Papers

It has been shown recently that chiral dynamical multiferroicity can be generated on a ferroelectric lattice whose electric dipoles respond masslessly under chiral optical pumping. Here we demonstrate that, when driven by ultrafast electric pulses, chiral dynamical multiferroicity can also emerge even in situations where the external field is achiral. We reveal this striking phenomenon using a prototypical system of a BaTiO$_3$ moiré ferroelectric lattice, emphasizing the key factor that its chiral electric dipoles inevitably behave massively upon ultrafast driving. At a deeper level, the massive nature is attributed to the anisotropic and nonadiabatic dipolar responses, as captured by the phase difference between the faster longitudinal and slower transverse components of the ferroelectric polarization. Crucially, such a phase difference naturally also gives rise to dynamical magnetization, which exhibits chiral magnetic textures with monopole-like topology coexisting with the ferroelectric chirality. These findings establish the dipolar mass as an enabling and tunable degree of freedom in inducing chiral dynamical multiferroicity, offering new avenues for ultrafast, non-contact magnetic control using pure electric probes.

A topological pump transports a conserved quantity. Yet temporal modulation exchanges energy with the field, so the transported quantity must be identified from Maxwell's equations. Here we connect band topology to the temporal displacement of conserved Maxwell wave action in a photonic time crystal. The temporal Wannier function of an isolated positive-action band carries unit action with zero net energy flux, and its temporal center is a Berry polarization. Over one adiabatic cycle, that center shifts by the band Chern number: one cell for a rigid translation and two for a two-tone cycle within a single band.

The efficient operation of accelerator facilities increas- ingly relies on rapid access to heterogeneous operational knowledge, including logbooks, interlock reports, machine parameters, and historical archive data. At ELBE, we pro- posed a Retrieval-Augmented Generation (RAG) frame- work that integrates facility documentation and operational records into a unified AI-assisted support tool for operators. The system is expected to index electronic logbooks, ma- chine archive time-series data, and subsystem manuals using domain-adapted embeddings stored in a vector database. User queries will be expected to be processed through a large language model that retrieves the most relevant oper- ational context and generates structured, operator-oriented responses with traceable source references. This contribu- tion presents the system architecture, data integration strat- egy, and challenges toward real-time AI-assisted accelerator operation

Bi4Ti3O12-based ceramics are promising candidates for high-temperature piezoelectric devices owing to their high Curie temperature (> 600 {\deg}C). However, their low piezoelectric constants and poor mechanical reliability hinder their use in some engineering applications. Here, we fabricate nacre-like <00l>-textured (f_00l > 94%) Bi3.96Ce0.04Ti2.965W0.0175Nb0.0175O12 (NL-BCWNT) ceramics via a scalable magnetic-assisted slip casting (MASC) self-assembly process. In addition to crystallographic texture, the final material presents a brick-and-mortar microstructure with micro-sized grains with a median aspect ratio of 15. NL-BCWNT exhibits a high fracture toughness for piezoceramics, with both $K_{IC}$ and $K_J$ reaching 2.2 $\pm$ 0.4 $MPa \cdot m^{0.5}$ and 4.2 $\pm$ 0.4 $MPa \cdot m^{0.5}$, respectively. The toughening originates from deflection and stable crack propagation within the nacre-like structure. The $d_{33}$ is 30 $\pm$ 3 $pC/N$ with a Curie temperature of 661${\deg}C$, and $d_{33}^*$ reaches 46 $\pm$ 3 $pm/V$ at 160 ${\deg} C$ with less remanent strain than random BCWNT. The improvements are attributed to aligned domain along spontaneous polarization direction <h00> with better mobility. NL-BCWNT exhibited excellent ferroelectricity fatigue resistance with higher than 106 cycles without degradation. Furthermore, similar improvements are observed in pure BiT, suggesting the general applicability of this strategy to other BiT-based systems. The nacre-like architecture thus provides a promising addition to the design toolbox for high-performance electromechanical materials.

In the ultrastrong light-matter coupling regime, the ability to confine the electric field to subwavelength scales and define an electromagnetic mode is essential. This task is typically achieved through dedicated cavities, such as THz metal resonators. Here, we instead introduce ultrastrong coupling directly between distinct magnetoplasmon excitations, leveraging solely the spatial symmetry of a confined electronic medium in the presence of a magnetic field. By patterning an AlGaN/GaN single quantum well hosting a two-dimensional electron gas into micrometer-scale patches, we tailor the mutual interactions between topologically protected edge and bulk magnetoplasmons, achieving coupling strengths of up to 0.1. The progressive breaking of rotational symmetry determines the coupling rules and leads to the emergence of energy gaps and unique chiral-mode hybridization. Our results highlight a path towards exploiting the symmetry class and topology of the magnetoplasmon wavefunction as a new parameter space for ultrastrong light-matter interaction without a dedicated cavity.

Consider the space of $C^\infty$-functions on the two-dimensional sphere $S^2$ and its decomposition $\oplus\mathcal H_n$ into a direct sum of minimal rotation-invariant spaces. We consider elements of $\oplus\mathcal H_n$ as functions of two variables, a nonnegative integer variable $n$ and a complex variable $u$ (a restriction of such function to the set $n=k$ is a polynomial in $u$ of degree $\le 2k$). For operators of multiplication by $x_1$, $x_2$, $x_3$ in $C^\infty(S^2)$ we obtain the corresponding operators in $\oplus\mathcal H_n$, they are differential-difference operators in the variables $u$, $n$ (including second derivatives in $u$ and shifts $n\mapsto n\pm1$). We obtain the similar correspondence for operators of differentiation along conformal vector fields on $S^2$.

The Jupiter Icy Moons Explorer (Juice) embarked in 2023 on a 8-year interplanetary journey to Jupiter and its icy moons. The Submillimetre Wave Instrument (SWI) is one of the ten science instruments aboard the spacecraft. SWI is a sophisticated and first-of-its-kind payload visiting the outer solar system, featuring dual-band tunable receivers, two independent pointing mechanisms, and spectrometers capable of high resolution (up to a resolving power of 10^{7}). It is designed to support the diverse science objectives of the Juice mission targeting Jupiter's middle atmosphere, icy-moon's exospheres as well as near sub-surface thermophysical properties. For this purpose the Juice mission adopts a complex trajectory tour within the Jovian system, which further necessitates a sophisticated, mission-driven operations concept for SWI. This presents significant planning, operations and commanding challenges which are described in this paper in the context of the Lunar and Earth Gravity Assist (LEGA). After the development and ground calibration of the instrument, the SWI Team has designed a comprehensive calibration strategy applicable during the Cruise Phase of Juice. Among the various opportunities for calibration, including the Near-Earth Commissioning Phase and more than ten Payload Checkout Windows, the LEGA offers the means not only to improve the calibration of the instrument, but also to validate the operational strategy of future icy moon flybys.

We use direct numerical simulations to study the turbulent transonic flow over a supercritical airfoil, spanning the transition from stable conditions to fully developed buffet at chord-based Reynolds numbers of $3\times10^5$ and $6\times10^5$. The Reynolds number determines the incoming boundary-layer state, thereby affecting the separation behaviour. Spectral proper orthogonal decomposition reveals a single dominant mode that emerges below onset and persists across the transition to buffet. The energy of this mode increases with the angle of attack while its spatial structure and fundamental frequency remain nearly unchanged, consistent with a global instability that saturates into a nonlinear limit cycle. Geometrical acoustics provides a first-order description of the global mode propagation and identifies two paths connecting the acoustic source, located in the near wake, to the shock. A shorter path impinges on the shock from behind, while a longer one circumvents the shock tip before reaching it from the front. Linearised shock–acoustic interaction theory predicts a stronger shock response to low-frequency, front-impinging acoustic disturbances. Space–time correlations link the establishment of a downstream path to complete boundary-layer separation, which is induced intermittently by the upstream motion of the shock. The sum of the upstream acoustic time along the front-impinging path and the downstream convective time is compatible with the measured buffet period at both Reynolds numbers. Together, these results are consistent with a unified picture of buffet, where an aeroacoustic feedback mechanism provides the physical pathways through which perturbations can sustain the global dynamics.

Short-range correlations (SRCs) dominate the nuclear force at short distances, including the repulsive core and intermediate-range attraction, and are one of the most fascinating aspects of the nucleon-nucleon (NN) interaction. In this work, we investigate the effects of SRCs on the final-state observables in $^{16}$O+$^{16}$O collisions at $\sqrt{s_{NN}}=5.36$~TeV, using the iEBE-VISHNU hybrid model with {T\raisebox{-0.5ex}{R}ENTo} initial conditions. We embed the nucleon configurations of $^{16}$O generated from variational Monte Carlo (VMC) simulations with realistic SRCs in the initial stage, along with uncorrelated VMC samples and Woods–Saxon distributions implementing a hard repulsive core or short-range attraction as comparison runs. We find that SRCs reduce both $v_2\{2\}$ and $v_2\{4\}$ in the most central collisions, with the decrease of $v_2\{4\}$ being more pronounced due to the event-by-event flow fluctuations. Meanwhile, SRCs noticeably enhance the correlation between the elliptic flow and the mean transverse momentum, $\rho_2(v_2^2,[p_T])$. These effects are mainly attributed to the strong repulsive core of the SRCs, which suppresses the probability of finding nucleon pairs at short relative distances and renders the initial geometry more uniform. This interpretation is supported by the calculations based on Woods–Saxon distributions with a hard repulsive core, which reproduce similar results, while the contribution from a pure intermediate-range attraction is negligible. Our results demonstrate that relativistic nuclear collisions provide a complementary probe of the short-range structure of the nuclear force, beyond the traditional nuclear experiments at low energies.

Highly entangled and highly non-stabilizer quantum states need not be hard to learn. We give efficient algorithms for testing and recovering hidden tensor-product structure in unknown pure state vectors of the form $\lvert\psi\rangle = U_C \bigotimes_i \lvert\psi_i\rangle$, where $U_C$ is an arbitrary unknown Clifford unitary. Although the Clifford can thoroughly scramble the visible product structure, we prove that the Bell distribution retains a characteristic family of quadratic symmetries. By simultaneously block-diagonalising these symmetries, our algorithms linearize the problem and manage to recover both a disentangling Clifford and the hidden partitions with polynomial sample and computational complexity. This may be viewed as an extension of the abelian StateHSP paradigm in which classical post-processing exposes genuinely quadratic structure. Applied to Choi states, the method yields efficient proper learning algorithms for typical $t$-doped Clifford unitaries in regimes containing exponentially more $T$ gates than previously accessible: the required condition fails only for an exponentially small fraction of circuits when $t\sim n$, and continues to hold for a constant fraction even when $t=2n$. Our framework also provides tools for compressing structured many-body Hamiltonians and suggests benchmarking protocols for encoded logical product states in the early fault-tolerant regime.

Cryovolcanism is a fundamental geodynamical process that has been observed on several icy moons. Europa stands out as a primary target for investigating potential cryovolcanic activity and its role in shaping icy moon surfaces. This work characterizes the physical state of ascending cryomagma and evaluates the relevance of terrestrial analogues to explain Europa's surface features. After investigating cryomagma depressurization, we developed CryoPy, a numerical model based on Smoothed-Particle Hydrodynamics (SPH) for computational fluid dynamics and heat transfer. We simulated flow propagation and surface cooling using this model. Our simulations show that snow is a relevant physical analogue for cryolava, as the resulting flows closely match the smooth plains observed by Galileo in both extent and morphology. Additionally, we established the temporal thermal signatures of these events. Such active cryovolcanic events are within the detection limits of, primarily, the E-THEMIS infrared imager, providing a predictive framework for the Europa Clipper mission.

This reply addresses a recent comment concerning the proof of the Nernst theorem. I clarify how a Carnot engine can consistently operate at $T=0$ through a continuous deformation of a cycle operating at $T>0$. By examining the limit where heat exchange with the cold reservoir vanishes, I show that the Nernst theorem ensures that the concept of temperature remains physically consistent at the absolute zero limit.

We investigate stellar oscillations driven by the time-dependent gravitational potential of ultralight dark matter (ULDM) in the de Broglie regime. The response is controlled by the ratio of the ULDM coherence time to the stellar mode damping time. When the field decoheres faster than the damping time, ULDM acts as a stochastic source that excites modes below a characteristic de Broglie frequency, while higher-frequency modes are suppressed. In the opposite, long-coherence regime, individual modes can be resonantly driven. Focusing on solar oscillations, we find a signal far below current sensitivity, and estimate that other stars are similarly unlikely to provide observable signals.

The thermal continuum of Cygnus X-1 in the soft state is often modelled with a multicolour disc in a Newtonian spacetime approximation. That choice is convenient for estimating the inner radius, but it neglects relativistic effects near the black hole; these are usually restored through colour-correction and boundary-condition factors. Using Suzaku data from one exemplary observation, we compare this Newtonian description with some fully relativistic disc models, keeping the same treatment of absorption, ionised winds, Comptonization and reflection. With the mass, distance and inclination fixed to the best current dynamical values, the Newtonian inner radius is consistent with a high-spin Kerr innermost stable circular orbit. The relativistic models do not provide a uniformly better description of the spectrum: some worsen the fit or leave spin, inclination and hardening unconstrained, while the formally best model requires an inclination much larger than the dynamical one or a smaller spin. Apparent tensions with the models arise from data degeneracies and from the limited energy band, not from a failure of general relativity.

Wavelength-division multiplexing (WDM) is pivotal for expanding the capacity and functionality of photonic systems, from communications to computing. However, on-chip implementation for broadband operation is fundamentally limited by the narrow free spectral range (FSR) and inefficient drop transmission of conventional optical microcavities. Here, we transcend this limit with a scalable integrated WDM processing platform based on cascaded dual-sided coupled Fabry-Pérot add-drop resonators. This unit achieves a record-large FSR-free bandwidth (> 300 nm) and low insertion loss (< 0.5 dB), while enabling independent manipulation of monochromatic light in both the wavelength and intensity domains. Leveraging these performances, we architect programmable cores with up to 20 channels in a single bus waveguide to demonstrate application versatility by configuring as: a high-capacity on-chip WDM communication fabric (2.4-Tbps single-link WDM transmission and O-to-C-band multi-subband (de)triplexing), a reconfigurable optical processor (broadband and hitless wavelength-selective switching), and a parallel computing accelerator (theoretically capable of 1.28-TOPS convolution operations, 16-channel modulation). This work establishes a unified and versatile WDM processing platform that bridges high-speed optical communication with in-line computing, charting a scalable and backward-compatible path toward petabit-per-second-class links and hundreds of TOPS of on-chip computation, resolving a critical bottleneck for next-generation photonic systems.

I summarise the expanding class of white dwarf pulsars for which the prototype, AR Scorpii, was only discovered in 2016. At the time of this meeting, two further systems had been found (eRASSU J191213.9-441044 and SDSS J230641.47+244055.8). These are thought to be detached (or nearly detached) white-dwarf–red-dwarf binaries, where the white dwarf's magnetic field interacts with the M-star's corona, resulting in the capture and acceleration of electrons to relativistic velocities in the magnetosphere. This gives rise to non-thermal synchrotron emission across the electromagnetic spectrum. The first discovered, and brightest, system, AR Sco (which is the focus of this paper), shows a white dwarf spin-down consistent with magnetic dipole emission in a strongly magnetic white dwarf. The polarisation properties of the two systems for which polarimetry has been obtained (AR Sco and eRASSU J191213.9-441044) show spin-modulated polarisation, primarily linear, which remarkably reaches 40% in AR Sco. Furthermore, the Stokes Q and U parameters vary in the same manner as the optical polarisation of the Crab pulsar, consistent with a rotating magnetic dipole. These systems are intriguing in that each one seems to show different behaviours (e.g. pulse profiles and light-curve properties), presumably mainly due to different viewing aspect angles. It has recently been postulated that these systems represent a short-lived phase of binary evolution linking asynchronously rotating intermediate polars and synchronous polars.

Earth matter effects are a leading systematic in long-baseline (LBL) determinations of the CP-violating phase delta13, and eV scale sterile neutrinos remain a phenomenologically open extension of the three-flavor paradigm motivated by short-baseline anomalies. We extend the constant density versus realistic Earth profile analysis of Ref. 1 to a four-flavor (3+1) framework, in which a fourth, mostly sterile mass eigenstate with deltam2 41 = 0.30 eV2 and active-sterile mixing angles theta14 = 8.13degree, theta24 = 5.40degree couples to the active sector both through its mixing and through an additional neutral current (NC) matter potential that acts on the active flavors but not on the sterile state. We derive an analytical, leading-order account of how the NC potential ANC enters the reconstructed delta13 bias through an effective non standard interaction like term generated by adiabatically integrating out the fast deltam241 oscillation; replace the four-shell Earth density model with the continuous, polynomial PREM profile of Dziewonski & Anderson (1981) for the layered true trajectory; and extend the baseline scan to four representative values of the sterile CP phase delta14 is 0, pi/2, pi, 3pi/2 and to a non-zero mixing angle theta34 = 5degree. Within this benchmark, the bias remains below our scan resolution for L <= 5000 km. It grows once the trajectory samples the lower mantle and core, with the sterile sector redistributing rather than uniformly amplifying or suppressing the bias across baseline, in agreement with our original finding and now traced to a specific interference mechanism identified analytically below.

Dynamical black hole scalarization describes the process by which a “no-hair" black hole transitions to a scalarized hairy state. This transition significantly alters the spacetime geometry, including the structure of stable circular orbits of the test particles, which are critical for astrophysical observations and tests of gravity. In this work, we employ numerical relativity simulations to model the time-dependent evolution of a vacuum black hole undergoing scalarization. By evolving timelike geodesic equations within the dynamically changing spacetime background, we investigate how the scalarization process impacts initially stable circular orbits. Our results reveal that the growth of the scalar hair destroys the circular nature of these orbits, forcing them to either become eccentric or plunge into the black hole. This orbital destabilization arises from the rapid change of spacetime curvature induced by the scalar field. Our findings provide novel insights into the interplay between scalar fields and black hole dynamics, with significant implications for gravitational-wave signatures, accretion disk stability, and observational tests of extended theories of gravity.

Universal information extracted from a critical quantum state depends on how the state is probed. Spatial entanglement, participation statistics, and stabilizer Rényi entropy correspond to different replica geometries and need not isolate the same boundary data. We show that the complete distribution of Pauli magnitudes in critical Ising chains carries an exact geometric fingerprint of boundary termination, distinguishing lattice realizations that flow to the same infrared boundary fixed point. This structure is organized by discrete Selberg ensembles associated with the classical root systems $A$, $B$, $C$, and $D$: three open chains sharing the free–free Ising boundary condition retain distinct $B_L$, $C_L$, and $D_L$ trigonometric wall geometries. The standard symmetry-breaking representatives instead produce rectangular, pinned, and character-inserted $C$ ensembles. Their four boundary moments contain exactly two independent multiplicative combinations invariant under local endpoint normalizations. One of these reduces exactly at finite rank to a moment of the fundamental symplectic character and provides a lattice target for a defect–measurement-boundary junction amplitude. A conditional Gaussian-character law predicts its values throughout the unlocked phase, while exact-arithmetic finite-rank results at the $\alpha=4$ transition depart sharply from the Gaussian continuation. These results show that the full Pauli spectrum resolves boundary information invisible to the infrared boundary fixed point alone and provide concrete targets for replicated boundary conformal field theory.

The fate of average symmetry-protected topological (ASPT) states based on the one-dimensional cluster state is investigated by using the Choi mapping, namely, the doubled Hilbert-space formalism. By introducing two effective spins, $\tau$ and $\eta$, on each doubled rung, we obtain a transparent representation of the ASPT parent Hamiltonian and systematically identify the conserved stabilizers and the corresponding orders. We further study symmetry-preserving operations that deform the ASPT by combining qualitative effective-Hamiltonian and systematic parent-Hamiltonian analyses with numerical matrix-product-state filtering calculations. We find that although the ASPT remains robust over a broad range of decoherence strengths, strong-to-weak spontaneous symmetry breaking (SWSSB) becomes exact in the maximal-decoherence limit. In addition, we consider symmetry preserving no-click postselection, which removes the exact conservation law supporting the Rényi-2 string order of the ASPT and drives the system toward weak-symmetry spontaneous symmetry breaking (WSSB). Again, the ASPT remains robust over a broad range of postselection strengths, with WSSB becoming pronounced only near the projective limit and exact at the limit itself.

We investigate quark stars (QSs) described by three quark matter (QM)equations of state (EoSs) and analyse their radial and quasiradial oscillation modes within the slowly rotating relativistic approximation. The considered EoSs describe massless quarks, massive quarks, and massive quarks with a temperature-dependent gluon mass. Our analysis of radial modes shows that the mode separation depends on the stellar mass and radius for a given compactness, as well as on the stellar temperature. The considered QS models satisfy the slowly rotating relativistic condition of Hartle, Thorne and Chitre formalism, allowing rotation to be treated as a small perturbation of the non-rotating configuration. We find that, although more massive and larger stars can exhibit greater surface eccentricity and quadrupole deformation, their stronger self-gravity results in a lower tendency to deform than less massive and smaller stars. For all models, the variation in mass distribution increases towards the stellar surface, while the variations in pressure, energy density, and number density remain small near the center and become more pronounced towards the surface. More compact stars exhibit stronger twisting of the local inertial frame but weaker frame dragging for a given angular velocity. Rotation shifts the oscillation modes from their non-rotating values and leads to different vibrational decay times at different angular velocities. The fundamental modes considered here exhibit frequencies below $2$ kHz and show non-continuous behaviour across the investigated rotational configurations.

Symmetry-protected bound states in the continuum (SP-BICs) offer exceptional optical confinement but remain nonradiative. Here, we demonstrate that magnetically lifting their protecting symmetry enables nonreciprocal beam steering with intrinsic angular information encoding. In a magneto-optical photonic crystal slab, an in-plane magnetic field converts an SP-BIC into a radiative quasi-BIC and, together with vertical dielectric asymmetry, continuously displaces the associated band extremum away from the Gamma point. The steered beam exhibits two independent locking relations: its wavelength is locked to the elevation angle, while its polarization orientation is locked to the azimuthal angle. These relations embed complementary spectral and polarization information into the scanning beam, providing additional sensing channels for multidimensional LiDAR. Moreover, the nonreciprocal dispersion gives different resonance frequencies at opposite wave vectors, supporting resonant emission at +k while back-reflected light at the same frequency is off resonance at -k, opening a route to intrinsic self-isolation and reduced optical feedback. These findings establish a unified framework connecting magnetic beam steering, angular information encoding, and nonreciprocal feedback suppression, with prospects for compact reconfigurable light sources and integrated optical engines.

kicad-pycbnew is an open-source Python library for the automated, script-based generation of KiCad PCB designs, tailored to the precise geometric and impedance constraints of particle detector readout electronics. By enabling the programmatic definition of copper traces, zones, vias, and footprints — without a graphical interface — it addresses the challenges of designing large-scale, repetitive, or parameterized layouts (e.g., Resistive Plate Chamber (RPC) strips or controlled-impedance signal paths). Key features include constraint-driven routing, parallel track arrays with rounded corners, via grids with exclusion zones, and full compatibility with KiCad's native file format. Standalone operation (no KiCad runtime required) facilitates integration into CI/CD pipelines and ensures reproducibility. The library, released under the MIT License, includes validated examples such as trapezoidal RPC readout boards and extension boards for the COMET experiment, alongside comprehensive tests and documentation.

Coronal mass ejections (CMEs) are driven by the eruption of magnetic flux ropes (MFRs) whose footpoints are often observed indirectly as coronal dimming regions. However, the relationship between observed dimmings and true MFR footpoint locations remains uncertain due to limitations in both detection methods and coronal magnetic field modelling caused by the complexity of eruptive events. We aim to investigate the M4 flare and CME event on 28 March 2022 in AR 12975 to determine how well observed coronal dimmings trace the footpoints of an erupting MFR. We also assess how these signatures compare with the MFR evolution from a data-driven magnetofrictional simulation. We combined multiwavelength SDO/AIA observations with a time-dependent data-driven magnetofrictional simulation of the AR. We identified coronal dimmings using intensity-thresholding and minimum-intensity maps. For challenging regions we used a tailored region growth algorithm from strong gradients. We extracted MFR structures in the simulation using a combined twist and squashing factor metric. We compared the location of the footpoints and derived magnetic fluxes from both dimmings and the modelled MFR. The simulation reproduces the formation, evolution, and eruption of the observed MFR whose footpoints migrate during the eruption. The footpoints match well with the dimming location. The southern dimming shows characteristics of a moving flux rope dimming, while the northern dimming behaves as a shrinking flux rope dimming that is rapidly closed by the flare ribbons. Quantitative comparisons of area and magnetic flux show good overall agreement between simulated footpoints and observed dimmings, with discrepancies mainly arising from detection limitations and event complexity. The dimmings at the northern footpoint region is particularly challenging in observations due to pre-existing low intensities and its fast shrinkage.

Existing general-relativistic magnetohydrodynamics (GRMHD) codes offer complementary capabilities, but these capabilities remain distributed across different frameworks. To unify them, we introduce PANGU–Parthenon-Based Astrophysics for Numerical Relativity and GRMHD in a Unified Framework–a modular computational framework that integrates a shared solver across physical regimes, flexible spacetime geometry, and extensible computational infrastructure within a single architecture. In the first paper of this series, we present and validate the fixed-spacetime GRMHD component of PANGU. The shared solver combines finite-volume Godunov methods with constrained transport on uniform and block-structured, statically refined meshes, and covers hydrodynamics and magnetohydrodynamics in Newtonian, special-relativistic, and general-relativistic regimes. PANGU provides a flexible geometry interface supporting coordinate selection and either on-the-fly or precomputed evaluation of prescribed stationary spacetimes, demonstrated here in Kerr spacetime with Cartesian Kerr-Schild and modified Kerr-Schild coordinates; additional components can be incorporated without restructuring the core solver. Verification covers all three regimes on uniform and statically refined meshes: smooth Newtonian and special-relativistic problems approach second order against their analytic solutions, with deliberately matched double-precision trajectories agreeing with AthenaK to roundoff; in fixed-spacetime GRMHD, the stationary analytic solutions are preserved to second order, and the turbulent accretion reproduces the same flow and flux scales as BHAC. Together, these results establish the fixed-spacetime matter-sector foundation for the broader PANGU framework. Numerical-relativity and coupled dynamical-spacetime GRMHD capabilities will be presented in subsequent work.

We investigate the fast-advection limit ($\varepsilon \to 0$) of the stochastically forced two-dimensional incompressible Navier-Stokes equations on the torus. Numerical simulations are performed at resolution $N = 128$ for four different forcing shells on both the square torus and a thin torus, with the advection parameter $\varepsilon$ varied over approximately one decade. We find that the stationary distributions become increasingly concentrated on the lowest Fourier modes as $\varepsilon \to 0$, with the energy-to-enstrophy ratio $E/\Omega$ and the fraction $R$ of enstrophy in the lowest modes both increasing monotonically. At finite $\varepsilon$ the degree of concentration depends on the forcing shell through the effective spectral value $B_1/B_0$, in agreement with the condensation bound of Sznitman and Widmayer. Linear extrapolation to $\varepsilon = 0$ suggests that the limiting values may be forcing-independent, with $B_1/B_0$ governing only the rate of convergence. The same qualitative behaviour persists on the thin torus.

We revisit the classic 1959 paper of L. D. Landau on possible singularities of the integral associated to a Feynman graph. Focusing on the real setup, we relate it to convex geometry by representing a collection $p$ of incoming momenta as the weighted normals of a convex polytope $Q$ via the Minkowski problem. Then, a regular polyhedral subdivision $\mathcal{P}$ of $Q$ exhibits $p$ as a Landau singularity labelled by the dual graph of $\mathcal{P}$ with masses being the areas of the faces. Positivity of the Landau/Feynman/Schwinger multipliers is interpreted as strict convexity of a PL-function. This gives an interesting class of “polyhedral” Landau singularities. In the planar case going back to the original 1959 paper, Landau graphs can also be identified with plane webs of Gaiotto-Moore-Witten that provide a language dual to that of regular polygonal subdivisions.

The paper presents a 3D numerical model of plasma in which a fully implicit PIC method with exact conservation of global energy and local charge is generalized to the electromagnetic case. This opens the possibility of simulating plasma equilibria with a high (up to an extreme) ratio of plasma pressure to magnetic field pressure, which are formed in open magnetic traps. The main goal of this work is to find out whether a fully implicit model, which usually performs numerous nonlinear iterations when solving the coupled Vlasov–Maxwell system, can compete in performance with semi-implicit models that achieve the same conservative properties at the cost of only a single particle push per time step. It turns out that in 3D geometry such competition is quite possible due to the growing computational cost of evaluating the mass matrices in the semi-implicit approach. The software implementation of the proposed numerical model is written in C++ within the parallel xpic code. Testing the code on problems of the development of the Weibel instability and the formation of plasma with extreme pressure showed good agreement between the semi-implicit and fully implicit approaches and made it possible to establish their relative speed.

Context. MWC 656 is a Be/X-ray binary identified as an emission-line object, X-ray and radio source and might be a weak gamma-ray source, harbouring an enigmatic secondary component. Aims. Our aim here is to study the orbital modulation of the H-alpha emission line, disc truncation and to evaluate the binary parameters. Methods. During the period 2021-2026, we obtained high resolution (30000) optical spectra of MWC 656 and analysed them together with the published data. Results. We find an orbital modulation of the H_alpha emission line with period P orb = 60.43 +/- 0.03 d. By assuming that the Be circumstellar disc is truncated by the companion, we estimate orbital eccentricity e = 0.11 +/- 0.01, semimajor axis a=160 R_sun, and mass of the binary M_1 + M_2 = 15.1 M_sun. Conclusions. The orbital modulation of the H_alpha emission suggests that (1) in this object we have a new type of cyclic variability of a Be disc; (2) the orbit is mildly eccentric; and (3) the secondary component of MWC 656 is a massive object 5 M_sun, more massive than the neutron stars - a stellar-mass black hole or a massive stripped star.

The ability to recover weak signals without sacrificing their spectral information is central to precision spectroscopy, yet conventional lock-in detection achieves noise rejection at the expense of spectral dimensionality and ultimately imposes a trade-off between detection bandwidth and sensitivity. Here, we introduce spectral lock-in detection, a versatile framework that extends lock-in noise rejection independently to every resolved component of a broadband spectrum. By separating the fast-time coordinate encoding spectral information from the slow-time coordinate carrying temporal modulation, the measured waveform is spectrally resolved before demodulation, enabling each frequency channel to be independently detected and integrated. We show analytically that, for spectrally stable signals, the signal power in each spectral channel remains invariant, while the noise power ideally decreases by 10 dB per decade of integration time, enabling spectral features buried beneath the instantaneous noise floor to emerge without loss of frequency information. We experimentally validate this framework in both phase-incoherent heterodyne terahertz spectroscopy and phase-coherent terahertz time-domain spectroscopy, demonstrating more than six orders of magnitude of sensitivity enhancement across the spectrally resolved channels. Because spectral discrimination is performed computationally on the acquired waveform, the approach requires neither sequential spectral scanning nor additional spectral-selection, multichannel-detection, or interferometric hardware. Spectral lock-in detection therefore provides a broadly applicable route to enhancing sensitivity across diverse spectroscopic platforms and frequency regimes, opening new opportunities for high-sensitivity, information-rich measurements across the electromagnetic spectrum.