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Monday 12 October

High Energy Physics (Phenomenology)

MadNIS, Ready for Production at LO

Theo Heimel, Olivier Mattelaer, Daniele Massaro et al. (+1 more)

We extend neural multi-channel importance sampling in MadNIS to full proton-proton processes in a production-ready event-generation setup. We benchmark a wide range of LHC processes, including multi-jet, vector-boson, top-quark, and Higgs production, and obtain event-generation speed-ups of up to a factor of 250 without process-specific hyperparameter tuning. We quantify how the speed-up scales with training time and final-state multiplicity, and when the training cost amortizes. MadNIS will become the default for phase-space integration and event generation at leading order in MadGraph.
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All authors Theo Heimel, Olivier Mattelaer, Daniele Massaro, Ramon Winterhalder

Quantum Physics

Moving quantum sensors

Evan Zhang, Erfan Abbasgholinejad, Yu-Xin Wang et al. (+6 more)

We investigate whether controlled motion of a quantum sensor offers a metrological advantage in a field-detection task. We consider a localized field of known strength $B$ occupying an unknown contiguous region making up a fraction $1/N$ of the total search space, with a qubit sensor controlled for a total time $T$ to maximize the probability of detecting the field. We study the regime in which the characteristic timescale of the field is slow compared to the time to move the sensor between any two regions, and we distinguish classical motion, where the sensor follows a definite trajectory, from quantum motion, where the sensor can be in a coherent superposition of locations. For a single classically moving sensor, we derive an optimal multi-stop protocol and obtain the exact maximum detection probability. Allowing coherent spatial superposition maps the single-sensor problem onto Hamiltonian search and reduces the interrogation time for successfully detecting the field from $\Theta(N/B)$ to $\Theta(\sqrt{N}/B)$. We then extend the problem to $M$ sensors and identify a hierarchy of optimal time scalings for constant success probability determined by the available spatial and inter-sensor quantum resources. Unentangled coherently moving sensors achieve $T=\Theta(\sqrt{N/M}/B)$ by searching disjoint regions in parallel, while entanglement among the sensors can further enhance the effective field coupling and achieve $T=\Theta(\sqrt{N}/(MB))$. Matching lower bounds establish the optimality of these scalings in the presence of arbitrary controls and ancilla systems. Our results separate the roles of classical motion, spatial coherence, and entanglement in spatial field detection.
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All authors Evan Zhang, Erfan Abbasgholinejad, Yu-Xin Wang, Ali Fahimniya, Daniel J. Spencer, Sean R. Muleady, Mohammad Hafezi, Andrew M. Childs, Alexey V. Gorshkov

Materials Science

Comprehensive Workflow for Uncertainty-Aware Ionic Liquid Solvent Discovery

Alexander Lobo, Urvi Awasthi and Leonid Zhukov

Designing synthesizable materials with targeted properties remains one of the central objectives in materials sciences. Ionic liquids (ILs) are well suited to this goal due to their "tunability", where physical and chemical properties can be precisely customized by modifying their molecular structure, specifically by varying the combination of cations and anions. At the same time, current data-driven property models for ionic liquids often degrade in scarce, noisy, and uneven data regimes, where measurements cover only a small fraction of chemical space and a limited range of thermodynamic conditions. This makes out-of-distribution screening brittle: even when point predictions look plausible, it is difficult to compare candidates consistently, quantify downstream implications, or trust rankings enough to guide molecular discovery. We present a property-prediction and optimal candidate selection workflow that treats data processing, deep learning modeling, and physics-based calculations as a coupled system, linking property prediction with uncertainty estimation and physics-based filtering. By tightening the link between predicted properties and the criteria used for down-selection, the workflow supports reliable out-of-distribution ranking and enables prioritization of previously untested ionic liquid candidates with favorable predicted trade-offs. We demonstrate the application of our workflow by designing novel ionic liquids for CO2 capture from flue gas, predicting their properties and selecting Pareto-optimal candidates based on CO2 solubility, IL viscosity and working capacity.
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Quantum Physics

Fractional and quantum Latin squares: real solutions of quantum 36 officers problem

Mykhailo Hontarenko and Karol Życzkowski

A Latin square can be extended by replacing its symbols with probabilities or quantum states. We relate these two extensions through explicit examples, from classical and fractional Latin squares to quantum Latin squares and a real solution of Euler's quantum 36 officers problem. A simultaneous cyclic-shift ansatz on a four-torus of tensor coefficients gives a real absolutely maximally entangled (AME) state of four six-level systems. A local orthogonal change of basis yields a representative with 96 nonzero amplitudes. Two single-party arrays obtained from the corresponding quantum orthogonal Latin square yield fractional Latin squares. Signs matter: comparison with the independent real construction of Bruzda and its sign variant distinguishes three local-unitary classes, two of which have identical probabilities. We extend this probability representation to existing seven- and nine-party AME states with six levels each. Their amplitude matrices reveal 48 complex Hadamard blocks of order $3^3$ and six of order $6^4$, respectively. These constructions separate what can be read from a probability picture from the coherent conditions responsible for maximal entanglement.
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Instrumentation and Methods for Astrophysics

OASIS: On-the-fly ASynchronous Image Stream classification – Transformer-based models for the early detection of strongly lensed supernovae

Satadru Bag, Raoul Canameras, Sherry H. Suyu et al. (+4 more)

Time-domain surveys often produce asynchronous image sequences across irregular observation times and photometric bands. In many applications, predictions are needed after each new observation, particularly when transient sources must be identified early to trigger follow-up. Strongly lensed supernovae (LSNe), for which follow-up is particularly time-critical, provide a useful example. We formulate this setting as On-the-fly ASynchronous Image Stream (OASIS) classification and explore reusable transformer architectures for causal, on-the-fly classification. We demonstrate these architectures on the lensed-transient classification problem studied by Bag et al. (2026a,b), distinguishing LSNe Ia from unlensed astrophysical transients. We compare them with the recurrent baseline adopted by Bag et al. (2026b), which combines a ConvLSTM branch for image processing with a separate LSTM branch for encoding observation times. The baseline maps asynchronous observations onto a fixed band-by-observation grid, filling unobserved bands with zeros. Using a common training setup, we compare two transformer-based approaches to modeling interactions among spatio-temporal tokens: factorized attention, which separates spatial and temporal interactions, and joint attention, which models them together. On the demonstration dataset, factorized architectures achieve mean losses of $0.095$–$0.100$, compared with $0.128$ for the recurrent baseline and $0.107$ or higher for joint architectures. A selective readout further reduces the best loss to $0.089$ for a factorized model. These results suggest that factorized attention suits this dataset better, without implying universal architectural superiority. We release the architectures as reusable foundations for time-domain astronomy and other applications involving evolving spatial features that require on-the-fly predictions.
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All authors Satadru Bag, Raoul Canameras, Sherry H. Suyu, Stefan Schuldt, Stefan Taubenberger, Irham Taufik Andika, Alejandra Melo

Optics

Programmable Hard-X-Ray Spectral Comb Generation via Laser-Compton Scattering

Hao Zhang, 1Ji Qiang, Shukui Zhang et al. (+1 more)

Independent control of line spacing and offset underpins programmable frequency-comb spectroscopy, yet it has not been established for hard-X-ray sources based on inverse Compton scattering after electron transport and angular collection. Self-consistent multi-particle tracking and Li'enard-Wiechert radiation calculations model a transported 10 pC beam and its angle-integrated spectrum near 11 keV. Laser pulse separation programs the comb spacing, while pulse-to-pulse phase translates the entire line grid at fixed spacing. The spacing model agrees within 0.52%, while transport and optics change the phase-transfer slope by less than 0.2%. At fixed electron spot size, the largest resolvable separation scales as the inverse square of normalized emittance; subnanometer bunches also produce a mode-locked train with 13.9 as spacing. This two-coordinate programmability enables phase-stepped multicolor measurements and offers routes to hard-X-ray Ramsey interferometry, coherent control of core and nuclear excitations, and attosecond nonlinear spectroscopy.
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All authors Hao Zhang, 1Ji Qiang, Shukui Zhang, Sergio Carbajo

High Energy Physics (Theory)

Modular Flow and Holographic Timelike Entanglement Entropy in AdS and Flat Holography

Mehdi Hakami Shalamzari, Zahra Paygozar and Mahdi Kord Zangeneh

Timelike entanglement entropy provides a useful probe of holographic theoris, yet an explicit bulk realization of the modular flow underlying its timelike extremal curve construction has so far been lacking. We construct modular flows associated with spacelike and timelike intervals in AdS$_{3}$/CFT$_{2}$ and extend this framework to flat$_{3}$/CCFT$_{2}$. Beginning with the boundary symmetry generators, we explicitly derive the boundary modular flows and extend them into the bulk, providing a systematic procedure that relates bulk modular flows to the extremal curves and holographic (timelike) entanglement entropy. For spacelike intervals, the resulting bulk modular flows determine the extremal curves, whose integrated line elements reproduce the standard holographic entanglement entropy. We then generalize this approach to timelike intervals, explicitly constructing the modular flows whose fixed points reproduce the extremal spacelike and timelike curves which gives the holographic timelike entanglement entropy. To the best of our knowledge, this is the first explicit construction of the modular flow associated with a timelike extremal curve for a timelike interval. The same procedure is then carried over to flat$_{3}$/CCFT$_{2}$, which give rise to the holographic (timelike) entanglement entropy. Finally, we show that the flat space results obtained in this work can be recovered from their AdS$_3$ counterparts in the flat space limit.
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Quantum Physics

Bosonic unstructured search: quantum enhancement without entanglement

Yu-Xin Wang, Erfan Abbasgholinejad, Supratik Sarkar et al. (+4 more)

We consider unstructured search using multimode bosonic quantum systems under energy constraints. The task is to locate an unknown marked mode among $N$ possibilities using arbitrary control, subject to a time-averaged mean-boson-number budget $n_{{\text{b}}}\gg 1$. We analyze a continuous-time phase-shift oracle of strength $B_{0}$, with cost given by the total oracle time, and a discrete oracle with fixed phase $\phi_{0}$, with cost given by the number of queries. We give algorithms that identify the target with query complexity $O(\sqrt{N}/{n_{{\text{b}}}}B_{0})$ for continuous-time oracles or $O(\sqrt{N}/n_{{\text{b}}} |{\sin(\phi_{0}/{2})}|)$ for discrete oracles with $n_{{\text{b}}} |{\sin(\phi_{0}/{2})}|=O(1)$. In contrast, for discrete oracles with $n_{{\text{b}}} |{\sin(\phi_{0}/{2})}|=\Omega(1)$, we provide an algorithm using $O(\max\{1,\sqrt{N/n_{{\text{b}}}|{\sin(\phi_{0}/{2})}|}\})$ queries. We also prove matching lower bounds on the query complexity, showing that these algorithms are asymptotically optimal. Furthermore, we show that, in the absence of loss, non-Gaussianity is necessary to achieve the optimal joint query scaling in $N$ and $n_{{\text{b}}}$, but entanglement is not. Under uniform boson loss at rate $\gamma$, we prove a query lower bound of $\Omega ( \gamma N / n _{{\text{b}}} B_{0}^{2} )$, attained for $\gamma = \Omega(B_{0} \sqrt{n _{{\text{b}}}/N})$ using coherent-state probes. Finally, we propose experimental implementations using multipass optical microscopy or superconducting circuits as potential routes to speeding up imaging or device calibration with a low boson-number budget.
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All authors Yu-Xin Wang, Erfan Abbasgholinejad, Supratik Sarkar, Sharoon Austin, Andrew M. Childs, Alexey V. Gorshkov, Mohammad Hafezi

Quantum Physics

Programmable Floquet Response for Quantum Sensing

Dionisio Cendoya, Kang Xu, Lisandro Buljubasich et al. (+1 more)

Quantum sensing is typically based on phase accumulation and is therefore fundamentally tied to the coherence time of the sensing system. Here we introduce an alternative sensing paradigm based on programmable Floquet locking in periodically driven two-level systems. We show that periodic control generates an effective Floquet locking field whose orientation and amplitude depend on global offset, allowing information to be encoded in the driven population relaxation dynamics, not in the integrated phase. By controlling transfer between distinct Floquet locking manifolds, external perturbations can be mapped onto engineered relaxation responses whose characteristics are programmable through the driving sequence. We numerically demonstrate this approach for both DC and frequency-selective AC sensing, and show that temporal encoding of the response can provide enhanced precision in the presence of slow instrumental fluctuations. These results illustrate the potential of programmable Floquet responses and open the way to exploring new sensing strategies in driven quantum systems.
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All authors Dionisio Cendoya, Kang Xu, Lisandro Buljubasich, Carlos A. Meriles

Data Analysis and Statistics · Cross-listed from stat.ME

Implicit and explicit reparameterizations of the Folded Normal and Rice distributions

Luis Aldama, Kevin Dalton, Minhuan Li et al. (+1 more)

Variational inference is a flexible tool for modeling experimental data and has proven useful in crystallography. Pathwise gradient estimators provide low-variance gradients for reparameterized variational inference, but are not readily available for some distributions central to crystallography. This work derives and implements implicit and explicit reparameterized gradient estimators for the folded Normal and Rice distributions in \prog{PyTorch}, and compares their variance analytically and empirically. In each case the implicit estimator achieves lower variance for the location derivative, particularly at small location-to-scale ratios, while the scale-derivative variances are nearly equal. For both distributions, implicit estimator is proved to be the conditional expectation of the explicit estimator given the sampled magnitude, so its variance is never larger. As a practical application, French-Wilson scaling is formulated as a variational inference problem, using the folded Normal and Rice distributions as variational families for centric and acentric reflections, respectively. Both estimators recover the exact posterior to better than $1\%$ on the amplitude, and converge at the same rate. The implementations are available in the open-source package \prog{rs-distributions}.
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All authors Luis Aldama, Kevin Dalton, Minhuan Li, Doeke Hekstra

Adaptation and Self-Organizing Systems

Global synchronization in time-varying directed higher-order networks

Wilfried Segnou, Timoteo Carletti and Dibakar Ghosh

Global synchronization has been largely investigated in static higher-order networks and little attention has been brought to directed, temporal higher-order networks. We hereby make a step in this direction by studying the emergence of global synchronization in periodically fast switching systems with directed higher-order interactions. By working in the framework of the Master Stability Function, we show that the linearized dynamics includes two time-dependent Jacobian matrices, both evolving on the timescale of the synchronous solution, together with a generalized Laplacian evolving on a fast switching timescale, resulting from the hypergraph time evolution. To address this two-timescale structure, we establish a fast-switching stability criterion for directed balanced higher-order structures. The latter condition allows to decouple the parallel and transverse perturbations to the synchronization manifold. By relying on the average theory for dynamical systems, we are able to prove exponential stability of global synchronization in the fast switching higher-order network. The proposed theory is then illustrated by using a higher-order Stuart–Landau model, which provides a natural benchmark for the theory. Directionality can move Laplacian eigenvalues into instability regions off the real axis, hence destabilizing synchronization; our results nevertheless reveal that temporal switching can counteract this destabilizing effect and restore global synchronization when the directed structures alternate sufficiently rapidly, even though the instantaneous directed higher-order structures are individually unstable.
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Superconductivity

H$_2$-Like Units and Pressure-Tunable High-$T_\mathrm{c}$ Superconductivity in NaH$_6$

Tianran Chen and Taner Yildirim

Hydrogen-rich materials offer a route to high-temperature conventional superconductivity, but often require extreme pressures. Here we report a first-principles study of NaH$_6$, identified in our large-scale hydride search and independently predicted in a subsequent high-throughput study. Several phases compete, with $R\bar{3}m$ and $Pm\bar{3}m$ dominant over broad pressure ranges. The $R\bar{3}m$ phase remains dynamically stable down to 10 GPa, where its calculated $T_\mathrm{c}$ is 34 K, rising to 99 K at 50 GPa. Cubic $Pm\bar{3}m$ becomes thermodynamically competitive at higher pressures and reaches a calculated $T_\mathrm{c}$ of 230 K at 50 GPa, decreasing only weakly upon further compression. Molecular dynamics and phonon-renormalization calculations support structural persistence over the sampled timescale and indicate relatively small anharmonic effects. Despite their high $T_\mathrm{c}$, both phases contain elongated H$_2$-like units, often considered unfavorable for high-$T_\mathrm{c}$ hydrides. Mode-resolved electron-phonon coupling links Raman-active hydrogen vibrations to superconductivity. In $R\bar{3}m$, the linewidths of these modes increase with the pressure-induced tilt of H$_2$ units relative to the threefold axis, alongside the rise in $T_\mathrm{c}$. A minimal symmetry-based model of the vibration-induced second-moment tensor of the hydrogen sublattice shows that these trends are consistent with a significant contribution from response components perpendicular to the threefold axis. NaH$_6$ thus represents an unusual molecular-like hydride in which hydrogen-sublattice reorganization may enable high-$T_\mathrm{c}$ superconductivity at comparatively moderate pressures.
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Quantum Physics

On the Computational Complexity of Blind Quantum Machine Learning

Rex Fleur, Tzula B. Propp and Sebastian Feld

Can quantum advantages in computational efficiency coexist with quantum advantages in privacy? In this paper, we construct and use MasonQ, a universal brickwork transpiler, to answer this question with a resounding yes. We approach this question by bridging two seemingly disparate paradigms: universal blind quantum computation (UBQC), based on measurement-based quantum computation, and quantum machine learning (QML) algorithms such as the Harrow-Hassidim-Lloyd (HHL) algorithm and quantum recommendation systems. We provide new upper bounds on the depth of UBQC brickwork graphs, establishing that $D = \mathcal{O}(\omega n)$, where $\omega$ is the circuit width and $n$ its computational gate complexity. This is enabled by our newly developed transpiler MasonQ, which maps arbitrary quantum circuits to computational brickwork graph states. Given an optimal Qiskit circuit as input, we prove optimality (up to logarithmic corrections) of the MasonQ transpiler in terms of asymptotic scaling of the total brickwork graph width and depth after decomposition into bricks, enabling systematic cost analyses of blind implementations in near-term experiments and asymptotic regimes. Leveraging MasonQ, we derive depth bounds for several representative blind quantum machine learning (B-QML) algorithms, including the quantum Fourier transform, the HHL algorithm, recommendation systems, and quantum transformers. Lastly, we analyze concrete resource estimates for near-term demonstrations of blind quantum machine learning. We propose a minimal B-QML implementation requiring only a $12$ qubit quantum server. To the best of our knowledge, MasonQ is the first functional and optimal universal circuit-to-brickwork-graph transpiler to implement the full brickwork transpilation process from first principles.
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Solar and Stellar Astrophysics

The nearby Type II supernova 2024ggi beyond 600 days: circumstellar interaction and dust formation

L. Ferrari, G. Folatelli, C. P. Gutiérrez et al. (+16 more)

The Type II SN 2024ggi is one of the nearest core-collapse SNe to have exploded in recent decades. Its proximity has enabled extensive multiwavelength monitoring from early times through the nebular phase. Signatures of late-time interaction between the SN ejecta and hydrogen-rich circumstellar material (CSM) have recently been reported. Here we extend its study using late-time optical photometry and spectroscopy from 570 to 820 d after explosion. We investigate the emergence and evolution of late-time ejecta-CSM interaction and constrain the geometry of the interaction region and the properties of newly formed dust. Comparisons with other interacting SNe II and with synthetic spectra are presented. We model the H$\alpha$ profile with the Monte Carlo radiative-transfer code Damocles, including both gas and dust components. Spectroscopic signatures of interaction precede the photometric flattening. The spectra evolve from ejecta-dominated to interaction-dominated as H$\alpha$ develops a broad, boxy profile. The optical light curves subsequently flatten relative to the $^{56}$Co decay rate at approximately 650-670 d. The emission lines show a systematic blue-to-red asymmetry that requires a dust component newly formed within the ejecta. The inferred dust mass formed in the ejecta is $10^{-6}-10^{-5}$ M$_\odot$ if the grains are amorphous carbon or a carbon-silicate mixture, but can reach up to $10^{-3}$ M$_\odot$ for pure silicates.
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All authors L. Ferrari, G. Folatelli, C. P. Gutiérrez, A. Méndez, C. Ashall, K. Medler, K. Ertini, H. Kuncarayakti, N. Morrell, M. Stritzinger, W. Hoogendam, E. Hueichapán, R. Cartier, J. P. Anderson, M. Bersten, L. Galbany, J. L. Prieto, C. Cárdenas Uribe, S. Vazhayil

Mathematical Physics · Cross-listed from math.SP

(Sharp arithmetic) localization beyond transversality

Svetlana Jitomirskaya, Netanel Levi and Tom Stoiber

We prove sharp arithmetic localization for one-dimensional quasiperiodic potentials with jump discontinuities, beyond uniform transversality. Our results include every non-constant $C^1$ monotone sampling function, even with arbitrarily large flat regions, and also certain non-monotone potentials. A key new mechanism is a symbolic unique-continuation principle: first-return words to the region where $f'>0$ have no common Dirichlet resonance, forcing eigenfunction mass to transfer away from flat or negatively sloped regions and recovering quantitative monotonicity of finite-volume eigenvalue branches.
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Quantum Physics

Cyclotomic Structure and Exact Recurrences in Floquet Many-Body Quantum Dynamics

Amit Anand, Dinesh Valluri and Shohini Ghose

Periodically driven quantum systems exhibit a wide range of complex dynamics, including chaos. Yet, at special parameter values, their evolution can recur exactly. Several quantum protocols have recently been proposed that exploit exact Floquet recurrences to demonstrate genuine quantum advantage. Such recurrences can be studied through the arithmetic structure of the Floquet unitary. In this work, we establish a necessary and sufficient arithmetic criterion for exact recurrence and determine the minimal recurrence period when one exists. Because recurrence is a global property of the unitary, it holds for every initial state. Applying our framework requires only knowledge of the number field associated with the Hamiltonian parameters. We demonstrate the method using the kicked Ising chain, establishing exact recurrences in both Clifford and non-Clifford regimes. We further show that, in the recurrent non-Clifford regime, magic–a resource for quantum computation–is generated at intermediate times and undergoes exact periodic revivals enforced by the recurrence of the full Floquet unitary. By connecting number theory, quantum many-body dynamics, and quantum information, our work shows that exact recurrence extends beyond Clifford circuits and opens new avenues for magic generation and quantum hardware benchmarking.
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Earth and Planetary Astrophysics

JWST Imaging of Edge-on Protoplanetary Disks. V. Flux Ratio Reversal and Disk-edge Structure in the Flying Saucer

Jie Ma, Karl R. Stapelfeldt, Marion Villenave et al. (+8 more)

We present near- and mid-infrared broadband imaging observations of the edge-on protoplanetary disk 2MASS J16281370-2431391, a.k.a. the 'Flying Saucer', obtained with NIRCam and MIRI on board JWST. These data are combined with archival optical and near-IR broadband imaging from HST, millimeter dust continuum emission from ALMA, and optical lightcurves from the K2 and TESS for a comprehensive multi-wavelength study. The JWST observations reveal a reversal of the flux ratio between the two reflection nebulae at near-infrared wavelengths (2-3 $\mu m$), which can be explained by a misaligned inner disk. For the first time, JWST reveals the bright lining along the disk edge at 2 and 3 $\mu m$, arising from forward scattering of background photons by dust grains near the $\tau\approx 1$ layer. By combining the dust lane thickness measured with HST and JWST, we find the dust grains up to at least $\sim$3$\mu$m are vertically mixed throughout the disk and have undergone significant growth. In addition, comparison of earlier HST/NICMOS J and K band images with those from JWST/NIRCam reveals variability in the scattered-light morphology, as well as measurable proper motion of the system with respect to the background stars, confirming that the Flying Saucer is co-moving with the young star population of $\rho$ Ophiuchi.
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All authors Jie Ma, Karl R. Stapelfeldt, Marion Villenave, Gaspard Duchêne, François Ménard, Ryo Tazaki, Youcef I. Bouarour, Greta Guidi, Laurine Martinien, Maxime Roumesy, Christophe Pinte

High Energy Physics (Phenomenology)

Charged Lepton Flavor Violation: A Theory Overview

P. S. Bhupal Dev

We present a theory-oriented overview of the significance of charged-lepton flavor violation – one of the cleanest windows onto physics beyond the Standard Model. We also summarize the current experimental landscape and illustrate how different measurements can diagnose the underlying new physics.
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Fluid Dynamics

One vertex generates the hard-sphere Boltzmann collision hierarchy

I. Karlin

The Boltzmann equation is the fundamental kinetic bridge between molecular mechanics and fluid behaviour. It converts binary encounters into the evolution of a velocity distribution, underlies rigorous routes from hard-sphere dynamics to Euler and Navier–Stokes–Fourier equations, and remains indispensable when continuum descriptions fail, from hypersonic shock layers and atmospheric re-entry to rarefied multiscale flows. Yet its nonlinear collision term is conventionally represented by an infinite three-index tensor of collisional brackets, with apparently new coefficients at every polynomial order. Here we prove that this entire hard-sphere tensor contains only one primitive collision law: the exact rank-two stress-production vertex $S$. Every polynomial collision vertex is obtained from $S$ by a finite sequence of universal differential and tensor operations, and every conventional bracket follows by differentiation. Thus the interaction physics and its representation separate exactly: all hard-sphere-specific information is concentrated in $S$, whereas the hierarchy above it is universal algebra. A blind eighth-order test in a Mach-5 shock agrees with independent collision sampling and strongly amplifies a weak kinetic precursor. The hard-sphere hierarchy is infinite in dimension, but its primitive collision content consists of a single scalar law.
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Optics

Chiral Vector Beams for Topological Enantio-Sensitive Imaging

A. Rodriguez, J. Edginton, A. Löhr et al. (+7 more)

Molecular chiral discrimination is vital across chemistry and life sciences, yet optical approaches remain highly inefficient for small organic molecules. Here we turn vector beams, whose polarization carries a topological charge, into an efficient probe of molecular handedness. We show that the combination of a tightly focused radially polarized beam at the fundamental frequency {\omega} and an azimuthally polarized beam at 2{\omega} creates chiral vector beams, a locally chiral field with structured handedness. Using state-of-the-art computational modeling in the chiral molecule carvone, we show that the nonlinear response (notably sum-frequency generation) of randomly oriented chiral molecules to this chiral vector beam captures the fields' local handedness and is highly enantio-sensitive. The two enantiomers emit light at frequency 3{\omega} with topological ring structures of different divergence, and thus the molecular handedness can be read out directly from the ring radius. The signal inherits the Poincaré index of the driving field, opening up new ways to robust, ultrafast, and and all-optical chiral discrimination.
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All authors A. Rodriguez, J. Edginton, A. Löhr, J. Terentjevas, P. Vindel-Zandbergen, A. Ordóñez, J. Vogwell, O. Smirnova, D. Ayuso, L. Rego

Soft Condensed Matter

Skyrmion gears: translation-to-rotation conversion of skyrmion clusters along periodic substrates

N. P. Vizarim, C. J. O. Reichhardt and C. Reichhardt

We investigate how the translational motion of a compact skyrmion cluster can be converted into collective rotation through interactions with a periodic obstacle substrate. Using an effective particle model, we consider a seven-skyrmion cluster driven along a one-dimensional array of repulsive obstacle sites. For suitable obstacle spacings and interaction strengths, repeated interactions with the substrate produce coherent clockwise or counterclockwise rotation, giving rise to gear-like cluster dynamics. We characterize these states using the translational velocity, Hall angle, angular velocity, structural deformation, and a dimensionless gear ratio that relates cluster rotation to motion over the substrate periodicity. Dynamical phase diagrams identify rotating, nonrotating, wall-guided, transverse, and deformed regimes. We further show that coherent rotation persists in the overdamped limit, demonstrating that the conversion mechanism does not require an intrinsic Magnus force and may therefore extend to other driven cluster systems, including colloidal assemblies. These results provide a simple route for controlling collective rotation through structured substrates.
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Materials Science

Spin-orbit torque effects in all-electrical spin-wave spectroscopy experiments

José Solano Córdova, Jone Mencos, Richard Schlitz et al. (+10 more)

Electrical excitation and detection of propagating spin waves are key elements of magnonic devices. While conventional antennas consisting of non-magnetic metals such as Au or Cu excite spin waves predominantly through radio-frequency (RF) Oersted fields, antennas comprising Pt can additionally generate spin-orbit torques (SOTs) via the spin Hall effect. Recent theoretical work has proposed RF-SOT as an alternative mechanism for coherent spin-wave excitation, predicting distinct characteristics compared with conventional inductive excitation. Here, we investigate Pt antennas for the excitation of coherent spin waves in 105-nm-thick epitaxial $\text{Y}_3\text{Fe}_5\text{O}_{12}$ (YIG) films through two potential mechanisms: an oscillating Oersted field and an oscillating spin current. The raw experimental transmission spectra are strongly affected by fabrication-induced modifications to the YIG film associated with the etching process together with spatially inhomogeneous interface conditions induced by Pt. After removing these contributions, we find the remaining two wave propagation consistent with a combined excitation from Oersted fields and SOTs.
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All authors José Solano Córdova, Jone Mencos, Richard Schlitz, Quentin Rossi, Denise Reustlen, Javed Ali, Sebastian Sailler, Michaela Lammel, Matthieu Bailleul, Daniel Stoeffler, Felix Casanova, Sebastian T. B. Goennenwein, Helena Reichlova

Instrumentation and Methods for Astrophysics · Cross-listed from cs.HC

Particle Selection in Virtual Reality

Boaz Keren-Gil, James Gain, Lucia Marchetti et al. (+2 more)

Point-cloud representations of 3D data are used in many fields, from astronomical surveys of galaxies to medical imaging and laser scans of buildings. A task common to all of these is interactive selection: picking out a meaningful subset of points for closer analysis. The data is inherently 3D, yet the traditional workflow uses a 2D mouse on a 2D projection and inherits the limitations of a flat screen. This paper compares Virtual Reality (VR) and desktop environments for 3D particle selection, asking whether VR's six-degree-of-freedom hand interaction yields measurable gains in accuracy, speed, usability, workload and flow. In a counterbalanced within-subjects experiment (N = 34), participants selected 90 target galaxies from a catalogue of 16,816 galaxies, using mouse-driven selection with keyboard camera control on the desktop and a hand-held spherical brush that adds or removes particles in VR. We measured task accuracy, completion time, and three standard questionnaires: the System Usability Scale (SUS), the NASA Task Load Index (NASA-TLX) and the Flow State Scale (FSS). Accuracy was comparable (91.6% VR vs. 93.1% desktop; p = 0.858), but every other measure favoured VR. Tasks were 23% faster (p = 0.001, d = 0.93), usability was higher (SUS 84.6 vs. 54.0; d = -1.78), workload was lower (NASA-TLX 20.4 vs. 34.7; d = 0.90), and flow was higher (FSS 83.2 vs. 70.2; d = -1.23). Because the underlying problem, making a 3D selection through a 2D interface, is not specific to astronomy, we expect the pattern to carry over to point-cloud selection in other fields.
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All authors Boaz Keren-Gil, James Gain, Lucia Marchetti, Patrick Marais, Alexander Sivitilli

General Relativity and Quantum Cosmology

Bartnik's splitting conjecture and the cosmological wall: a Cauchy Busemann function approach

E. Minguzzi

Bartnik's conjecture states that a timelike geodesically complete cosmological spacetime satisfying the timelike convergence condition splits as a static product. We show that any counterexample exhibits a peculiar global causal structure: two disjoint open regions, the future and the past cosmological developments, separated by a non-empty closed causally convex set: the cosmological wall. The developments are bounded by $C^0$ null hypersurfaces, the cosmological horizons, and a component of each horizon contains a lightlike line. These objects are natural and hence carry physical significance, as they do not depend on the choice of Cauchy hypersurface. They can be defined through the Cauchy Busemann functions $b^\pm$ of a compact Cauchy hypersurface $\Sigma$, the developments being their finiteness domains. Using a product trick we show that $b^+$ is the graph function of a Cauchy horizon in $M\times \mathbb{R}$, and so inherits the regularity and dynamical properties of horizons: $b^+$ is continuous, locally Lipschitz and locally semi-concave on its finiteness domain, and its calibrated curves are timelike rays. We prove that if the two cosmological developments intersect, which happens whenever $b^+$ is $C^1$ on its finiteness domain, then the spacetime contains a timelike line and hence splits, a result which recovers several positive results of the literature. We also obtain a localized rigidity version of Hawking's singularity theorem: if some compact Cauchy hypersurface has non-positive mean curvature on the future development, the spacetime splits. Hence, in a counterexample, every compact Cauchy hypersurface expands somewhere in the future development and contracts somewhere in the past one. If the wall has empty interior, it coincides with both horizons and is ruled by lightlike lines, and under null completeness its components are smooth totally geodesic null hypersurfaces.
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High Energy Physics (Phenomenology)

Decay-Assisted Leptogenesis during Preheating

Wenbin Zhao

We revisit the non-thermal leptogenesis mechanism during preheating using the quantum Boltzmann equations. This framework allows us to study the production and decay of heavy right-handed neutrinos in a consistent manner. Due to their fermionic nature, right-handed neutrino production can saturate after a few inflaton oscillations when their occupation numbers approach unity. Right-handed neutrino decays can deplete their occupation numbers, allowing more particles to be produced and generating a larger lepton asymmetry. Compared with the case where right-handed neutrinos decay only after production has finished, we find that the final baryon asymmetry can be enhanced by two orders of magnitude.
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Fluid Dynamics

DeboRheo v2.0: Improved Robustness for Geometrical VOF Simulations of Viscoelastic Two-Phase Flows

Daulet Izbassarov, Matthias Niethammer, Rahul Subburaj et al. (+5 more)

We present DeboRheo v2.0, an unstructured, geometrically unsplit Volume-of-Fluid framework implemented in OpenFOAM for viscoelastic two-phase flows. Version 2.0 improves numerical robustness when large viscosity contrasts coincide with strongly deformed interfaces and thin viscoelastic lamellae or filaments. The revised interfacial viscosity treatment retains a sharp geometric interface while regularizing the viscous contribution to the momentum equation. The solver combines mass-momentum-consistent phase advection, optional SIMPLEC pressure-velocity coupling, and a modular rheological framework with conformation-tensor stabilization. We assess the method using two-dimensional, axisymmetric, and three-dimensional benchmarks governed by the Oldroyd-B and exponential Phan-Thien-Tanner models. The results agree well with published numerical and experimental data and demonstrate improved robustness for demanding viscoelastic free-surface configurations on unstructured meshes.
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All authors Daulet Izbassarov, Matthias Niethammer, Rahul Subburaj, Dieter Bothe, Francesco Romanò, Renjie Hao, Metin Muradoglu, Tomislav Maric

Instrumentation and Methods for Astrophysics

Extinction by non-spherical particles with the Nanoparticle Transition Matrix Code: perspectives for interstellar medium and exoplanetary atmospheres

G. La Mura, G. Mulas, M. A. Iatì et al. (+4 more)

The Transition Matrix formalism (T-matrix) offers an optimal solution to the problem of radiation scattering and absorption by particles characterized by a high degree of chemical and structural complexity. However, its application to particle models composed by large numbers of constituents has been classically limited by the substantial computational burden of the method. As a consequence, the investigation of light scattering and absorption processes, in cases where particle asymmetry and non-homogeneity play an important role, typically need to rely on simplifying assumptions which affect the correct interpretation of transmission spectra and extinction curves. This problem has a huge impact on many fields of scientific application. In particular, it has a critical role in astrophysics, because the ability to model highly non homogeneous particles is a fundamental requirement to understand the role of extinction in different phases of the interstellar medium (ISM), as well as to probe the physics of light transmission in planetary atmospheres within the Solar System and beyond. In this work we describe the application of a new implementation of the T-matrix formalism, based on the framework originally developed by Borghese, Denti & Saija and named Nano-particle Transition Matrix code, which leverages the power of modern hardware architectures to reduce the computational costs related to the solution of relevant particle models for the investigation of dust in the ISM and of hot-Jupyter class planets atmospheric aerosols. This new implementation of the T-matrix formalism can handle calculations of increasing complexity with a direct impact in the interpretation of the transmission spectra of transiting exoplanets produced by the James Webb Space Telescope (JWST) and of those expected from the Atmospheric Remote-sensing Infrared Exoplanet Large survey (ARIEL).
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All authors G. La Mura, G. Mulas, M. A. Iatì, C. Cecchi-Pestellini, G. Aresu, S. Rezaei, R. Saija

Mesoscale and Nanoscale Physics

Non-volatile Orbital magnetoelectric effect in a two-dimensional electron gas

Yu Chen, Martando Rath, Julien Brehin et al. (+10 more)

Electrical control of orbital magnetism is a central goal of orbitronics. While current-induced orbital polarization has recently been demonstrated in inversion-asymmetric systems, nonvolatile electrical control of an equilibrium orbital moment has remained elusive. Here, using x-ray absorption spectroscopy with in situ electric-field control of the FE polarization, we demonstrate non-volatile switching of the equilibrium orbital magnetization of the oxide q2DEGs formed at the LaAlO$_3$/EuTiO$_3$/Ca-STO (001) interface. X-ray linear dichroism reveals a reversible modulation, driven by the FE-polarization direction, of the Ti-3$d$ crystal-field splitting and orbital occupancy, establishing a ferroelectric-like metallic state. X-ray magnetic circular dichroism shows a polarization-controlled switching of the Eu$^{2+}$ orbital magnetic moment induced by the orbital magnetization of the q2DEG projected onto Eu-5$d$ states and detected at the Eu-$M_{4,5}$ edge through Eu-5$d$/Eu-4$f$ hybridization in the inversion-symmetry-broken interface. These results provide spectroscopic evidence of ferroelectric control of orbital magnetism in an oxide q2DEG.
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All authors Yu Chen, Martando Rath, Julien Brehin, Cinthia Piamonteze, Daniele Preziosi, Payal Wadhwa, Alessio Filippetti, Yuri Fukaya, Mario Cuoco, Filomena Forte, Daniela Stornaiuolo, Manuel Bibes, Marco Salluzzo

Materials Science

Symmetry-constrained coexistence of charge-three and charge-one Weyl points in nonmagnetic crystals

Ze-Xin Xue, Ke-Xin Pang, Yun-Yun Bai et al. (+2 more)

High-charge Weyl semimetals (WSMs), particularly those hosting charge-three Weyl point (C-3 WPs), have attracted considerable interest owing to their unconventional topological properties and enhanced boundary phenomena. However, ideal C-3 WSMs remain rare, and the symmetry-constrained coexistence of charge-three and charge-one Weyl point (C-1 WPs) in nonmagnetic crystals remains largely unexplored. Here, we investigate a representative eight-node Weyl configuration, consisting of two C-3 WPs and six C-1 WPs with opposite chirality, corresponding to two identical $\{3,-1,-1,-1\}$ irreducible Weyl molecules. By combining topological charge conservation with space-group symmetry analysis, we systematically classify all 230 space groups and identify 12 and 23 candidate groups without and with spin–orbit coupling (SOC), respectively. First-principles calculations without SOC reveal that the boron allotropes TBR-B$_{48}$ and chiral OBD-B$_{48}$ realize this configuration, hosting hourglass-type and non-hourglass-type C-3 WPs, respectively. Surface-state calculations reveal six Fermi-arc branches at the shared projection of the charge-three pair and three at each individual projection. Reversing the structural chirality of OBD-B$_{48}$ reverses the signs of all Weyl charges, establishing a direct correspondence between crystal and momentum-space chirality. Furthermore, breaking the protecting $C_6$ symmetry in TBR-B$_{48}$ splits each C-3 WP into three C-1 WPs and reconstructs the surface Fermi arcs. Our work establishes symmetry-based guidelines for designing and searching for nonmagnetic WSMs hosting charge-three and charge-one Weyl-point coexistence.
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All authors Ze-Xin Xue, Ke-Xin Pang, Yun-Yun Bai, Yanfeng Ge, Yan Gao

Optics

Image Priors for Single-Shot Coded Diffraction Phase Retrieval

Zhiyuan Hu, YoonSeok Baek, Sylvain Gigan et al. (+2 more)

Phase retrieval recovers complex-valued objects from intensity-only measurements. In its classical Fourier form, reconstruction suffers from twin-image stagnation. Coded diffraction imaging, which adds a random phase mask before the Fourier transform, has so far required several masks. We show that an image prior makes single-shot coded diffraction imaging possible, with a single random mask followed by a Fourier transform. We validate this claim in simulation and in an optical experiment, in which a spatial light modulator displays the phase object together with the random mask. Our experimental validation covers five test signals and 530 images from the public Brno quantitative phase microscopy dataset of five adherent cell lines. With no image prior or with Fourier-only measurements, reconstruction of complex-valued objects from a single diffraction pattern consistently fails. An out-of-the-box pretrained image denoiser enables accurate reconstruction, in simulation even with fewer measurements than unknowns. Five regularization frameworks built on the same denoiser and one learned weakly convex regularizer all reconstruct the experimental images with peak signal-to-noise ratios within one decibel of each other. A single random phase mask and image priors thus turn coded diffraction imaging into a practical single-shot modality for quantitative phase imaging.
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All authors Zhiyuan Hu, YoonSeok Baek, Sylvain Gigan, Michael Unser, Jonathan Dong