Showing 1–50 of 21,883 results for author: D

Asymptotic Simplicity and Scattering in General Relativity from Quantum Field Theory

Authors: Stefano De Angelis, Aidan Herderschee, Radu Roiban, Fei Teng

Abstract: We investigate the fate of asymptotic simplicity in physically relevant settings of compact-object scattering. Using the stress tensor of a two-body system as a source, we compute the spacetime metric in General Relativity at finite observer distance in an asymptotic expansion. To do so, we relate the metric to the final-state graviton one-point function in momentum space, which is computed using… ▽ More We investigate the fate of asymptotic simplicity in physically relevant settings of compact-object scattering. Using the stress tensor of a two-body system as a source, we compute the spacetime metric in General Relativity at finite observer distance in an asymptotic expansion. To do so, we relate the metric to the final-state graviton one-point function in momentum space, which is computed using perturbative QFT techniques. Both the simple pole and the infrared-related logarithmic branch cut in the virtuality of the external graviton contribute nontrivially. We focus on determining the fall-off behavior of the Newman-Penrose scalars, confirming previous predictions that Sachs's peeling property is violated at leading order in the post-Minkowski expansion. Our analysis at higher orders in the post-Minkowskian expansion reveals a significantly stronger breakdown of the peeling property than previously recognized, which is the result of nonlinear, long-range interactions between localized sources and the surrounding gravitational field. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Comments: 41 pages + references

Generating optimal Gravitational-Wave template banks with metric-preserving autoencoders

Authors: Giovanni Cabass, Digvijay Wadekar, Matias Zaldarriaga, Zihan Zhou

Abstract: We present a geometric placement algorithm for constructing template banks. We specialize in the case of Gravitational Wave searches, and use autoencoders for non-linear compression of the space of waveforms after these have been represented by a finite number of basis functions using an SVD decomposition. To ensure that the autoencoder is suitable for geometric placement we try to find a coordina… ▽ More We present a geometric placement algorithm for constructing template banks. We specialize in the case of Gravitational Wave searches, and use autoencoders for non-linear compression of the space of waveforms after these have been represented by a finite number of basis functions using an SVD decomposition. To ensure that the autoencoder is suitable for geometric placement we try to find a coordinate system describing the manifold of SVD coefficients such that distances in the latent and embedding space are equal. We show that the curvature of the banks is negligible and that such a system can be found. We then show that a geometric placement algorithm via a uniform grid in the latent space combined with rejection of unphysical points using a normalizing flow results in templates that, while slightly less in number than the similar construction using random forests of Ref.~\cite{Wadekar:2023kym}, perform slightly better in the effectualness tests, especially for high-mass binary systems. We discuss briefly how these dimensionality reduction techniques might be used in the context of cosmology, and a simple toy example where the periodicity of a flat manifold slightly complicates finding a distance-preserving coordinate system. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Comments: 17 figures, 1 table

Gravitational Atoms from Topological Stars

Authors: Ibrahima Bah, Emanuele Berti, Bogdan Ganchev, David Pereñiguez, Nicholas Speeney

Abstract: We study the bound states of a massive scalar field around a topological star, and show that these are strictly normal modes. This yields a genuine gravitational atom, sharply distinguishing horizonless objects from black holes. It is shown that the modes are controlled by the field's Compton wavelength compared to the size of the star. When the Compton wavelength is large, the field forms a cloud… ▽ More We study the bound states of a massive scalar field around a topological star, and show that these are strictly normal modes. This yields a genuine gravitational atom, sharply distinguishing horizonless objects from black holes. It is shown that the modes are controlled by the field's Compton wavelength compared to the size of the star. When the Compton wavelength is large, the field forms a cloud with a hydrogen-like spectrum, while in the opposite regime it localizes along timelike trajectories. When the two scales are comparable the spectrum becomes richer, and we characterize it in detail allowing the field to carry electric charge and Kaluza--Klein momentum. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Comments: 21 pages, 14 figures + Appendix

Work distribution and fluctuation theorem in AdS/CFT

Authors: Daichi Takeda

Abstract: From the AdS/CFT dictionary, we derive a bulk dual of the work distribution defined by the two-point measurement on the boundary, yielding a bulk formulation of the Tasaki-Crooks fluctuation theorem. We argue that this not only provides a holographic prescription of the work distribution, but is also expected to capture some "mesoscopic" aspects of quantum gravity. From the AdS/CFT dictionary, we derive a bulk dual of the work distribution defined by the two-point measurement on the boundary, yielding a bulk formulation of the Tasaki-Crooks fluctuation theorem. We argue that this not only provides a holographic prescription of the work distribution, but is also expected to capture some "mesoscopic" aspects of quantum gravity. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Comments: 8 pages (4+4), 2 figures

Report number: RIKEN-iTHEMS-Report-25

Traversable wormhole with double trace deformations via gravitational shear and sound channels

Authors: Fitria Khairunnisa, Hadyan Luthfan Prihadi, M. Zhahir Djogama, Donny Dwiputra, Freddy Permana Zen

Abstract: We investigate how non-local gravitational couplings from double-trace deformation between two asymptotic boundaries of an AdS$_5$ black brane can lead to the violation of the Averaged Null Energy Condition (ANEC). The first-order gravitational perturbations backreact with the background metric at second-order, creating a wormhole opening. The wormhole becomes traversable in both the gravitational… ▽ More We investigate how non-local gravitational couplings from double-trace deformation between two asymptotic boundaries of an AdS$_5$ black brane can lead to the violation of the Averaged Null Energy Condition (ANEC). The first-order gravitational perturbations backreact with the background metric at second-order, creating a wormhole opening. The wormhole becomes traversable in both the gravitational shear and sound channels within the hydrodynamic approximation. This shows that dynamical metric perturbations can facilitate information transfer in a purely gravitational setting, with the emergence of $G_N$ indicating the gravitational origin. For the shear channel, we consider three different coupling configurations, whereas for the sound channel, we vary both the speed of sound and the attenuation constant, as these parameters control the wormhole traversability. Furthermore, we obtain late-time power-law behavior in the ANEC using fitting function and present a generalization that applies to both shear and sound channels. Due to its propagating nature, the sound channel exhibits late-time power-law remnants at low sound speed similar to the vector diffusive probes, but it prefers an exponential decay at higher sound speed similar to the scalar non-diffusive probes, as the power-law exponent weakened with increasing sound speed. For superluminal sound channels, the wormhole opens for an extremely brief duration at late insertion times, rendering it non-traversable. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: 23 pages, 9 figures, 3 tables

Hybrid model for inspiral-merger-ringdown gravitational waveforms from comparable-mass, nonspinning binary black holes

Authors: Nur E. M. Rifat, David A. Nichols, Kent Yagi

Abstract: Gravitational waves from comparable-mass binary-black-hole mergers are often described in terms of three stages: inspiral, merger and ringdown. Post-Newtonian and black-hole perturbation theories are used to model the inspiral and ringdown parts of the waveform, respectively, while the merger phase has been modeled most accurately using numerical relativity (NR). Nevertheless, there have been seve… ▽ More Gravitational waves from comparable-mass binary-black-hole mergers are often described in terms of three stages: inspiral, merger and ringdown. Post-Newtonian and black-hole perturbation theories are used to model the inspiral and ringdown parts of the waveform, respectively, while the merger phase has been modeled most accurately using numerical relativity (NR). Nevertheless, there have been several approaches used to model the merger phase using analytical methods. In this paper, we adapt a hybrid approximation method that applies post-Newtonian and black-hole perturbation theories at the same times in different spatial regions of a binary-black-hole waveform (and which are matched at a boundary region with prescribed dynamics). Prior work with the hybrid method used leading post-Newtonian theory and the perturbation theory of nonrotating black holes, which led to errors during the late inspiral and disagreement with the dominant quasinormal-mode frequency extracted from NR simulations during the ringdown. To obtain a better match with NR waveforms of binary-black-hole mergers, we made several phenomenological modifications to the hybrid method. Specifically, to better capture the inspiral dynamics, we use the effective-one-body method for modeling the trajectory of the boundary between the two spatial regions. The waveform is determined by evolving a Regge-Wheeler-Zerilli-type equation for an effective black-hole perturbation theory problem with a modified Poschl-Teller potential. By tuning the potential to match the dominant quasinormal-mode frequency of the remnant black hole and also optimizing the boundary data on the matching region, we could match NR waveforms from nonspinning, comparable-mass binary black holes with mass ratios between one and eight, with a relative error of order $10^{-3}$. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: 16 pages, 7 figures

Dark matter by design: $Q$-balls, neural networks and galaxy rotation curves

Authors: Alexandre M. Pombo, Lorenzo Pizzuti, Alessandra di Giacomo

Abstract: Can a dynamically robust (\textit{aka} stable) $Q$-ball reproduce the rotation curve of a disk galaxy? In an astrophysical environment, $Q$-balls are non-topological solitons that are transparent and only perceived by their gravitational effects. Traditionally, scalar $Q$-balls are modelled with a polynomial potential, but axion-like periodic potentials are also expected to support such solitonic… ▽ More Can a dynamically robust (\textit{aka} stable) $Q$-ball reproduce the rotation curve of a disk galaxy? In an astrophysical environment, $Q$-balls are non-topological solitons that are transparent and only perceived by their gravitational effects. Traditionally, scalar $Q$-balls are modelled with a polynomial potential, but axion-like periodic potentials are also expected to support such solitonic configurations. In the presence of angular momentum, $Q$-balls acquire a toroidal structure with a central density void, qualitatively resembling the structure of disk galaxies. Motivated by this similarity, we investigate whether rotating scalar $Q$-balls can reproduce the observed galactic rotation curves. In this work, we use a recently developed hybrid numerical framework that combines a high-accuracy pseudo-spectral method with a physics-informed neural network approach to construct both static and rotating $Q$-ball solutions. We then assess their ability to act as the dark matter halos in galaxies by fitting the observed rotation curves of a sample of disk galaxies from the SPARC catalogue. Our simplified model provides an overall good agreement with observational data; we have further found an average constraint on the scalar field particle's mass $m\sim 10^{-27}$ eV, in agreement with similar galactic-scale soliton solutions. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: 22 pages, 6 figures

Dark-Energy Anisotropic Compact Configurations in 4D Einstein-Gauss-Bonnet Gravity: From Structure to Observational Viability

Authors: Anirudh Pradhan, Takol Tangphati, Ayan Banerjee, Javlon Rayimbaev

Abstract: We address the equilibrium configurations and stability properties of anisotropic compact stars whose interior is described by a modified Chaplygin gas (MCG) equation of state in the framework of the regularized four-dimensional Einstein-Gauss-Bonnet (4DEGB) theory. Applying a quasi-local prescription for the pressure anisotropy, we derive the modified Tolman-Oppenheimer-Volkoff (TOV) equations an… ▽ More We address the equilibrium configurations and stability properties of anisotropic compact stars whose interior is described by a modified Chaplygin gas (MCG) equation of state in the framework of the regularized four-dimensional Einstein-Gauss-Bonnet (4DEGB) theory. Applying a quasi-local prescription for the pressure anisotropy, we derive the modified Tolman-Oppenheimer-Volkoff (TOV) equations and integrate them numerically over a large parameter space in the Gauss-Bonnet coupling $α$ and the degree of anisotropy $β$. We provide mass-radius sequences, mass-compactness, energy density, and pressure profiles, and perform a full stability analysis based on the turning-point criterion, the radial adiabatic index $γ_r$, and the radial and transverse sound speeds $v_r^2$ and $v_t^2$. Our results show that positive $α$ and positive anisotropy $(β> 0)$ systematically increase the maximum mass and radius, enabling then configurations that exceed $2\,M_\odot$ while still obeying causality and the modified Buchdahl bound in 4DEGB gravity. A comparison with the latest astrophysical constraints (NICER, GW170817, GW190814, and massive-pulsar measurements) identifies regions of the $(α,β)$ parameter space that are observationally allowable. In conclusion, anisotropic dark-energy stars in 4DEGB gravity provide viable, observationally testable ultra-compact alternatives to normal neutron stars and black holes, and also potentially open rich avenues for further multi-messenger searches for higher-curvature effects. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: 17 pages, 7 figures

Thermodynamic uncertainty relations for relativistic quantum thermal machines

Authors: Dimitris Moustos, Obinna Abah

Abstract: We investigate a two-qubit SWAP thermal machine -- a streamlined analogue of the four-stroke Otto cycle -- whose working medium comprises inertially moving Unruh-DeWitt qubit detectors, each coupled to a thermal quantum field bath prepared at a different temperature. In the presence of relative motion between the working medium and the thermal baths, we derive thermodynamic uncertainty relations (… ▽ More We investigate a two-qubit SWAP thermal machine -- a streamlined analogue of the four-stroke Otto cycle -- whose working medium comprises inertially moving Unruh-DeWitt qubit detectors, each coupled to a thermal quantum field bath prepared at a different temperature. In the presence of relative motion between the working medium and the thermal baths, we derive thermodynamic uncertainty relations (TURs) that quantify the trade-off between performance, entropy production, and power fluctuations. Our analysis identifies regimes where relativistic motion leads to stronger violation of classical TURs, previously observed in static quantum setups. In addition, we establish generalized performance bounds for the thermal machine operating as either a heat engine or a refrigerator, and discuss how relativistic motion can enhance their performances beyond the standard Carnot limits defined by rest-frame temperatures. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Novel scalar degrees of freedom emerging from hybrid metric-Palatini gravity

Authors: David S. Pereira, Salvatore Capozziello, Francisco S. N Lobo, José Pedro Mimoso

Abstract: Hybrid metric-Palatini gravity unifies the metric and Palatini formalisms while preserving a propagating scalar degree of freedom, offering a compelling route to modified gravity consistent with current observations. Motivated by this success, we consider an extended framework -- the hybrid metric-Palatini scalar-tensor (HMPST) theory -- in which an additional scalar field $φ$ modulates the curvat… ▽ More Hybrid metric-Palatini gravity unifies the metric and Palatini formalisms while preserving a propagating scalar degree of freedom, offering a compelling route to modified gravity consistent with current observations. Motivated by this success, we consider an extended framework -- the hybrid metric-Palatini scalar-tensor (HMPST) theory -- in which an additional scalar field $φ$ modulates the curvature couplings, enriching the dynamics and enabling nontrivial self-interactions through scalar potentials. We focus on the analytically tractable linear-$f(\hat{R})$ subclass and study its cosmological, strong-field, and weak-field regimes. In homogeneous and isotropic settings, we identify de Sitter and matter-dominated cosmological solutions describing accelerated expansion and early-universe behavior. For static, spherically symmetric configurations, the field equations yield analytic solutions generalizing the Janis-Newman-Winicour and Buchdahl metrics, including the Schwarzschild-de Sitter limit. In the weak-field regime, linearized perturbations around Minkowski space lead to Yukawa-type corrections to the gravitational potential, with an effective Newton constant $G_{\rm eff}$ and post-Newtonian parameter $γ$ that recover General Relativity for heavy or weakly coupled scalars. These results show that the linear-$f(\hat{R})$ HMPST subclass provides a consistent and unified description of gravity across cosmological, astrophysical, and Solar System scales, offering a fertile framework for connecting modified gravity to observations and effective field-theoretic extensions. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: 19 pages

Scalar field scattering in a Schwarzschild-de Sitter geometry

Authors: Marco de Cesare, Marcello Miranda, Achilleas P. Porfyriadis

Abstract: We solve analytically the low-frequency s-wave dynamics of a massless scalar field propagating on a Schwarzschild-de Sitter black hole background. A rigorous application of the method of matched asymptotic expansions allows us to connect the scalar's evolution in the proximity of the black-hole horizon with that on cosmological scales. The scattering coefficients, greybody factors, and Wigner time… ▽ More We solve analytically the low-frequency s-wave dynamics of a massless scalar field propagating on a Schwarzschild-de Sitter black hole background. A rigorous application of the method of matched asymptotic expansions allows us to connect the scalar's evolution in the proximity of the black-hole horizon with that on cosmological scales. The scattering coefficients, greybody factors, and Wigner time delay are computed explicitly. We consider both small and large black holes, with black-hole to cosmological horizon radii parametrically small and of order unity, respectively. This extends previous studies confined to the small black-hole regime only. In addition, for small black holes we perform a calculation that remains agnostic about the relative size between the ratio of the geometry's horizons and the scalar's frequency in units of the black-hole radius. When the two are comparable, we find that they are interchangeable in the greybody factor, which is symmetric under $ω\leftrightarrow 1/r_c$ (where $ω$ is the scalar's frequency and $r_c$ the cosmological horizon radius). △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: 10 pages, 8 figures

Report number: CCTP-2025-12, ITCP-IPP 2025/12

Quantum Symmetry and Geometry in Double-Scaled SYK

Authors: Jeremy van der Heijden, Erik Verlinde, Jiuci Xu

Abstract: The emergence of the quantum $R$-matrix in the double-scaled SYK model points to an underlying quantum group structure. In this work, we identify the quantum group $\mathcal{U}_q(\mathfrak{su}(1,1))$ as a subalgebra of the chord algebra. Specifically, we construct the generators of $\mathcal{U}_q(\mathfrak{s} \mathfrak{u}(1,1))$ from combinations of operators within the chord algebra and show that… ▽ More The emergence of the quantum $R$-matrix in the double-scaled SYK model points to an underlying quantum group structure. In this work, we identify the quantum group $\mathcal{U}_q(\mathfrak{su}(1,1))$ as a subalgebra of the chord algebra. Specifically, we construct the generators of $\mathcal{U}_q(\mathfrak{s} \mathfrak{u}(1,1))$ from combinations of operators within the chord algebra and show that the one-particle chord Hilbert space decomposes into the positive discrete series representations of $\mathcal{U}_q(\mathfrak{s} \mathfrak{u}(1,1))$. Using the coproduct structure of the quantum group, we build the multi-particle Hilbert space and establish its equivalence with previous results defined by the chord rules. In particular, we show that the quantum $R$-matrix acts as a swapping operator that reverses the ordering of open chords in each fusion channel while incorporating the corresponding $q$-weighted penalty factors. This action enables an explicit derivation of the chord Yang-Baxter relation. We further explore a realization of the quantum group generators on the quantum disk, and present a novel factorization formula for the bulk gravitational wavefunction in the presence of matter. We further discuss the relation between the $\mathcal{U}_q(\mathfrak{s} \mathfrak{u}(1,1))$ structure uncovered here and the $\mathcal{U}_q(\mathfrak{s} \mathfrak{l}(2, \mathbb{R}))$ algebra previously studied from the boundary perspective. Finally, we study the gravitational wavefunction with matter in the Schwarzian regime. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Encounter between an extended hyperelastic body and a Schwarzschild black hole with quadrupole-order effects

Authors: Nishita Jadoo, J. David Brown, Charles R. Evans

Abstract: We model the general relativistic interaction of a small hyperelastic sphere with a Schwarzschild black hole as it follows an initially marginally-bound orbit through a close encounter. While the interaction reveals effects that are encoded by the Mathisson-Papapetrou-Dixon (MPD) multipolar equations through quadrupole order, the calculation is made using an independent general relativistic finite… ▽ More We model the general relativistic interaction of a small hyperelastic sphere with a Schwarzschild black hole as it follows an initially marginally-bound orbit through a close encounter. While the interaction reveals effects that are encoded by the Mathisson-Papapetrou-Dixon (MPD) multipolar equations through quadrupole order, the calculation is made using an independent general relativistic finite element scheme that we described earlier (Phys.~Rev.~D 108(8):084020, October 2023). The finite element calculation is done in Schwarzschild coordinates, following a large and scalable number of mass elements in interaction with each other through elastic forces derived from a potential energy function and with the spacetime geometry. After the fact, we analyze the dynamics using a local Fermi coordinate system, computing (1) the deviation of the center of mass of the body relative to the initial marginally-bound orbit, (2) changes in orbital and spin angular momenta, and (3) the decrease in orbital energy and accompanying deposition of energy into internal elastic dynamics. The interaction leads to the capture of the small body into a highly eccentric orbit ($e \simeq 0.99998$ in a sample calculation). △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: 28 pages, 15 figures

Exploring the Impact of Systematic Bias in Type Ia Supernova Cosmology Across Diverse Dark Energy Parametrizations

Authors: Drishti Sharma, Purba Mukherjee, Anjan A Sen, Suhail Dhawan

Abstract: We investigate the impact of instrumental and astrophysical systematics on dark energy constraints derived from Type~Ia supernova (SN-Ia) observations. Using simulated datasets consistent with current SN-Ia measurements, we explore how uncertainties in photometric calibration, intergalactic dust, progenitor evolution in luminosity and light-curve stretch, and intrinsic color scatter affect the inf… ▽ More We investigate the impact of instrumental and astrophysical systematics on dark energy constraints derived from Type~Ia supernova (SN-Ia) observations. Using simulated datasets consistent with current SN-Ia measurements, we explore how uncertainties in photometric calibration, intergalactic dust, progenitor evolution in luminosity and light-curve stretch, and intrinsic color scatter affect the inferred dark energy equation of state parameters (w0, wa). We test the Generalised Scale Factor (GEN) evolution and benchmark it against three time-evolving dark energy models; namely Chevallier Polarski Linder (CPL), Jassal Bagla Padmanabhan (JBP) and Logarithmic (LOG) parametrizations; comparing their sensitivity to these systematic effects. Calibration biases and progenitor evolution emerge as the dominant sources of uncertainty, while simpler parametrisations, viz. GEN, which directly describes the expansion rate, remains relatively stable under all systematic injections, unlike CPL, JBP and LOG that rely on the dark energy equation of state. These findings underscore the need for sub-per cent calibration precision and enhanced astrophysical modelling to ensure the robustness of dark energy inferences from current and future SN-Ia cosmology experiments. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: 13 pages, Latex Style. Comments are Welcome

Nonlinear Gravitational Wave Memory : Universal Low-Frequency Background

Authors: Caner Ünal, Doğa Veske

Abstract: A universal contribution exists in the infrared (low frequency) regime of all gravitational waves, which results from nonlinear memory. Nonlinear memory is sourced by linear order gravitational waves and exists for any gravitational-wave background. We calculate the stochastic nonlinear memory signal of various stochastic backgrounds of cosmological (scalar induced, reheating, phase transition, to… ▽ More A universal contribution exists in the infrared (low frequency) regime of all gravitational waves, which results from nonlinear memory. Nonlinear memory is sourced by linear order gravitational waves and exists for any gravitational-wave background. We calculate the stochastic nonlinear memory signal of various stochastic backgrounds of cosmological (scalar induced, reheating, phase transition, topological defect, turbulence) and astrophysical (binary mergers of stellar-mass, intermediate mass, supermassive, and primordial black holes) origins. These results allow us to derive the complete frequency spectrum of cosmological and astrophysical SGWB. We calculate how to probe the thermal state of the universe, i.e. the equation of the state, via the memory spectrum's slope and also discuss the detection prospects at various frequency bands with future experiments. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: 5 pages, 2 figures, and appendix. Comments welcome

Earth-orbit bounds on screened dark energy

Authors: Fabiano Feleppa, Welmoed Marit de Graaf, Philippe Brax, Gaetano Lambiase

Abstract: We test dark-energy-motivated screening mechanisms with near-Earth space-based measurements. Within a post-Newtonian treatment, we compute leading corrections to three observables, namely geodetic precession (Gravity Probe B), pericenter advance of LAGEOS-2, and Sagnac time delay in a prospective orbital configuration. We then map these corrections to bounds on chameleon, symmetron, and dilaton mo… ▽ More We test dark-energy-motivated screening mechanisms with near-Earth space-based measurements. Within a post-Newtonian treatment, we compute leading corrections to three observables, namely geodetic precession (Gravity Probe B), pericenter advance of LAGEOS-2, and Sagnac time delay in a prospective orbital configuration. We then map these corrections to bounds on chameleon, symmetron, and dilaton models. LAGEOS-2 data yield the strongest Earth-orbit limits for symmetron and dilaton models, while a prospective Sagnac setup provides the tightest constraint for chameleons. These results highlight the relevance of low-density, space-based experiments as sensitive probes of screened dark energy and exclude previously allowed regions of parameter space. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: 17 pages, 6 figures (4 subfigures)

Chaotic motion of particles around a dyonic Kerr-Newman black hole immersed in the Melvin-swirling universe

Authors: Deshui Cao, Lina Zhang, Songbai Chen, Qiyuan Pan, Jiliang Jing

Abstract: We employ the Poincaré section, fast Lyapunov indicator, recurrence analysis, bifurcation diagram and basins of attraction to investigate the dynamical behaviors of the motion of particles around a new dyonic Kerr-Newman black hole immersed in the Melvin-swirling universe presented in [A. Di Pinto, S. Klemm, and A. Viganò, J. High Energy Phys. {\bf 06}, 150 (2025)]. We note that the swirling param… ▽ More We employ the Poincaré section, fast Lyapunov indicator, recurrence analysis, bifurcation diagram and basins of attraction to investigate the dynamical behaviors of the motion of particles around a new dyonic Kerr-Newman black hole immersed in the Melvin-swirling universe presented in [A. Di Pinto, S. Klemm, and A. Viganò, J. High Energy Phys. {\bf 06}, 150 (2025)]. We note that the swirling parameter $j$ and magnetic field strength $B$ make the equations of motion for particles nonseparable, and confirm the presence of chaotic behavior in the motion in this dyonic Kerr-Newman-Melvin-swirling spacetime and its sub-cases by removing the conical singularities and removing both the conical singularities and the Dirac strings. We observe that both the number of chaotic orbits and the chaotic region increase with the increase of the parameters $j$ and $B$, but decrease as the electric charge $Q$, magnetic charge $H$ or spin parameter $a$ increases. Moreover, we find that the presence of $j$ changes the ranges of $B$, $Q$, $H$ and $a$ where the chaotic motion appears for particles. The swirling parameter together with the magnetic field strength, electric charge, magnetic charge and spin parameter yields richer physics in the motion of particles for the spacetime of a dyonic Kerr-Newman black hole immersed in the Melvin-swirling universe. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: 23 pages, 13 figures

Journal ref: Eur. Phys. J. C 85, 1250 (2025)

Ringdown of a black hole embedded in a Burkert dark matter halo

Authors: Yi Yang, Gaetano Lambiase, Ali Ovgun, Dong Liu, Zheng-Wen Long

Abstract: We construct a new static, spherically symmetric black hole spacetime embedded in a dark matter halo whose density follows the cored Burkert profile. Starting from the halo-only geometry determined by the rotation curve relation, we solve the Einstein equations with the Burkert stress-energy and enforce a Schwarzschild boundary condition, obtaining closed form metric functions in which the halo co… ▽ More We construct a new static, spherically symmetric black hole spacetime embedded in a dark matter halo whose density follows the cored Burkert profile. Starting from the halo-only geometry determined by the rotation curve relation, we solve the Einstein equations with the Burkert stress-energy and enforce a Schwarzschild boundary condition, obtaining closed form metric functions in which the halo contribution deforms the redshift or shape functions and reduces to the Schwarzschild limit when the halo parameters vanish. On this background we study linear perturbations of test fields with spins $s=0,1,2$ and compute their quasinormal spectra using both a high order WKB scheme and continued fraction method, complemented by time domain evolutions. We find that increasing either the Burkert core radius $r_0$ or the central density $ρ_0$ generically shifts the real part of the frequencies upward and enhances damping, while the multipole index $l$ primarily increases the oscillation frequency with a milder impact on the decay rate. The two frequency extraction methods agree to within small, systematic offsets across the explored parameter space. Our results quantify how a cored dark matter environment imprints itself on the ringdown of a central black hole and provide benchmarks for future gravitational wave tests of halo properties. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Tests of General Relativity with Einstein Telescope

Authors: Andrea Begnoni, Walter Del Pozzo, Matteo Pegorin, Joachim Pomper, Angelo Ricciardone

Abstract: Gravitational wave signals from compact binary coalescences offer a powerful and reliable probe of General Relativity. To date, the LIGO-Virgo-KAGRA collaboration has provided stringent consistency tests of General Relativity predictions. In this work, we present forecasts for the accuracy with which General Relativity can be tested using third-generation ground-based interferometers, focusing on… ▽ More Gravitational wave signals from compact binary coalescences offer a powerful and reliable probe of General Relativity. To date, the LIGO-Virgo-KAGRA collaboration has provided stringent consistency tests of General Relativity predictions. In this work, we present forecasts for the accuracy with which General Relativity can be tested using third-generation ground-based interferometers, focusing on Einstein Telescope (ET) and binary black hole mergers. Given the expected high detection rate, performing full Bayesian analyses for each event becomes computationally challenging. To overcome this, we adopt a Fisher matrix approach, simulating parameter estimation in an idealized observation scenario, which allows us to study large populations of compact binary coalescences with feasible computational efforts. Within this framework, we investigate the constraints that ET, in its different configurations, can impose on inspiral post-Newtonian coefficients, by jointly analyzing events using a Bayesian hierarchical methodology. Our results indicate that ET could in principle achieve an accuracy of $\mathcal{O}(10^{-7})$ on the dipole radiation term and $\mathcal{O}(10^{-3})$ on higher-order post-Newtonian coefficients, for both the triangular and the two L-shaped designs, with $10^4$ catalog events. We also assess the number of detections required to confidently identify deviations from General Relativity at various post-Newtonian orders and for different detector configurations. △ Less

Submitted 10 November, 2025; originally announced November 2025.

Comments: 31 pages, 9 figures, 4 appendices

samsara: A Continuous-Time Markov Chain Monte Carlo Sampler for Trans-Dimensional Bayesian Analysis

Authors: Gabriele Astorino, Lorenzo Valbusa Dall'Armi, Riccardo Buscicchio, Joachim Pomper, Angelo Ricciardone, Walter Del Pozzo

Abstract: Bayesian inference requires determining the posterior distribution, a task that becomes particularly challenging when the dimension of the parameter space is large and unknown. This limitation arises in many physics problems, such as Mixture Models (MM) with an unknown number of components or the inference of overlapping signals in noisy data, as in the Laser Interferometer Space Antenna (LISA) Gl… ▽ More Bayesian inference requires determining the posterior distribution, a task that becomes particularly challenging when the dimension of the parameter space is large and unknown. This limitation arises in many physics problems, such as Mixture Models (MM) with an unknown number of components or the inference of overlapping signals in noisy data, as in the Laser Interferometer Space Antenna (LISA) Global Fit problem. Traditional approaches, such as product-space methods or Reversible-Jump Markov Chain Monte Carlo (RJMCMC), often face efficiency and convergence limitations. This paper presents samsara, a Continuous-Time Markov Chain Monte Carlo (CTMCMC) framework that models parameter evolution through Poisson-driven birth, death, and mutation processes. samsara is designed to sample models of unknown dimensionality. By requiring detailed balance through adaptive rate definitions, CTMCMC achieves automatic acceptance of trans-dimensional moves and high sampling efficiency. The code features waiting time weighted estimators, optimized memory storage, and a modular design for easy customization. We validate samsara on three benchmark problems: an analytic trans-dimensional distribution, joint inference of sine waves and Lorentzians in time series, and a Gaussian MM with an unknown number of components. In all cases, the code shows excellent agreement with analytical and Nested Sampling results. All these features push samsara as a powerful alternative to RJMCMC for large- and variable-dimensional Bayesian inference problems. △ Less

Submitted 10 November, 2025; originally announced November 2025.

Comments: 22 pages, 9 figures, 2 tables, 5 appendices, comments are welcome

The Geometric View of Theories

Authors: Sebastian De Haro

Abstract: Recent critiques of the semantic conception of scientific theories suggest that a theory is not best formulated as a collection of models satisfying some set of kinematical or dynamical conditions. Thus it has been argued that additional structure on the set of models is required. Furthermore, there are calls for developing a 'theory of theories', where what was formerly a 'theory' is seen as a 'm… ▽ More Recent critiques of the semantic conception of scientific theories suggest that a theory is not best formulated as a collection of models satisfying some set of kinematical or dynamical conditions. Thus it has been argued that additional structure on the set of models is required. Furthermore, there are calls for developing a 'theory of theories', where what was formerly a 'theory' is seen as a 'model' within a larger theoretical structure. This paper makes a two-pronged proposal for the "shape" that physical theories should take, based on recent insights on dualities and quasi-dualities in physics. First, I develop a geometric view of theories, according to which a physical theory is a set of models with topological and geometric structure on it. This general view is briefly illustrated in an example from quantum cosmology. Second, I make a more specific proposal for a natural structure that can encompass various 'theories' as its models, with topological and algebraic-geometric structure on them. I call the latter more specific structure a 'model bundle', where the models are in the fibres and there is a moduli space in the base. I illustrate my second proposal in the Seiberg-Witten theory (Seiberg and Witten, 1994a,b), where the moduli space is the complex plane with three punctures, the states and quantities are in the fibres, and the modular group is the structure group that acts on the fibres. This view highlights the important role of quasi-dualities as local transition functions between fibres; dualities are recovered as global transition functions when the bundle is trivial. I discuss some philosophical issues that this geometric view of physical theories opens up, such as its realist interpretation. △ Less

Submitted 10 November, 2025; originally announced November 2025.

Comments: 25+15 pages, 2 figures

Topological Thermodynamics of Black Holes: Revisiting the methods of winding numbers calculation

Authors: A. A. M. Silva, G. Alencar, C. R. Muniz, M. Nilton, R. R. Landim

Abstract: In this paper, the equivalence between two methods for computing winding numbers is established: the approach of $φ$-mapping topological current and the residue method. The methods are shown to be equivalent when the condition $M'' S' - S'' M' \neq 0$ holds, while deviations appear when this relation fails, signaling subtle connections between mass $M(r_h)$, entropy $S(r_h)$, and topological struc… ▽ More In this paper, the equivalence between two methods for computing winding numbers is established: the approach of $φ$-mapping topological current and the residue method. The methods are shown to be equivalent when the condition $M'' S' - S'' M' \neq 0$ holds, while deviations appear when this relation fails, signaling subtle connections between mass $M(r_h)$, entropy $S(r_h)$, and topological structure, with $r_h$ being the horizon radius. We first verify this equivalence to Schwarzschild and Reissner-Nordstr"om black holes, recovering known classifications and confirming the consistency of our approach with respect to the validity of the above condition. We then extend the analysis to four-dimensional black strings, regarded as cylindrically symmetric black hole solutions in asymptotically AdS spacetimes. Our results show that both neutral and charged black strings possess the same global topological number, $W = +1$, implying that electric charge does not influence their topological classification. This insensitivity to charge mirrors earlier findings for BTZ black holes in three dimensions, suggesting that it may represent a universal property of cylindrically symmetric black holes in AdS backgrounds. △ Less

Submitted 9 November, 2025; originally announced November 2025.

Comments: 11 Pages, 3 figures

AthenaK Simulations of Magnetized Binary Neutron Star Mergers

Authors: Jacob Fields, David Radice

Abstract: We present new numerical-relativity simulations of a magnetized binary neutron star merger performed with AthenaK. The simulations employ a temperature- and composition-dependent tabulated nuclear equation of state, with initially dipolar fields with a maximum initial strength of ${\sim}10^{16}\ {\rm G}$ which extend outside the stars. We employ adaptive mesh refinement and consider three grid res… ▽ More We present new numerical-relativity simulations of a magnetized binary neutron star merger performed with AthenaK. The simulations employ a temperature- and composition-dependent tabulated nuclear equation of state, with initially dipolar fields with a maximum initial strength of ${\sim}10^{16}\ {\rm G}$ which extend outside the stars. We employ adaptive mesh refinement and consider three grid resolutions, with grid spacing down to $Δx_{\rm min} \simeq 92\ {\rm m}$ in the most refined region. When comparing the two highest resolution simulations, we find orbital dephasing of over 7 orbits until merger of only $0.06$ radians. The magnetic field is amplified during the merger and we observe the formation of a magnetized funnel in the polar region of the remnant. Simulations are continued until about $30$ milliseconds after merger. However, due to significant baryonic pollution, the binary fails to produce a magnetically-dominated outflow. Finally, we discuss possible numerical and physical effects that might alter this outcome. △ Less

Submitted 8 November, 2025; originally announced November 2025.

Comments: 9 pages, 3 figures, submitted to ASTRONUM-2025 proceedings

A Universal Framework for Horizon-Scale Tests of Gravity with Black Hole Shadows

Authors: Wentao Liu, Yang Liu, Di Wu, Yu-Xiao Liu

Abstract: In this Letter, we have developed a numerically efficient framework for evaluating parameters in metric theories of gravity, and applied it to constrain the horizon-scale magnetic field in the Kerr-Bertotti-Robinson (Kerr-BR) spacetime using the latest EHT observations. The method's adaptive ray-tracing strategy achieves near-linear computational efficiency without loss of numerical accuracy. Owin… ▽ More In this Letter, we have developed a numerically efficient framework for evaluating parameters in metric theories of gravity, and applied it to constrain the horizon-scale magnetic field in the Kerr-Bertotti-Robinson (Kerr-BR) spacetime using the latest EHT observations. The method's adaptive ray-tracing strategy achieves near-linear computational efficiency without loss of numerical accuracy. Owing to this efficiency, the framework enables high precision shadow modeling at minimal computational cost and, for the first time, supports statistically robust inference of black hole parameters from horizon-scale observations for arbitrary stationary black holes. The above framework is applied to the recently obtained Kerr-BR black hole, an exact magnetized and rotating solution to the Einstein field equations. We have evaluated the horizon-scale magnetic fields of M87* and Sgr A*, with the latter showing a field strength of $93.3^{+14.7}_{-23.8}G$, consistent with the equipartition estimate of $71G$ from polarized ALMA observations, thereby supporting Einstein's gravity. △ Less

Submitted 8 November, 2025; originally announced November 2025.

Comments: 8 pages, 8 figures

Quantum enforcement of strong cosmic censorship

Authors: Damien A. Easson

Abstract: We show that the trace anomaly of quantum field theory is sufficient to enforce strong cosmic censorship in any stationary spacetime with an inner horizon of nonzero surface gravity. In the two-dimensional dilaton reduction of four-dimensional Einstein-Maxwell theory coupled to $N$ conformal fields, the anomaly-induced Polyakov term yields a finite $\langle T_{vv}\rangle \to \frac{N}{48π}κ_-^2$ ne… ▽ More We show that the trace anomaly of quantum field theory is sufficient to enforce strong cosmic censorship in any stationary spacetime with an inner horizon of nonzero surface gravity. In the two-dimensional dilaton reduction of four-dimensional Einstein-Maxwell theory coupled to $N$ conformal fields, the anomaly-induced Polyakov term yields a finite $\langle T_{vv}\rangle \to \frac{N}{48π}κ_-^2$ near the Cauchy horizon, while the affine-frame energy grows as $T_{kk}\propto e^{2κ_- v}$. The resulting tidal blow-up converts the inner horizon into a null, Tipler-strong singularity. The mechanism is local, universal, and state-independent, and extends to Kerr/Kerr-Newman, $Λ>0$, and nonsingular interiors. Thus, the trace anomaly is the minimal quantum ingredient restoring strong cosmic censorship. △ Less

Submitted 11 November, 2025; v1 submitted 7 November, 2025; originally announced November 2025.

Comments: 4 pages, 1 figure, references added

Analytic One-loop Scattering Waveform in General Relativity

Authors: Giacomo Brunello, Stefano De Angelis, David A. Kosower

Abstract: Leveraging the computational framework presented in reference [JHEP 07, 062 (2024)], we evaluate the analytic scattering waveform in General Relativity to second order, $G^3 M^3 /r b^2$ and to all orders in velocity. This new representation of the next-to-leading order waveform is well-suited for numerical evaluation. Integrating the [modulus square of the] waveform over the angles on the celestia… ▽ More Leveraging the computational framework presented in reference [JHEP 07, 062 (2024)], we evaluate the analytic scattering waveform in General Relativity to second order, $G^3 M^3 /r b^2$ and to all orders in velocity. This new representation of the next-to-leading order waveform is well-suited for numerical evaluation. Integrating the [modulus square of the] waveform over the angles on the celestial sphere, we also compute the power spectrum of the radiation to order $G^4$ numerically. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Comments: 11 pages + references + appendices

Generalized Effective Field Theory for Four-Dimensional Black Hole Evaporation

Authors: Bing-Nan Liu, David A. Lowe, Larus Thorlacius

Abstract: The quantum induced stress tensor of 3+1-dimensional Einstein gravity, with conformally coupled matter, is studied in an effective field theory approach. In this context, Riegert's non-local effective action is sufficient to reproduce the trace anomaly in curved spacetime but in general the effective action can include additional non-local but scale invariant terms that influence the semiclassical… ▽ More The quantum induced stress tensor of 3+1-dimensional Einstein gravity, with conformally coupled matter, is studied in an effective field theory approach. In this context, Riegert's non-local effective action is sufficient to reproduce the trace anomaly in curved spacetime but in general the effective action can include additional non-local but scale invariant terms that influence the semiclassical physics without affecting the trace anomaly. Here, a truncated model, with only one additional term involving the square of the Weyl tensor, is used to find the induced stress tensor in a black hole background. With suitable physical conditions, a solution of the resulting 4th order equations leads, in a static limit, to a unique quantum state matching expected properties of the Unruh state. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Comments: 15 pages

Focus Point on Tensions in Cosmology from Early to Late Universe: Part II: New Directions in the Light of Observations from the Most Modern Astronomical Facilities

Authors: S. Capozziello, E. Di Valentino, V. G. Gurzadyan

Abstract: The papers included in this Focus Point collection are devoted to the studies on the cosmological tensions and challenges stimulated by the latest observational data. The first results of the LARES-2 laser ranging satellite on the high precision testing of the frame-dragging effect predicted by General Relativity are presented. The data on the S-stars monitoring in the Galactic center obtained by… ▽ More The papers included in this Focus Point collection are devoted to the studies on the cosmological tensions and challenges stimulated by the latest observational data. The first results of the LARES-2 laser ranging satellite on the high precision testing of the frame-dragging effect predicted by General Relativity are presented. The data on the S-stars monitoring in the Galactic center obtained by GRAVITY collaboration were analysed within the Physics-informed neural network (PINN) approach. The results enabled to probe the role of the cosmological constant, of the dark matter, the star cluster in the core of the Galaxy obtaining an upper limit for the star density. The topics include the conversion of high-frequency relic gravitational waves into photons in cosmological magnetic field, cosmological gravitational waves stochastic background generation through the spontaneous breaking of a global baryon number symmetry, observational predictions of the Starobinsky inflation model and other studies. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Comments: 3 pages; Eur Phys J Plus

Journal ref: Eur. Phys. J. Plus 140, 1011 (2025)

Poissonian Analysis of Glitches Observed in the LIGO Gravitational Wave Interferometers

Authors: Giovanna Souza Rodrigues Costa, Julio Cesar Martins, Odylio Denys Aguiar

Abstract: This work investigates the temporal distribution of glitches detected by LIGO, focusing on the morphological classification provided by the Gravity Spy project. Starting from the hypothesis that these events follow a Poisson process, we developed a statistical methodology to evaluate the agreement between the empirical distribution of glitches and an ideal Poisson model, using the coefficient of d… ▽ More This work investigates the temporal distribution of glitches detected by LIGO, focusing on the morphological classification provided by the Gravity Spy project. Starting from the hypothesis that these events follow a Poisson process, we developed a statistical methodology to evaluate the agreement between the empirical distribution of glitches and an ideal Poisson model, using the coefficient of determination ($R^2$) as the main metric. The analysis was applied to real data from the LIGO detectors in Livingston and Hanford throughout the O3 run, as well as to synthetic datasets generated from pure Poisson distributions. The results show that while several morphologies exhibit good agreement with the proposed model, classes such as 1400Ripples, Fast Scattering, and Power Line display significant deviations ($R^2 \leq 0.6$), suggesting that their origins do not strictly follow Poissonian statistics. In some cases, a dependence on the detector or the observing run was also observed. This analysis provides a quantitative basis for distinguishing glitch classes based on their degree of "Poissonness", potentially supporting the development of more effective glitch mitigation strategies in gravitational wave detector data. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Inflation and de Sitter conjectures in 8-dimensional $R+γR^n$ Gravity

Authors: Hai Dang Nguyen, Hoang Nam Cao

Abstract: In this work, we study two potentials, the single-field and the two-field, from the modified ($R+γR^n$) gravity in D=8 dimensions. From those potentials, we calculate four observable quantities in inflation, including scalar-to-tensor ratio, spectral index, running index and scalar amplitude. Then, we compare them to the experimental data to verify the righteousness of the models. Last but not lea… ▽ More In this work, we study two potentials, the single-field and the two-field, from the modified ($R+γR^n$) gravity in D=8 dimensions. From those potentials, we calculate four observable quantities in inflation, including scalar-to-tensor ratio, spectral index, running index and scalar amplitude. Then, we compare them to the experimental data to verify the righteousness of the models. Last but not least, de Sitter conjectures are brought up with these two potentials to investigate that it is possible or not the theory lay in the Landscape of quantum gravity. △ Less

Submitted 7 November, 2025; originally announced November 2025.

How Low Can You Go: Constraining the Effects of Catalog Incompleteness on Dark Siren Cosmology

Authors: Madison VanWyngarden, Maya Fishbach, Aditya Vijaykumar, Alexandra G. Guerrero, Daniel E. Holz

Abstract: Gravitational waves (GWs) serve as standard sirens by directly encoding the luminosity distance to their source. When the host galaxy redshift is known, for example, through observation of an electromagnetic (EM) counterpart, GW detections can provide an independent measurement of the Hubble constant, $H_0$. However, even in the absence of an EM counterpart, inferring $H_0$ is possible through the… ▽ More Gravitational waves (GWs) serve as standard sirens by directly encoding the luminosity distance to their source. When the host galaxy redshift is known, for example, through observation of an electromagnetic (EM) counterpart, GW detections can provide an independent measurement of the Hubble constant, $H_0$. However, even in the absence of an EM counterpart, inferring $H_0$ is possible through the dark siren method. In this approach, every galaxy in the GW localization volume is considered a potential host that contributes to a measurement of $H_0$, with redshift information supplied by galaxy catalogs. Using mock galaxy catalogs, we explore the effect of catalog incompleteness on dark siren measurements of $H_0$. We find that in the case of well-localized GW events, if GW hosts are found in all galaxies with host halo masses $M_h > 2 \times10^{11} M_{\odot}h^{-1}$, catalogs only need to be complete down to the 1% brightest magnitude $M_i < -22.43$ to draw an unbiased, informative posterior on H0. We demonstrate that this is a direct result of the clustering of fainter galaxies around brighter and more massive galaxies. For a mock galaxy catalog without clustering, or for GW localization volumes that are too large, using only the brightest galaxies results in a biased $H_0$ posterior. These results are important for informing future dark siren analyses with LIGO-Virgo-KAGRA as well as next-generation detectors. △ Less

Submitted 6 November, 2025; originally announced November 2025.

Comments: To be submitted to ApJ, 12 pages, 7 figures

On the Bondi accretion of a self-interacting complex scalar field

Authors: Dražen Glavan, Alexander Vikman, Tom Zlosnik

Abstract: Scalar fields with a global U(1) symmetry often appear in cosmology and astrophysics. We study the spherically-symmetric, stationary accretion of such a classical field onto a Schwarzschild black hole in the test-field approximation. Thus, we consider the relativistic Bondi accretion beyond a simplified perfect-fluid setup. We focus on the complex scalar field with canonical kinetic term and with… ▽ More Scalar fields with a global U(1) symmetry often appear in cosmology and astrophysics. We study the spherically-symmetric, stationary accretion of such a classical field onto a Schwarzschild black hole in the test-field approximation. Thus, we consider the relativistic Bondi accretion beyond a simplified perfect-fluid setup. We focus on the complex scalar field with canonical kinetic term and with a generic quartic potential which either preserves the U(1) symmetry or exhibits spontaneous symmetry breaking. It is well known that in the lowest order in gradient expansion the dynamics of such a scalar field is well approximated by a perfect superfluid; we demonstrate that going beyond this approximation systematically reduces the accretion rate with respect to the perfect fluid case. Hence, black holes can provide a way to distinguish a perfect fluid from its ultraviolet completion in form of the complex scalar field. △ Less

Submitted 6 November, 2025; originally announced November 2025.

Comments: 47 pages, 24 figures

Twist and higher modes of a complex scalar field at the threshold of collapse

Authors: Krinio Marouda, Daniela Cors, Hannes R. Rüter, Alex Vaño-Viñuales, David Hilditch

Abstract: We investigate the threshold of collapse of a massless complex scalar field in axisymmetric spacetimes under the ansatz of Choptuik et al. 2004, in which a symmetry depending on the azimuthal parameter $m$ is imposed on the scalar field. This allows for both non-vanishing twist and angular momentum. We extend earlier work to include higher angular modes. Using the pseudospectral code bamps with a… ▽ More We investigate the threshold of collapse of a massless complex scalar field in axisymmetric spacetimes under the ansatz of Choptuik et al. 2004, in which a symmetry depending on the azimuthal parameter $m$ is imposed on the scalar field. This allows for both non-vanishing twist and angular momentum. We extend earlier work to include higher angular modes. Using the pseudospectral code bamps with a new adapted symmetry reduction method, which we call $m$-cartoon, and a generalized twist-compatible apparent horizon finder, we evolve near-critical initial data to the verge of black hole formation for the lowest nontrivial modes, $m=1$ and $m=2$. For $m=1$ we recover discrete self-similarity with echoing period $Δ\simeq0.42$ and power-law scaling with exponent $γ\simeq0.11$, consistent with earlier work. For $m=2$ we find that universality is maintained within this nonzero fixed-$m$ symmetry class but with smaller period and critical exponents, $Δ\simeq0.09$ and $γ\simeq0.035$, establishing an explicit dependence of the critical solution on the angular mode. Analysis of the relation between the angular momentum and the mass of apparent horizons at the instant of formation, $J_{\mathrm{AH}}{-}M_{\mathrm{AH}}$, shows that the effect of angular momentum is minimal at the threshold, with $χ_{\mathrm{AH}}=J_{\mathrm{AH}}/M_{\mathrm{AH}}^2\to0$, and, therefore, excludes extremal black holes for the families under consideration. Our results demonstrate that while universality and DSS hold within each $m$-sector, the critical universal values vary with $m$, and neither extremality nor bifurcation occur in the complex scalar field model within the families considered here. △ Less

Submitted 6 November, 2025; originally announced November 2025.

Comments: 20 pages, 10 figures

Addressing the DESI DR2 Phantom-Crossing Anomaly and Enhanced $H_0$ Tension with Reconstructed Scalar-Tensor Gravity

Authors: Dimitrios Efstratiou, Evangelos Achilleas Paraskevas, Leandros Perivolaropoulos

Abstract: Recent cosmological data, including DESI DR2, highlight significant tensions within the $Λ$CDM paradigm. When analyzed in the context of General Relativity (GR), the latest DESI data favor a dynamical dark energy (DDE) equation of state, $w(z)$, that crosses the phantom divide line $w=-1$. However, this framework prefers a lower Hubble constant, $H_0$, than Planck 2018, thereby worsening the tensi… ▽ More Recent cosmological data, including DESI DR2, highlight significant tensions within the $Λ$CDM paradigm. When analyzed in the context of General Relativity (GR), the latest DESI data favor a dynamical dark energy (DDE) equation of state, $w(z)$, that crosses the phantom divide line $w=-1$. However, this framework prefers a lower Hubble constant, $H_0$, than Planck 2018, thereby worsening the tension with local measurements. This phantom crossing is a key feature that cannot be achieved by minimally coupled scalar fields (quintessence) within GR. This suggests the need for a new degree of freedom that can simultaneously: (A) increase the best-fit value of $H_0$ in the context of the DESI DR2 data, and (B) allow the crossing of the $w=-1$ line within a new theoretical approach. We argue that both of these goals may be achieved in the context of Modified Gravity (MG), and in particular, Scalar-Tensor (ST) theories, where phantom crossing is a natural and viable feature. We demonstrate these facts by analyzing a joint dataset including DESI DR2, Pantheon+, CMB, and growth-rate (RSD) data in the context of simple parametrizations for the effective gravitational constant, $μ_G(z) \equiv G_{eff}/G_N$, and the DDE equation of state, $w(z)$. This MG framework significantly alleviates the tension, leading to a higher inferred value of $H_0 = 70.6 \pm 1.7 \, \text{km s}^{-1} \text{Mpc}^{-1}$. We also present a systematic, data-driven reconstruction of the required underlying ST Lagrangian and provide simple, generic analytical expressions for both the non-minimal coupling $F(Φ) = 1+ξΦ^{2}e^{nΦ}$ and the scalar potential $U(Φ) = U_{0}+ae^{bΦ^{2}}$, which well-describe the reconstructed functions. △ Less

Submitted 6 November, 2025; originally announced November 2025.

Comments: 28 pages, 13 Figures. The numerical analysis file used for the construction of the figures may be found at https://github.com/Dimitrios1993/Reconstructing-Scalar-Tensor-Theories (Python and Mathematica v13)

Thermal superpotential and thermodynamics of neutral hairy black holes in extended SUGRA

Authors: Andrès Anabalòn, Dumitru Astefanesei, David Choque, Antonio Gallerati

Abstract: We present a family of exact neutral hairy black-hole solutions with spherical horizon topology in extended supergravity with Fayet--Iliopoulos terms. We consider a consistent dilaton truncation and analyze in detail a sector where the magnetic part of the FI terms vanishes. Using appropriate dilaton counterterms, we compute the thermodynamic quantities and show the existence of Hawking--Page phas… ▽ More We present a family of exact neutral hairy black-hole solutions with spherical horizon topology in extended supergravity with Fayet--Iliopoulos terms. We consider a consistent dilaton truncation and analyze in detail a sector where the magnetic part of the FI terms vanishes. Using appropriate dilaton counterterms, we compute the thermodynamic quantities and show the existence of Hawking--Page phase transitions. As a holographic application, we derive the thermal superpotential in closed form and use it as a counterterm, explicitly demonstrating that no additional finite counterterms are required to regularize the Euclidean action and the quasi-local stress tensor. The dual stress tensor matches that of a thermal gas of massless particles and is consistent with mixed dilaton boundary conditions that preserve conformal symmetry. △ Less

Submitted 12 November, 2025; v1 submitted 6 November, 2025; originally announced November 2025.

Comments: 20 pages, 5 figures

Apparent horizon as a membrane

Authors: Daniel R. Terno

Abstract: The requirement that a trapped spacetime domain forms in finite time for distant observers is logically possible and sometimes unavoidable, but its consequences are not yet fully understood. In spherical symmetry, the characterization of the near-horizon geometry of these physical black holes is complete and shows marked differences from their eternal counterparts. Whether these differences lead t… ▽ More The requirement that a trapped spacetime domain forms in finite time for distant observers is logically possible and sometimes unavoidable, but its consequences are not yet fully understood. In spherical symmetry, the characterization of the near-horizon geometry of these physical black holes is complete and shows marked differences from their eternal counterparts. Whether these differences lead to observable signatures remains unclear. We construct an approximate near-horizon metric that encapsulates them and is suitable for modeling. The timelike apparent horizon of physical black holes provides a natural surface for a consistent membrane description: we obtain closed-form expressions for the redshift, proper acceleration, and extrinsic curvature, and assign a two-dimensional viscous-fluid stress tensor via junction conditions. These results also provide an additional perspective on the relation between Rindler and near-horizon geometries. Among dynamical generalizations of surface gravity, only a subset applies to these models. We complete their analysis and recover the intuitive definition of surface gravity -- the acceleration in the frame of a near-horizon observer, redshifted to infinity -- directly from the membrane acceleration. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 8+4 pages. Comments welcome!

Limits on the Statistical Description of Charged de Sitter Black Holes

Authors: Lars Aalsma, Puxin Lin, Jan Pieter van der Schaar, Gary Shiu, Watse Sybesma

Abstract: The thermodynamics of de Sitter black holes is complicated by the presence of two horizons and the absence of a globally defined timelike Killing vector. The standard choice of the Gibbons-Hawking Killing vector is at odds with the interpretation of the surface gravity as an acceleration measured by a physical observer at rest. Focusing on four-dimensional Reissner-Nordström de Sitter black holes… ▽ More The thermodynamics of de Sitter black holes is complicated by the presence of two horizons and the absence of a globally defined timelike Killing vector. The standard choice of the Gibbons-Hawking Killing vector is at odds with the interpretation of the surface gravity as an acceleration measured by a physical observer at rest. Focusing on four-dimensional Reissner-Nordström de Sitter black holes we show that this issue can be resolved by adopting a normalization originally proposed by Bousso and Hawking, which defines thermodynamic quantities relative to the unique freely-falling observer at a fixed radial coordinate. Within this framework, we derive new first laws for the black hole and cosmological horizon and re-examine the black hole's heat capacity. We find that the heat capacity remains finite in the near-extremal Nariai limit, thus averting a breakdown of the semi-classical thermodynamic description. However, the heat capacity does vanish in the cold limit, as expected, and for Nariai black holes in the ultracold limit, indicating that fundamental limitations on the statistical description persist in these regimes. We discuss the implications of our results for log-$T$ corrections to near-extremal de Sitter black holes. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 33 pages + 2 pages appendices

Quadrature-witness readout for backscatter mitigation in gravitational-wave detectors limited by back-action

Authors: Niels Böttner, Roman Schnabel, Mikhail Korobko

Abstract: Disturbances in gravitational wave (GW) observational data are often caused by non-stationary noise in the detector itself, such as back-scattering of laser stray light into the signal field. Unlike GW signals, non-stationary noise can appear in both the GW-signal quadrature and the orthogonal quadrature, which is usually not measured. Simultaneous sensing of this orthogonal quadrature provides a… ▽ More Disturbances in gravitational wave (GW) observational data are often caused by non-stationary noise in the detector itself, such as back-scattering of laser stray light into the signal field. Unlike GW signals, non-stationary noise can appear in both the GW-signal quadrature and the orthogonal quadrature, which is usually not measured. Simultaneous sensing of this orthogonal quadrature provides a witness channel that can be used to reconstruct the disturbance in the signal quadrature enabling a subtraction of non-stationary noise. Here, we present the concept of quadrature witness that is compatible with frequency-dependent squeezing, which is already used to simultaneously reduce photon shot noise and photon radiation pressure noise. We demonstrate that implementing this approach in a GW detector could reduce noise caused by loud back-scatter events, thereby improving the overall sensitivity and robustness of GW observatories. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 10 pages, 7 figures

The first year of LISA Galactic foreground

Authors: Riccardo Buscicchio, Federico Pozzoli, Daniele Chirico, Alberto Sesana

Abstract: Galactic white-dwarf binaries play a central role in the inference model for the Laser Interferometer Space Antenna. In this manuscript, we employ the $\texttt{bahamas}$ codebase to characterize, in a global-fit fashion, the reconstruction of the Galactic foreground during the first year of observation. To account for its statistical properties, we represent the data in time--frequency domain, and… ▽ More Galactic white-dwarf binaries play a central role in the inference model for the Laser Interferometer Space Antenna. In this manuscript, we employ the $\texttt{bahamas}$ codebase to characterize, in a global-fit fashion, the reconstruction of the Galactic foreground during the first year of observation. To account for its statistical properties, we represent the data in time--frequency domain, and characterize the effectiveness of multiple approaches, e.g. statistically viable likelihoods, sampling schemes, segmentation widths, and gaps density. Our analysis yields consistent results across, with overwhelming evidence in favor of a non-stationary model in less than a month of data. Moreover, we show robustness against the presence of additional extragalactic foregrounds, and test the suitability of our approximations on the more complex simulated data in the $\textit{Yorsh}$ data challenge. △ Less

Submitted 6 November, 2025; v1 submitted 5 November, 2025; originally announced November 2025.

Comments: 16 pages, 13 figures

Wald Entropy in Extended Modified Myrzakulov Gravity Theories: \(f(R, T, Q, R_{μν}T^{μν}, R_{μν}Q^{μν}, \dots)\)

Authors: Davood Momeni, Ratbay Myrzakulov

Abstract: We investigate black hole entropy in a broad class of modified Myrzakulov gravity theories defined by generalized Lagrangians of the form \( \mathcal{L} = αR + F(T, Q, R_{μν}T^{μν}, R_{μν}Q^{μν}, \dots) \), where \( R \), \( T \), and \( Q \) represent curvature, torsion, and non-metricity scalars. Using the vielbein formalism, we derive the Wald entropy for various subclasses of these models, ext… ▽ More We investigate black hole entropy in a broad class of modified Myrzakulov gravity theories defined by generalized Lagrangians of the form \( \mathcal{L} = αR + F(T, Q, R_{μν}T^{μν}, R_{μν}Q^{μν}, \dots) \), where \( R \), \( T \), and \( Q \) represent curvature, torsion, and non-metricity scalars. Using the vielbein formalism, we derive the Wald entropy for various subclasses of these models, extending the classical entropy formula to accommodate non-Riemannian geometry. Our focus is on how the additional geometric degrees of freedom modify the entropy expression. The analysis shows that such corrections arise systematically from the extended structure of the action and preserve diffeomorphism invariance. These results refine the theoretical framework for gravitational thermodynamics in extended geometry settings. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 11 PAGES, Published in: Int.J.Theor.Phys. 64 (2025) 10, 268

Journal ref: Int.J.Theor.Phys. 64 (2025) 10, 268

A Case for an Inhomogeneous Einstein-de Sitter Universe

Authors: Peter Raffai, Dominika E. R. Kis, Dávid A. Ködmön, Adrienn Pataki, Rebeka L. Böttger, Gergely Dálya

Abstract: In our local-to-global cosmological framework, cosmic acceleration arises from local dynamics in an inhomogeneous Einstein-de Sitter (iEdS) universe without invoking dark energy. An iEdS universe follows a quasilinear coasting evolution from an Einstein-de Sitter to a Milne state, as an effective negative curvature emerges from growing inhomogeneities without breaking spatial flatness. Acceleratio… ▽ More In our local-to-global cosmological framework, cosmic acceleration arises from local dynamics in an inhomogeneous Einstein-de Sitter (iEdS) universe without invoking dark energy. An iEdS universe follows a quasilinear coasting evolution from an Einstein-de Sitter to a Milne state, as an effective negative curvature emerges from growing inhomogeneities without breaking spatial flatness. Acceleration can arise from structure formation amplifying this effect. We test two realizations, iEdS(1) and iEdS(2), with $H_0=\{70.24,74.00\}\ \mathrm{km\ s^{-1}\ Mpc^{-1}}$ and $Ω_{\mathrm{m},0}=\{0.290,0.261\}$, against CMB, BAO, and SN Ia data. iEdS(1) fits better than $Λ$CDM and alleviates the $H_0$ tension, whereas iEdS(2) fully resolves it while remaining broadly consistent with the data. Both models yield ${t_0\simeq13.64\ \mathrm{Gyr}}$, consistent with globular-cluster estimates. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: Code and posterior plots available at https://zenodo.org/records/17288919

Wormhole spacetimes in an expanding universe: energy conditions and future singularities

Authors: Taishi Katsuragawa, Shin'ichi Nojiri, Sergei D. Odintsov

Abstract: We study wormhole geometries embedded in an expanding universe within a four-scalar non-linear $σ$ model, where the target-space metric is identified with the spacetime Ricci tensor. In this framework, wormholes can remain stable even when conventional energy conditions are violated. However, once cosmological expansion is included, the effective energy density and pressure are modified by the cos… ▽ More We study wormhole geometries embedded in an expanding universe within a four-scalar non-linear $σ$ model, where the target-space metric is identified with the spacetime Ricci tensor. In this framework, wormholes can remain stable even when conventional energy conditions are violated. However, once cosmological expansion is included, the effective energy density and pressure are modified by the cosmological fluid, enabling the energy conditions to be satisfied. We further present intriguing geometries in which a finite future singularity appears in our universe but not in another universe connected by the wormhole. Near the throat, the hypersurface becomes timelike, allowing trajectories to traverse to the other universe before the singularity and return afterwards. We also construct wormhole solutions motivated by galactic dark-matter halo profiles, where the required non-vanishing pressure arises naturally from the four-scalar non-linear $σ$ model. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 22 pages, 7 figures

Report number: KEK-TH-2774, KEK-Cosmo-0396

Dynamic and Thermodynamic Stability of Superconducting-superfluid Stars

Authors: Delong Kong, Yu Tian, Hongbao Zhang

Abstract: We give a comprehensive analysis of the dynamic and thermodynamic stability of neutron stars composed of superconducting-superfluid mixtures within the Iyer-Wald formalism. We derive the first law of thermodynamics and the necessary and sufficient condition under which dynamic equilibrium implies thermodynamic equilibrium. By constructing the phase space and canonical energy, we show that the dyna… ▽ More We give a comprehensive analysis of the dynamic and thermodynamic stability of neutron stars composed of superconducting-superfluid mixtures within the Iyer-Wald formalism. We derive the first law of thermodynamics and the necessary and sufficient condition under which dynamic equilibrium implies thermodynamic equilibrium. By constructing the phase space and canonical energy, we show that the dynamic stability for perturbations, restricted in symplectic complement of trivial perturbations with the ADM 3-momentum unchanged, is equivalent to the non-negativity of the canonical energy. Furthermore, dynamic stability against restricted axisymmetric perturbations guarantees the dynamic stability against all axisymmetric perturbations. We also prove that the positivity of canonical energy on all axisymmetric perturbations within the Lagrangian displacement framework with fixed angular momentum is necessary for thermodynamic stability. In particular, the equivalence of dynamic and thermodynamic stability for spherically symmetric perturbations of static, spherically symmetric isentropic configurations is established. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: arXiv admin note: text overlap with arXiv:1309.0177 by other authors

Viscous Fluid Models of Cosmic Acceleration in FRW Spacetime Using MCMC Constraints

Authors: Mohit Thakre, Praveen Kumar Dhankar, Behnam Pourhassan, Safiqul Islam

Abstract: This study combines theoretical advancements with observational limitations to investigate the cosmological implications of a bulk viscous modified Chaplygin gas (MCG) in a Friedmann--Robertson--Walker (FRW) in (3+1) dimensional spacetime framework. We provide analytical solutions for both viscous and non-viscous cases, pointing out variations in the energy density evolution, the Hubble parameter… ▽ More This study combines theoretical advancements with observational limitations to investigate the cosmological implications of a bulk viscous modified Chaplygin gas (MCG) in a Friedmann--Robertson--Walker (FRW) in (3+1) dimensional spacetime framework. We provide analytical solutions for both viscous and non-viscous cases, pointing out variations in the energy density evolution, the Hubble parameter dynamics, and the deceleration parameter transitions. Bulk viscosity suppresses oscillations in structure creation, a well-known drawback of Chaplygin gas models in larger dimensions, as shown by a thorough perturbation analysis. Using the bulk viscosity coefficient and Hubble expansion parameter, which are incorporated by the total pressure and the appropriate pressure and by using energy momentum conservation law determined time time-dependent density. With the help of three conditions ($ξ= 0$, $ξ\neq0$, and we neglect both bulk viscosity and presence of Chaplygin gas, i.e $A=0$ and $ξ=0$) created three different models as the Hubble parameter is a function of redshift $z$. By applying the MCMC method to these models, we have gone through observational analysis by using the Hubble and BAO datasets. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 23 pages, 11 figures

Mechanics of non-Killing horizons

Authors: Francesco Del Porro, Jacopo Mazza

Abstract: We investigate the mechanics of stationary axisymmetric non-Killing horizons, which emerge in spacetimes that do not enjoy the symmetry known as circularity -- as is commonly the case for rotating black holes beyond general relativity. Specifically, we define and compute three notions of surface gravity: inaffinity, normal, and peeling; and find that the inaffinity and normal definitions generical… ▽ More We investigate the mechanics of stationary axisymmetric non-Killing horizons, which emerge in spacetimes that do not enjoy the symmetry known as circularity -- as is commonly the case for rotating black holes beyond general relativity. Specifically, we define and compute three notions of surface gravity: inaffinity, normal, and peeling; and find that the inaffinity and normal definitions generically differ, while the normal and peeling definitions always agree, although none of them is constant over the horizon. We then derive a version of Smarr's formula, which appears to involve an average over the horizon of the normal surface gravity. We also compute, via the tunnelling method, the spectrum of Hawking's radiation, verifying that its temperature is controlled by the (non-constant) peeling surface gravity. Finally, we recapitulate the status of the four laws of black hole mechanics in situations in which the event horizon fails to be Killing. Our results thus pave the way to a deeper understanding of black hole thermodynamics beyond general relativity. △ Less

Submitted 4 November, 2025; originally announced November 2025.

Comments: 26 pages

Nested Apparent Horizons and Quantized Separation from Intense Hawking Backreaction

Authors: Steven J. Silverman

Abstract: When Hawking radiation from a rotating or non-rotating black hole becomes sufficiently intense, its own stress energy can no longer be treated as a perturbation on a fixed background. In this regime the outgoing flux may generate an additional, transient trapping surf ace exterior to the original event horizon. Using a simple spherically symmetric semi classical model we demonstrate that strong ou… ▽ More When Hawking radiation from a rotating or non-rotating black hole becomes sufficiently intense, its own stress energy can no longer be treated as a perturbation on a fixed background. In this regime the outgoing flux may generate an additional, transient trapping surf ace exterior to the original event horizon. Using a simple spherically symmetric semi classical model we demonstrate that strong outgoing null energy can create nested apparent horizons, a feature reminiscent of the Penrose process but mediated by quantum back reaction. The effect is illustrated using a smooth Vaidya type mass profile, and conditions for bifurcation and merger of horizons are derived. We further propose that the separation between nested horizons may obey a discrete quantization rule analogous to the Bohr Sommerfeld condition,suggesting a geometric route toward quantum-gravity discreteness. △ Less

Submitted 4 November, 2025; originally announced November 2025.

Comments: 3 pages

The simple reason why classical gravity can entangle

Authors: Andrea Di Biagio

Abstract: Ever since gravity-induced entanglement (GIE) experiments have been proposed as a witness of the quantum nature of gravity, more and more theories of classical gravity coupled to quantum matter have been shown to predict GIE, despite the existence of several theory-independent no-go theorems purportedly claiming that it should not be possible. This note explains why this is possible, and why this… ▽ More Ever since gravity-induced entanglement (GIE) experiments have been proposed as a witness of the quantum nature of gravity, more and more theories of classical gravity coupled to quantum matter have been shown to predict GIE, despite the existence of several theory-independent no-go theorems purportedly claiming that it should not be possible. This note explains why this is possible, and why this makes the GIE experiments an even more urgent matter in quantum gravity research. △ Less

Submitted 5 November, 2025; v1 submitted 4 November, 2025; originally announced November 2025.

Comments: 5 pages, comments welcome

Observational properties and quasinormal Modes of the Hayward black Hole surrounded by a cloud of strings

Authors: Qi-Qi Liang, Zi-qiang Cai, Dong Liu, Zheng-Wen Long

Abstract: In this work, we explored the Hayward black hole surrounded by a cloud of strings, with a focus on the effects of the regularization parameter $l$ and the string cloud parameter $a$ on its observational properties and quasinormal modes (QNMs). Utilizing the spacetime metric and geodesic equations, we calculated several geometric quantities characterizing the black hole. To visualize the observatio… ▽ More In this work, we explored the Hayward black hole surrounded by a cloud of strings, with a focus on the effects of the regularization parameter $l$ and the string cloud parameter $a$ on its observational properties and quasinormal modes (QNMs). Utilizing the spacetime metric and geodesic equations, we calculated several geometric quantities characterizing the black hole. To visualize the observational appearance of the accretion disk, we employed the Novikov--Thorne model to simulate both its primary and secondary images. Furthermore, we analyzed the QNMs of the black hole under scalar and electromagnetic perturbations for different parameter values. The results indicate that as the regularization parameter $l$ increases, the outer horizon radius $r_{+}$, photon-sphere radius $r_{\text{ph}}$, critical impact parameter $b_{c}$, and innermost stable circular orbit $r_{\text{isco}}$ exhibit a gradual decrease, while the inner horizon radius $r_{-}$ and the real part of the QNMs frequency $ω_{r}$ increase. In contrast, as the string cloud parameter $a$ increases, $r_{+}$, $r_{\text{ph}}$, $b_{c}$, and $r_{\text{ isco}}$ demonstrate a rapid increase, whereas $r_{-}$ and $ω_{r}$ decrease. In both cases, the absolute value of the imaginary part of the QNMs frequency decreases with the increase $l$ or $a$. This work offers a theoretical foundation for understanding the coupling between regular black holes and surrounding string clouds. △ Less

Submitted 4 November, 2025; originally announced November 2025.

Comments: 13 pages, 10 figures, submitted

Dynamical Tidal Response of Schwarzschild Black Holes

Authors: Oscar Combaluzier--Szteinsznaider, Daniel Glazer, Austin Joyce, Maria J. Rodriguez, Luca Santoni

Abstract: Dynamical Love numbers capture the conservative response of an object to a time-dependent external tidal gravitational field. We compute the dynamical Love numbers of Schwarzschild black holes in general relativity within a point-particle effective field theory framework. In addition to the known logarithmic running, we compute the finite scheme-dependent contributions to the Love number couplings… ▽ More Dynamical Love numbers capture the conservative response of an object to a time-dependent external tidal gravitational field. We compute the dynamical Love numbers of Schwarzschild black holes in general relativity within a point-particle effective field theory framework. In addition to the known logarithmic running, we compute the finite scheme-dependent contributions to the Love number couplings. We do this by matching the renormalized one-point function in the effective theory to the classical field profile computed in general relativity. On the general relativity side, we solve the Regge-Wheeler and Zerilli equations perturbatively in a small frequency expansion. In order to match on the effective field theory side we include gravitational interactions using the Born series and employ dimensional regularization to obtain a renormalized field profile. △ Less

Submitted 4 November, 2025; originally announced November 2025.

Comments: 63 pages

Charged Bardeen black hole with a cosmological constant and surrounded by quintessence and a cloud of strings

Authors: F. F. Nascimento, V. B. Bezerra, J. M. Toledo, P. H. Morais, J. C. Rocha

Abstract: Exact solutions which generalize the Bardeen black hole solution, in the sense that several sources are taken into account, are derived. The most general case corresponds to a charged Bardeen black hole with a cosmological constant and surrounded by quintessence and a cloud of strings. A discussion is presented concerning the Kretschmann scalar and its dependence with the parameters associated to… ▽ More Exact solutions which generalize the Bardeen black hole solution, in the sense that several sources are taken into account, are derived. The most general case corresponds to a charged Bardeen black hole with a cosmological constant and surrounded by quintessence and a cloud of strings. A discussion is presented concerning the Kretschmann scalar and its dependence with the parameters associated to the different sources. Finally, the geodesics and effective potential are analyzed. △ Less

Submitted 3 November, 2025; originally announced November 2025.