cauchy horizon, which is in direct contrast to the corresponding metric in general relativity. For example, for certain parameter values, a ``nested black hole'' is seen to exist; in such a spacetime, we find a Cauchy horizon trapped between two event horizons, which is not a structure known to be obtainable in standard general relativity. In addition to such exotic spacetimes, we also find a critical value for the electric and magnetic charges, at which the stable and unstable photon spheres of the metric merge, and we obtain extremal limits where three horizons collide.

Yi-Ping Chen, Tien Hsieh, Da-Shin Lee

Published: 2025-10-07

Categories: gr-qc

The motion of a spinning particle in the exterior of the Kerr-Newman black hole is studied. The dynamics is governed by the Mathisson-Papapetrou equations in the pole-dipole approximation through the spin-curvature coupling to the leading order in its spin. In terms of conserved quantities, one can transform the dynamical equations in the Mino time into an integral form for both aligned and misaligned spins with orbital motion. These non-geodesic equations can be solved analytically with the solutions involving Jacobi elliptic functions. The radial potential can be derived in order to study the parameter space of the particle for various types of orbit, based on its roots obtained with the corrections of the particle's spin. We consider motion oscillating around two turning points, which are the two outermost roots of the radial potential on the equatorial plane in the misaligned case. In this case, there is an induced oscillatory motion out of the equatorial plane. In particular, the oscillation periods of the motion are obtained. When the orbits become a source of gravitational wave emission, these periods of motion will play a key role in determining the gravitational waves in the frequency domain. Numerical kludge waveforms are constructed. The gravitational wave amplitudes are found to be sensitive to the turning points of the orbits as measured from the black holes. The implications for gravitational wave emission due to extreme mass-ratio inspirals (EMRIs) are discussed.

Thippayawis Cheunchitra, Andrew Melatos, Rachel Webster

Published: 2025-10-07

Categories: astro-ph.CO

The luminosity distance-redshift ($D_{\rm L}$--$z$) relation derived from Type Ia supernovae (SNe Ia) yields evidence for a nonzero cosmological constant. SNe Ia analyses typically fit to the functional form $D_{\rm L}(z)$ derived theoretically from the homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) metric. Yet, the metric in the epoch relevant to SNe Ia measurements deviates slightly from FLRW due to gravitational clumping of mass into large-scale structures like filaments and voids, whose sizes span many orders of magnitude. The small deviation is modeled typically by scalar perturbations to the FLRW metric. Each line of sight to a SNe Ia passes through a random sequence of structures, so $D_{\rm L}$ differs stochastically from one line of sight to the next. Here, we calculate the $D_{\rm L}$ dispersion in an exact Lemaitre-Tolman-Bondi Swiss-cheese universe with a power-law hole size distribution, as a function of the lower cut-off $R_{\rm min}$ and logarithmic slope $\gamma$. We find that the standard deviation of $D_{\rm L}$ scales as $\sigma_{D_{\rm L}} \propto z^{2.25\pm0.01} (R_{\rm min}/24\pm1\,{\rm Mpc})^{(0.157\pm0.003)\left[\gamma - (1.16\pm0.02)\right]}$ for redshifts in the range $0.5 \lesssim z \lesssim 2.1$. The scaling shows that the $D_{\rm L}$ dispersion is dominated by a few large voids rather than the many small voids.

Hong-Yi Zhang

Published: 2025-10-07

Categories: gr-qc

Magnification of total image fluxes is typically considered a defining feature of gravitational microlensing. In contrast, I will show that nonminimal couplings to gravity can generate regions of negative gravitational potential curvature, giving rise to the distinctive possibility of demagnification. Such events, appearing as flux troughs in microlensing light curves, provide a direct probe of dark matter structures and, crucially, offer a means to disentangle nonminimal couplings to gravity from other astrophysical and cosmological models.

Diego A. Martínez-Valera

Published: 2025-10-07

Categories: gr-qc

In this work, we prove that the classical Schwarzschild-de Sitter spacetime is an exact solution of a class of weakly non-local, UV finite conformal quantum gravity theories, without the necessity of including a cosmological constant term in the action, thus associating the effective cosmological constant $\Lambda$ appearing in the metric with the coupling constants of the quantum gravity theory. Furthermore, exploiting the inherent conformal symmetry of the theory, we take advantage of the natural enlargement of the exact solutions to motivate the construction of a regular spacetime via conformal rescaling of the Schwarzschild-de Sitter spacetime. Moreover, we ensure the spacetime completeness by investigating the regularity of the curvature invariants and the geodesic completeness of conformally/non-conformally coupled massive and massless particles. We also study the global causal structure by explicitly constructing the Penrose diagram of the regular spacetime. Furthermore, as a result of the spacetime completeness analysis, we generalize the range of conformal factors that generate regular spacetimes, by considering the $N$ parameter of the conformal factor as a real parameter with a lower bound, and not only a positive integer, as constrained in previous studies on regular Schwarzschild/Kerr black holes. Thus, the present analysis broadens the range of solutions of the finite conformal quantum theory and opens the window to more precise observational tests of the theory using astrophysical data, by considering the accelerated expansion of the universe.

Limin Zeng

Published: 2025-10-06

Categories: hep-th

We study the holographic dual of the extended thermodynamics of spherically symmetric, charged Gauss-Bonnet AdS black holes in the context of the AdS/CFT correspondence. The gravitational thermodynamics of Gauss-Bonnet AdS black holes can be extended by allowing for variations of the cosmological constant and Newton's constant. In the dual CFT this corresponds to including the central charge C and its chemical potential $\mu$ as a new pair of conjugate thermodynamic variables. In addition, compared to Einstein's theory of gravity, Gauss-Bonnet gravity introduces higher-order curvature terms. The coupling constants of these higher-order curvature terms $\alpha$ can serve as new thermodynamic quantities, which will also be dual to thermodynamic quantities on the boundary CFT, a feature not present in the CFT dual to Einstein's gravity previously. Based on the holographic dictionary, we consider the critical behavior and phase transition phenomena of the CFT description of the charged Gauss-Bonnet black holes in $d=4$ and $d=5$ in the ensemble at fixed $(C, \mathcal{V}, \tilde{Q}, \tilde{\mathcal{A}})$. We find that the conventional description of free energy cannot adequately describe the phase transitions and critical behavior of the CFT in this ensemble. This may stem from the fact that the constraints we have adopted are different from the conventional ones.

Anjali B. Yelikar, Karan Jani

Published: 2025-10-06

Categories: gr-qc

Binary neutron star mergers are unique probes of matter at extreme density and standard candles of cosmic expansion. The only such event observed in both gravitational waves and electromagnetic radiation, GW170817, revealed the origin of heavy elements, constrained the neutron star equation of state, and provided an independent measurement of the Hubble constant. Current detectors such as LIGO, Virgo, and KAGRA capture only the final minutes of inspiral, offering limited advance warning and coarse sky localization. In this study, we present a comprehensive analysis of binary neutron star signals for lunar-based gravitational-wave observatories (LILA, LGWA, GLOC) envisioned within NASA's Artemis and Commercial Lunar Payload Services programs, and compare their performance with current and next-generation Earth-based facilities. For GW170817-like sources, we find that lunar detectors can forecast mergers weeks to months in advance and localize them to areas as small as 0.01 deg$^{2}$, far beyond the reach of terrestrial detectors. We further show that lunar observatories would detect on the order of 100 well-localized mergers annually, enabling coordinated multi-messenger follow-up. When combined in a multi-band LIGO+Moon network, sky-localization areas shrink to just a few arcsec$^{2}$, comparable to the field of view of the James Webb Space Telescope at high zoom. Multi-band parameter estimation also delivers dramatic gains: neutron star mass-ratio uncertainties can be measured with $\sim0.1\%$ precision, spin constraints to 0.001$\%$ with luminosity distance errors to 1$\%$ level, enabling precision measurements of the equation of state and the cosmic expansion rate. Our results demonstrate that lunar gravitational-wave observatories would revolutionize multi-messenger astrophysics with binary neutron stars and open a unique discovery landscape in the Artemis era.

Sagnik Saha, Hector O. Silva

Published: 2025-10-06

Categories: gr-qc

We present a comprehensive study of the Kerr-Newman quasinormal mode spectrum in the Dudley-Finley approximation, where the linear gravitoelectromagnetic perturbations are decoupled by "freezing" either one of the fields to its background value. First, we reassess the accuracy of this approximation by comparing it to calculations that solve the coupled system of gravitoelectromagnetic perturbation equations across the subextremal spin-charge parameter space. We find that for the $(\ell,m,n) = (2,2,0)$, $(2,2,1)$, and $(3,3,0)$ modes, the agreement is typically within $10\%$ and $1\%$ for the real and imaginary parts of the frequencies, respectively. Next, we investigate the spectrum in the near-extremal limit, and study the family of long-lived ("zero-damped") gravitational modes. We find that the near-extremal parameter space consists of subregions containing either only zero-damped modes, or zero-damped modes alongside modes that retain nonzero damping. We derive analytic expressions for the boundaries between these regions. Moreover, we discuss the connection between the zero-damped and damped modes in the Dudley-Finley approximation and the "near-horizon/photon-sphere" modes of the full Kerr-Newman spectrum. Finally, we analyze the behavior of the quadrupolar gravitational modes with large overtone numbers $n$, and study their trajectories in the complex plane.

Christos G. Tsagas, Leandros Perivolaropoulos, Kerkyra Asvesta

Published: 2025-10-06

Categories: astro-ph.CO

Observations have repeatedly confirmed the presence of large-scale peculiar motions in the universe, commonly referred to as ``bulk flows''. These are vast regions of the observable universe, typically spanning scales of several hundred Mpc, that move coherently with speeds of the order of several hundred km/sec. While there is a general consensus on the direction of these motions, discrepancies persist in their reported sizes and velocities, with some of them exceeding the predictions of the standard $\Lambda$CDM model. The observed large-scale peculiar-velocity fields are believed to have originated as weak peculiar-velocity perturbations soon after equipartition, which have subsequently grown by structure formation and by the increasing inhomogeneity of the post-recombination universe. However, the evolution and the implications of these bulk velocity fields remain poorly understood and they are still a matter of debate. For instance, it remains a challenge for the theoreticians to explain the high velocities measured by several bulk-flow surveys, like those recently reported using the CosmicFlows-4 data. Such extensive and fast velocity fields could have played a non-negligible role during structure formation and they might have also ``contaminated'' our observations. After all, in the history of astronomy, there are examples where relative-motion effects have led us to a serious misinterpretation of reality (shortened abstract due to length limits).

Debadri Bhattacharjee, Pradip Kumar Chattopadhyay

Published: 2025-10-06

Categories: gr-qc

The correct choice for the matter Lagrangian $(\mathcal{L_{M}})$ in the framework of $f(R,T)$ theory of gravity, has been a perennial problem. It has been a long-standing issue, whether to choose $\mathcal{L_{M}}=p$ or $-\rho$ as the proper definition of matter sector. In this work, we summarise that both choices lead to the same energy-momentum tensor. However, for these two choices, the structure of the TOV equations are different. We construct and solve TOV equations using MIT bag model equation of state for $\mathcal{L_{M}}=p$ and $-\rho$, and study the impact of the choices for matter Lagrangian on the maximum mass limit as well as M-R plot of compact stars. It is interesting to note that allowed range of gravity-matter coupling coefficient is also different for $\mathcal{L_{M}}=p$ and $\mathcal{L_{M}}=-\rho$.

James B. Dent, Bhaskar Dutta, Mudit Rai

Published: 2025-10-06

Categories: hep-ph

Primordial black holes (PBHs) formed during first-order phase transitions provide a powerful link between the early-universe microphysics and observable signatures today, including dark matter and gravitational waves. In this work we develop a unified description of PBH formation based on the Israel junction conditions, which capture collapse dynamics without relying on conventional overdensity or pressure-balance arguments. As a first application, we show that exotic objects such as Fermi-balls can collapse into PBHs even when most of the vacuum energy is trapped in solitonic cores, leading to a different gravitational-wave signal relative to vacuum-only scenarios. As a second application, we study multiple phase transitions in a hidden sector, which generate correlated gravitational-wave spectra and PBH abundances across transitions. Our framework, while analytically controlled, is broadly applicable to hidden-sector models with general vacuum, radiation, and matter contributions. We present the resulting predictions for PBH mass spectra, dark matter fractions, and gravitational-wave signals, highlighting parameter regions that remain open in current searches and motivating future probes.

Iosif Bena, Angèle Lochet

Published: 2025-10-06

Categories: hep-th

We identify singularity-free Running-Kerr-Taub-Bolt solutions of eleven-dimensional supergravity that descend to four-dimensional rotating solutions with flat-space asymptotics. We compute their spin-induced quadrupole moment and find that for a certain range of charges this quadrupole moment is positive. This behavior differs from the Kerr black hole and from most other spinning objects constructed with ``normal'' four-dimensional matter, and we discuss the top-down physics of these solutions that could be responsible for this unusual behavior.

Kelvin Ka-Ho Lam, Adrian Ka-Wai Chung, Nicolás Yunes

Published: 2025-10-06

Categories: gr-qc

A key obstacle for theory-specific tests of general relativity is the lack of accurate black-hole solutions in beyond-Einstein theories, especially for moderate to high spins. We address this by developing a general framework--based on spectral and pseudospectral methods--to obtain analytic, closed-form spacetimes representing stationary, axisymmetric black holes in effective-field-theory extensions of general relativity to leading order in the coupling constants. The approach models the spacetime (and extra fields) as a stationary, axisymmetric deformation of the Kerr metric in Boyer-Lindquist-like coordinates, expands metric deformations as a spectral series in radius and polar angle, and converts the resulting beyond-Einstein field equations into algebraic equations for the spectral coefficients. For any given spin, these equations are solved via standard linear-algebra methods; the coefficients are then fitted as functions of spin with non-linear functions, yielding fully analytic metrics for rotating black holes in beyond-Einstein theories. We apply this to quadratic gravity theories--dynamical Chern-Simons, scalar-Gauss-Bonnet, and axi-dilaton gravity--obtaining solutions valid for any spin, including near-extremal cases with errors below machine precision for $a \leq 0.9$ and $\lesssim 10^{-8}$ for $a \leq 0.999$. We show that existing slowly-rotating solutions break down at $a \sim (0.2, 0.6)$, depending on approximation order and chosen accuracy. We then use our metrics to compute observables, such as the surface gravity, horizon angular velocity, and the locations of the innermost circular orbit and the photon ring. The framework is general and applicable to other effective-field-theory extensions for black holes of any spin.

Shuntaro Aoki, Alessandro Strumia

Published: 2025-10-06

Categories: hep-ph

Normal particles carry a microscopic arrow of causality. Lee-Wick ghosts carry the reversed arrow, mediating characteristic collider signals in flat space: opposite-sign scattering amplitudes that violate positivity bounds; acausality on time scales set by their negative decay rate. During inflation, the corresponding cosmo-collider ghost signals are: opposite-sign non-Gaussianities; Boltzmann-unsuppressed local oscillatory signals without their non-local counterparts; IR-enhanced bi-spectrum and power spectrum, depending on the dimension of the interaction operator, which decreases if the ghost decay rate is comparable to the Hubble rate.

Pierre Heidmann, Paolo Pani, Jorge E. Santos

Published: 2025-10-06

Categories: hep-th

We construct a new class of smooth, horizonless, non-supersymmetric solutions in five-dimensional minimal supergravity, which we call rotating topological stars. Built from a Kerr-Taub-bolt geometry embedded in five dimensions, they constitute the first rotating generalization of the topological star compatible with both smoothness in the interior and standard Kaluza-Klein asymptotics, S$^1\times\mathbb{R}^{1,3}$. The solutions carry angular momentum, magnetic and electric charges, and form a discrete tower of states labeled by a primary quantum number controlling the spin. Remarkably, despite lying outside the black-hole extremality bound, they can approach arbitrarily closely (in conserved charges) the Kerr black string with a large boost along the fifth dimension, making them relevant prototypes for rotating and astrophysical black-hole microstates. We analyze their geometry in detail, including their gravitational multipoles that can significantly deviate from those of black holes and the presence of an ergoregion, and show that both geodesics and scalar perturbations separate, paving the way for analyzing their dynamics in future work.

Craig J. Copi, Amirhossein Samandar, Glenn D. Starkman, Javier Carrón Duque, Yashar Akrami, Stefano Anselmi, Andrew H. Jaffe, Arthur Kosowsky, Fernando Cornet-Gomez, Johannes R. Eskilt, Mikel Martin Barandiaran, Deyan P. Mihaylov, Anna Negro, Joline Noltmann, Thiago S. Pereira, Andrius Tamosiunas

Published: 2025-10-06

Categories: astro-ph.CO

If the Universe has non-trivial spatial topology, observables depend on both the parameters of the spatial manifold and the position and orientation of the observer. In infinite Euclidean space, most cosmological observables arise from the amplitudes of Fourier modes of primordial scalar curvature perturbations. Topological boundary conditions replace the full set of Fourier modes with specific linear combinations of selected Fourier modes as the eigenmodes of the scalar Laplacian. In this paper we consider the non-orientable Euclidean topologies \E{7}--\E{10}, \E{13}--\E{15}, and \E{17}, encompassing the full range of manifold parameters and observer positions, generalizing previous treatments. Under the assumption that the amplitudes of primordial scalar curvature eigenmodes are independent random variables, for each topology we obtain the correlation matrices of Fourier-mode amplitudes (of scalar fields linearly related to the scalar curvature) and the correlation matrices of spherical-harmonic coefficients of such fields sampled on a sphere, such as the temperature of the cosmic microwave background (CMB). We evaluate the detectability of these correlations given the cosmic variance of the CMB sky. We find that in manifolds where the distance to our nearest clone is less than about $1.2$ times the diameter of the last scattering surface of the CMB, we expect a correlation signal that is larger than cosmic variance noise in the CMB. Our limited selection of manifold parameters are exemplary of interesting behaviors, but not necessarily representative. Future searches for topology will require a thorough exploration of the parameter space to determine what values of the parameters predict statistical correlations that are convincingly attributable to topology.[Abridged]

Rhiannon Udall, Sophie Bini, Katerina Chatziioannou, Derek Davis, Sophie Hourihane, Yannick Lecoeuche, Jess McIver, Simona Miller

Published: 2025-10-06

Categories: gr-qc

Gravitational waves from black hole binary mergers carry information about the component spins, but inference is sensitive to analysis assumptions, which may be broken by terrestrial noise transients known as glitches. Using a variety of simulated glitches and gravitational wave signals, we study the conditions under which glitches can bias spin measurements. We confirm the theoretical expectation that inference and subtraction of glitches invariably leaves behind residual power due to statistical uncertainty, no matter the strength (signal-to-noise ratio; SNR) of the original glitch. Next we show that low-SNR glitches - including those below the threshold for flagging data-quality issues - can still significantly bias spin inference. Such biases occur for a range of glitch morphologies, even in cases where glitches and signals are not precisely aligned in phase. Furthermore, we find that residuals of glitch subtraction can result in biases as well. Our results suggest that joint inference of the glitch and gravitational wave parameters, with appropriate models and priors, is required to address these uncertainties inherent in glitch mitigation via subtraction.

Fangyi Fitz Hu, Ilya Mandel, Rebecca Nealon, Daniel J. Price

Published: 2025-10-06

Categories: astro-ph.HE

When debris from a star that experienced a tidal disruption events (TDE) after passing too close to a massive black hole returns to pericenter on the second passage, it is compressed, leading to the formation of nozzle shocks (in the orbital plane) and pancake shocks (perpendicular to the orbital plane). Resolving these shocks is a long-standing problem in the hydrodynamic simulations of parabolic TDEs. Excessive numerical energy dissipation or heating unrealistically expands the stream. In this Letter, we apply adaptive particle refinement to our 3D general relativistic smoothed particle simulations to locally increase the resolution near the pericenter. We achieve resolutions equivalent to $6.55\times10^{11}$ particles, allowing us to converge on the true energy dissipation. We conclude that only $4\times10^{-5}$ of the orbital energy is dissipated in nozzle shocks for a Sun-like star tidally disrupted by a $10^6$ solar-mass black hole, therefore the nozzle shocks are unlikely to be important in the evolution of TDEs.

Gerasimos Kouniatalis

Published: 2025-10-06

Categories: gr-qc

We develop a quantum-cosmological framework in which the inflationary potential emerges from the structure of the wave function of the universe rather than being postulated. Starting from the Wheeler-DeWitt equation for a flat Friedmann-Robertson-Walker minisuperspace, we express the wave function in terms of an amplitude and a phase and, in a semiclassical regime where the expansion dominates the field's evolution, separate these into purely geometric and purely field-dependent pieces. This yields a closed expression for an emergent potential that makes transparent the roles of the cosmological constant, the momenta associated with expansion and field dynamics, and quantum corrections from the amplitude. Slow-roll conditions follow from properties of the phase and amplitude, leading to wave-function-level expressions for the usual slow-roll parameters and to direct links between cosmic microwave background observables and derivatives of the phase. The approach ties inflation to the quantum state of the universe and suggests testable relationships between cosmological data and features of the wave function.

Divyansh Srivastava, Andrzej Niedzielski

Published: 2025-10-06

Categories: cs.CV

Transient noise (glitches) in LIGO data hinders the detection of gravitational waves (GW). The Gravity Spy project has categorized these noise events into various classes. With the O3 run, there is the inclusion of two additional noise classes and thus a need to train new models for effective classification. We aim to classify glitches in LIGO data into 22 existing classes from the first run plus 2 additional noise classes from O3a using the Vision Transformer (ViT) model. We train a pre-trained Vision Transformer (ViT-B/32) model on a combined dataset consisting of the Gravity Spy dataset with the additional two classes from the LIGO O3a run. We achieve a classification efficiency of 92.26%, demonstrating the potential of Vision Transformer to improve the accuracy of gravitational wave detection by effectively distinguishing transient noise. Key words: gravitational waves --vision transformer --machine learning

Saeed Fakhry, Maryam Shiravand, Antonino Del Popolo

Published: 2025-10-06

Categories: astro-ph.GA

The James Webb Space Telescope (JWST) has unveiled a population of unexpectedly massive and luminous galaxies at redshifts $z \gtrsim 7$, posing a significant challenge to the standard $\Lambda$CDM cosmological paradigm. In this work, we address the tension between early JWST observations of luminous high-redshift galaxies and predictions of the standard $\Lambda$CDM model by revisiting the physics of dark matter halo formation. Employing refined halo mass functions derived by Del Popolo \textit{et al.} (DP1 and DP2) that incorporate angular momentum, dynamical friction, and redshift-dependent collapse barriers, we demonstrate a significant enhancement in the abundance of massive halos at $z \gtrsim 7$ compared to the conventional Sheth-Tormen (ST) formalism. Using a semi-empirical framework linking halo mass to UV luminosity, we show that the DP2 model reproduces the observed UV luminosity functions from $z = 7$ to $14$ with moderate star formation efficiencies, whereas the ST model requires implausibly high efficiencies. Our results suggest that the JWST overabundance problem stems not from new physics beyond $\Lambda$CDM, but from oversimplified treatments of gravitational collapse, highlighting the critical role of small-scale dissipative dynamics in early structure formation.

Zhe Zhao, Swarnim Shashank, Debtroy Das, Cosimo Bambi

Published: 2025-10-06

Categories: gr-qc

Gravitational wave astronomy has opened an unprecedented window onto tests of gravity and fundamental physics in the strong-field regime. In this study, we examine a series of well-motivated deviations from the classical Kerr solution of General Relativity and employ gravitational wave data to place constraints on possible deviations from the Kerr geometry. The method involves calculating the phase of gravitational waves using the effective one-body formalism and then applying the parameterized post-Einsteinian framework to constrain the parameters appearing in these scenarios beyond General Relativity. The effective one-body method, known for its capability to model complex gravitational waveforms, is used to compute the wave phase, and the post-Einsteinian framework allows for a flexible, model-independent approach to parameter estimation. We demonstrate that gravitational wave data provide evidence supporting the Kerr nature of black holes, showing no significant deviations from General Relativity, thereby affirming its validity within the current observational limits. This work bridges theoretical waveform modeling with observational constraints, providing a pathway to test the no-hair theorem and probe the astrophysical viability of modified black holes.

Tekin Dereli, Yorgo Senikoglu

Published: 2025-10-06

Categories: gr-qc

Linearized Einstein-Weyl equations are solved precisely in the context of sandwich gravitational waves. The neutrino's energy-momentum depends on the geometry and composition of the gravitational pulse when it is scattered. Since the background remains unchanged at the test field level, the neutrino's energy density will exhibit fluctuations between positive and negative extremes when traversing the sandwich wave. These variations could provide insights into the behavior of models concerning neutrino oscillations.

Marta Volonteri

Published: 2025-10-06

Categories: astro-ph.GA

These notes review theoretical models of massive black hole formation, growth and observables. They start with a brief summary of basic properties of massive black hole properties. The current view on massive black holes and active galactic nuclei at high redshift is then summarized, highlighting the JWST ``revolution'' and the questions raised by the recent observations. The notes then touch on massive black hole formation and growth mechanisms, emphasizing the processes at play at early cosmic times. Then techniques for modeling the cosmic massive black hole evolution, are reviewed with an emphasis on cosmological simulations, before approaching how observables are derived from models. They conclude with a section reflecting on the main questions on the JWST-discovered population in light of the material presented in the earlier sections.

Sharon Mary Tomson, Boris Goncharov, Rutger van Haasteren

Published: 2025-10-06

Categories: astro-ph.HE

Galaxy observations suggest there is about one merger of supermassive black hole binaries (SMBHB) throughout the observable universe in a year. Here, we introduce the methodology to search for gravitational waves from these events with Pulsar Timing Arrays (PTAs). Modelling the inspiral, the merger, the ringdown, and the gravitational wave memory components of the signal in simulated data, we demonstrate a proof of principle for detection and parameter estimation. We study a few representative SMBHB mergers with chirp masses spanning $10^{8} - 10^{10}~M_\odot$ at distances from a few Mpc to 100~Mpc to asses their detectability in PTA observations. Assuming the fixed binary inclination angle of $90^{\circ}$ corresponding to the maximum displacement memory signal, these signals appear distinct for a PTA with 25 pulsars timed for 13 years with 100 ns precision. We demonstrate the capabilities of PTAs to constrain chirp masses and distances of detected merging binaries, as well as to place limits. The sky position uncertainties of the order of $1^{\circ}$, which we find in this optimistic example, could potentially enable electromagnetic follow-up and multi-messenger observations of SMBHB mergers. Finally, we show that the measurement uncertainties on the parameters of simulated merging binaries depend weakly on the presence of the gravitational wave background with Hellings-Downs correlations in our simulated data.

Ravil R. Fatykhov, Sergey V. Sushkov

Published: 2025-10-06

Categories: gr-qc

This paper explores cosmological scenarios in a scalar-tensor theory of gravity, including both a non-minimal coupling with scalar curvature of the form $R\phi^2$ and a non-minimal derivative coupling of the form $G^{\mu\nu}\phi_{,\mu}\phi_{,\nu}$ in the presence of a scalar field potential with the monomial dependence $V(\phi) = V_0\phi^n$. Critical points of the system were obtained and analyzed. In the absence of a scalar field potential, stability conditions for these points were determined. Using methods of dynamical systems theory, the asymptotic behavior of the model was analyzed. It was shown that in the case of $V(\phi)\equiv0$ or $n < 2$, a quasi-de Sitter asymptotic behavior exists, corresponding to an early inflationary universe. This asymptotic behavior in the approximation $V_0 \rightarrow 0,\ \xi \rightarrow 0$ coincides with the value $H = \frac{1}{\sqrt{9|\eta|}}$ obtained in works devoted to cosmological models with non-minimal kinetic coupling. For $|\xi|\ \rightarrow \infty$, this asymptotic behavior tends to the value $H = \frac{1}{\sqrt{3|\eta|}}$. Moreover, unstable regimes with phantom expansion $w_{eff} < -1$ were found for the early dynamics of the model. For the late dynamics, the following stable asymptotic regimes were obtained: a power-law expansion with $w_{eff} \ge 1$, an expansion with $w_{eff} =\frac{1}{3}$ ($V(\phi)\equiv0$), at which the effective Planck mass tends to zero, and an exponential expansion with $w_{eff} = 0$ as $n = 2$. In this case, the asymptotic value of the Hubble parameter depends only on $V_0 = \frac{1}{2}m^2$ and $\xi$. Numerical integration of the model dynamics was performed for specific values of the theory parameters. The results are presented as phase portraits.

Shoulong Li, Liang Liang, Liang Ma

Published: 2025-10-06

Categories: gr-qc

Einstein-bumblebee gravity is one of the simplest vector-tensor theories that realizes spontaneous Lorentz symmetry breaking. In this work, we first construct an exact dyonic Reissner-Nordstr\"om-like black hole solution in four dimensions, carrying both electric and magnetic charges and admitting general topological horizons. We then study its thermodynamic properties, and employ the Wald formalism to compute the conserved mass and entropy, thereby establishing the first law of black hole thermodynamics. Furthermore, we generalize these results to Taub-Newman-Unti-Tamburino case and higher dimensions case.

Divyajyoti, Isobel M. Romero-Shaw, Vaishak Prasad, Kaushik Paul, Chandra Kant Mishra, Prayush Kumar, Akash Maurya, Michael Boyle, Lawrence E. Kidder, Harald P. Pfeiffer, Mark A. Scheel

Published: 2025-10-05

Categories: gr-qc

While the majority of gravitational wave (GW) events observed by the LIGO and Virgo detectors are consistent with mergers of binary black holes (BBHs) on quasi-circular orbits, some events are also consistent with non-zero orbital eccentricity, indicating that the binaries could have formed via dynamical interactions. Moreover, there may be GW events which show support for spin-precession, eccentricity, or both. In this work, we study the interplay of spins and eccentricity on the parameter estimation of GW signals from BBH mergers. We inject eccentric signals with no spins, aligned spins, and precessing spins using hybrids, TEOBResumS-DALI, and new Numerical Relativity (NR) simulations, respectively, and study the biases in the posteriors of source parameters when these signals are recovered with a quasi-circular precessing-spin waveform model, as opposed to an aligned-spin eccentric waveform model. We find significant biases in the source parameters, such as chirp mass and spin-precession ($\chi_p$), when signals from highly-eccentric BBHs are recovered with a quasi-circular waveform model. Moreover, we find that for signals with both eccentricity and spin-precession effects, Bayes factor calculations confirm that an eccentric, aligned-spin model is preferred over a quasi-circular precessing-spin model. Our study highlights the complex nature of GW signals from eccentric, precessing-spin binaries and the need for readily usable inspiral-merger-ringdown eccentric, spin-precessing waveform models for unbiased parameter estimation.

Mikhail Molodyk, András Vasy

Published: 2025-10-05

Categories: gr-qc

On a large class of asymptotically flat spacetimes which includes radiative perturbations of Minkowski space, we define a distinguished global Feynman propagator for massive Klein-Gordon fields by means of the microlocal approach to non-elliptic Fredholm theory, working in the de,sc-pseudodifferential algebra due to Sussman. We extend the limiting absorption principle (the "$i\varepsilon$ prescription" for the Feynman propagator) to this setting. Motivated by the complicated Hamilton flow structure arising in this problem, we also prove a new localized radial point estimate in the spirit of Haber-Vasy which, under appropriate nondegeneracy assumptions, allows one to propagate microlocal regularity into a single radial point belonging to a larger radial set which can be a source, sink, or saddle for the Hamilton flow.

M. D. Danarianto, A. Sulaksono

Published: 2025-10-05

Categories: gr-qc

We investigate quasi-universal relations in neutron stars linking standard observables, such as tidal deformability ($\Lambda$) and normalized moment of inertia ($\bar{I}$), with normalized curvature scalars in general relativity. These curvature scalars include the Ricci scalar ($\mathcal{R}$), the Ricci tensor contraction ($\mathcal{J}$), the Weyl scalar ($\mathcal{W}$), and the Kretschmann scalar ($\mathcal{K}$). We systematically examine both piecewise polytropic and color-flavor-locked equations of state, finding: (1) significant correlations between both local (central and surface) and global (volume-averaged) curvature scalars with $\bar{I}$ and $\Lambda$; (2) especially strong correlations between surface and volume-averaged curvature scalars and both $\bar{I}$ and $\Lambda$; (3) a near equation-of-state-independent maximum for the normalized Ricci scalar, suggesting a link to the trace anomaly; and (4) new universal relations involving normalized central and volume-averaged pressure and energy density, which also correlate strongly with $\bar{I}$ and $\Lambda$. Using constraints from GW170817 and low-mass X-ray binaries, we demonstrate that $\Lambda$ measurements directly constrain both scalar curvature quantities and the interior properties of canonical-mass neutron stars. These findings agree with the literature on equation-of-state-dependent Bayesian inference estimates. Our identified relations thus provide an equation-of-state-insensitive connection between stellar observables, spacetime geometry, and the microphysics of compact stars.

Yan Peng, Guohua Liu

Published: 2025-10-05

Categories: gr-qc

This paper investigates the bounds on the minimum orbital period for test objects around d-dimensional charged black holes in asymptotically flat spacetimes. We find numerically that the minimum orbital period decreases as the charge of the black hole increases. Thus, the upper limit is reached for an uncharged black hole, while the lower limit is attained for a maximally charged one. We then analytically derive the upper and lower bounds for the minimum orbital period. These results improve our understanding of dynamics around d-dimensional black holes and impose constraints on candidate gravity theories.

Shyamalee Bora, Dhruba Jyoti Gogoi, Pralay Kumar Karmakar

Published: 2025-10-05

Categories: gr-qc

We explore the modified thermodynamics of a Hayward-Anti de Sitter (H-AdS) black hole in atypical conditions, incorporating a string fluid, Hayward regularisation, and quantum entropy corrections. Our analysis reveals a first-order phase transition between small and large black hole phases, characterised by a swallowtail behaviour in the Gibbs free energy profiles. It is found that the key parameters - string fluid strength, Hayward regularisation scale, and quantum correction coefficients significantly influence the critical temperature and phase stability of the H-AdS system. It is further noticed that a large black hole phase is stabilised by these modifications, with quantum corrections smoothing the transition. This model offers a valuable framework to study quantum gravity effects on black hole thermodynamics with potential implications in analysing black hole evolution and astrophysical observations.

Leonardo Modesto, Edoardo Rattu

Published: 2025-10-05

Categories: gr-qc

We carefully investigate, extend, and shed new light on the McVittie exact solution of Einstein's gravity (EG) with the focus on the implications in the Universe we live in. It turns out that the only known exact solution of EG, which interpolates between an asymptotic homogeneous and isotropic Universe and a Schwarzschild black hole, is actually singular in 2M, namely, the curvature invariants diverge and the spacetime is geodetically incomplete in 2M. Very important: all energy conditions are satisfied except the dominant one (DEC), which is violated inside the radius 8M/3. Notice that 2M is not the event horizon, but a curvature singularity covered by an apparent horizon that, at the actual stage of the Universe, nearly coincides with 2M. Moreover, the curvature singularity is not analytic with respect to the dynamics of the Universe encoded in the Hubble function $H(t)$: for arbitrarily small but not zero $H^\prime(t)$, the curvature invariants are singular, while for $H^\prime(t)$ identically zero, they are regular. Therefore, we can not analytically decouple the black hole from the entire Cosmos, namely, we can not assume the Schwarzschild solution locally and the FRW metric at large scale without violating the analyticity of the metric. Since the spacetime does not exist for $r \leqslant$2M, and since the DEC is violated for r<8M/3, we are allowed to doubt the existence of black holes in our Universe as understood up to now. In particular, the violation of DEC seems catastrophic for the spacetime stability below 8M/3. We build and study a toy model for the gravitational collapse, generalizing the Vaidya to the McVittie-Vaidya metric. Although dynamical, the singularities remain in the same locations. Finally, in order to achieve the curvature smoothness and geodesic completion, we propose two solutions: one in Einstein's conformal gravity, and the other replacing M with M(r).

Shi-Cheng Liu, Lei-Hua Liu, Bichu Li, Hai-Qing Zhang, Peng-Zhang He

Published: 2025-10-05

Categories: gr-qc

Many quantum gravitational frameworks, such as DBI inflation, k-essence, and effective field theories obtained by integrating out heavy modes, can lead to a non-trivial sound speed. Meanwhile, our universe can be described as an open system. Under the non-trivial sound speed, we employ the method of open quantum systems combined with Arnoldi iterations to study the Krylov complexity throughout the early universe, including the inflationary, radiation-dominated, and matter-dominated epochs. A key ingredient in our analysis is the open two-mode squeezed state formalism and the generalized Lanczos algorithm. To numerically compute the Krylov complexity, we are the first time to derive the evolution equations for the parameters $r_k$ and $\phi_k$ within an open two-mode squeezed state. Our results indicate that the Krylov complexity exhibits a similar trend in both the standard case and the case with non-trivial sound speed. To distinguish between these two scenarios, we also investigate the Krylov entropy for completeness. The evolution of the Krylov entropy shows a clear difference between the standard case and the non-trivial sound speed case. Furthermore, based on the behavior of the Lanczos coefficients, we find that the case of non-trivial sound speed behaves as a maximally chaotic system. However, our numerical results suggest that the Krylov complexity does not saturate to a constant value due to the huge expansion of spacetime background. This study offers a new perspective for exploring the early universe through the quantum information.

Zhilong Liu, Wentao Liu, Xiaofang Liu, Jieci Wang

Published: 2025-10-05

Categories: gr-qc

Motivated by the profound connection between quantum mechanics and spacetime geometry, particularly the conjectured correspondence between wormholes and quantum entanglement as proposed in the ER=EPR framework, this study aims to investigate the influence of wormhole geometries on quantum information extraction. We examine the correlation-specifically mutual information (MI) and entanglement-extracted by two Unruh-DeWitt (UDW) detectors from the quantum vacuum field in the presence of a BTZ wormhole featuring a null-like throat, also known as an Einstein-Rosen bridge. First, we analyze how the detector's position relative to the wormhole throat and the throat's size affect the extracted MI. Our results indicate that the wormhole enhances MI extraction, with maximal MI achieved when the detectors are located at specific image-symmetric points connected by the wormhole. By analyzing the behavior of the nonlocal contribution term and the classical noise term, it is found that the correlations extracted contain genuine non-classical components. This work highlights the feasibility of extracting quantum correlations through null-like wormhole geometries and provides a novel perspective for probing the potential relationship between spacetime topology and the nonlocal characteristics of quantum mechanics.