Fluid Dynamics · Cross-listed from cond-mat.soft
Singularities in Soft Matter Systems
Vatsal Sanjay
When a
liquid thread pinches off, its neck thins as it separates into two unconnected regions. Using continuum mechanics, we can predict that the neck reaches zero radius in finite time while its
curvature grows without bound. Together, the vanishing neck and diverging
curvature form a finite-time singularity. However, a real fluid does not realise these mathematical limits as molecular or material physics takes over once the neck becomes sufficiently small. Similar singularities arise throughout soft matter whenever a smooth continuum description is used at vanishing length scales. This review asks what the shrinking region forgets, what it retains, and which material length, time, or stress cuts off the apparent divergence. The dynamics near a singularity often become self-similar, with profiles at different times collapsing onto one shape when rescaled by the shrinking local length. Sometimes that collapse is universal enough that the surrounding geometry and forcing no longer determine the local dynamics. Nonetheless, the measured output could still depend on how the shrinking region is fed by the surrounding flow and on the small-scale physics that finally replaces the ideal divergence. Complex fluids and active matter change the same local balance by bringing their own timescales into the shrinking region. Beyond interfaces, the same logic applies when the localised object is a stress concentration or a defect in geometry or order rather than a moving surface. Singularities matter because they show where continuum theory stops being the relevant description and how the small-scale cutoff sets the outputs that count in printing, coating, aerosols, and stretchable solids.
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Plasma Physics
Machine-learning surrogate models for nonlinear energetic-particle transport predictions in ITER
Yashika Ghai, Donald A. Spong, Jacobo Varela et al. (+1 more)
Fast and accurate prediction of energetic-particle transport driven by Alfvén eigenmode (AE) instabilities is essential for integrated modeling workflows used in the design and optimization of burning
plasma fusion reactors. In this work, we develop machine-learning-based surrogate models for rapid prediction of energetic beam and alpha-particle transport fluxes, together with predictive uncertainty estimates, for an ITER steady-state scenario. Two complementary surrogate methodologies, Gaussian process (GP) regression and hierarchical neural networks (NNs), are trained using nonlinear FAR3d gyrofluid simulations of energetic-particle transport. A flux-variability analysis demonstrates that the selected
plasma-state representation provides a sufficiently unique parameterization of the nonlinear transport response over most of the sampled feature space, thereby justifying the surrogate formulation. Both surrogate models reproduce the nonlinear transport fluxes with high predictive accuracy while reducing the computational cost of transport evaluation by approximately five to six orders of magnitude relative to direct nonlinear FAR3d simulations. Although the two approaches achieve comparable predictive accuracy, they exhibit distinct uncertainty characteristics: the GP provides more consistent global uncertainty estimates, whereas the NN more clearly distinguishes between different transport regimes. This work establishes a proof of concept for developing machine-learning surrogate models of energetic-particle transport that are sufficiently accurate and computationally efficient to be incorporated into future integrated modeling workflows.
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All authors Yashika Ghai, Donald A. Spong, Jacobo Varela, Luis Garcia
Computational Physics · Cross-listed from cs.LG
Derivative Computation in PINNs: Automatic Differentiation, Finite Differences and Beyond
Maciej J. Mikulski and Tadeusz Uhl
We systematically investigate finite-difference (FD) derivative computation in Physics-Informed Neural Networks (PINNs) as an alternative to automatic differentiation (AD). On three
benchmark PDEs we show that, with a properly calibrated step size, FD matches AD in accuracy on every problem while running faster across the full tested batch-size range and using substantially less GPU
memory, and that a
stochastic variant we propose outperforms AD on a stationary problem. We further show that for neural architectures with inter-sample dependencies (e.g. BatchNorm, self-
attention) the standard PyTorch autograd idiom is silently incorrect; the correct per-sample alternative is computationally infeasible at PINN-relevant batch sizes, while FD provides a forward-only approximation that is empirically an order of magnitude closer to the true per-sample derivative.
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Geophysics
A Spectral-Domain Pseudo-Inverse Method for True 3D Gravity Inversion
Shengchang Chen
The main difficulty in 3D
gravity inversion is that surface observations lack vertical wavenumber information, making the problem underdetermined and depth resolution poor. Building on the author's spectral-domain pseudo-inverse theory for
unitary diagonalizable systems, this paper presents a true 3D inversion method. Surface data are analytically continued upward via Laplace's equation to form a 3D data volume, providing the vertical wavenumber sampling for the 3D
Fourier transform. A general analytical expression for the half-space spectrum is derived, separating the horizontal spectrum from the vertical propagation kernel. The Green's function of the 3D Poisson equation is unitarily diagonalized, yielding the forward spectral response $\lambda(\kk) = -i 4\pi G k_z / K^2$, and a stable inverse filter $q_\alpha(\lambda) = \bar{\lambda}/(|\lambda|^2 + \alpha)$ is constructed. This filter is proved to have bounded stability and consistency (reducing to the exact inverse as $\alpha \to 0^+$). Validation with a homogeneous sphere model shows correct recovery of the anomaly location and singular behavior at the source. The contributions are twofold: (1) upward continuation constructs a 3D volume from 2D surface data, which does not add physical observations but unfolds the 3D spatial variation information (data innovation) derived through the governing physical equation; (2) the inversion is reduced to one forward 3D
Fourier transform, one spectral scaling, and one inverse transform. The framework extends to any linear potential-field inverse problem with a translation-invariant forward operator, including
magnetic inversion.
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Optics
Non-resonant laser-driven narrowing of particle velocity distributions
Ashwini Vaishnav, Matthias Rupp, Olivier De Castro et al. (+2 more)
Stark acceleration and deceleration based techniques for generating particle ensembles with low velocity spread are useful in many experimental applications. For a given velocity distribution of a particle ensemble, these techniques accelerate or decelerate a small subset of the total population, with a low velocity uncertainty. However, narrowing the original velocity distribution by accelerating or decelerating the ensemble particles near the mean velocity is fundamentally limited and not yet explored. We present a numerical study of particle dynamics using neutral cesium atoms as an example. We investigate different interaction regimes, identify key limitations, and propose an interaction regime in which optical Stark deceleration can be used to narrow the velocity distribution of a propagating ensemble about its mean velocity. These findings have potential implications for optical manipulation and control, controlled collisions, and matter interferometry.
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All authors Ashwini Vaishnav, Matthias Rupp, Olivier De Castro, Mikhail N. Shneider, Alexandros Gerakis
Optics
Plasmonic Fourier Surfaces Revisited: Relating Bandgaps with Bound States in the Continuum
Alexander A. Antonov, Connor Heimig, Hannah Niese et al. (+5 more)
Periodically corrugated metal interfaces supporting surface plasmon polaritons (SPPs) belong to the earliest nanoplasmonic platforms. Even simplest reliefs described by a few harmonics - plasmonic
Fourier surfaces - display markedly different far-field signatures depending on the corrugation depth and
symmetry: shallow reliefs exhibit a plasmonic bandgap (PBG) between two hybridized SPP standing waves, while deeper reliefs support asymmetry-induced single sharp resonances, termed over the last decade as quasi-bound states in the continuum (qBICs). Although these spectral features have long been observed experimentally and treated empirically, the underlying eigenmode
evolution connecting the shallow and deep corrugation regimes has remained largely unexplored. Here we revisit this long-standing problem by analyzing it in terms of modern eigenstate formalism. Starting from the Rayleigh hypothesis, we develop a concise first-principle analytical description that explicitly captures how one eigenmode transforms from a dark bound state into an observable qBIC, while the other turns from bright into an overcoupled, unobservable state - thus unifying the SPP manifestations featuring PBG and qBIC within the same eigenmode framework. Finally, we demonstrate the practical relevance of the theory by showing how precise eigenstate engineering can enhance the SPP refractive index sensitivity.
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All authors Alexander A. Antonov, Connor Heimig, Hannah Niese, Yannik M. Glauser, Sander J. W. Vonk, David J. Norris, Maxim V. Gorkunov, Andreas Tittl
Accelerator Physics
High-energy electron-positron beam collisions with large-angle disruptions
W. Zhang, T. Grismayer and L. O. Silva
We show that the beam and field dynamics in high-energy electron-positron ($e^-e^+$) collisions are characterized by a new dimensionless parameter introduced as $\varepsilon$ in this study. The disruption effect deflects the particles transversely at angles equal to $\varepsilon$. The particles simultaneously undergo deceleration of longitudinal velocities (a “braking effect"). The deceleration scales as $\propto \varepsilon^2$. A longitudinal electric field is further provoked, whose amplitude scales as $\propto \varepsilon$. We identify $\varepsilon \gtrsim 1$ (with large-angle disruptions) as a novel extreme regime, where the transverse motion becomes strongly relativistic. The braking effect completely stops and further reverses the beam propagation. Our theoretical model is in excellent agreement with electromagnetic particle-in-
cell simulations. The previous beam-beam studies, including legacy numerical codes, apply only to the $\varepsilon \ll 1$ regime. They fail to capture the correct beam features and collision luminosities, and overestimate beam-beam effects (including beamstrahlung and pair production) for considerable $\varepsilon$, thus demonstrating the need for fully electromagnetic particle-in-
cell codes to study these regimes.
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Physics and Society
Radicalization Kinetics under Algorithmic Exposure in a Stochastic Multiplex Model of Opinion Dynamics
Ruben E. Araújo
We study how physical mobility, algorithmic exposure, and repulsive social influence interact in a
stochastic multiplex model of opinion dynamics.
Agents diffuse in physical space while a directed digital network rewires under a conserved
attention budget, so digital exposure displaces rather than supplements local interaction. With purely assimilative bounded-confidence influence, opinion-blind long-range exposure reduces locality-induced fragmentation whereas homophilic recommendation preserves echo chambers. When a contested repulsive response to sufficiently distant opinions is activated, this ordering reverses at the reference parameters: a neutral platform reaches the maximal polarization permitted by the bounded opinion space, controversy-seeking curation drives faster initial separation but slows sharply near the boundary, and homophilic curation delays radicalization by suppressing cross-bloc exposure. In a late-stage symmetric two-bloc reduction, any curation kernel maps to a state-dependent cross-bloc exposure profile $p(y)$ and an exact quadrature for the radicalization time. Pointwise-ordered profiles inherit a global kinetic ordering; crossing profiles yield target- and horizon-dependent rankings. For similarity-driven curation the quadrature has a closed form involving the exponential integral. Simulations, finite-size scans to $N=1600$, structural controls, and a well-mixed particle comparison support the mechanism. Heavy-tailed influence strengths are not required for the inversion; in the well-mixed heavy-tail regime they additionally produce a non-self-averaging stable-weighted asymptotic description. Finally, opinion-independent Brownian mobility produces no detectable geographic opinion structure in the explored regime, whereas opinion-dependent drift produces spatial domains through a Péclet-controlled crossover near $\chi\ell/D \sim 1$.
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Fluid Dynamics · Cross-listed from math.AP
Couette-Taylor instabilities in the small gap regime: the very counter-rotating case
Dongfen Bian and Gérard Iooss
In this paper, we study the Couette-Taylor instability of a viscous fluid between two rotating cylinders in the small-gap, slow rescaled rotation rate, high Reynolds number regime, focusing on the very counter-rotating case $\mu < \mu_c \approx -0.8$ where the primary instability is non-axisymmetric. Starting from the Navier-Stokes equations, we derive a limit system that captures the leading-order dynamics and compute the critical Taylor number $T_c(\mu)$ together with the critical axial and azimuthal wavenumbers. Near criticality, the weakly nonlinear behaviour is governed by a system of two coupled complex Ginzburg-Landau equations. All coefficients of this amplitude system including the cubic nonlinear terms are evaluated numerically from the linearised eigenfunctions and the associated adjoint problem. The reduced equations admit helicoidal waves (travelling in both the axial and azimuthal directions) and ribbon waves (standing axially, travelling azimuthally), and their existence and stability criteria are discussed. We also examine more exotic spatially modulated solutions that satisfy a third-order dynamical system, whose complete classification remains an open challenge.
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Atomic Physics · Cross-listed from nucl-th
Laser spectroscopy illuminates the $N=32$ shell closure
Tim E. Lellinger, Liss V. Rodriguez, Patrick Muller et al. (+29 more)
Atomic
nuclei are strongly correlated
quantum many-body systems, and how their shell structure evolves with increasing
neutron excess remains a central open question in
nuclear physics. Calcium isotopes are an ideal testing ground: alongside the traditional magic numbers $N=20,28$, new shell closures have been proposed at $N=32,34$ ($^{52,54}\mathrm{Ca}$). While the charge radius rises rapidly towards $N=32$, further moments and radii in the isotopic chain have remained inaccessible due to the low production yield of a few ions per second. Here we apply a highly sensitive collinear
laser spectroscopy technique, which reveals a strikingly simple behaviour: adding one
neutron to $^{52}\mathrm{Ca}$ yields a pure single-particle
magnetic dipole moment in $^{53}\mathrm{Ca}$, while the charge-radius slope towards $^{54}\mathrm{Ca}$ exceeds that towards $^{52}\mathrm{Ca}$. This provides strong evidence for a robust $N=32$ shell closure and stringently constrains
nuclear structure models.
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All authors Tim E. Lellinger, Liss V. Rodriguez, Patrick Muller, Osama Ahmad, Mark L. Bissell, Klaus Blaum, Emily Burbach, Bradley Cheal, Till Fabritz, Ronald F. Garcia Ruiz, Matthias Heinz, Jack Hughes, Phillip Imgram, Kristian Konig, Yinshen Liu, Bernhard Maass, Edward N. Matthews, Takayuki Miyagi, Witold Nazarewicz, Rainer Neugart, Gerda Neyens, Lukas Nies, Wilfried Nortershauser, Julian Palmes, Peter Plattner, Paul-Gerhard Reinhard, Laura Renth, Rodolfo Sanchez, Achim Schwenk, Julien Spahn, Xiaofei Yang, Deyan T. Yordanov
Applied Physics
SERS study of single-live-cell electrical permeabilization dynamics via plasmonic nanotubes
Yuge Liang, Peilin Xin, Enock Adjei Agyekum et al. (+6 more)
There is a growing demand for minimally invasive methods to analyze intracellular processes and signaling activities in individual living
cells, including the identification of tumorigenic
cell subpopulations. However, most conventional analytical methods require
cell lysis, precluding repeated measurements in the same
cell over time, or rely on exogenous labels and reporters that may perturb cellular function. Various applications based on vertical nanotubes have been developed that enable live
cell monitoring and analysis by electroporation with low voltages. However, the extent and duration of membrane permeability and kinetics of membrane repair remain elusive. Here, we built a plasmonic platform with the capacity of surface enhanced Raman spectroscopy (SERS) to monitor the electroporation-induced membrane permeability dynamics in individual live
cells attached onto 100-nm diameter nanotubes of 2 um height. Fibronectin was employed as extracellular
matrix (ECM)-coating to facilitate
cell attachment onto nanotubes. Using fluorescent-dye delivery as an independent validation method, we show that the fabricated nanostructures induce localized electrical permeabilization of the
plasma membrane and enable monitoring of its subsequent recovery. We further use SERS to track molecular changes at the membrane during permeabilization and resealing. The SERS spectra provide molecular-level insight into changes in membrane-associated components and the ECM during electroporation and subsequent membrane recovery. Real time monitoring of pulse induced molecular changes holds great promise for characterizing intracellular signaling, cellular states, and cellular heterogeneity at the single
cell level, including the identification of tumorigenic subpopulations. This capacity could facilitate the development of novel biosensing assay.
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All authors Yuge Liang, Peilin Xin, Enock Adjei Agyekum, Jiaming Zhang, Yingqi Zhao, Jinglai Duan, Francesco De Angelis, Aki Manninen, Jianan Huang
Optics · Cross-listed from quant-ph
Boosting self hybridized exciton polaritons with metal clad WS2 waveguides
Filip Majstorovic, Masoud Taleb, Victor DeManuel-Gonzalez et al. (+2 more)
The formation of Fabry Perot and guided wave self hybridized
exciton polaritons in two dimensional materials results in long range
exciton energy transfer and strong
exciton exciton interactions. Here, we demonstrate that the coupling strength between photonic modes and
excitons is significantly boosted by
embedding the active excitonic layer in a metal clad WS2 waveguide. The photonic modes in this waveguide exhibit modified dispersion properties for both Fabry Perot type and guided wave
exciton polaritons compared to pure WS2 flakes, and show an increased couplingr strength. Our results provide a robust approach for controlling
exciton photon interactions and their coupling strength in hybrid
heterostructures.
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All authors Filip Majstorovic, Masoud Taleb, Victor DeManuel-Gonzalez, Kai Rossnagel, Nahid Talebi
Physics and Society
Universality and Heterogeneity of Stylized Facts in Cryptocurrency and Equity Markets
Jaesung Kim, Changhee Cho and Jae Woo Lee
This study investigates whether the macroscopic statistical maturity of cryptocurrencies implies dynamical equivalence with an equity-
market benchmark. We analyze one-minute data (2020–2025) for Bitcoin, Ethereum, XRP, and E-mini S&P~500 futures using the Complexity–
Entropy Causality Plane (CECP) and directed horizontal visibility graphs (DHVG). While conventional stylized facts overlap across the analyzed assets, cryptocurrencies exhibit weaker local ordinal organization and a larger divergence between their high-degree in- and out-visibility distributions relative to matched surrogate baselines under the primary specification. This high-degree separation is strongest at the one-minute scale and weakens under 5- and 10-minute aggregation, while the direction of the underlying asymmetry remains more asset- and preprocessing-dependent. We therefore conclude only that macroscopic similarity can coexist with diagnostic-specific structural differences in the assets and period examined.
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Fluid Dynamics
Inelastic spreading of viscoelastic drops
Mete Abbot, Thijs Varkevisser, Manglesh Singh et al. (+3 more)
When a
liquid drop impacts a solid surface, rebound and splashing are known to be suppressed by additives that induce elastic effects; however, the influence of elasticity on the maximum spreading radius remains debated. The difficulty lies in isolating elastic resistance from the enhanced spreading caused by viscous shear thinning. Here, we experimentally decouple these effects by investigating Boger fluid drops (constant-viscosity solutions with high elasticity) of polyethylene
oxide (PEO) and polyacrylamide (PAAM). We demonstrate that elastic properties do not alter the maximum spreading ratio, even at high concentrations up to 1000 ppm. We formulate an energy balance that accounts for the inertial, capillary, viscous, and elastic contributions, and yields a dimensionless criterion ($\Gamma$) that estimates the degree of elastic effects. We show that $\Gamma \ll 1$ for all impact conditions tested, demonstrating that elastic effects are energetically negligible during droplet spreading, opposite to what Weissenberg and Deborah numbers would predict.
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All authors Mete Abbot, Thijs Varkevisser, Manglesh Singh, Antoine Gaillard, Devranjan Samanta, Daniel Bonn
Biological Physics
Impact of Higher-Order Interactions on Collective Motion
Maryam Masoumi, Amir Kargaran and Reza Jafari
Collective motion in self-propelled particle systems has been widely studied using the Vicsek model, which relies on pairwise
alignment interactions. We introduce a generalized Vicsek model that incorporates higher-order (triadic)
alignment interactions. Using
agent-based simulations and mean-field theory, we demonstrate that pure triadic
alignment induces a discontinuous phase transition, evidenced by hysteresis, a double-well free-energy landscape, and a Binder cumulant minimum that deepens with system size, whereas the standard pairwise model exhibits a continuous transition at the same system sizes. We further show that higher-order interactions require higher particle densities to sustain collective order and produce sharper fluctuation peaks near the transition with lower critical noise. These results establish that the microscopic structure of the
alignment interaction, whether pairwise or many-body, is an independent control parameter for the order of the phase transition in active matter, with implications for understanding collective behavior in biological and synthetic systems.
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Fluid Dynamics
Deep reinforcement learning for separation control in turbulent wind-tunnel flow
Sofia Avdiiv, Andre Weiner and Ben Steinfurth
This work investigates Deep Reinforcement Learning (DRL) as a tool for model-free closed-loop active separation control in a fully turbulent wind tunnel flow over a one-sided diffuser. The
agent controls an array of
magnetic valves (on/off) that eject compressed air into the boundary layer, while the environmental state is reduced to the signal from a single wall-shear-stress sensor placed near the natural transitory detachment point. The control law is learned in real time using Proximal Policy Optimization. Compared to the standard learning design based on the weighted sum of all rewards following an action, we demonstrate that a horizon aligned with the convective time of the flow leads to faster convergence and a more robust control strategy. The resulting control law corresponds to a low-duty-cycle actuation pattern that yields a forward-flow fraction of approximately $53\%$. This compares favorably with conventional and optimized periodic open-loop control ($\sim 40\%$ and $\sim 51\%$, respectively). The findings of this article indicate that, when embedded into an online experiment, DRL represents an efficient tool to identify robust and interpretable active separation control strategies.
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Optics
Optical-Memory Transport Imaging: A Transport-History Framework for Finite-Memory Tracers
Haichun Liu and Jerker Widengren
Finite-
memory optical tracers encode upstream transport histories rather than instantaneous local flow velocities. We introduce optical-
memory transport (OMT) imaging, a framework in which finite
memory couples internal-state relaxation to transport through
memory kernels. Under structured illumination, these histories are converted into measurable complex spatial-frequency response, whose local transfer-function limit yields constant-velocity inversion. Fisher-information analysis establishes kernel-dependent information limits and design principles for finite-
memory transport imaging.
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Optics
Rf beam steering using on-ohip optical true time delay on 3 micrometer siliocn on insulator platfrom
Somnath Paul, Jussi Saily, Markus Schroder et al. (+2 more)
We present the design, packaging, and system-level experimental demonstration of a reconfigurable 5-bit, 4-channel optical true time delay (OTTD) chip realized on a 3 micrometer thick silicon on
insulator (SOI) platform at VTT. The chip enables 32 discrete delay states over a 0 to 101 picoseconds range, with a delay resolution of 3.25 picoseconds, making it well suited for broadband RF beamforming with upcoming 6G FR3 band systems around 10 GHz. Each channel incorporates five binary weighted delay stages controlled by Mach-Zehnder interferometer (MZI) based thermo-optic switches with an extinction ratio exceeding 25 decibels and an average switching power of 25 milliwatts. The chip is embedded within an analog
radio-over-fibre (A-RoF) link, and the outputs are connected to a PCB-based four-element patch
antenna array. Accurate RF beam steering is demonstrated at broadside and at 30 degrees from broadside using a 16 - QAM signal modulated at 100 MBaud on a 10 GHz carrier. An error vector magnitude (EVM) degradation of approximately 1 percent is observed upon steering, and an extinction ratio exceeding 50 decibels is measured between the two receiver positions. The results confirm the potential of integrated OTTD technology for compact, power-efficient, and broadband beamforming in next-generation wireless and radar systems.
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All authors Somnath Paul, Jussi Saily, Markus Schroder, Mikko Harjanne, Timo Aalto
Optics
Quantum Theory of Third-harmonic Generation in Epsilon-Near-Zero Materials
Sonia Alipour, Riccardo Franchi, Tornike Shubitidze et al. (+3 more)
We present a theoretical framework, based on the Green's tensor quantization method, to describe third-harmonic generation in epsilon-near-zero (ENZ) materials and derive analytical, closed-form solutions for the generation efficiency. We validate our model against experimental measurements of wavelength- and angle-resolved third-harmonic generation efficiency from 30 nm-thin ITO nanolayers at low pump intensity, described under the undepleted pump approximation. Our results provide a local and scalar effective model for
quantum nonlinear processes in dispersive and lossy ENZ media, and establishes a simple and reliable framework for investigating a variety of nonlinear optical phenomena with applications to
quantum sensing,
quantum information, and
quantum nondemolition measurements.
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All authors Sonia Alipour, Riccardo Franchi, Tornike Shubitidze, Smridhi Chawla, Luca Dal Negro, Marco Ornigotti
Physics and Society
The Triadic Stress Index in Financial Markets
Alberto Acedo
The Triadic Stress Index (TSI) takes a network index whose four factors were first observed in soil microbiome co-occurrence networks and applies it, without alteration, to the correlation network of financial assets. We test it on five
markets spanning 2006-2026 (equities including banking crises and the AI sector, cryptocurrencies, commodities, foreign exchange and sovereign debt), against three independent definitions of a crisis episode, at a fixed alarm budget, out of sample, with block-bootstrap intervals and a Holm correction across the family of tests. The
benchmarks are the Absorption Ratio, the industry standard used by MSCI and central banks; the effective rank and the Vendi score, the sharpest spectral measures available; Ollivier-
Ricci curvature; and the global and local balance indices of signed correlation networks. Three comparisons favour the index. It carries a per-node decomposition, diag(A^3), naming which asset is carrying the concentration with no parameter to select, and scores 0.97-0.99 against 0.33-0.84 for the only published per-node alternative, whereas spectral attribution must first choose how many components to read and collapses under a standard but wrong choice. Its alarms are the cleanest of anything tested, 4.0% of them with no matching episode against 14.7% for the effective rank and roughly 59% for the Absorption Ratio. And it beats the Absorption Ratio on detection by 0.273 in F1 out of sample, p<0.0005. The remaining comparisons are ties. Against the effective rank and the Vendi score the index ties in every scheme and both samples, and the margin over the Absorption Ratio narrows under the strictest labelling. On real
matrices the far simpler node degree reproduces the attribution. A lead-lag analysis puts the peak cross-correlation at zero lag: this is a coincident state index, not a forecast.
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Atomic Physics · Cross-listed from hep-ex
First measurement of kaonic deuterium X-ray transitions
Massimiliano Bazzi, Francesco Clozza, Carlo Guaraldo et al. (+38 more)
The study of the strong interaction among
hadrons at low energies remains one of the key challenges in fundamental physics because of its non-perturbative nature, which makes theoretical descriptions strongly dependent on experimental input. Although substantial progress has been made for systems involving up and down
quarks, theoretical models in the strangeness sector continue to face limitations due to the lack of experimental data. Kaonic atoms provide a powerful tool to study the low-energy strong interaction with strangeness through the energy shifts and widths induced on their lowest atomic levels. In this context, kaonic deuterium X-ray spectroscopy has long represented one of the major open challenges in hadronic-atom physics because of its extremely low X-ray yield. This measurement is particularly important because it gives access to the poorly constrained $K^-n$ interaction at threshold. Here, we report the first observation of kaonic deuterium X-ray transitions, performed with the SIDDHARTA-2 experiment at the DA$\Phi$NE
collider. We determine the strong-interaction shift and width of the $1s$ level to be $\varepsilon_{1s}=-810.9\pm24.5\,(\mathrm{stat})\pm2.1\,(\mathrm{syst})\,\mathrm{eV}$ and $\Gamma_{1s}=812\pm97\,(\mathrm{stat})\pm33\,(\mathrm{syst})\,\mathrm{eV}$, respectively. This measurement constitutes the most precise experimental determination of the $K^-d$ strong interaction at threshold and allows discrimination among competing theoretical models. Combined with the kaonic hydrogen measurement, this result provides the experimental input required to determine the isospin-dependent $K^-N$ scattering lengths, with implications for the description of the nature of the molecular interpretation of the $\Lambda(1405)$, and
neutron-rich matter.
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All authors Massimiliano Bazzi, Francesco Clozza, Carlo Guaraldo, Mihail Antoniu Iliescu, Alessandro Scordo, Francesco Sgaramella, Diana Sirghi, Florin Sirghi, Johann Zmeskal, Leonardo Abbene, Claude Amsler, Francesco Artibani, Giacomo Borghi, Damir Bosnar, Mario Bragadireanu, Antonino Buttacavoli, Marco Carminati, Alberto Clozza, Luca De Paolis, Raffaele Del Grande, Kamil Dulski, Carlo Fiorini, Ivica Friščić, Masa Iwasaki, Aleksander Khreptak, Simone Manti, Johann Marton, Catia Milardi, Pawel Moskal, Fabrizio Napolitano, Hiroaki Ohnishi, Kristian Piscicchia, Fabio Principato, Michał Silarski, Magdalena Skurzok, Antonio Spallone, Kairo Toho, Marlene Tüchler, Oton Vazquez Doce, Eberhard Widmann, Catalina Curceanu
Space Physics
LQR Design For Formation Flying Near Halo Orbits Exploiting Quasi-Periodic Symmetry In Toroidal Coordinates
Joaquin G. Lopez-Cepero, Rafael Vazquez and Julio C. Sanchez
This work presents the design of a Linear Quadratic Regulator for relative motion control near periodic orbits in the Circular Restricted Three-Body Problem (CR3BP), formulated in non-singular toroidal coordinates. The key result exploits the rotational quasi-periodicity of the toroidal coordinate transformation. A uniqueness argument on the stabilizing solution of the associated difference Riccati equation proves the optimal control gains need only be computed for a single orbital period. The controller is validated against the full non-linear CR3BP dynamics on an L1 Northern
halo orbit in the Earth-Moon system, and further against a high-fidelity ephemeris model, demonstrating successful reconfiguration maneuvers on the invariant
torus with low control effort. Compared with an impulsive targeting and station-keeping baseline, the proposed controller attains a comparable tracking accuracy while reducing the total control effort by approximately 40%.
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Optics · Cross-listed from cond-mat.mes-hall
Revealing time characteristics of optical excitations in dielectric and plasmonic structures through cathodoluminescence interferometry
Evelijn Akerboom, Hirohsi Sugimoto, Minoru Fujii et al. (+5 more)
Cathodoluminescence (CL) spectroscopy provides access to optical excitations with nanometer spatial resolution, but direct time-resolved measurements of optical resonances remain challenging. Here, we demonstrate that CL interferometry provides access to the temporal response, phase behavior, and modal spectral structure of resonant nanoscale scatterers without requiring ultrafast pump-probe schemes. We develop an analytical framework in which
Fourier transformation angle- and frequency-resolved CL interferograms yields the decay time of optical resonances governed by the linear optical response. Multimode resonators exhibit characteristic temporal CL beating signatures associated with spectral mode splitting. By exploiting transition radiation emitted from a nearby metallic surface as a broadband reference, we further demonstrate phase
retrieval and cross-correlation measurements between instantaneous and resonant emission processes. Experimental measurements on Au nanoparticles, broadband plasmonic emitters, Au nanostars, and Si nanospheres supporting multipolar Mie resonances confirm the theoretical predictions, and decay times in the range 1-10 fs are derived for each system. Our results establish CL interferometry as a powerful approach for accessing spectral, spatial, and phase information within a single nanoscale measurement with fs resolution.
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All authors Evelijn Akerboom, Hirohsi Sugimoto, Minoru Fujii, Nicolas Pazos-Perez, Ramon A. Álvarez Puebla, A. Femius Koenderink, F. Javier García de Abajo, Albert Polman
Chemical Physics
Spin Rotatory Strength as the Equilibrium Observable for Chiral-Induced Spin Selectivity
Rubén Dar\io Guerrero
We identify the
spin rotatory strength—a chirality-odd, finite-frequency
spin–dipole cross response—as the
equilibrium observable for
chiral-induced
spin selectivity. Time-reversal
symmetry forces the static response to vanish, while nonzero SU(2) Wilson-loop flux is an independent necessary condition. Exact diagonalization of a Kane–Mele–Hubbard model ($N{=}4,6,8$) reveals that gapped molecules robustly suppress the response, whereas near-degenerate systems show amplification at small $N$ whose persistence at larger sizes remains open.
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Atomic Physics · Cross-listed from quant-ph
Helium-like ions $(Z,e,e)$ in Lagrange Mesh method, interpolating the highly-accurate energy spectra vs. Z
H Olivares-Pilon, JC Lopez-Vieyra and AV Turbiner
Two alternative approaches for studying Helium-like atomic ions in non-relativistic
quantum mechanics are proposed: (I) a numerical approach, based on the Lagrange-mesh method which can easily reach up to 14-15 significant digits in the energy spectrum for any
nuclear charge $Z$ with modest CPU time in single processor mode and (II) a highly-accurate, few-parametric interpolation formula for the energies vs. $Z$. The interpolation formula of general nature is proposed, it can be applied to the energies of any excited state of the helium-like sequence. It is based on matching the $1/Z$-expansion at large $Z$ and the Puiseux expansion with integer and half-integer powers around the so-called second critical charge $Z_B$, introduced by F and D Stillinger (1969, 1974), confirmed by the present authors in 2019 for the ground state $1^1 S$, then revisited here, and extended to the excited states in the present work. For example for the first two
spin-singlet $1^1 S$, $2^1 S$ and the first two
spin-triplet $2^3 S$, $3^3 S$ states this interpolation formula with nine free parameters can reach an accuracy of 10-14 significant digits (s.d.) in the energies for any physically-relevant
nuclear charge $Z$, giving absolute accuracy at large $Z$. Many results are obtained for the first time.
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Computational Physics
Analysis of degradation in perovskite solar cells through physics-based machine learning
Kjeld O. Jensen, Gemma Giliberti, Aldo Di Carlo et al. (+5 more)
Degradation in lead halide perovskite
solar cells is analysed by inverse modelling of published measurements of characteristics of a single
solar cell at ages 0, 90, 280, 480 minutes. We employ machine learning to deduce distributions of material parameter values and hence the physics linked to measured changes.
Bayesian parameter estimation is coupled with drift
diffusion simulations using the IonMonger code combined with an optical model. We accurately replicated measured changes in device performance with age through variations in model input parameters. Our key result is that degradation is influenced by correlated changes in the concentrations and
diffusion coefficients of mobile ions and by interface recombination at large mobile ion concentrations. This study demonstrates the power of machine learning combined with simulations to reliably interpret experimental results, a task which is problematic if using simulation models with only manual exploration of the input parameter space.
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All authors Kjeld O. Jensen, Gemma Giliberti, Aldo Di Carlo, Will Clarke, Giles Richardson, Taylor Blackwell, Petra J. Cameron, Alison B. Walker
Optics
Stability of Orbital Angular Momentum Modes in Conventional and Ring-Core Optical Fibers
Hassan Asgharzadeh B., Regina Gumenyuk and Marco Ornigotti
Modal dynamics in multimode optical fibers are fundamentally governed by the inter- play between phase matching and intermodal coupling. In this work, we investigate the fundamental coupling mechanisms in ring-core fibers and identify a geometry-induced cou- pling suppression that significantly reduces coupling coefficients between orbital angular momentum modes compared to conventional multimode step-index fibers. This mechanism provides a clear physical explanation for the superior transmission stability of orbital angular momentum modes in ring-core fibers and establishes specific
geometric constraints for the design of ring-core fiber-based mode converters.
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Medical Physics
Real-Time Requirements and Transferability in Compton Imaging: From the Detector Chain to the Application
F. Albiol, Elena Larrea Estrelles, Salvador Tortajada et al. (+4 more)
Compton cameras are proposed for tasks whose value decays with delay: verifying a range during irradiation, guiding an intervention, characterising an inaccessible volume, surveying a band no
telescope covers. Whether a device can serve such a task is settled by the composition of its whole chain, while the literature that would answer the question is organised by stage – so claims made at application level routinely rest on evidence obtained at component level. This review walks that chain, asking at each stage what binds first and what a reader can determine from the published text, and then asks what governs whether a capability transfers between groups and between application domains. The evidence is of two kinds: 83 full texts scored in context against defined markers, and, for five application domains measured alike, the size of the receiving literature, of the need it states, of the incumbent and of deployment commitment. Performance is reported at one operating point in 65 of 83 full texts, with count rate swept in none: the field reports values where transfer requires gradients. An accelerator is used in 39 works and a learned model in 31, while separability is discussed in 28, a
memory footprint given in 9, and the cost of a precomputation or the inference time of a model in none. Across domains, neither the size of the receiving literature, nor of the incumbent, nor of the stated need orders the domains as deployment commitment does, while whether the incumbent can serve the task at all, and how many domain boundaries the output must cross, do so consistently. The distribution of publication is close to the inverse of the distribution of deployment commitment. We give the quantities a report must contain for a third party to judge whether a method fits an application it was not built for.
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All authors F. Albiol, Elena Larrea Estrelles, Salvador Tortajada, Luis Caballero, Jose Escalante, Alberto Albiol, Jose Luis Leganes-Nieto
Chemical Physics
Compression of virtual spaces in transcorrelated methods via singular value decomposition: application to the G2 set
Yifan Cheng, Kristoffer Simula, Johannes Hauskrecht et al. (+3 more)
We introduce a new singular-value-decomposition-based scheme for constructing small virtual spaces out of large basis sets for transcorrelated (TC) calculations, termed SVD-TC. This work builds on the recent finding that the residual basis error in the TC reference energy converges more slowly than that of the correlation energy. Within the new workflow, the post Hartree-Fock TC calculation is performed in a compressed virtual orbital subspace, obtained by projecting the canonical virtual orbitals from a large basis set onto a smaller basis set through singular value decomposition (SVD). This allows us to achieve the high accuracy allowed by the large basis, whilst the bottleneck steps - TC integral calculation and post-HF correlation method such as CCSD(T) - incur the cost of only a small virtual space calculation. The method therefore is highly efficient, whilst avoiding the composite nature of the reference correction method. Using the new scheme, we widen the scope of
benchmark-quality TC results into more complex molecules than previously considered: using the G2-1 set of 55 molecules with first- and second-row atoms, we apply SVD-xTC-CCSD(T) to compute atomization energies. We compare our results against the near-exact semistochastic heat-bath configuration interaction (SHCI) reference values and experiment. We find that SVD-xTC-CCSD(T) delivers chemical accuracy already with triple-$\zeta$ basis sets. Finally, we use the quadruple-$\zeta$ results to analyze the accuracy of pseudopotentials within the TC method, and show that pseudopotential TC workflow provides faster basis-set convergence than all-electron TC. We also present timings for computing the atomization energies on G2-1 set, demonstrating the efficiency of our TC workflows.
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All authors Yifan Cheng, Kristoffer Simula, Johannes Hauskrecht, Evelin Martine Corvid Christlmaier, Daniel Kats, Ali Alavi
Optics
Strong, Mode-Selective Evxciton-Photon Coupling Driven by Polariton Scattering in the Mo2 Complexes at Ambient Conditions
Miao Meng, Ying Ning Tan, Zi Cong He et al. (+2 more)
Quadruply bonded Mo2 complexes provide a distinctive molecular platform in which multiple two-level electronic transitions interact with quantized scattering modes under ambient conditions. Here we show that, in the Mo2 complexes, the intrinsic photonic modes selectively couple to molecular excitations, including the characteristic delta-delta(
star), ligand to metal charge transfer (LMCT) and metal to ligand charge transfer (MLCT) transitions, to form the well-resolved
exciton-
photon hybrid states. By combining steady-state absorption, resonance fluorescence, and ultrafast transient spectroscopies, we identify distinct polaritonic branches associated with these electronic
manifolds, with coupling strengths spanning the strong and ultrastrong regimes (g/omega0 up to 0.1). Mode-selective coupling accounts for the pronounced spectral reorganization for the singly oxidized complexes, including the emergence of absorption valleys and sidebands of the associated resonances in the steady-state spectra, characteristic polaritonic emissions in the photoluminescence spectra, and long-lived low-energy hybrid states in the transient spectra. These results support the picture that the Mo2 unit functions as an integrated molecular resonator whose intrinsic quantized field selectively drives and redistributes molecular excitations. This work strengthens the emerging view of bonded dimetal complexes as ambient-condition molecular
quantum systems and provides a chemically defined platform for exploring polaritonic chemistry.
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All authors Miao Meng, Ying Ning Tan, Zi Cong He, Yuli Zhou, Chun Y. Liu