We present an exact analytical investigation of spin precession for a test gyroscope in the magnetized Kerr spacetime—an exact electrovacuum solution to the Einstein-Maxwell equations. Our approach accommodates arbitrary magnetic field strengths, enabling a unified treatment across both weak and ultrastrong field regimes. The analysis reveals distinct spin precession behaviors near rotating collapsed objects, which differ characteristically between black holes and naked singularities, offering a potential observational means to differentiate them. The external magnetic field induces a nontrivial modification of the precession frequency through its interaction with the spacetime’s gravitoelectromagnetic structure. In the weak-field limit, magnetic fields generally reduce the precession rate, though the effect depends sensitively on the motion and orientation of the test gyro close to the collapsed object. As a special case, we show that in the presence of magnetic fields, the spin precession frequency due to gravitomagnetic effect acquires a long-range $1/r$ (where $r$ is the distance from the central object to the test gyro) correction in contrast to the standard $1/r^3$ falloff. In addition, we obtain the exact geodetic precession (gravitoelectric effect) frequency for a gyroscope in magnetized Schwarzschild spacetime, showing that the magnetic field enhances ($\propto r^{1/2}$) geodetic precession in contrast to the standard $1/r^{5/2}$ falloff. Our results provide observationally testable predictions relevant for black holes in strong magnetic environments, including those possibly realized near magnetars or in the early universe. In particular, the strong-field behavior of spin precession could have important implications for transmuted black holes formed via collapse or mergers of magnetized progenitors in both astrophysical and cosmological contexts.

Rotating black holes can amplify ultralight bosonic fields through superradiance, forming macroscopic clouds known as gravitational atoms. When the cloud forms around one of the components of a binary system, it can undergo a series of distinctive interactions, comprising both secular effects, such as dynamical friction or accretion, and resonant behavior. These processes are expected to leave a distinctive signature on the gravitational waveform emitted by the binary, whose detectability we investigate in this paper. To do so, we implement a numerical code that integrates these effects, computed within a Newtonian approximation, for small-to-intermediate mass-ratio binaries on circular equatorial orbits. Realistic waveforms incorporating these environmental influences are generated and analyzed using the Fisher-matrix formalism to evaluate the detectability of bosonic clouds with current and next-generation ground-based gravitational-wave observatories. Our results demonstrate the potential for gravitational-wave astronomy to probe the existence and properties of ultralight bosons.

Einstein-aether theory provides a model to test the validity of local Lorentz invariance in gravitational interactions. The speed of gravitational waves as measured from the binary neutron star event GW170817 sets stringent limits on Einstein-aether theory, but only on a combination of the theory’s free parameters. For this reason, a significant part of the theory’s parameter space remains unconstrained by observations. Motivated by this, we explore the propagation of gravitational waves in Einstein-aether theory over an inhomogeneous background (i.e., gravitational wave lensing) as a potential mechanism to break the degeneracies between the theory’s free parameters, and hence enable new constraints on the theory to be obtained. We reduce our analysis to gravitational waves that pass far from the lens’ center and short wavelength signals, both compared to the lens’ gravitational radius (eikonal limit). By applying these approximations and bringing the field equations into the form of the so-called kinetic matrix and applying a formalism known as the propagation eigenstate framework, we find that the speed of gravitational waves is modified by inhomogeneities in the aether field. However, the modification is common to both gravitational polarizations and vanishes in the limit in which gravitational waves propagate with luminal speed. This lens-dependent gravitational wave speed contrasts with the lens-induced birefringence observed in other theories beyond general relativity, like Horndeski’s theory. While the potential to improve tests based on gravitational-wave speed is limited, our formalism sets the basis to fully describe signal propagation over inhomogeneous spacetimes in Einstein-aether theory and other extensions of general relativity.

We investigate strong gravitational lensing by a marginally unstable photon sphere in a Reissner-Nordström naked singularity spacetime. Using the Picard-Fuchs equation, we derive full-order power series expressions for the deflection angle in various regimes, including the strong deflection limits from both outside and inside the photon sphere. We show that the deflection angle diverges nonlogarithmically in both cases, refining existing asymptotic formulas. Comparing truncated approximations with numerical results, we find that higher-order corrections are essential to achieve comparable accuracy to logarithmic divergence cases. Using these improved formulas, we also derive precise approximations for image positions that are not restricted to the almost perfectly aligned cases.

Gravitational wave data are often contaminated by non-Gaussian noise transients, “glitches,” which can bias the inference of astrophysical signal parameters. Traditional approaches either subtract glitches in a preprocessing step, or a glitch model can be included from an agnostic wavelet basis (e.g., BayesWave). In this work, we introduce a machine-learning-based approach to build a parametrized model of glitches. We train a normalizing flow on known glitches from the Gravity Spy catalog, constructing an informative prior on the glitch model. By incorporating this model into the Bayesian inference analysis with bilby, we estimate glitch and signal parameters simultaneously. We demonstrate the performance of our method through bias reduction, glitch identification, and Bayesian model selection on real glitches. Our results show that this approach effectively removes glitches from the data, significantly improving source parameter estimation and reducing bias.

With ongoing advancements in nuclear theory and experimentation, together with a growing body of neutron star (NS) observations, a wealth of information on the equation of state (EOS) for matter at extreme densities has become accessible. Here, we utilize a hybrid EOS formulation that combines an empirical parametrization centered around the nuclear saturation density with a generic three-segment piecewise polytrope model at higher densities. We incorporate data derived from chiral effective field theory ($\chi \mathrm{EFT}$), perturbative quantum chromodynamics (pQCD), and experiments such as PREX-II and CREX. Furthermore, we examine the influence of a total of 70 NS mass measurements up to April 2023, as well as simultaneous mass and radius measurements derived from the x-ray emission from surface hot spots on NSs. Additionally, we consider constraints on tidal properties inferred from the gravitational waves emitted by coalescing NS binaries. To integrate this extensive and varied array of constraints, we utilize a hierarchical Bayesian statistical framework to simultaneously deduce the EOS and the distribution of NS masses. We find that incorporating data from $\chi \mathrm{EFT}$ significantly tightens the constraints on the EOS of NSs near or below the nuclear saturation density. However, constraints derived from pQCD computations and nuclear experiments such as PREX-II and CREX have minimal impact. Taking into account all available data, we derive estimates for key parameters characterizing the EOS of dense nuclear matter. Specifically, we determine the slope ($L$) and curvature ($K_{\mathrm{sym}}$) of the symmetry energy to be ${54}_{-10}^{+10}$ and $-158_{-63}^{+73}\mathrm{MeV}$ with 90% credibility, respectively. Additionally, we infer the radius and tidal deformability of an NS with a mass of 1.4 solar masses ($M_{\odot }$) to be ${12.34}_{-0.53}^{+0.43}\mathrm{km}$ and ${436}_{-117}^{+109}$, respectively. Furthermore, we estimate the maximum mass of a nonrotating NS to be ${2.22}_{-0.19}^{+0.21}{M}_{\odot }$ with 90% credibility.

In this paper, a simulation environment for a Hartmann wavefront sensor is presented and discussed in the context of a gravitational wave detectors. Thermal effects occur in the optics of the gravitational wave detector and precise measurements is crucial. Hartmann wavefront sensors have been used for this purpose but need to be configured individually. In this work, an optical simulation is implemented to test different Hartmann wavefront sensor configurations. A figure of merit is developed allowing to quantize the wavefront sensor performance. Theoretical evaluations allow to define parameter sets of common measurement range and to fairly compare them across the parameter space. Core parameters are the number of apertures, aperture diameter, and the Hartmann-plate-to-camera distance. The approach is demonstrated based on a thermal deformation estimate with a measurement range represented by a maximum displacement angle of ${\alpha }_{\max }=4\mathrm{mrad}$. A parameter set including sixty-one apertures is derived allowing best resolution of $\mathrm{res}=3\mathrm{pm}$ for ten-fold averaging. This work can be used to find parameters for an optimal Hartmann wavefront sensor for a third-generation gravitational wave detector such as the Einstein Telescope once the thermal deformation due to the coating and the material of the gravitational wave detector test masses is known.

We use a worldline-instanton formalism to study the momentum spectrum of Schwinger pair production in spacetime fields with multiple stationary points. We show that the interference structure changes fundamentally when going from purely time-dependent to space-time-dependent fields. For example, it was known that two time-dependent pulses give interference if they are antiparallel, i.e., $E_z(t)-E_z(t-\mathrm{\Delta }t)$, but here we show that two spacetime pulses will typically give interference if they instead are parallel, i.e., $E_z(t,z)+E_z(t-\mathrm{\Delta }t,z-\mathrm{\Delta }z)$. We take into account the fact that the momenta of the electron, $p_z$, and of the positron, $p_z^{\prime }$, are independent for $E_z(t,z)$ [it would be $p_z+p_z^{\prime }=0$ for $E(t)$], and find a type of fields which give moiré patterns in the $p_z-p_z^{\prime }$ plane. Depending on the separation of the two pulses, we also find an Aharonov-Bohm phase. We also study complex momentum saddle points in order to obtain the integrated probability from the spectrum. Finally, we calculate an asymptotic expansion for the eigenvalues of the Sturm-Liouville equation that corresponds to the saddle-point approximation of the worldline path integral, use that expansion to compute the product of the eigenvalues, and compare this with the result obtained with the Gelfand-Yaglom method.

Gauge-field configurations with nontrivial topology have profound consequences for the physics of Abelian and non-Abelian gauge theories. Over time, arguments have been gathering for the existence of gauge-field configurations with fractional topological charge, called fractons. Ground-state properties of gauge theories can drastically change in presence of fractons in the path integral. However, understanding the origin of such fractons is usually restricted to semiclassical argumentation. Here, we show that fractons persist in strongly correlated many-body systems, using the multiflavor Schwinger model of quantum electrodynamics as a paradigm example. Through detailed numerical tensor-network analysis, we find strong fracton signatures even in highly discretized lattice models, at sizes that are implementable on already existing quantum-simulation devices. Our work sheds light on how the nontrivial topology of gauge theories persists in challenging nonperturbative regimes, and it shows a path forward to probing it in tabletop experiments.

The Belle II experiment has recently reported the first measurement of $B^{+}\to K^{+}\nu \overline{\nu }$ decay which exceeds the Standard Model prediction by approximately $2.7\sigma$. The deviation may indicate the presence of new physics beyond the Standard Model in the $b\to s\nu \overline{\nu }$ sector. Under this assumption, we study the hadronic ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }(\to p\pi )\nu \overline{\nu }$ and ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}^{*}(\to N\overline{K})\nu \overline{\nu }$ decays within both the Standard Model and beyond. We work in a low-energy effective field theory framework with additional light right-handed neutrinos. We calculate the differential branching ratios of these decay modes and explore the implications of the Belle II results through various observables.

Electron-capture decays of ${}^{125}\mathrm{Xe}$ and ${}^{127}\mathrm{Xe}$, and double-electron-capture decays of ${}^{124}\mathrm{Xe}$, are backgrounds in searches for weakly interacting massive particles (WIMPs) conducted by dual-phase xenon time projection chambers such as LUX-ZEPLIN (LZ). These decays produce signals with more light and less charge than equivalent-energy $\beta$ decays and correspondingly overlap more with WIMP signals. We measure three electron-capture charge yields in LZ: the 1.1 keV M-shell, 5.2 keV L-shell, and 33.2 keV K-shell at drift fields of 193 and $96.5\mathrm{V}/\mathrm{cm}$. The LL double-electron-capture decay of ${}^{124}\mathrm{Xe}$ exhibits even more pronounced shifts in charge and light. We provide a first model of double-electron-capture charge yields using the link between ionization density and electron-ion recombination, and identify a need for more accurate calculations. Finally, we discuss the implications of the reduced charge yield of these decays and other interactions creating inner-shell vacancies for future dark matter searches.

The dynamics of superfluid systems exhibit significant similarities to their classical counterparts, particularly in the phenomenon of vortex shedding triggered by a moving obstacle. In such systems, the universal behavior of shedding patterns can be classified using the classical concept of the Reynolds number $\mathrm{Re}=\frac{v\sigma }{\nu }$ (characteristic length scale $\sigma$, velocity $v$, and viscosity $\nu$), which has been shown to generalize to quantum systems at absolute zero temperature. However, it remains unclear whether this universal behavior holds at finite temperatures, where viscosity arises from two distinct sources: thermal excitations and quantum vortex viscosity. Using a holographic model of finite-temperature superfluids, we investigate the vortex shedding patterns and identify two distinct regimes without classical counterparts: a periodic vortex dipole pattern and a vortex dipole train pattern. By calculating the shedding frequency, Reynolds number, and Strouhal number at different temperatures, we find that the relations between these quantities are qualitatively similar to empirical observations that are extracted from both classical and quantum vortex shedding systems, which implies the robustness of vortex shedding dynamics at finite-temperature superfluid systems.

In this paper, we aim to study the quantum transition between a Schwarzschild black hole and a string black hole in the large $D$ limit. Classically, such a transition between these two distinct black hole geometries is forbidden. The only feasible discussion is centered on how a black hole evaporates, loses mass, and transitions into highly excited fundamental strings. Building upon our previous work on T-duality between the Schwarzschild and string black holes, we reduce the problem to two dimensions, where the corresponding Wheeler–de Witt equation can be derived. Using this equation, we identify the two black hole geometries as distinct wave function states. This allows us to easily compute the transition probability between these two geometries, driven by the string coupling.

We introduce a new family of field modes in flat spacetime—termed $\kappa$-plane wave modes—constructed from $\kappa$-dependent linear combinations of Minkowski plane waves. These modes define a one-parameter family of vacua $|0_{\kappa }⟩$ that smoothly interpolate between different quantizations, reducing to the Minkowski vacuum in the limit $\kappa \to 0$. We show that $|0_{\kappa }⟩$ is uniquely characterized as a continuous-mode squeezed vacuum, with frequency-dependent squeezing parameter $r(\nu )$ satisfying $\tanh r(\nu )=e^{-\pi \nu /\kappa }$. We also derive two Bogoliubov transformations between $\kappa$-plane wave and $\kappa$-Rindler operators, which exhibit a universal form and smoothly interpolate between all known mode decompositions, including those of Minkowski, Rindler, and Unruh quantizations as limiting cases.

Conserved currents are discussed for static conformal Killing gravity, with explicit expressions in static spherical symmetry with anisotropic matter fluid or coupled to (non)linear electromagnetism. They are found in the reformulation of the third order equations by Harada as Einstein equations with sources supplemented by a divergence-free anisotropic conformal Killing tensor. A conserved current proposed by Altas and Tekin is also evaluated, and found nonzero for the vacuum solution by Harada.

In this work, we study a vector model of spontaneous spacetime symmetry breaking coupled to gravity: the bumblebee model. The primary focus is on static spherically symmetric solutions. Complementing previous work on black hole solutions, we study the effects on the solutions when the vector field does not lie at the minimum of its potential. We first investigate the flat spacetime limit, which can be viewed as a modified electrostatic model with a nonlinear interaction term. We study the stability of classical solutions generally and in the spherically symmetric case. We also find that certain potentials, based on hypergeometric functions, yield a Hamiltonian bounded from below. With gravity, we solve for the spherically symmetric metric and vector field, for a variety of choices of the potential energy functions, including ones beyond the quadratic potential like the hypergeometric potentials. Special case exact solutions are obtained showing Schwarzschild-anti–de Sitter and Reissner-Nordström spacetimes. We employ horizon and asymptotic analytical expansions along with numerical solutions to explore the general case with the vector field away from the potential minimum. We discover interesting features of these solutions including naked singularities, repulsive gravity, and rapidly varying gravitational field near the source. Finally, we discuss observational constraints on these spacetimes using the resulting orbital behavior.

The memory effect, in the context of gravitational-waves (GWs), manifests itself in the permanent relative displacement of test masses when they encounter the GWs. A number of works have explored the possibility of detecting the memory when the source and detector are separated by large distances. A special type of memory, arising from Bondi–Metzner–Sachs (BMS)-like symmetries, called “black-hole memory,” has been recently proposed. The black hole memory only manifests itself in the vicinity of its event horizon. Therefore, formally observing it requires placing a GW detector at the horizon of the BH, which prima-facie seems unfeasible. In this work, we describe toy models that suggest a possible way the black hole memory may be observed, without requiring a human-made detector near the event horizon. The models consider a binary black hole (BBH), emanating GWs observable at cosmological distances, as a proxy for an idealized detector in the vicinity of a supermassive black hole that is endowed with a supertranslation hair by sending a shock-wave to it. This sudden change affects the geometry near the horizon of the supertranslated black hole and it induces a change in the inspiraling orbital separation (and hence, orbital frequency) of the binary, which in turn imprints itself on the GWs. Using basic GW data analysis tools, we demonstrate that the black hole memory should be observable by a LISA-like space-based detector.

Gravitational perturbations of higher-dimensional black holes in the Einstein-Gauss-Bonnet theory, proposed by Boulware and Deser, have been extensively studied in numerous works, primarily focusing on the fundamental mode. These studies have shown that for sufficiently small black holes, comparing to the Gauss-Bonnet coupling parameter, a dynamical instability arises. In this work, for the first time, we conduct a comprehensive analysis of the behavior of overtones. We demonstrate that while the fundamental mode remains largely unchanged due to the limited stability region, the first few overtones deviate from their Tangherlini limits at an increasing rate. This deviation reflects the impact of the coupling parameter on the near-horizon structure of the black hole.

Wave or fuzzy dark matter produced with high momenta behaves in many ways like hot particle dark matter while also possessing seemingly different phenomenology due to wave interference. We develop wave perturbation theory to show that white noise density fluctuations generated by the interference of high-momenta waves are gravitationally unstable in the usual way during matter domination above the free-streaming scale and stabilize below the free-streaming scale, much like the analogous effects for massive neutrinos in hot dark matter. We verify and illustrate these effects in the density power spectra of Newtonian Schrödinger-Poisson simulations. In the cosmological context, this would cause a gradual suppression of the initial white noise isocurvature perturbations below the free-streaming scale at matter radiation equality, unlike cold dark matter isocurvature fluctuations, and virial stability of dark matter halos.

We propose heavy axions as a natural superheavy dark matter candidate in string theory, with the relic density of dark matter originating in quantum fluctuations during cosmic inflation. String theory is well known for the possibility of having tens to hundreds of axionlike particles—the axiverse. Moduli stabilization generates high-scale masses for many of these, placing them naturally in the “superheavy” regime of particle physics. We consider moduli stabilization in the Kachru-Kallosh-Linde-Trivedi framework, featuring a single volume modulus and $C_4$ axion, and a fiducial inflation model minimally coupled to the volume modulus. We demonstrate that both the volume modulus and the axion can be abundantly produced through gravitational particle production. The former is unstable and readily decays to Standard Model particles while the latter (the axion) can be stable and survives to constitute the present day dark matter.