Papers

In this work, we present the Simpson-Visser black-bounce (SV-BB) spacetime with both electric and magnetic charges (the dyonic SV-BB) as an exact solution of general relativity coupled to Maxwell electrodynamics and an anisotropic fluid with vanishing radial pressure. We assume the anisotropic fluid represents an Einstein cluster, which consists of a dense system of particles moving in circular orbits that generate only tangential pressure and zero radial pressure. We show that the dyonic SV-BB metric, which provides a regular black hole spacetime, can be obtained as an exact solution to the Einstein field equations sourced by a combination of an Einstein cluster (which is responsible for providing the exotic matter required to keep a black-bounce throat open) and an electromagnetic field in the framework of Maxwell electrodynamics.

To study the onset of scalarization, we investigate linear scalar perturbations around Kerr–Newman black holes in the Einstein-Chern-Simons-Maxwell-scalar theory with quadratic Chern–Simons (CS) coupling $\gamma$ ($\hat\gamma=\gamma/M^2$) and Maxwell coupling $\eta$. For this purpose, we employ hyperboloidal Rácz–Tóth evolution and a stationary axisymmetric zero-mode computation. The resulting thresholds are compared with the time-domain response at representative points. For $\hat\gamma=0$, we find two asymmetric threshold branches in $\eta$, while for $\hat\gamma=\eta$, the two branches have opposite signs and unequal magnitudes. For unequal CS and Maxwell couplings, the two real threshold branches merge as the spin or CS coupling increases.

We formulate a nonlocal spin-$1/2$ field theory in curved spacetime in which the form factor is a nonpolynomial entire function of the covariant Dirac operator. We derive the corresponding nonlocal Dirac equation and analyze its coupling to gravity and to a $\rm U(1)$ gauge field. As an application, we study the theory in the open chart of de Sitter spacetime and construct the associated nonlocal Bunch–Davies modes. The nonlocal dynamics can be mapped, branch by branch, onto the local Dirac equation with an effective mass $M_n$. For the exponential form factors considered here, the effective masses are expressed in terms of branches of the Lambert-$W$ function. We show that the Euclidean analyticity structure of the Bunch–Davies construction is preserved. On the physical positive-residue branch, the Bogoliubov coefficients, squeezing parameter, occupation number, and entanglement entropy acquire explicit nonlocal corrections, while the absence of physical fermionic supercurvature modes is preserved. The local theory is smoothly recovered in the limit $\Lambda\to\infty$.

We study scalaron quasinormal modes and quasi-bound states of Schwarzschild black holes directly within the Bondi-Sachs formulation of metric $f(R)$ gravity, combining frequency-domain analyses with characteristic time evolution. Starting from the linearised characteristic equations, we obtain the massive scalar master equation and show that the tensor master equation takes the same form as in general relativity. For the analytic models considered here, the linear scalar spectra depend on the $f(R)$ theory only through the dimensionless combination $\mu M$. We compute both quasinormal and quasi-bound spectral branches using Leaver's continued-fraction method and compare them with independent literature benchmarks. To complement the frequency domain analysis, we evolve the scalaron perturbation equations using a fourth order convergent characteristic scheme. Applying matrix-pencil stability scans to the resulting waveforms, we independently recover fundamental quasinormal frequencies consistent with the continued-fraction results within the measured extraction-stability scales. Finally, for a selected finite-mass case, we demonstrate the extraction of both oscillation frequencies and damping rates of the fundamental quasinormal mode and quasi-bound state from separate time windows of the same waveform at one extraction radius, without imposing either spectral branch at the finite outer boundary.

The mean Hawking flux does not determine how quantum stress fluctuations perturb a black-hole geometry. That information resides in field correlations, including vacuum contributions absent from the outgoing luminosity. Here we connect the complete exterior Unruh Wightman function to a finite-band stochastic reconstruction of Schwarzschild geometry. We retain the incoming vacuum and both outgoing frequency branches, form the connected stress covariance before angular projection, and propagate its monopole through a density-driven radial response. A shared Gaussian reconstruction then resolves how the value and derivative of the lapse control different geometric observables. For the specified covariance and noise amplitude, 2,200 realizations give relative widths of 0.0185 for the local horizon radius and 0.0483 for the surface-gravity temperature parameter, consistently across histograms and reconstruction checks. Covariance derivatives explain this unequal sensitivity. The construction separates the quantum-state input from the gravitational closure and spatial sampling assumptions, providing a reproducible finite-resolution description of how Hawking-field correlations affect horizon positions and surface-gravity statistics.

We present a semi-analytic framework that computes the gravitational-wave background (GWB) from supermassive black hole (SMBH) binaries by direct integration of an $N$-body-recalibrated extended Press-Schechter accretion kernel, bypassing Monte Carlo merger trees entirely. The calculation is resolution-free and fast enough to be sampled directly against pulsar-timing data with no emulator or precomputed model bank. Between halo accretion and black-hole binary formation, we couple the satellite's simulation-calibrated tidal mass loss continuously to Chandrasekhar dynamical friction. Satellites below a sharp, nearly redshift-independent mass-ratio threshold, $\xi \simeq 0.04$, are stripped faster than they sink and stall: their drag collapses onto the stellar core, and 38% of accreted satellites are unmerged by $z=0$. Combining this population model with per-binary stellar-hardening turnovers and eccentric spectra, we sample the five-parameter posterior directly against the NANOGrav 15 yr Hellings-Downs-correlated free spectrum, excluding the $15.8$ nHz bin, whose excess power a subsequent chromatic-noise reanalysis attributes to pulsar noise. The data prefer a black-hole mass normalization $+0.31^{+0.20}_{-0.23}$ dex above the locally calibrated black-hole-bulge mass relation, consistent with earlier indications that the nanohertz background is loud relative to local SMBH calibrations and robust to the delay model, merger kernel, local mass calibration, and its redshift evolution. The spectrum is compatible with, but does not require, eccentric binaries or dense stellar environments.

We establish complete outer-horizon thermodynamics for four exact rotating embeddings of Kerr–Newman and Kaluza–Klein seeds in four-dimensional, asymptotically flat Einstein–Maxwell–Maxwell–dilaton theory without a scalar potential. Constant-coefficient field maps determine the allowed couplings and charge variations. We obtain single-valued mass functions and verify the first law, Smarr relation, and scalar-shift identity on the stated regular branches and finite-area extremal boundaries, including magnetic patch contributions where required. For two distinct regular horizons with positive finite areas, the horizon combinations $2T_\pm S_\pm$ and $S_\pm\Omega_\pm/\pi$ satisfy a common quadratic relation with the long-range-force parameter determined by the asymptotic mass, electromagnetic charges, and scalar charge.

In this work we investigate the behaviour of early inflationary cosmic correlation functions under the flow of the infrared scale for interacting spectator scalar field theories. We start with the derivation of the one-loop effective potentials for $\phi^4$, $\phi^4$-Yukawa and broken phase $O(N)$ model in the inflationary de Sitter spacetime, first using the local Schwinger-DeWitt expansion propagator, and next using the exact de Sitter propagator. The Schwinger-DeWitt expansion being valid in a sub-Hubble length scale, furnishes suitable framework to determine the leading curvature corrections to high energy phenomena having sub-Hubble Compton wavelengths. These effective potentials show spontaneous symmetry breaking pattern, and are next used as ultraviolet boundary conditions in the Wetterich equation generating the desired IR flow. The flow is shown to drive the theory towards symmetry restoration. Using these IR-improved effective potentials, we next compute the stochastic power spectra and spectral indices for the temporally coincident two point correlation function of the spectator scalar. We show that the results corresponding to the aforementioned two kind of propagators are roughly in qualitative agreement with each other, but may differ quantitatively significantly. Both of them show increase in the spectral index in the deep IR for $\phi^4$ and $\phi^4$-Yukawa. The effect of fermionic interaction has been emphasised. Also for the case of the $O(N)$ scalar, we demonstrate that the effective potential's shape becomes more and more insensitive to the flow as $N$ gets large. Implication of this on the correlation function has been discussed.

We investigate the relation between gravitational entropy and holographic entanglement entropy in braneworld gravity with gravitational dynamics localized on the brane. We first consider the DGP brane model, in which an Einstein-Hilbert term is included in the brane action, and derive the condition under which the gravitational entropy of a braneworld black hole agrees with the holographic entanglement entropy. We show that the two entropies coincide when a specific condition involving the extrinsic curvature of the brane is satisfied. In particular, this condition is automatically satisfied for static configurations. We then generalize the brane-localized Einstein-Hilbert term to higher-curvature gravitational theories. For Lovelock gravity and $f(R)$ gravity on the brane, we derive the corresponding conditions for the equality between gravitational entropy and holographic entanglement entropy and show that they take the same form as that obtained for Einstein gravity. Although the equality is not guaranteed for general stationary configurations, the required condition is satisfied for static braneworld black holes, leading to an agreement between the two entropies. These results clarify the relation between gravitational entropy and holographic entanglement entropy in braneworld gravity and contribute to a deeper understanding of holography in braneworld settings.

We investigate gravitational-wave echoes in a horizonless compact object model, a non-perturbative solution of the semi-classical Einstein equation that reproduces the entropy-area law from the bulk structure. By employing a model of anisotropic fluids in classical general relativity (GR), we show that odd-parity gravitational waves are not reflected at the object's surface but are trapped inside due to the exponentially strong redshift, and that the echo-delay time extremely exceeds the age of the Universe. Consequently, the echo signals are effectively unobservable, which is consistent with current null results from echo searches. We finally discuss how this quantum black hole and the conventional classical black hole could be distinguished observationally.

We investigate static and spherically symmetric black holes in Palatini Kalb-Ramond gravity, where a nonzero vacuum expectation value of the Kalb-Ramond field spontaneously breaks local Lorentz symmetry. Treating the metric and the torsion-free affine connection as independent variables, we derive the modified field equations and obtain an exact family of solutions encompassing positive, vanishing, and negative values of the cosmological constant $\Lambda$. Unlike the corresponding purely metric formulation, the Palatini theory consistently allows both Lorentz-violating parameters $\ell_1$ and $\ell_2$ to be nonzero. Using the Iyer-Wald formalism, we determine the conserved mass of the black hole solutions. For the $\Lambda\leq0$ sector, we further verify the first law and the Smarr relation, identifying the conserved mass as the thermodynamic enthalpy. We then confront the $\Lambda=0$ solution with Mercury's perihelion precession, solar light deflection, and the Shapiro time delay. Once the central mass parameter is calibrated by planetary dynamics, these observables constrain the Lorentz-violating parameters only through $q\equiv\ell_2/(1-\ell_1)$. Among these tests, Mercury's perihelion precession yields the most stringent constraint, $-7.4\times10^{-12} \leq q \leq 3.7\times10^{-11}$.

We construct an exact NUT-charged generalization of the Ellis-Bronnikov wormhole in the Einstein-phantom-scalar system. The solution is stationary, asymptotically locally flat at both ends and free of curvature singularities. It inherits characteristic features of the Taub-NUT geometry, including the Dirac-Misner string and closed timelike curves, while the absence of Killing horizons eliminates the horizon-induced infinite winding of geodesics and renders the spacetime geodesically complete. By allowing the phantom field to have a nontrivial scalar potential with an infinite sequence of AdS vacua, we also obtain an exact asymptotically locally AdS wormhole with a NUT charge, which interpolates between different vacua at its two asymptotic ends. Using the covariant phase space formalism, we show that the Hamiltonian charges associated with the two asymptotic regions are finite under appropriate scalar boundary conditions. By performing a double Wick rotation to Euclidean signature, we demonstrate that the conformal class of the resulting metric admits an ambi-Kähler structure.

We calculate quasi-bound states of neutral gauge-singlet scalars and charged scalar doublets and triplets around the asymptotically flat, nonminimal Einstein–Yang–Mills black hole. For neutral monopoles, the principal result is a reversal in the lifetime response to the nonminimal coupling: weakly bound clouds decay more slowly than on the corresponding Reissner–Nordström geometry, whereas increasing the field mass changes suppression into enhancement of absorption. The weak-binding behavior approaches a horizon-area law, but that law alone does not determine the finite-mass ordering. At representative couplings, dipole and quadrupole widths instead decrease substantially while their level energies change very little. Two-sided integration and an independent arbitrary-precision continued fraction check both the real frequencies and the much smaller imaginary parts. We recover the Schwarzschild and Reissner–Nordström limits, test hydrogenic binding and the low-frequency absorption scaling, and distinguish the loss of a potential well from the disappearance of a quasi-bound pole. An exact horizon-domain analysis fixes the black-hole parameter range, and a positive-potential argument excludes exponentially growing modes of the canonical test scalars. The magnetic Wu–Yang connection separates the charged multiplets into quantized monopole sectors, without an electric frequency shift. Their lowest channels exhibit twelve located lifetime crossings within the sampled trapping region and noninteger weak-binding decay powers. At fixed total angular momentum within the triplet, charged states can instead decay hundreds of times faster than neutral states. These comparisons show that neither gauge charge nor nonminimal coupling universally prolongs cloud survival.

We investigate equatorial timelike motion of a massive test particle and the associated gravitational radiation around a Kerr black hole surrounded by perfect fluid dark matter. In the presence of a dark matter fluid, the radius of the innermost stable circular orbit decreases, while the specific angular momentum is modified and the specific energy increases as the dark matter (DM) parameter, $\alpha$, increases. We compute periodic timelike orbits using the rational frequency ratio $q$, with the $(z,w,v)$ classification, which is modified by the presence of DM while preserving the topological class. We analyze the gravitational waveforms corresponding to these periodic orbits and find that dark matter modifies the timing and distribution of the oscillatory features of the orbits. For a representative extreme-mass-ratio system, the corresponding characteristic strain is concentrated mainly in the millihertz (mHz) frequency band relevant to LISA. These results establish a direct connection between the dark-matter-induced modifications of strong-field orbital dynamics and the corresponding gravitational-wave signatures.

Higher-dimension operators in the gravity sector of the Standard-Model Extension generate anisotropic interactions that grow rapidly at short range. Building on earlier striped-balance studies, we develop a finite-volume response and covariance-based optimization for the \(d=6\) and \(d=8\) pure-gravity sectors. We compare three, five, and seven stripes at \(d=8\) and left, centered, and right pattern registrations in both sectors, using horizontal and vertical stripe axes. Volume integration gives azimuth-dependent transfer matrices, while a Gaussian likelihood accounts for coefficient correlations and the unequal uncertainties of constant and sidereal amplitudes. Three stripes give the strongest aggregate \(d=8\) response. Reoptimizing two azimuths for each registration increases the noise-weighted \(D\)-optimal score by up to \(7.3\%\) at \(d=6\) and \(35.6\%\) at \(d=8\). The response matrices permit simultaneous fits of all 14 or 22 real coefficient components. The best marginalized \(1\sigma\) sensitivities reach \(10^{-9}\,\mathrm{m}^{2}\) and \(10^{-15}\,\mathrm{m}^{4}\), about two orders of magnitude beyond earlier inverse-square-law limits for the most favorable components. These results identify centerline registration as an additional route to improved short-range tests of Lorentz symmetry.

Finite-temperature quantum-gravitational corrections to the cosmological constant introduce two additional density parameters, $\Omega_{\Lambda_2}$ and $\Omega_{\Lambda_3}$, the associated terms of which scale as $a^{-4}$ and $a^{-2}$, respectively. In previous work (Papers I and II), these parameters were studied using machine-learning methods that identified a best-fit point. Here we complete the picture with two complementary analyses. First, we perform a Bayesian MCMC analysis using a modified version of class against the Planck 2018 likelihoods. This tells us what the data can constrain once all parameter uncertainties have been marginalized over. Both parameters are consistent with zero, with $\Omega_{\Lambda_3}$ constrained only from one side. Second, we build a CMB pipeline from scratch, following Weinberg's kinetic-theory formulation and validating it against class. This allows us to study the underlying physics. The response analysis carried out with it shows that $\Omega_{\Lambda_3}$ is almost entirely absorbed by a shift in $h$ over the well-measured acoustic multipoles. The part of the signal that cannot be absorbed resides at low $\ell$, where cosmic variance dominates. Meanwhile, the $\Omega_{\Lambda_2}$ signature is nearly degenerate with the overall amplitude of the spectrum. The effects of both parameters on the CMB power spectrum are small, since they represent higher-order thermal corrections to the cosmological constant. The resulting constraints are correspondingly weak: the induced shifts are largely absorbed by degeneracies with $h$ and with the overall normalization of the spectrum. This is the reason why neither parameter is detected.

We investigate inflationary magnetogenesis with massive vector fields, including charged scalar particle production via the Schwinger effect and its backreaction on the background electric energy density. Initially neglecting the Schwinger effect, we quantize the vector field and solve the equations of motion for transverse and longitudinal modes, computing the energy momentum tensor. We then incorporate the backreaction of the electric energy density and show that the longitudinal energy density is subleading compared to the electric background. Since the electric energy density dominates the magnetic contribution, we can treat the former separately from the perturbative contributions. We adopt this approach when studying particle production via the Schwinger effect, assuming that its backreaction acts only on the background electric energy density. The latter is computed using a classical background electromagnetic field minimally coupled to a quantum complex scalar field. The magnetic and longitudinal components are instead described through quantum fields. In this framework, the Schwinger production affects only the electric energy density, as long as it remains dominant compared to the other components. As a consistency check, we verify that for a null coupling constant we recover the same electric energy density as obtained within the fully quantum electromagnetic description. Finally, we show that for non-null coupling constants Schwinger particle production drastically reduces the electric energy density during the final stages of inflation.

We investigate the cosmological dynamics and thermodynamic properties of a viscous variable generalized Chaplygin gas (VVGCG) model in a spatially flat Friedmann–Lema^{\i}tre–Robertson–Walker universe, described by $P=-B/\rho^\alpha$, where $B=B_0V^{n/3}$. The model includes a bulk-viscous pressure $\Pi=-3\xi H$, with $\xi=\xi_0\rho^{1/2}$. We find that the physically viable branch corresponds to $\xi_0<0$, for which the positive viscous pressure dominates at early times, producing decelerated expansion. As the volume increases, the effective pressure changes sign at a finite volume $V_c$, while the transition to acceleration occurs at a larger volume $V_f$. At large volume, the equation-of-state parameter approaches a phantom-like regime for $n<0$. A detailed thermodynamic analysis of the thermal and caloric equations of state, entropy, heat capacity, and isothermal and adiabatic stability shows that the stability conditions and $c_V>0$ are simultaneously satisfied for $n<0$ and $\xi_0<0$. The entropy vanishes as $T\rightarrow0$, consistent with the third law, while the model admits a finite minimum volume and corresponding maximum temperature. Thermodynamic consistency is further verified through the fundamental thermodynamic identity. The framework also contains several existing Chaplygin-gas models as special cases. Constraints from the Hubble-57 data yield $\alpha=0.0024$, $n=-0.0182$, and $\xi_0=-0.0015$, consistent with the thermodynamically stable parameter region. Thus, the VVGCG model provides a consistent description of cosmic evolution from an early decelerating phase to late-time phantom-like acceleration while remaining thermodynamically stable throughout the evolution.

We study how the critical behavior of holographic superconductors controls the interior geometry of charged black holes. Although the exterior condensate vanishes at criticality, the critical zero mode develops logarithmic oscillations near the Reissner–Nordström Cauchy horizon, rendering the interior critical limit nonuniform. We show that the transmitted critical-mode amplitude, together with local Cauchy-horizon quantities, fixes both the leading Einstein–Rosen collapse $\Delta z_{\rm ER}$ width and the phase $\Theta_J$ in the subsequent Josephson regime. If the condensate obeys $t\equiv1-T/T_c\propto\epsilon^{2r}$, then $\Delta z_{\rm ER}\propto t^{1/r}$ and $\Theta_J\propto t^{-1/r}$. This Josephson phase is transferred to the first Kasner epoch, producing oscillatory Kasner exponents and an accumulation law $t_n\sim n^{-r}$ for successive zeros of the scalar velocity. The critical zero mode fixes the leading collapse and phase coefficients, which are quantitatively confirmed by fully nonlinear solutions in both the ordinary and tricritical cases. At low temperature, the interior instead depends on the infrared completion of the zero-temperature geometry. Thus near-critical scaling is governed by critical-mode transmission, whereas the low-temperature behavior is controlled by the infrared endpoint.

By applying the Iyer-Wald formalism to the modified Lagrangian form for the gravitational system, where the coupling constants appearing in the original Lagrangian form, such as the cosmological constant, are promoted to the dynamical scalar fields by introducing the corresponding auxiliary gauge fields, we derive the first law of the extended black hole thermodynamics, where the resulting thermodynamic volumes as the conjugate thermodynamic variables to the coupling constants are nevertheless independent of the auxiliary gauge fields and exactly the same as those obtained before via varying the coupling constants by brute force. In addition, it is further shown that such volumes can also be expressed in terms of the auxiliary gauge fields and evaluated on the black hole horizon, validating the proposal made in the previous literature.

We investigate the effective action of a 7-dimensional topological $BF$ theory under a 4-dimensional reduction. We discuss the topological implications of the resulting theory and analyze the corresponding field equations. In particular, we derive exact solutions to these equations of motion in both Minkowski and Schwarzschild spacetimes.

We study anomaly-induced semiclassical backreaction on an analytic family of discretely self-similar solutions of Einstein–Klein–Gordon theory at large spacetime dimension. Horizon regularity fixes a null-coordinate Floquet exponent and selects a unique regular quantum state. The Polyakov auxiliary field is affine-periodic rather than periodic, with a monodromy that is determined independently by a global zero-mode condition and by the conformal-coordinate scaling. Spherical reduction introduces a quantum coupling that grows toward the center, so the periodic first-order expansion is nonuniform. We construct the resulting nonlinear inner problem and find a critical dilaton surface. Generic crossings of this surface are singular, whereas matching to the regular zero-mass exterior selects a narrow, high-curvature throat. The anomaly also separates the effective null-energy boundaries from the classical matter flux and zero-curvature curves. These results show that the minimally coupled Polyakov model does not yield a generic smooth, exactly self-similar completion of the classical center.

An emergent gravity model was shown to contain an associated emergent breaking of Lorentz invariance and violations of stress-energy conservation. Its simplest flat dust solution accelerates at late times without vacuum energy and has already been used as an analytic benchmark for observational tests. We study the wider homogeneous dynamics and solutions of this theory. For a single non-conserved dust fluid, the variables $\Omega_m=\rho/(3H^2)$ and $u=(HL_2)^{-1}$ form a two-dimensional autonomous system with an exact first integral. The complete expanding solution space separates into three classes: trajectories ending on an asymptotically de Sitter fixed line, a critical trajectory corresponding to the analytic solution of Isichei and Magueijo, and trajectories that turn around and recollapse. We then consider the phenomenologically cleaner model in which only cold dark matter violates energy conservation (while the baryons and photons behave as normal). The phase space becomes three-dimensional, with a line of matter repellers and a line of vacuum fixed points. Each normally attracting vacuum point with $0<u_0<3$ possesses a two-dimensional stable sheet. The limit in which the CDM abundance tends to zero is singular: finite-$u_0$ sheets meet the exactly baryonic plane on trajectories containing a cosmological-constant-like integration constant, whereas the zero-integration-constant baryonic solution remains at $\Omega_b=1$ and runs to $u\to\infty$. The critical endpoint $u_0=3$ separates these late-time behaviours and generalizes the special single-fluid solution.

We study the pseudospectrum of the Kerr black hole for gravitational perturbations with spin weight $s=2$, the case of greatest interest in gravitational-wave astronomy. In the hyperboloidal framework with two-dimensional Chebyshev collocation, we formulate the quasinormal mode problem as a non-self-adjoint eigenvalue problem. For $s\neq0$ the fields $\Psi^{(s)}$ and $\Psi^{(-s)}$ are independent, so the conserved current method yields no single-field energy norm. We overcome this with the Teukolsky–Starobinsky identities, which relate $\Psi^{(-2)}$ to a fourth-order operator on $\Psi^{(2)}$ and yield an $H^2$ energy norm after symmetrization. With the $H^1$ norm known for $s=0$, this suggests the pattern $H^{|s|}$, verified for $s=0$ and $s=2$. All results use an $\omega$-independent two-field hierarchy. We find that the pseudospectrum tightens by $1.1$ to $3.5$ decades at each step of $L^2\to H^1\to H^2$, yet stays large in every norm. The $s=+2$ and $s=-2$ operators are isospectral but not isopseudospectral: at twelve of fourteen probes the $\psi_0$ resolvent exceeds the $\psi_4$ one by $0.19$ to $0.82$ decades in the $H^2$ norm, while at the two probes furthest along the QNM line the ordering reverses by $0.18$ to $0.19$ decades. The gravitational pseudospectrum exceeds the scalar one by $0.5$ to $5.2$ decades in the window minimum and by $5.9$ decades in $L^2$ at $\omega M=0.47-0.17\,i$, while along the damping direction the $s=2$ resolvent is non-monotonic and the $s=0$ resolvent smooth. QNM spectral instability is therefore a universal feature of Kerr, and is stronger for gravitational perturbations.

Striped jets, characterized by magnetically dominated regions with alternating polarity, can enable fast magnetic energy dissipation in global current sheets formed in between the stripes, and are thus considered as a viable source for the high-energy emission observed in blazars and gamma-ray burst prompt emission. We perform the first global axisymmetric GRMHD simulations that follow the evolution of striped jets from their launching, by accretion of poloidal magnetic loops with alternating polarity onto a spinning black-hole, to their energy dissipation at large distances. The accretion of each loop launches a Poynting-flux-dominated mini-jet carrying a helical magnetic field whose polarity is inherited from the loop, and the collection of which forms the jet core. The relativistic core is surrounded by a non-relativistic sheath composed of returning fieldlines from previously launched mini-jets in a nested configuration. Efficient mini-jet launching requires poloidal loops in the accretion disk to form close to the black hole ($r \lesssim 50\,r_g$); otherwise, they lose coherency due to turbulence. Once launched, the mini-jets accelerate electromagnetically, similar to steady-state jets, with the Lorentz factor increasing linearly with the jet cross-sectional radius as long as lateral causal contact with the jet axis is maintained. Current sheets form when two trailing mini-jets carrying oppositely directed magnetic fields come into contact. Early sheet formation is facilitated by the longitudinal expansion of the mini-jets, driven by internal pressure before the flow becomes super-fast-magnetosonic. We measure an energy dissipation rate of a few tens of percent of the jet Poynting power in the observer frame, within our simulation box of $10^4\,r_g$. Our results can account for the bright superluminal features observed in BL Lac type blazars.

Laboratory determinations of the Newtonian gravitational constant $G$ disagree by more than their quoted uncertainties allow. We examine the sixteen determinations comprising the CODATA-2018 archive using a proportional covariance-scale model that retains the full reported covariance matrix. Because the 2026 NIST torsion-balance redetermination shares apparatus lineage with the BIPM Mark II balance, our primary historical fit excludes the BIPM-14 determination, giving $\hat{\lambda} = 2.967$ for the remaining fifteen measurements. Evaluated against this historical model under the declared uniform covariance-scaling convention, the correlated four-configuration NIST result is highly unlikely under the archive's reported, unscaled covariance but is statistically unremarkable once the historically inferred extra dispersion is applied ($Q_\lambda = 4.840$; finite-sample $F$ tail $p = 0.382$); a mean-only scaling sensitivity leaves the vector discrepant. Retaining the complete archive also gives a comparable result. We further examine four matched free-minus-servo torque differences reported by NIST. They are consistent with a single common absolute torque offset across the four tested configurations, $\widehat{\Delta N} = 1.918 \pm 0.215$ pN m, and poorly described by an equally simple fractional-scale alternative under the stated independent-Type-A treatment, with a chi-square contrast of $\Delta\chi^{2} = 11.041$ between the two torque models. The paper provides a covariance audit of the historical archive, a lineage-qualified consistency check, and an experimentally testable diagnostic for dual-mode torsion balances, without proposing a revised value of $G$.

We present the first calculation showing that a material-asymmetric Sagnac speed meter can improve quantum-noise-limited sensitivity to $B-L$ vector dark matter by nearly two orders of magnitude over a Fabry–Perot Michelson position meter at the low-mass end of the band. We introduce material contrast into a dual-ring interferometer to probe composition-dependent $B-L$ forces and compare the two configurations at equal incident power, input-mirror transmissivity, and cavity round-trip length. For sapphire mirrors and a one-week benchmark, the quantum-noise-only median expected $95\%$ CL upper limit reaches $1.2\times10^{-27}$ at $m_A=4.1\times10^{-14}\,\mathrm{eV}/c^2$ ($10\,\mathrm{Hz}$), a factor-$57$ improvement. This band-edge forecast assumes negligible classical noise; sensitivity at $10\,\mathrm{Hz}$ is not established for a realizable suspension and isolation system. The material-induced displacement is essentially identical in both configurations, with the gain arising from reduced low-frequency quantum backaction. These results identify speed-meter readout as a promising route to lower-mass vector-dark-matter searches.

Black-hole (BH) quasinormal modes encode the properties of merger remnants and provide powerful tests of strong-field gravity. The BH spectroscopy has predominantly treated them as independent linear oscillations. Nonlinear ringdown can additionally reveal how these modes interact and which intermediate states mediate their interactions. Inspired by cosmological collider physics, we introduce quasinormal-mode collider spectroscopy (QCS), a framework for organizing and predicting nonlinear BH responses. We establish two structural results. First, at an isolated, nondegenerate intermediate pole, a cubic strain residue factorizes into an excitation amplitude and a quadratic conversion coefficient. This factorization imposes rank constraints across output channels and choices of second-order initial data, providing consistency tests of the intermediate-mode description. Second, the intermediate pole residue can be reconstructed from its horizon and infinity radiation. With the first-order field and third-order data held fixed, this reconstruction extends to the full cubic waveform difference generated by changing the second-order initial data. QCS thus connects lower-order radiation to higher-order observables and provides a framework for probing the interaction structure of nonlinear ringdown.

We construct a minisuperspace quantization of a dynamic, spherically symmetric thin-shell wormhole in the spirit of pilot-wave quantum cosmology, treating the throat radius $a(\tau)$ as the single degree of freedom of the Israel junction-condition constraint. For a pressureless shell of mass $M$ the Wheeler–DeWitt equation reduces exactly to Whittaker's equation, and to the modified Bessel equation as $M\to0$. When the exterior is asymptotically flat, boundedness of the wave function as $a\to\infty$ selects a unique state that can always be chosen real. Since any real solution has a vanishing Bohmian current, the throat is frozen for any linear equation of state and any operator ordering, independently of the choice between Euclidean and Lorentzian boundary conditions. This state is the exact $\epsilon\to0^+$ limit of the regularized Lorentzian path integral, as shown by resolvent analyticity and by an exact Picard–Lefschetz thimble calculation that agrees with the closed-form solution to $48$ digits. The near-throat self-adjointness ambiguity is resolved in closed form through the Whittaker connection formula. Replacing the exterior by Schwarzschild–de~Sitter removes the obstruction: the potential tends to $-\infty$ at large $a$, and the equation admits a genuinely dynamic, purely outgoing state. Propagated exactly through the classically forbidden barrier, it carries a conserved, nonzero Bohmian current everywhere, including the inner pocket. It describes a long-lived metastable wormhole that tunnels into unbounded expansion at a rate consistent with the WKB estimate. Airy connection formulas leave a residual prefactor constant $\kappa_\infty=0.814\pm0.004$ for sub-critical coupling, which we do not trace to its analytic origin, and the physical results do not depend on it.

Null homogeneous Petrov spaces $V^*_4(N)$ are considered. The geometry of $V^*_4(N)$ is determined by the geometry of the three-dimensional homogeneous Riemannian space $V_3(N)$, which is invariant under the action of the three-parameter motions group $G_3(N)$ ($N$ corresponds to the group number in the Bianchi classification). The canonical frame of the space $V_3(N)$ is used to construct the metric tensor of the space $V^*_4(N)$ and the components of the vector potential of the invariant electromagnetic field. Using this reper, we obtain Maxwell vacuum equations containing only the structure constants of the groups, the non-holonomic components of the contravariant metric tensor and vector potential, and their derivatives with respect to the wave variable. All non-equivalent exact solutions of Maxwell vacuum equations are found for the case of solvable motions groups $G_3(I)-G_3(VII)$. All solutions of Maxwell vacuum equations obtained in this article are written explicitly in terms of arbitrary independent functions of wave variable. Therefore, when integrating the Einstein-Maxwell equations, it has to consider only the remaining systems of Einstein equations which reduce to systems of ordinary differential equations that include only these independent functions.