The harvesting of quantum resources from the vacuum state of a quantum field is a central topic in relativistic quantum information. While several proposals for the harvesting of entanglement from the quantum vacuum exist, less attention has been paid to other quantum resources, such as nonstabilizerness, commonly dubbed magic and quantified by the stabilizer Rényi entropy (SRE). In this work, we show how to harvest SRE from the vacuum state of a massless field, using accelerated Unruh-DeWitt detectors in Minkowski spacetime. In particular, one can harvest a particular nonlocal form of SRE that cannot be erased by local unitary operations. This nonlocal SRE is a fundamental quantity to study the interplay between entanglement and nonstabilizer resources. We conclude our work with an analysis of the Clauser-Horne-Shimony-Holt inequalities: when restricting to stabilizer measurements, i.e., Pauli measurements, one cannot extract a violation from the quantum field.

The infinite series of 4D $\mathcal{N}=2$ superconformal field theories with central charge relation $a_{4\mathrm{D}}=c_{4\mathrm{D}}$ are closely related to the $\mathcal{N}=4$ super Yang-Mills theory. In this paper, we study the modular properties of their associated vertex operator algebras $\mathbb{V}[{\mathcal{T}}_{p,N}]$, where ${\mathcal{T}}_{p,N}$ are those $a=c$ theories with an $SU(N)$ gauge group. We exploit the closed-form formula for the Schur index of the $\mathcal{N}=4$ $SU(N)$ theories ${\mathcal{T}}_{SU(N)}$ to derive the space of characters of the vertex operator algebra $\mathbb{V}[{\mathcal{T}}_{p,N}]$ and the $S$, $T$ matrices, and find the (nonmonic) modular linear differential equations that constrain the module characters when possible. We investigate the geometric interpretation of some of these modular data from the viewpoint of 4D mirror symmetry. Using insights from the flavored modular differential equation and defect index, we investigate a map between module characters of $\mathbb{V}[{\mathcal{T}}_{SU(N)}]$ and those of $\mathbb{V}[{\mathcal{T}}_{p,N}]$.

In general relativity, the Einstein equations provide spherically symmetric static spacetimes with dynamics defined as an evolution along the radial coordinate $r$. The geometrical sector becomes a one-dimensional mechanical system, with the Misner-Sharp mass and lapse as canonically conjugate variables, and a vanishing Hamiltonian for pure gravity. Coupling classical or quantum matter fields, or introducing (quantum) corrections to general relativity, then, generates a nonvanishing effective Hamiltonian, leading to nontrivial evolutions of the mass and lapse. We illustrate this mechanism through various examples of classical matter fields and identify Hamiltonians describing the effective dynamics of gravity coupled to perfect fluids with a linear barotropic equation of state. Finally, we derive effective Hamiltonians that reproduce the gravitational semiclassical dynamics coupled to renormalized quantum matter fields and discuss the conditions for which the singularity at $r=0$ is resolved. In particular, we find a singularity-free black-hole-like solution, stabilized by quantum matter, smoothly transitioning from a bulk with a constant negative Ricci scalar to the standard outside Schwarzschild metric. This opens new possibilities for the modeling of both semiclassical corrections and deep quantum effects on the interior structure of self-gravitating compact objects and black holes.

We demonstrate analytically that gravitational waves, upon interacting with copropagating electromagnetic radiation in a plasma, induce distinctive sidebands on the modulated light, thereby providing a detectable signature of their presence. Employing a fully covariant coupled-wave framework, we envision gravitational waves as phase-insensitive luminal moving gratings and derive explicit phase-matching conditions that articulate such an interaction while conserving both energy and momentum. Beyond preserving the directional signature of gravitational waves, the coupling mechanism imposes no coherence requirements on the photon-by-graviton scattering, hence enabling possibilities for exploiting cosmic microwave background radiation. Although detection at low frequencies is constrained by the requirement of long interaction lengths, advances in laser technology are poised to enable high-frequency gravitational wave detection, potentially unveiling insights into the primordial spacetime ripples that have been traversing the cosmos since the inflationary epoch.

Vector boson stars, also known as Proca stars, exhibit remarkable dynamical robustness, making them strong candidates for potential astrophysical exotic compact objects. In search of theoretically well-motivated Proca star models, we recently introduced the $\ell$-Proca star, a multifield extension of the spherical Proca star, whose $(2\ell +1)$ constitutive fields have the same time and radial dependence, and their angular structure is given by all the available spherical harmonics for a fixed angular momentum number $\ell$. In this work, we conduct a nonlinear stability analysis of these stars by numerically solving the Einstein- (multi-, complex) Proca system for the case of $\ell =2$, which are formed by five constitutive independent, complex Proca fields with $m=0,|1|$, and $|2|$. Our analysis is based on long-term, fully nonlinear, three-dimensional numerical-relativity simulations without imposing any symmetry. We find that ($\ell =2$)-Proca stars are unstable throughout their entire domain of existence. In particular, we highlight that less compact configurations dynamically lose their global spherical symmetry, developing a nonaxisymmetric $\tilde{m}=4$ mode instability and a subsequent migration into a new kind of multifield Proca star formed by fields with different angular momentum number, $\ell =1$ and $\ell =2$, that we identify as unstable multi-$\ell$-Proca stars.

Inaccurate modeling of gravitational-wave signals can introduce systematic biases in the inferred source parameters. As detector sensitivities improve and signals become louder, mitigating such waveform-induced systematics becomes increasingly important. In this work, we assess the systematic biases introduced by an incomplete description of the ringdown signal from massive black hole binaries in the LISA band. Specifically, we investigate the impact of mode truncation in the ringdown template. Using a reference waveform composed of 13 modes, we establish a mode hierarchy and determine the minimum number of modes required to avoid parameter biases across a wide range of LISA sources. For typical systems with masses $\sim {10}^6–{10}^7{M}_{\odot }$ at redshifts $z\sim 2–6$, we find that at least 3–6 modes are needed for accurate parameter estimation, while high signal-to-noise ratio events may need at least 10 modes. Our results are a window-insensitive lower bound on the minimum number of modes, as more modes may be needed depending on the choice of time-domain windowing of the postmerger signal.

Compact stars in scalar-tensor (ST) gravity have been extensively investigated, but relatively few studies have focused on highly relativistic neutron stars (NSs) with an extremely dense core region where the trace of the energy-momentum tensor reverses its sign. In this regime, we identify the origin of the phenomenon where multiple scalarized solutions exist for a fixed central density, arising from the oscillatory profile of the scalar field inside the star. This origin further indicates that the multibranch structure emerges for both negative and positive $\beta$, the quadratic-term coefficient in the effective coupling function between the scalar field and conventional matter in the Einstein frame. By comparing the Damour–Esposito-Farèse and Mendes-Ortiz models of the ST gravity, we demonstrate that their distinct scalarization behaviors stem from whether the effective coupling function is bounded. We also compute for scalarized NSs with a highly relativistic dense core in ST theories the moment of inertia and tidal deformability that are relevant to pulsar-timing and gravitational-wave experiments.

Non-Abelian black holes that violate the no-hair conjecture are known to exist in the Einstein-Yang-Mills-Higgs field theory. The onset of hair formation in this composed physical system is marked by the presence of “cloudy” black-hole spacetimes, magnetically charged Reissner-Nordström black holes that support spatially regular linearized-field configurations. In the present paper, we explore, using analytical techniques, the physical and mathematical properties of the composed black-hole-linearized-field bound-state configurations of the Einstein-Yang-Mills-Higgs theory. In particular, we derive a remarkably compact analytical formula for the discrete resonance spectrum $\{{\mu }_k{\}}_{k=1}^{k=\infty }$ of the dimensionless mass-radius parameter $\mu \equiv m_{\mathrm{w}}{r}_{+}$ that characterizes the cloudy black-hole-field configurations in the regime $1\ll r_{+}\ll m_{\mathrm{w}}^{-1}$ of small-mass weakly magnetized black holes (here $r_{+}$ is the horizon radius of the central supporting black hole and $m_{\mathrm{w}}$ is the mass of the Yang-Mills field due to the Higgs effect). Interestingly, our results reveal that the excited black-hole-field resonances are characterized by the asymptotic $k$-independent dimensionless ratio ${\mu }_{k+1}/{\mu }_k=e^{-2\pi /\sqrt{3}}$.

In this work, we propose a novel symmetry-based approach to identifying topological densities in gravitational theories. Starting from a generic Lagrangian constructed from quadratic curvature invariants, we systematically analyze the symmetries admitted by such actions. We find that requiring invariance under a particular class of transformations singles out a unique combination of coefficients: precisely that of the Gauss-Bonnet term. This result provides an alternative route to identifying topological densities, independent of standard geometric or cohomological constructions. We show that this symmetry criterion provides new insight into the structure of effective gravitational actions and the role of topological terms in theories of gravity.

In this study, we investigate the thermodynamic properties of shift-symmetric Horndeski and beyond-Horndeski theories (theories in which only derivatives of the scalar field appear in the action). Utilizing Euclidean methods, we first analyze two specific cases that serve as foundational examples for the broader framework. We derive the general expression for entropy variation within this setting, for homogeneous spacetimes (with $g_{tt}=1/g_{rr}$), demonstrating that both parity-preserving and parity-violating terms contribute to the entropy formula. Given the functional form of the coupling terms, the black-hole entropy can be determined by integrating this relation with respect to the event horizon. Our general result is consistent with previously reported special cases in the literature. Notably, for particular constraints on the coupling functions, the entropy identically vanishes. Furthermore, we establish that homogeneous spacetimes within shift- and parity-symmetric beyond-Horndeski theories universally obey Bekenstein’s area law for entropy, irrespective of the specific form of the coupling functions.

Accurate and reliable gravitational waveform models are crucial in determining the properties of compact binary mergers. In particular, next-generation gravitational-wave detectors will require more accurate waveforms to avoid biases in the analysis. In this work, we extend the recent NRTidalv3 model to account for higher-mode corrections in the tidal phase contributions for binary neutron star systems. The higher-mode, multipolar NRTidalv3 model is then attached to several binary-black-hole baselines, such as the phenomenological IMRPhenomXHM and IMRPhenomXPHM models, and the effective-one-body-based model SEOBNRv5HM_ROM. We test the performance and validity of the newly developed models by comparing them with numerical-relativity simulations and other tidal models. Finally, we employ them in parameter estimation analyses on simulated signals from both comparable-mass and high-mass-ratio systems, as well as on the gravitational-wave event GW170817, for which we find consistent results with respect to previous analyses.

Parameter estimation (PE) for compact binary coalescence (CBC) events observed by gravitational wave (GW) laser interferometers is a core task in GW astrophysics. We present a method to compute the posterior distribution efficiently without relying on stochastic samplers. First, we show how to select sets of intrinsic and extrinsic parameters that efficiently cover the relevant phase space. We then show how to compute the likelihood for all combinations of these parameters using dot products. We describe how to assess and tune the integration accuracy, making the outcome predictable and adaptable to different applications. The low computational cost allows full PE in minutes on a single CPU, with the potential for further acceleration using multiple CPUs or GPUs. We implement this method in the dot-PE package, enabling sensitive searches using the full evidence integral for precessing CBCs and supporting large waveform banks ($\sim {10}^5–{10}^6$ waveforms), regardless of waveform generation cost.

The asymptotic structure of space-time is studied by imposing conditions on the asymptotics of the metric. These conditions are weak enough to include large classes of physically relevant isolated space-times, but have a rich enough structure to be able to define important physically meaningful quantities like mass, angular momentum, and gravitational waves. By using a unified expansion of the metric in a neighborhood of spatial infinity that includes a piece of null infinity, we connect the asymptotic expansions of solutions to Einstein’s equations in the different asymptotic regimes. Within the class of space-times under consideration, we find a connection between the peeling properties of the Weyl scalars and symmetries of initial data near spatial infinity. In particular, we show that for initial data that to leading order is symmetric under $\mathrm{parity}+\text{time}$ reversal, ${\mathrm{\Psi }}_2$ has the usual $1/r^3$ fall-off rate at null infinity. If, in addition, the subleading part of the data is antisymmetric under $\mathrm{parity}+\text{time}$ reversal, then ${\mathrm{\Psi }}_1$ has the usual $1/r^4$ fall-off rate at future null infinity.

Observations of gravitational-wave signals emitted by compact binary inspirals provide unique insights into their properties, but their analysis requires accurate and efficient waveform models. Intermediate- and extreme-mass-ratio inspirals (I/EMRIs), with mass ratios $q\gtrsim {10}^2$, are promising sources for future detectors such as the Laser Interferometer Space Antenna (LISA). Modeling waveforms for these asymmetric-mass binaries is challenging, entailing the tracking of many harmonic modes over thousands to millions of cycles. The FastEMRIWaveforms (few) modeling framework addresses this need, leveraging precomputation of mode data and interpolation to rapidly compute adiabatic waveforms for eccentric inspirals into zero-spin black holes. In this work, we extend few to model eccentric equatorial inspirals into black holes with spin magnitudes $|a|\le 0.999$. Our model supports eccentricities $e\le 0.9$ and semilatus recta $p\le 200$, enabling the generation of long-duration IMRI waveforms, and produces waveforms in $\sim 100\mathrm{ms}$ with hardware acceleration. Characterizing systematic errors, we estimate that our model attains mismatches of $\sim {10}^{-5}$ (for LISA sensitivity) with respect to error-free adiabatic waveforms over the majority of the parameter space. We find that kludge models can introduce errors in signal-to-noise ratios (SNRs) as great as ${}_{-40\%}^{+60\%}$ and induce marginal biases of up to $\sim 1\sigma$ in parameter estimation. We show that LISA’s horizon redshift for I/EMRI signals varies significantly with $a$, reaching a redshift of 3 (15) for EMRIs (IMRIs) with only minor $(\sim 10\%)$ dependence on $e$ for an SNR threshold of 20. For signals with $\mathrm{SNR}\sim 50$, spin and eccentricity at plunge are measured with uncertainties of $\delta a\sim {10}^{-7}$ and $\delta e_{\mathrm{f}}\sim {10}^{-5}$. This work advances the state of the art in waveform generation for asymmetric-mass binaries, providing open-source tools for the investigation of I/EMRI astrophysics and data analysis.

In order to detect the quantum nature of gravity, the quantum-gravity-induced entanglement of masses has been proposed in both flat and curved spacetime. In this paper, we propose an analogous quantum-gravity-induced entanglement of masses protocol using photons produced in astronomical processes as the quantum systems. Unlike massive particles, the gravitational interaction between photons—intrinsically relativistic particles—simultaneously satisfies both the “event” and “system” localities. So it can provide a clear test of whether the gravitational mediator must be nonclassical based on the local operations and classical communication principle. Although the gravitationally induced entanglement between massless relativistic photons is extremely small, our quantitative calculations clarify the characteristic features of the entanglement induced by the photon’s own gravitational field in astronomical process and may inspire other photon entanglement experiments.

In this communication, we address whether or not there is an equivalence between the kinematical and dynamical descriptions of the spatially flat $\mathrm{\Lambda }\mathrm{CDM}$ model. We address this by investigating whether an almost $\mathrm{\Lambda }\mathrm{CDM}$ expansion history [$j(z)\approx 1$] corresponds to an almost $\mathrm{\Lambda }\mathrm{CDM}$ model [$w_{\mathrm{DE}}(z)\approx -1$] by considering two particular explicit examples. At least for the cases considered, this turns out not to be the case. Instead, what we find is that an almost $\mathrm{\Lambda }\mathrm{CDM}$ cosmic evolution rather corresponds to an almost unified dark-fluid model. Considering that one never gets the exact condition $j(z)=1$ from any cosmographic datasets, this raises further questions on whether the $\mathrm{\Lambda }\mathrm{CDM}$ model is the best candidate for the standard model of the evolution of the Universe.

We investigate the extent to which the swampland conjecture can be employed to constrain large-field inflationary models from the perspective of quantum gravity consistency. In particular, we focus on the swampland distance conjecture, which imposes an upper bound on the amplitude of primordial gravitational waves predicted by large-field inflation scenarios. This provides a striking contrast with the well-known Lyth bound, which yields a lower bound on the tensor-to-scalar ratio in such models. The two bounds thus play complementary roles in assessing the viability of inflationary scenarios. We demonstrate that, for certain representative large-field inflation models, the swampland distance conjecture alone can impose more stringent upper limits on the tensor-to-scalar ratio than current observational constraints from the cosmic microwave background. These findings highlight the utility of swampland criteria as a theoretical discriminator among competing inflationary models, independent of empirical data.

We present a systematic study of likelihood functions used for stochastic gravitational wave background (SGWB) searches. By dividing the data into many short segments, one customarily takes advantage of the central limit theorem to justify a Gaussian cross-correlation likelihood. We show, with a hierarchy of ever more realistic examples—beginning with a single frequency bin and one detector, and then moving to two and three detectors with white and colored signal and noise—that approximating the exact Whittle likelihood by various Gaussian alternatives can induce systematic biases in the estimation of the SGWB parameters. We derive several approximations for the full likelihood and identify regimes where Gaussianity breaks down. We also discuss the possibility of conditioning the full likelihood on fiducial noise estimates to produce unbiased SGWB parameter estimation. We show that for some segment durations and bandwidths, particularly in space-based and pulsar-timing arrays, the bias can exceed the statistical uncertainty. Our results provide practical guidance for segment choice, likelihood selection, and data-compression strategies to ensure robust SGWB inference in current and next-generation gravitational wave detectors.

We investigate whether the latest combination of the dark energy spectroscopic instrument (DESI) Year 3 data release (DR2) baryon acoustic oscillation measurements, cosmic microwave background (CMB) data (Planck $2018+\mathrm{ACT}$), and Type Ia supernovae (SNe Ia) compilations (Pantheon+, Union3, and DES Y5) favor a dynamical dark energy component, and explore if such a scenario can simultaneously help resolve the Hubble tension. We contrast two frameworks: the widely used phenomenological $w_0{w}_a$ cold dark matter (CDM) model, and bimetric gravity—a fundamental modification of general relativity that naturally gives rise to phantom dark energy. The $w_0{w}_a\mathrm{CDM}$ model is moderately preferred over $\mathrm{\Lambda }\mathrm{CDM}$, at the $2–4\sigma$ level, when fitting DESI DR2 + $\mathrm{CMB}+\text{SNe}$ Ia, but it exacerbates the Hubble tension. By comparison, bimetric gravity provides a modest improvement in fit quality, at the $1\sigma$ level, but, by inferring $H_0=69.0\pm 0.4\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, it partially eases the Hubble tension, from a $5\sigma$ discrepancy to a $3.7\sigma$ tension. Including locally calibrated SNe Ia brings the overall preference for the bimetric model over $\mathrm{\Lambda }\mathrm{CDM}$ to the $2\sigma$ level, comparable to that of the $w_0{w}_a\mathrm{CDM}$ model when including the local SN Ia calibration.

Galaxy clusters are the vast and massive gravitationally bound structures in the Universe and are often considered as the largest reservoirs of high-energy cosmic-ray particles. However, no direct and conclusive detection of $\gamma$ rays from them has been reported to date. This would mean either our understanding of these systems is insufficient or it could be due to the limited sensitivity and poor localization capabilities of $\gamma$-ray telescopes. Moreover, strong interactions of $\gamma$ rays with intergalactic material along the line of sight allow detectable signals from only a few very nearby clusters. The detection prospects are further constrained to dynamically active clusters, which are theoretically expected to produce detectable $\gamma$-ray emissions. Given these constraints, we systematically shortlisted a suitable sample of nearby ($z<0.05$), dynamically active galaxy clusters and performed a comprehensive analysis of 14 years of Fermi-LAT data. In this work, we present a detailed study of diffuse $\gamma$-ray emission around one such galaxy cluster, Abell 119 (A119). Known for its ongoing merger activity, A119 exhibits significant x-ray luminosity and complex dynamical activity. We analyzed the data using the fermipy package and Fermi Science Tools for spatial and spectral models to account for all potential sources of $\gamma$-ray emission. Our analysis confirms all the Fourth Fermi Gamma-ray LAT (Large Area Telescope) (4FGL) point sources $4\mathrm{FGLJ}0059.3-0152$, $4\mathrm{FGLJ}0101.0-0059$, and $4\mathrm{FGLJ}0059.2+0006$ with significant test statistic values. It further reveals a $\sim 4\sigma$ excess of diffuse $\gamma$-ray emission, offset by $\sim 0.25°$ from the cluster center—suggesting a possible association with the cluster halo region. The extended model provides the most robust description for the detected $\gamma$-ray excess. The computed luminosity bounds for the extended models $\sim 12.21_{-3.95}^{+2.74}\times {10}^{42}\mathrm{erg}{\mathrm{s}}^{-1}$ and the particle spectrum $\sim 2.25_{-0.13}^{+0.38}$ are consistent with previous studies and provide further evidence for the presence of diffuse gamma rays in this galaxy cluster. With the available information, we conclude that the observed emission may arise from nonthermal processes in the intracluster medium, most likely hadronic process. Although the observed $\sim 4\sigma$ signal is significant, uncertainties in source localization and other parameters and instrumental limitations prevent us from confirming the detection. Nonetheless, our results underscore the potential for deeper exploration of $\gamma$ rays in the cluster environment with improved sensitivity and resolution. Moreover, an estimated neutrino flux $E^2{\varphi }_{\nu }\approx 3\times {10}^{-10}\mathrm{GeV}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$ telescope provides motivation for future observations with upcoming neutrino telescopes.