In this study, we investigate the relativistic dynamics of vector bosons within the context of rotating frames of negative curvature wormholes. We seek exact solutions for the fully-covariant vector boson equation, derived as an excited state of zitterbewegung. This equation encompasses a symmetric rank-two spinor, enabling the derivation of a non-perturbative second-order wave equation for the system under consideration. Our findings present exact results in two distinct scenarios. Notably, we demonstrate the adaptability of our results to massless vector bosons without compromising generality. The evolution of this system is shown to correlate with the angular frequency of the uniformly rotating reference frame and the curvature radius of the wormholes. Moreover, our results highlight that the interplay between the spin of the vector boson and the angular frequency of the rotating frame can give rise to real oscillation modes, particularly evident in excited states for massless vector bosons. Intriguingly, we note that the energy spectra obtained remain the same whether the wormhole is of hyperbolic or elliptic nature.

The gravitational wave (GW) signals from extreme mass-ratio inspirals (EMRIs), a key target for the Laser Interferometer Space Antenna (LISA), will be affected in the presence of dark matter (DM) halos. In this paper we explore whether the effects of DM are detectable by LISA within a fully relativistic framework. We model the massive EMRI component as a nonrotating black hole (BH) surrounded by a DM halo. We compute axial and polar GW fluxes for circular orbits at linear order in the mass ratio for DM density profiles with varying mass and compactness. By comparing the phase evolution with vacuum systems, we find that DM halos can induce dephasings of tens to hundreds of radians over a one-year observation period. We demonstrate that even highly diluted DM distributions can significantly affect the emitted waveforms, and that the resulting GW signals can usually be distinguished from each other. While it is important to generalize these findings to more generic orbits and to spinning BHs, our results suggest that LISA could not only reveal the presence of DM halos, but also discriminate between different halo models.

In this paper, we investigate the optical appearance of a charged black hole in the Kalb-Ramond background, incorporating a Lorentz-violating parameter $l=0.01$. By analyzing the null geodesics, we derive the photon sphere, event horizon, effective potential, and critical impact parameters. We then employ a ray-tracing technique to study the trajectories of photons surrounding a thin accretion disk. Three different emission models are considered to explore the observed intensity profiles of direct rings, lensing rings, and photon sphere. By comparing these results with those of the standard Reissner-Nordstr\"om black hole ($l=0$) and the Kalb-Ramond black hole with different values of Lorentz-violating parameter (specifically, $l=0.05$ and $l=0.1$ respectively), we find that the Lorentz symmetry breaking will lead to a decrease in the radii of the photon sphere, the event horizon, and the innermost stable circular orbit. Consequently, this makes the detection of these black holes more challenging.

We employ an adapted version of H\"ormander's asymptotic systems method to show heuristically that the standard good-bad-ugly model admits formal polyhomogeneous asymptotic solutions near null infinity. In a related earlier approach, our heuristics were unable to capture potential leading order logarithmic terms appearing in the asymptotic solution of the good equation (the standard wave equation). Presently, we work with an improved method which overcomes this shortcoming, allowing the faithful treatment of a larger class of initial data in which such logarithmic terms are manifest. We then generalize this method to encompass models that include stratified null forms as sources and whose wave operators are built from an asymptotically flat metric. We then apply this result to the Einstein field equations in generalized harmonic gauge and compute the leading decay in~$R^{-1}$ of the Weyl scalars, where~$R$ is a suitably defined radial coordinate. We detect an obstruction to peeling, a decay statement on the Weyl scalars~$\Psi_n$ that is ensured by smoothness of null infinity. The leading order obstruction appears in~$\Psi_2$ and, in agreement with the literature, can only be suppressed by a careful choice of initial

Frequency response function (FRF) measurements are widely used in Gravitational Wave (GW) detectors, e.g., for the design of controllers, calibrating signals and diagnostic problems with system dynamics. The aim of this paper is to present GraFIT: a toolbox that enables fast, inexpensive, and accurate identification of FRF measurements for GW detectors compared to the commonly used approaches, including common spectral analysis techniques. The toolbox consists of a single function to estimate the frequency response function for both open-loop and closed-loop systems and for arbitrary input and output dimensions. The toolbox is validated on two experimental case studies of the Virgo detector, illustrating more than a factor 3 reduction in standard deviation of the estimate for the same measurement times, and comparable standard deviations with up to 10 times less data for the new method with respect to the currently implemented Spectral Analysis method.

The gravitational deflection effect of relativistic massive and massless particles up to the first post-Minkowskian order caused by a moving Schwarzschild black hole with a two-dimensional equatorial velocity, which contains the radial and transversal components, is studied analytically, and a new unified formula for the deflection angle is achieved. The expression of the angle matches well with the results of the weak deflection of relativistic particles induced by a radially moving Schwarzschild source given in the literature, when the transversal component of the lens velocity vanishes. The joint velocity effect, which consists of the influences of the transversal and radial motions of the lens on the leading-order Schwarzschild deflection of the massive particles and light, is then discussed in the context of general relativity. We analyze the order of magnitude of this kinematical effect and evaluate the possibility of its astronomical detection subsequently.

Using an improved version of the Newman-Janis algorithm, we obtain metrics of rotating black holes for a set of extended gravity theories that extend general relativity in different ways: the Horndeski model, the bumblebee model, the Gauss-Bonnet scalar gravity, the loop quantum gravity, the conformal gravity, and $f(Q)$ (symmetric teleparallel gravity STEGR). The obtained metrics are used to model black hole shadows. It is shown that for some models the critical values of the angular momentum $a_{crit}$ emerge. The previous conclusion that the extended gravity theory corrects by itself the effects of rotation in both directions is confirmed. This appears to be important for further modelling of shadow profiles taking into account the constantly increasing accuracy of black hole images. Thus, when rotation is taken into account black hole shadow images, as the GW170817 test or the post-Newtonian formalism, can serve as a meaningful way to test and constrain extended theories of gravity.

We study exact static spherically symmetric vacuum solutions in generic six-derivative gravity (i.e., without assuming specific relations between the coupling constants). Using modified Schwarzschild coordinates, we systematically classify solutions through Frobenius expansions, determining their number of free parameters and confirming previously known cases, such as the regular solutions at the origin. Importantly, we identify novel solutions absent in four-derivative gravity, including those with (double-degenerate) extreme horizons (and their near-horizon limits) that exist without matter sources, which may indicate the existence of regular black holes. We also find asymptotically (anti-)de Sitter spacetimes, giving rise to an effective cosmological constant. The solutions can be classified into six main classes, and, when possible, we provide the description in standard Schwarzschild coordinates, in which they split into thirteen main solution classes.

We discuss new recurrence-based methods for calculating the complex frequencies of the quasinormal modes of black holes. These methods are based on the Frobenius series solutions of the differential equation describing the linearized radial perturbations. Within the general method, we propose two approaches: the first involves calculating the series coefficients, while the second employs generalized continued fractions. Moreover, as a consequence of this analysis, we present a computationally efficient and convenient method that uses double convergence acceleration, consisting of the application of the Wynn algorithm to the approximants obtained from the Hill determinants, with the Leaver-Nollert-Zhidenko-like tail approximations taken into account. The latter is particularly important for stabilizing and enabling the calculations of modes with small real parts as well as higher overtones. The method demonstrates exceptionally high accuracy. We emphasize that Gaussian elimination is unnecessary in all of these calculations. We consider $D$-dimensional ($3<D<10$) Schwarzschild-Tangherlini black holes as concrete examples. Specifically, we calculate the quasinormal modes of the $(2+1)$-dimensional acoustic black hole (which is closely related to the five-dimensional Schwarzschild-Tangherlini black holes), the electromagnetic-vector modes of the six-dimensional black holes and the scalar (gravitational tensor) modes in the seven-dimensional case. We believe that the methods presented here are applicable beyond the examples shown, also outside the domain of the black hole physics.

We combine the ghost-free bimetric theory of gravity with the concept of local Weyl invariance, realized in the framework of Einstein-Cartan gravity. The gravitational sector, characterized by two independent metrics and two independent connections, is coupled to a scalar field that can in principle develop a non-vanishing expectation value through radiative corrections. The spectrum of the model, apart from the massless standard graviton and a pair of axion-like pseudoscalars, associated with the presence of the Holst invariants in the action, includes an additional spin-$2$ state of a non-vanishing Fierz-Pauli mass proportional to the scalar field vacuum expectation value. We analyze the phenomenology of the model and specify the conditions under which the massive spin-$2$ state could be a primary dark matter candidate.

We demonstrate that wormholes must be entangled regardless of asymptotic boundary conditions. Assuming black hole complementarity, we argue that traversable wormholes instantiate entanglement-assisted quantum channels and that this entanglement must be present between the stretched horizons as an initial condition prior to traversability. This result demonstrates the forward direction of the ER/EPR conjectures.

The mass window of ultralight axion dark matter motivated by suppressing the growth of structure on subgalactic scales, $m\sim 10^{-22}\,\mathrm{eV}$, is now severely constrained by various observation data (e.g. Lyman-$\alpha$ forest). As an attempt to reopen this mass window, we investigate an alternative ultralight dark matter candidate, the complex scalar field dark matter (SFDM). We derive the relativistic hydrodynamics of the complex SFDM in the framework of cosmological perturbation theory. Our formalism contains two novel ingredients uniquely associated with the complex SFDM model: the Eckart frame defined by the conserved Noether current, and the stiff gauge condition, $c_s^2\equiv (\delta P/\delta\rho)|_s=1$. In the Eckart frame, the complex SFDM is effectively an imperfect fluid with a dissipative energy flux, distinguishing itself from axion dark matter. The energy flux can affect the growth of density fluctuations dynamically. Meanwhile, we apply the stiff gauge condition to find new constitutive equations for the complex SFDM. We revisit the homogeneous evolution of the complex SFDM and present illustrative early-stage solutions for perturbations of the complex SFDM in a simplified setting. We demonstrate the effects of varying the model parameters on the evolution of the perturbation variables.

There is a candidate electromagnetic counterpart to the binary black hole merger GW190521, identified as ZTF19abanrhr within AGN J124942.3 + 344929. Additionally, GW190514 is proposed as a plausible precursor merger to GW190521 within a hierarchical merger scenario. In this study, we investigate the potential association between GW190514 and GW190521 as a hierarchical triple merger associated with ZTF19abanrhr, taking into account of sky position, distance, and mass of the sources using a Bayesian criterion. Our analysis reveals that the association is favored over a random coincidence, with a log Bayes factor of 16.8, corresponding to an odds ratio of $\sim$$199:1$, assuming an astrophysical prior odds of $10^{-5}$. Notably, when accounting for the primary masses of the two gravitational wave events as potential products of mergers in the AGN formation channel, the Bayes factor increases significantly, further enhancing the preference for this association by a factor of $\sim$$10^2$, corresponding to a log Bayes factor of 21.5 and an odds ratio of $\sim$$2\times10^4:1$. Our results suggest strong evidence for the first hierarchical triple merger associated with an electromagnetic counterpart in the AGN formation channel. This work is crucial for understanding the formation mechanisms of massive black holes, the role of AGNs in hierarchical mergers, and the implications of multi-messenger astronomy.

We consider stably rotating highly magnetised neutron stars and glitching pulsars. We discuss the prospects for detecting continuous gravitational waves from these sources below 20 Hz with next-generation ground-based facilities such as the Einstein Telescope and Cosmic Explorer and space-based observatories such as DECIGO and Big Bang Observer. We demonstrate that these constitute interesting science targets. We use a robust sensitivity estimation method for future searches based on demonstrated performance. We show that the spin-down upper limit on the gravitational wave amplitude of more than 90% of all highly magnetised pulsars and magnetars suitable for a years-long fully coherent search, exceeds the smallest gravitational wave amplitude estimated detectable with DECIGO and Big Bang Observer. We find that the hidden magnetar candidate PSR J1852+0040 can be detected by Cosmic Explorer if it is emitting at least at 20% of its spin-down luminosity. Finally, post-glitch transient continuous gravitational waves from magnetars are an interesting target for deci-Hz detectors, with all but one of the recorded glitches giving rise to a spin-down limit signal above the smallest detectable level.

The geometric properties of quantum states are crucial for understanding many physical phenomena in quantum mechanics, condensed matter physics, and optics. The central object describing these properties is the quantum geometric tensor, which unifies the Berry curvature and the quantum metric. In this work, we use the differential-geometric framework of vector bundles to analyze the properties of parameter-dependent quantum states and generalize the quantum geometric tensor to this setting. This construction is based on an arbitrary connection on a Hermitian vector bundle, which defines a notion of quantum state transport in parameter space, and a sub-bundle projector, which constrains the set of accessible quantum states. We show that the sub-bundle geometry is similar to that of submanifolds in Riemannian geometry and is described by a generalization of the Gauss-Codazzi-Mainardi equations. This leads to a novel definition of the quantum geometric tensor, which contains an additional curvature contribution. To illustrate our results, we describe the sub-bundle geometry arising in the semiclassical treatment of Dirac fields propagating in curved spacetime and show how the quantum geometric tensor, with its additional curvature contributions, is obtained in this case. As a concrete example, we consider Dirac fermions confined to a hyperbolic plane and demonstrate how spatial curvature influences the quantum geometry. This work sets the stage for further exploration of quantum systems in curved geometries, with applications in both high-energy physics and condensed matter systems.

The strong gravitational field of a black hole bends light, forming multi-level images, yet extracting precise spacetime information from them remains challenging. In this study, we investigate how gravitational lensing leaves unique and detectable signatures in black hole movies using autocorrelation analysis. By examining the two-dimensional autocorrelation of a movie depicting a hotspot orbiting a Kerr black hole, as viewed by a near-axis observer, we identify a persistent secondary peak structure induced by gravitational lensing. Notably, these secondary peaks converge to a fixed point in the time-lag domain, largely independent of the hotspot's orbital radius. This key property suggests that combining future black hole flare observations with advanced autocorrelation analysis could effectively disentangle lensing effects from orbital dynamics, enabling direct measurement of black hole parameters. Our findings establish autocorrelation as a powerful tool for probing spacetime geometry, offering new insights into gravitational physics through time-resolved black hole images.

It has been shown that if one solves self-consistently the semiclassical Einstein equations in the presence of a quantum scalar field, with a cutoff on the number of modes, spacetime become flatter when the cutoff increases. Here we extend the result to include the effect of fields with spin 0, 1/2, 1 and 2. With minor adjustments, the main result persists. Remarkably, one can have positive curvature even if the cosmological constant in the bare action is negative.

We investigate black hole quasinormal modes using the exact WKB method. We perform an analytic continuation from the horizon to infinity along the positive real axis of the radial coordinate and impose appropriate boundary conditions at these asymptotic positions. We clarify the role of previously overlooked logarithmic spirals of Stokes curves and branch cuts emerging from the horizon. We carefully reformulate the derivation of the quasinormal mode conditions using the exact WKB analysis, incorporating the contributions from these features into the calculation. We successfully derive correct results for both solvable model examples and the Schwarzschild spacetime. Our formulation enjoys straightforward extensions to other background geometries as well as a wide range of other physical systems.