Biological Physics
Information-driven stepping in dimeric transport motors
Antonio Patrón Castro and David A. Sivak
Dimeric transport motors are nanoscale
protein complexes that move along cytoskeletal filaments. Here we introduce a theoretical model for their stepping dynamics, in which the two motor heads undergo Brownian motion with mobilities periodically switching in a position-dependent manner so that only one head moves at a time. Through consumption of chemical free energy, this mechanism produces directed motion. We characterize at steady state the motor's mean velocity and its energy and information flows. The motor operates as a pure information engine, where only information is transduced between its components, without energy exchange. For localized switching, the model yields a thermodynamically consistent expression for the mean motor velocity that reproduces experimentally observed behavior, and captures the stall force characteristic of tightly coupled motors. Finally, coarse-graining the model to a single mechanical degree of freedom produces a second-order non-Markovian dynamics, from which we compute the four distinct dwell-time distributions that can be directly observed in single-molecule experiments. Our findings highlight how information transduction, via implicit operation as a Maxwell demon, may underlie the remarkable performance of these molecular motors.
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Space Physics · Cross-listed from astro-ph.IM
Compton Polarimeter Prototype for the CUbesat Solar Polarimeter (CUSP) mission
Nicolas De Angelis, Andrea Alimenti, Riccardo Campana et al. (+41 more)
The space-based CUbesat
Solar Polarimeter (CUSP) mission aims to measure the linear polarization of
solar flares in the hard X-ray band (25-100 keV) by means of a dual-phase Compton polarimeter. CUSP will allow to study the
magnetic reconnection and particle acceleration in the flaring
magnetic structures of our
star with its unprecedented sensitivity to
solar flare polarization. CUSP is a project under development as part of the Alcor Program of the Italian Space Agency aimed at developing new CubeSat missions. In the frame of CUSP's Phase B, which started in December 2024, a flight-representative prototype of the Compton polarimeter has been developed and characterized with hard X-ray sources in the laboratory. This prototype consists of a 4$\times$4 central
matrix of plastic scintillator bars surrounded by 4 strips of 8 elongated GAGG scintillators, respectively coupled to a multi-anode photomultiplier tube and arrays of avalanche photodiodes. These sensors are read out by custom front-end electronics based on MAROC-3A and SKIROC-2A ASICs with a Xilinx Artix 7 FPGA. The plastic scintillators act as scatterers, while the GAGG bars fully absorb the scattered
photons. Coincident plastic-GAGG events allow for reconstructing the Compton scattering direction, whose distribution allows for inferring the polarization parameters of the source. We report here the measured performance of the polarimeter prototype using well-known radioactive isotopes and X-ray tubes, allowing us to assess the performance of our polarimeter prototype over the full 25-100 keV energy range.
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All authors Nicolas De Angelis, Andrea Alimenti, Riccardo Campana, Mauro Centrone, Giovanni De Cesare, Ettore Del Monte, Sergio Di Cosimo, Enrico Costa, Sergio Fabiani, Abhay Kumar, Pasqualino Loffredo, Giovanni Lombardi, Gabriele Minervini, Fabio Muleri, Paolo Romano, Alda Rubini, Enrico Silva, Paolo Soffitta, Giovanni Cucinella, Vito Di Bari, Simone Di Filippo, Andrea Negri, Massimo Perelli, Davide Albanesi, Valerio Campamaggiore, Giulia de Iulis, Andrea Del Re, Paolo Leonetti, Alessandro Zambardi, Ilaria Baffo, Pierluigi Fanelli, Costantino Zazza, Andrea Curatolo, Nicolas Gagliardi, Dario Modenini, Daniele Pecorella, Alice Ponti, Paolo Tortora, Valerio Vagelli, Daniele Brienza, Immacolata Donnarumma, Matteo Mergè, Emanuele Zaccagnino, Alessandro Turchi
Fluid Dynamics
Role of gravity on preferential clustering of microparticles in unsteady wake flows
Siddhi Arya and Partha S. Goswami
Direct numerical simulations are carried out for particle-laden flow over the cylinder to investigate preferential clustering of particles in an unbounded vertical channel flow. The flow is examined at Reynolds numbers Re=100 and 200 for varying particle Stokes number, particle loadings and Froude numbers to quantify the combined influence of particle inertia and gravitational settling on particle motion. The unladen flow exhibits the classical
vortex shedding pattern observed in flow over bluff bodies at both Reynolds numbers. Reynolds number dependent wake width, wake recovery, and velocity-deficit
evolution are observed, characterizing the coherent flow structures that govern particle dynamics. In particle-laden unsteady wake flows, the non-uniform particle distribution leads to formation of coherent voids and clusters, whose shape are directly correlated with background flow dynamics.
Gravity modifies particle-fluid interaction, which leads to an increase in slip velocity, weakens
vortex-induced particle clustering and promotes them to travel through
vortices, resulting in a transition of the void shape from individual leaf-like structure to snake-like void zone and eventually into a nearly vertical void structure. In upstream region infront of the cylinder, inertial particles form a bow-shock-like structure whose extent increases with increase in Stokes number and finite Froude conditions. Voronoi based analysis combined with local Q values is used to investigate effect of
gravity and inertia on particle distribution. The dimensionless settling velocity, St/Fr^2, is identified as the governing parameter controlling the
evolution of void shape, normalized void
cell area and the probability distribution of Voronoi
cell areas. The effect of wake dynamics, particle inertia, and
gravity is reported to jointly govern preferential clustering in bluff-body wakes.
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Optics · Cross-listed from astro-ph.IM
Testing of machine learning wavefront sensing algorithms on the Tiny Observatory for Telescope Optimization (TOTO) testbed
Sanchit Sabhlok, Solvay A. Blomquist, Maggie Y et al. (+16 more)
Phase
retrieval techniques are utilized to correct low order wavefront aberrations originating from misalignments of the optical system in space based
telescope concepts. Traditional phase
retrieval involves observation of the Point Spread Function (PSF) and a diversity measurement, usually focus diversity although other measures are possible, to reconstruct the incident wavefront at the science detector. We consider a Machine Learning model trained originally on simulated data, and then augmented with real focus diversity data from the Tiny Observatory for
Telescope Optimization (TOTO) testbed at the University of Arizona. We then compare the wavefront sensing performance of the Machine Learning model with known truth values of the generated
dataset. The model predictions for low order Zernikes on TOTO data after training and validation show a reasonable agreement with the true Zernike coefficients.
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All authors Sanchit Sabhlok, Solvay A. Blomquist, Maggie Y, Kautz, Debstuti Biswas, Kevin Derby, Jaren N. Ashcraft, Hyukmo Kang, Simran Agarwal, Alexandra Kupersmith, Adam Schilperoort, Stephanie F. Rinaldi, Kelsey L. Miller, Kyle J. Van Gorkom, Corey Fucetola, Patrick Ingraham, Ewan S. Douglas, Heejoo Choi, Daewook Kim
Applied Physics
Phase noise analysis and control of VO$_2$-based relaxation type oscillators
Artem Litvinenko, Erbin Qiu, Sambit Ghosh et al. (+5 more)
VO$_2$-based relaxation oscillators form a rapidly developing field that finds applications in neuromorphic computing, Ising machines, and numerous signal processing concepts. These oscillators operate in a deeply nonlinear relaxation regime based on rapid phase transitions between insulating and metallic states in the VO$_2$ material. This process is governed by thermal effects, which lead to additional voltage fluctuations and contribute to a considerably wide spectral linewidth in the VO$_2$-based oscillator signal. In this work, we thoroughly study the phase noise in VO$_2$-based relaxation oscillators and demonstrate that the broadening of the generation spectrum linewidth at low oscillation frequencies is caused by an increased susceptibility to thermal fluctuations during the incubation phase. We explore the types of noise affecting oscillator stability and show that synchronization with an external square-wave signal improves the phase noise more effectively than a sinusoidal-shape injection locking signal.
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All authors Artem Litvinenko, Erbin Qiu, Sambit Ghosh, Juan Andres Hofer, Akash Kumar, Jong-Guk Choi, Ivan K. Schuller, Johan Åkerman
Biological Physics
Do ions have a coating in neuronal electrolytes under an electric field?
János Végh
Ions in electrolytes can have coatings and can combine into different complexes that significantly affects their size, mass, and transport features. Measuring such coatings of ions traveling in narrow, limited spaces inside biological objects is challenging. We assumed that the coating changes the size of the ion and that the speed of the complex may influence its composition. The original Stokes-Einstein relation for
diffusion assumes a simple, spherical particle in a homogeneous Newtonian fluid. It was modified to describe an electric-field-driven drift. One possible application of the result is describing the propagation of axonal impulses, especially since
soliton theory models it as a mechanical vibration, i.e., its speed changes rapidly. Hodgkin and Huxley measured the membrane current (due to axonal current) as a function of the clamping voltage, and they confirmed the linear dependence, that is, the independence of the ions' coating state from their speed.
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Fluid Dynamics
Kinetic Linear Stability Theory for High-Speed Compressible Flows: A High Performance Computing Framework
Irmak Taylan Karpuzcu, Deborah Levin and Vassilis Theofilis
Shock waves in high-speed compressible flows contain finite-thickness, high-gradient regions where the continuum assumption becomes questionable and translational non-
equilibrium arises, including non-Maxwellian micro-velocity distributions. Classical shock stability analyses rely on Navier-Stokes or moment closures and cannot retain bi-modal velocity distributions inside the shock. We develop and apply, for the first time, a kinetic linear stability theory (kLST) for one-dimensional normal shocks by linearizing the Boltzmann-BGK equation about kinetic BE-BGK base flows. Perturbations are posed in reduced distribution functions, with macroscopic fields recovered by velocity-space moments, so the stability operator acts on the VDF rather than a closed continuum system. Verified against compressible Couette
eigenvalue benchmarks near continuum, the framework is applied to argon shocks at $M_\infty=1.2$, $3.0$, and $4.0$. At low Mach number, where BE-BGK and Gilbarg-Paolucci profiles nearly coincide, the spectra recover stable continuous branches. At higher Mach number, comparing Maxwellian and non-
equilibrium VDF-based eigenspectra shows that kinetic effects shift the spectrum toward less stable regions, so continuum predictions can miss important changes even when macroscopic profiles appear well resolved. For large high-Mach
matrices–$O(10^5)$ unknowns and up to billions of nonzeros–we develop a parallel SLEPc/PETSc infrastructure using shift-and-invert Arnoldi with MUMPS LU for moderate sizes and Jacobi-Davidson (JD) with block-Jacobi ILU for the largest systems. Coupled spatial/micro-velocity sparsity causes severe LU fill-in, making direct solvers
memory-limited and motivating JD. We compute kLST spectra for an $M_\infty=4.0$ shock with 281088 unknowns, to our knowledge the highest-Mach kinetic linear stability calculation reported for isolated finite-thickness shock layers.
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Fluid Dynamics · Cross-listed from math.NA
Comparison of a Parametric Physics-Informed Neural Network and a Tensorial Reduced-Order Model for the Shallow-Water Dam-Break Problem
Anton Myshak, Md Rezwan Bin Mizan and Ilya Timofeyev
We develop two parametric data-driven reduced models: a physics-informed neural network (PINN) and a non-intrusive tensorial reduced-order model (TROM), and apply both approaches to the parametrized one-dimensional shallow-water dam-break problem. Neither reduced model requires time integration: both learn a direct parameter-to-solution map from space, time, and dam-break parameters to the physical state, with the PINN providing predictions at arbitrary times and the TROM reconstructing solutions at the stored snapshot times. In addition, we demonstrate that it is essential to introduce shock-aware collocation to improve the robustness of the PINN model.
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Medical Physics
Rethinking Artificial Intelligence in Medical Imaging: Assumptions, Reality, and Reframing
Arman Rahmim, Nourhan Bayasi, Xiaoxiao Li et al. (+2 more)
Medical imaging has served as primary proving ground for clinical artificial intelligence (AI), yet a decade of intense research has not translated into proportionate bedside impact. We argue that this gap is not primarily a product of insufficient algorithmic performance, inadequate regulation, or limited explainability. Rather, it reflects a structural misalignment, between how AI systems are designed and evaluated, and how clinical decisions are made. This Perspective identifies six interconnected dimensions of this misalignment: the dominance of pixel-only models in a
multimodal clinical world; the erosion of physician trust through opaque and inflexible systems; the unfulfilled promise of foundation models in data-sparse medical domains; the persistent bottleneck of non-shareable, under-curated
datasets; the gap between validated
algorithms and deployable clinical platforms; and the failure of prediction-centric AI to generate actionable clinical guidance. For each dimension, we reframe the problem and propose a path forward, culminating in a
vision of agentic, physician-aligned AI that extends, rather than replaces, clinical judgment.
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All authors Arman Rahmim, Nourhan Bayasi, Xiaoxiao Li, Babak Saboury, Fereshteh Yousefirizi
Fluid Dynamics
A sub-grid-scale model for polydisperse bubbly flows with heat and mass transfer
Anand Radhakrishnan and Spencer H. Bryngelson
Ensemble-averaged models of polydisperse bubbly flows require statistics of the evolving bubble population. Prior quadrature-based moment formulations close bubble pressure with a polytropic relation that omits heat and mass transfer at the bubble wall. We formulate constant-transfer equations for bubble pressure and vapor mass within a conditional
hyperbolic quadrature method. Second-order conditional inversion produces four joint radius–radial-velocity nodes per
equilibrium-radius bin. Bubble pressure and vapor mass are advanced at each node. The node values close the ensemble-averaged flow equations without adding mixed pressure or vapor-mass moments to the transported moment set. The model is implemented in MFC. Monte Carlo calculations verify the
evolution of quadrature nodes and the mean bubble variables for a harmonically forced population. Bubble-screen calculations quantify closure error as the
equilibrium radius is discretized and the initial distributions vary. The constant-transfer calculation does not exhibit the high-frequency pressure oscillations observed with the polytropic closure under the conditions considered. 3D bubble-screen calculations give a 1.5% relative root-mean-square error between the Euler–Euler center pressure and the mean of 40 volume-averaged Euler–Lagrange realizations.
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Biological Physics
Continuous Game of Life: cell emergence and self-organization at the edge of growth
Alexandre Guillet and Frank Jülicher
Conway's Game of Life shows that simple rules can generate a rich diversity of emerging structures. This cellular automaton has been translated to continuous space by Rafler (2011) in a simulation called SmoothLife. The isotropic rule of this continuous Game of Life generates patterns whose beauty has attracted the
attention of a growing community at the intersection of science and computer art. We study a minimal variant of this model, continuous in space and time, that generates
cell-like patterns capable of self-replicating, gliding and disappearing. The phenomenology of these unit patterns is reported and related to homogeneous-state bifurcations,
symmetry breaking, observed shape instabilities, finite-amplitude morphological changes, and a dilute-to-dense transition associated with
cell proliferation. Its mapping onto a large reaction-
diffusion system is interpreted in terms of homeostatic concentrations of morphogens, regulated by the nonlinear survival rule and generated through a
cell-sourced cascade of auxiliary reactions. Introducing a global conservation law that limits resource availability causes the system to self-organize at this dilute-to-dense transition, which we call the edge of growth. A further exploration of parameter space reveals a variety of phases and the richness of life-like morphologies organized around this edge. Resemblance to biological processes such as division, motility, and death, together with a concise formulation and numerical implementation, makes the continuous Game of Life an appealing model system for investigating the emergence and self-organization of life-like patterns.
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General Physics
Multiplicity of Massive Stars at Low Metallicity: Early Results from the BLOeM Campaign
T. Shenar, J. Bodensteiner, M. Abdul-Masih et al. (+73 more)
Massive
stars at low
metallicity (Z) play a central role in shaping the high-
redshift Universe, yet their multiplicity remains poorly constrained. The Binarity at Low
Metallicity (BLOeM) campaign is a two-year survey of 929
stars in the Small Magellanic Cloud with the Fibre Large Array Multi Element Spectrograph (FLAMES) instrument at ESO's Very Large
Telescope, providing the first large-scale spectroscopic monitoring of massive
stars at low Z (1/5
solar). Analysis of the initial nine epochs reveals high intrinsic binary fractions (>70%) on the main sequence and a steep decline in evolved objects. Analysis of the full
dataset will yield orbital solutions, identify black-hole companions, and allow a derivation of the initial mass function for single and binary
stars at low Z.
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All authors T. Shenar, J. Bodensteiner, M. Abdul-Masih, F. Backs, S. R. Berlanas, J. M. Bestenlehner, A. Bobrick, D. M. Bowman, N. Britavskiy, P. A. Crowther, K. Deshmukh, M. Fabry, M. Gieles, A. Gilkis, G. González i Torà, G. Gräfener, M. Gull, Y. Götberg, C. Hawcroft, V. Hénault-Brunet, A. Herrero, G. Holgado, R. G. Izzard, S. Janssens, H. Jin, V. M. Kalari, Z. Katabi, A. de Koter, J. Klencki, B. Kubátová, J. Kubát, N. Langer, T. Lechien, D. Lennon, R. Lefever, B. Ludwig, L. Mahy, J. Maíz Apellániz, I. Mandel, A. Mang Román, G. Maravelias, P. Marchant, A. Menon, F. Najarro, A. O'Grady, L. Oskinova, R. Ovadia, L. R. Patrick, D. Pauli, M. Pawlak, M. Bernini Peron, A. Picco, V. Ramachandran, M. Renzo, D. F. Rocha, H. Sana, A. A. C. Sander, T. Sayada, A. Schootemeijer, F. R. N. Schneider, R. Seeburger, K. Sen, S. Shahaf, S. Simón-Díaz, M. Stoop, S. Toonen, F. Tramper, R. Valli, P. Van Daele, J. Th. van Loon, L. van Son, A. Vigna-Gómez, J. I. Villaseñor, J. S. Vink, C. Wang, X.-T. Xu
Optics
Fresnel Drag in the Homogenization Limit with Space-Time-Modulated Wire Media
A. B. Yakovlev, M. G. Silveirinha, A. Pal et al. (+1 more)
Space-time modulations of the electromagnetic response offer new opportunities for wave control. In particular, such systems can emulate moving-medium responses and the associated Fresnel drag in the homogenization limit. Existing approaches require the simultaneous microscopic modulation of both permittivity and permeability, which is difficult to realize in practice. Here, we show that modulating a metallic response overcomes this limitation and enables strong moving-medium-like effects using purely electric modulation. We illustrate this mechanism with a space-time-modulated wire medium, described through Lorentz transformations and quasi-static homogenization. The resulting effective medium is nonreciprocal and bianisotropic and supports a pronounced synthetic Fresnel-drag effect. For a finite-thickness slab, this response leads to nonreciprocal scattering while preserving global energy conservation for propagating waves. Remarkably, the synthetic Fresnel drag also produces velocity-dependent reflection and transmission Goos-Hänchen shifts, providing a direct signature of the effective motion.
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All authors A. B. Yakovlev, M. G. Silveirinha, A. Pal, M. H. Zadeh
Atomic Physics · Cross-listed from quant-ph
Geometry-Induced Domain-Wall Pinning and $\mathbb{Z}_2$ Asymmetry in Nominally One-Dimensional Rydberg Arrays
Elijah Pelofske, Frank Barrows and Cristiano Nisoli
We perform experiments on QuEra's neutral-Rydberg-atom Aquila
quantum computer, using quasi-adiabatic
evolution on 1-dimensional models. We use hardware fine-tuning to balance the measurement statistics close to zero net magnetization, in two different
geometric outlines: one closed triangular model with 33 atoms, and one 47-atom square with an engineered atom vacancy. The nature of this processor restricts the geometry of the atoms that can be programmed to a 2D plane. We report effects not predicted by the pure 1D Ising model, such as pinning of domain walls and $\mathbb{Z}_2$
symmetry breaking due to the interplay between van der Waals interactions and the Rydberg blockade. In particular, atoms around the atom vacancy and at the vertices of the 1-dimensional square-outline model strongly prefer the Rydberg state, leading to the effective model having a
ferromagnetic bond across the vacancy.
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Optics
Physics-Informed Neural Networks for 2D Plane Wave Scattering in Arbitrary Dielectric Structures
Zheng-Yu Huang, Yu Tian, Jing-Wen Zhang et al. (+1 more)
In this paper, we introduce a meshless physics-informed neural network based computational framework for solving two-dimensional electromagnetic wave scattering in inhomogeneous media. The framework embeds frequency-domain Maxwell equations and radiation boundary conditions directly into the neural network loss function, enabling accurate prediction of scattered fields for both transverse
magnetic (TM) and transverse electric (TE) polarizations across various dielectric configurations. Application of the method to single-cylinder, concentric multilayer cylindrical shells, three arbitrarily arranged cylinders, and composite irregular structures demonstrates that for the TM polarization, all relative $L^{2}$ errors mostly remain at particularly low levels of $\le0.1$. For the TE polarization, sharp variations of the dielectric properties of scatterers lead to singularities in the governing equations, which result in decreased accuracy of the method. This challenge is overcome by introducing at dielectric boundaries a
hyperbolic-tangent smoothing function. This procedure significantly improves the accuracy of the method, with the corresponding results closely matching the predictions of the finite-difference time-domain method. This framework exhibits stable convergence behavior across all of the investigated configurations, thus confirming its robustness and scalability to complex electromagnetic scattering problems.
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All authors Zheng-Yu Huang, Yu Tian, Jing-Wen Zhang, Nicolae C. Panoiu
Optics
New techniques for high-resolution imaging and high-precision wavefront sensing via masked-aperture interferometry
Nithyanandan Thyagarajan, Bojan Nikolic, Chris Carilli et al. (+2 more)
Achieving high-angular-resolution imaging on subarcsecond scales is fundamentally limited by wavefront aberrations imparted by the propagation medium and by optical elements along the light path. Accurate recovery of source structure at these fine angular scales therefore relies on precise, real-time sensing and correction of wavefront aberrations. Drawing inspiration from
radio interferometry, we have developed different approaches using masked apertures that directly measure both the amplitude and phase of the distortions to the electromagnetic wavefront while simultaneously reconstructing the underlying source structure. First is
radio interferometry style self-calibration which can recover the complex electric field aberrations across the aperture with subarcsecond phase accuracy, equivalent to nanometer-level precision in optical pathlength, and simultaneously reconstruct the source structure with milliarcsecond (sub-micron) accuracy. Second is closure invariant-based source reconstruction which allows to bypass self-calibration and errors therein entirely while achieving comparable fidelity in the recovered source structure. These methods have been validated on the ALBA synchrotron beamline. Together, these methods provide a reliable framework for nanometre-scale high-precision wavefront sensing and subarcsecond-scale high angular resolution imaging, enabling new possibilities for masked-aperture interferometry. Potential applications span laboratory and synchrotron facilities to astronomy, including beam diagnostics in the Large
Hadron Collider and masked-aperture interferometry on space
telescopes such as the James Webb Space
Telescope.
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All authors Nithyanandan Thyagarajan, Bojan Nikolic, Chris Carilli, Laura Torino, Ubaldo Iriso
Plasma Physics · Cross-listed from astro-ph.CO
Andrew Liu, Anirudh Prabhu, Akaxia Cruz et al. (+1 more)
Dark matter that self interacts through long-range forces exhibits coherent, collective effects that are absent in short-range interactions. In the case where dark matter interacts through a hidden-
photon mediator, its dynamics closely resemble those of Standard Model
plasmas. In such models, various astrophysical environments, including cluster collisions and subhalos orbiting their host
halo, are susceptible to
plasma instabilities: processes that modify the dark matter velocity distribution and lead to exponential growth of dark electromagnetic fields. In this paper, we present the first study of the non-linear
evolution of electrostatic instabilities in dark matter subhalos orbiting within the Milky Way potential using a suite of particle-in-
cell simulations. We find that the growth and saturation of these instabilities produce substantial turbulent heating and mass loss, with an efficiency that depends sensitively on subhalo mass and orbital eccentricity. For highly eccentric orbits,
plasma heating can reduce the initial mass of a $10^7$ ($10^9$) $\text{M}_\odot$ subhalo by as much as $\sim 97\%$ ($\sim 84\%$) soon after first pericenter.
Plasma-induced heating and stripping may therefore leave observable signatures in the Milky Way subhalo population, including a suppression of the low-mass subhalo mass function.
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All authors Andrew Liu, Anirudh Prabhu, Akaxia Cruz, Mariangela Lisanti
History and Philosophy of Physics
Ghosts that Connect
Henrique Gomes
What is a Faddeev–Popov ghost? The textbook answer is that it is a trick: a way of writing a functional determinant as a term in the action, and nothing more. Dougherty 2021 and Dougherty and Read 2026 have argued that this undersells the ghost, which on their account encodes classical structure of the configuration space, viz. the degree-one generators of the Chevalley–Eilenberg complex of the action Lie algebroid. I agree with them that the ghost encodes classical structure. But I think the structure is bigger than they say. The ghost, I argue, is a principal connection $\varpi$ on the bundle $F \to F/G$ of gauge potentials over physical configurations; the BRST operator is the exterior derivative along the orbits; and the Chevalley–Eilenberg ghost coincides with $\varpi$ restricted to the orbits (and every $\varpi$ has the same restriction). The restriction drops the horizontal complement, and I show that gauge-fixed quantisation needs that complement. A gauge-fixing installs it as a pairing of configurations across orbits (a counterpart relation, in Lewis's sense); dressed observables and local counterfactuals rely on this pairing, but it is discarded by the quotient $\F/\G$. In the non-Abelian case Singer's
theorem forbids a flat $\varpi$, and there the pairing exists only as parallel transport. Finally, BRST survives gauge-fixing because it is vertical and rigid, and so leaves any such pairing unchanged.
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Data Analysis and Statistics · Cross-listed from cs.LG
DoTime: A Synthetic Benchmark Generator for Interventional and Counterfactual Time Series
Dennis Thumm, Billy Tim Anthony and Ying Chen
Most
benchmarks for causal inference over time series are observational, small, or domain-specific, leaving interventional and counterfactual estimation under-served exactly where it matters most, such as in healthcare, policy evaluation, and
climate science. We introduce DoTime, an open, scalable, and theoretically grounded generator of multivariate temporal structural causal models (TSCMs) with interventions, released as the \code{dotime} PyPI package together with four frozen evaluation suites. Beyond existing work, it adds capabilities absent from prior generators: continuous-time intervention windows, counterfactual sampling modes with a positivity guard, regime-switching SCMs as a strict generalization of interrupted time series, non-stationary dynamics by construction with switching SCM parameters, and deterministic ramp and sinusoidal intervention profiles that place trends and structural breaks inside the evaluation window. Moreover, it demonstrates the suitability of the generator as a prior for a causal foundation model reference implementation. The released suites span a training-scale snapshot of $100{,}000$ trajectories and eight named identification structures, each with exact ground truth: paired interventional trajectories from the same SCM throughout, and shared-noise counterfactuals in the continuous-time suite. We ship reference baseline implementations with an evaluation harness, and pose a falsifiable claim: interventional training buys a measurable direction-accuracy advantage over an observational model of identical capacity. It is tested across three training seeds per arm. Under structure-matched evaluation on held-out episodes, the interventional prior-fitted network's (PFN) gap is positive in every structure, trajectory length, and seed tested.
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Classical Physics
The Maxwell Conjecture is False
Philip Arathoon, Gavin Ball and Matthew D. Kvalheim
We exhibit a configuration of five point charges in Euclidean space whose electrostatic potential admits at least 24 critical points all of which are non-degenerate. Maxwell's
conjecture that the field of \(n\) point charges has at most \((n-1)^2\) critical points which are all non-degenerate is therefore false.
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Fluid Dynamics · Cross-listed from math.AP
Geometry of strong forces in continuum mechanics
Theodore D. Drivas and Daniil Glukhovskiy
Consider a material point in finite dimensions moving under the influence of a potential force according to Newton's laws. Suppose the potential energy function is a generalized well, strictly convex transverse to a smooth submanifold $M$ on which it is minimal. If the potential is steep, one expects the particle will oscillate rapidly about this submanifold and, if the initial displacement is not too great, should approximately move along $M$ as if it were ideally constrained (e.g. geodesic). This expectation is true if the initial conditions are very well prepared but may fail otherwise - additional potential forces determined by how the Hessian of the potential varies along $M$ may be present. The origin of this force is that the transversal motion acts as a simple harmonic oscillator with a slowly varying frequency, which approximately conserves action, not energy. In this work, we regard continuum mechanical systems such as the elastic thread or compressible fluid as material points moving in an infinite dimensional space according to Newton's laws for appropriate potential energy functionals. We show how to arrive at ideally constrained systems such as the inextensible thread and incompressible fluid as a limit of a strong potential force, computing also corrections to the naive predictions when the data is not very well prepared. For example, for the thread we find a resistance to bending emerge from a strong resistance to compression/expansion. For the fluid, the effective incompressible dynamics may be driven by a remnant acoustical wavefield. Both of these emergent features are nonlinear and non-local. Finally, we give examples of some limits for which the naive models robustly hold because the additional force is trivial. These include the homogeneous incompressible Euler, anelastic Euler, as well as the lake and great lake equations.
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Optics · Cross-listed from cond-mat.mes-hall
Inhomogeneous saturation of excitons in monolayer transition-metal dichalcogenides
Blake T. Hipsley, Adam Alfrey and Steven T. Cundiff
We observe that the apparent inhomogeneous broadening, as measured by two-dimensional coherent spectroscopy (2DCS), of the
exciton resonance in transition-metal dichalcogenide monolayers depends on the excitation strength. A key strength of 2DCS is the ability to separate inhomogeneous broadening, which primarily contributes to the diagonal linewidth, from homogeneous broadening, which dominates the cross-diagonal linewidth. We show that the fluence dependence of the diagonal linewidth arises from the effective saturation fluence varying with the
exciton's resonance energy, i.e., inhomogeneous saturation. These results are critical for interpreting the
exciton linewidths, which are often used as a measure of sample quality.
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Applied Physics · Cross-listed from cs.AR
Investigating reservoir computing for branch prediction in pipelined processors using emerging CMOS memristor devices
Harvey Samuel George Johnson and Sendy Phang
This project aimed to develop a novel reservoir compute (RC) implementation framework targeting high-speed operation and integration with CMOS digital logic. With the target workload of branch prediction (BP) for multistage pipelined central pro-cessing unit (CPU) cores. For this, a novel memristor based RC design framework was developed within the context of the workload requirements. This was then implemented in simulation using industry standard modelling
languages of System Verilog (SV) and Verilog-AMS (VAMS).The developed RC design framework was subsequently verified using a basic sequence detection task before further benchmarking for its effectiveness at BP. The developed RC framework was tested using the Dhrystone performance
benchmark, while targeting the RISC-V RV64GC instruction set architecture (ISA). Conducted testing demonstrates that RC shows great promise for ap-plication to BP and is capable of achieving impressive overall prediction accuracy. However, testing also shows that further refinement of the developed RC design framework is necessary to address shortfalls in the adaptability of the proposed RC system. As comparison against the state of the art TAGE predictor showed the proposed RC design framework to be 15x slower to adapt to changes in branching behaviour.
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Plasma Physics
SPECTRE: A robust solver for 3D equilibria with arbitrary topology
E. Balkovic, J. Loizu, E. Lanti et al. (+6 more)
We present SPECTRE, a new
equilibrium code based on the Multi-Region relaxed MHD model for robustly calculating 3D
equilibria with general
magnetic topology, allowing for flux surfaces,
magnetic islands, and chaos. The code builds on a previous MRxMHD solver, SPEC, but performs significantly better thanks to a new formulation of force, the use of a stable trust-region-based least squares minimization scheme, as well as several additional features. SPECTRE is verified through application to configurations with known
equilibrium solutions, in
vacuum and with finite beta, both in the fixed boundary and the free boundary mode. Notably, these include
vacuum equilibria of a quasi-axisymmetric (QA) device in fixed-boundary mode, and of W7-X in the free-boundary mode, along with a classical stellarator finite-beta free-boundary case. Finally, the solver is applied to a modern optimized finite-beta quasi-isodynamic (QI) configuration, where we demonstrate calculation of a strongly-shaped
equilibrium with a core island which is in agreement with a HINT calculation.
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All authors E. Balkovic, J. Loizu, E. Lanti, C. Smiet, C. Lazzati, R. Ramasamy, A. Goodman, J. Geiger, J. P. Graves
Plasma Physics
Divertor topology and vacuum vessel design for stellarators
Andrew Giuliani, Raffael Wendlinger, Misha Padidar et al. (+4 more)
We present stellarator optimization
algorithms for designing the edge
magnetic structure in
vacuum fields, together with the
vacuum vessel. First, we introduce a numerical method that robustly computes periodic-orbit fixed points of any type (
elliptic,
hyperbolic, or
parabolic), which could form the basis of a divertor. To couple divertor and
vacuum vessel design, we introduce parametric families of
vacuum vessels for which point-to-vessel distances, and their derivatives, can be computed efficiently. The resulting
algorithms use signed distance functions to enforce coil-vessel clearance while allowing coils to be placed on or off the vessel. Using these methods, we jointly optimize modular coils and the
vacuum vessel to realize a wide range of
magnetic topologies for diverting exhaust, including standard X-point divertors, and single- and double-null configurations. For the first time, we show that precise snowflake divertors can be achieved in stellarators. Using this framework, we generate a number of quasi-axisymmetric stellarator designs with compatible
vacuum vessels and diverse divertor architectures, which we consider to be candidates for a next-generation
STAR Lite prototype.
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All authors Andrew Giuliani, Raffael Wendlinger, Misha Padidar, Robert Davies, Shibabrat Naik, Calvin Lowe, Georg Harrer
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Formation of $\mathrm{L}1_2$-ordered $\gamma'$-$\mathrm{Ni}_3\mathrm{Al}$ precipitates in ternary Cu-Ni-Al alloys modelled using an ab initio concentration wave theory and atomistic simulations
Christopher D. Woodgate, Hubert J. Naguszewski, Samuel L. Deacon et al. (+4 more)
Precipitation-strengthened Cu-Ni-Al
alloys are of interest for technological applications because coherent, $\mathrm{L}1_2$-ordered $\gamma'$-$\mathrm{Ni}_3\mathrm{Al}$ precipitates can confer high mechanical strength while allowing the material to retain many of the good transport properties characteristic of elemental Cu. In this work, we study the thermodynamics and phase stability of the pseudobinary $\textrm{Cu}_x (\textrm{Ni}_{3/4} \textrm{Al}_{1/4})_{1-x}$ system, $0 \leq x \leq 1$. We use a computational modelling framework combining first-principles electronic structure calculations with a concentration wave analysis from which atom-atom effective pair interactions are extracted for use in atomistic Monte Carlo simulations. Our modelling reveals three distinct, composition-dependent regimes of phase behaviour, in qualitative agreement with the experimentally determined phase diagram. At low Cu content, Cu is soluble in the $\mathrm{L}1_2$-ordered $\mathrm{Ni}_3\mathrm{Al}$ phase, with a single identifiable phase transition corresponding to chemical ordering between Ni and Al. At intermediate compositions, this high-temperature ordering is followed at lower temperatures by phase separation of Cu and $\mathrm{L}1_2$-ordered $\mathrm{Ni}_3\mathrm{Al}$. Finally, at high Cu content, $\mathrm{L}1_2$-ordered $\mathrm{Ni}_3\mathrm{Al}$ precipitates directly from the solid solution, with no clearly identifiable secondary transition. We relate these phase transformations to features of the underlying electronic structures of the considered
alloys. Overall, this work demonstrates a computationally efficient workflow capturing both chemical ordering and coherent precipitation in multicomponent substitutional
alloys, with relevance to the study of phenomena such as precipitation strengthening.
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All authors Christopher D. Woodgate, Hubert J. Naguszewski, Samuel L. Deacon, Mathys P. Potel, Ján Minár, David Quigley, Julie B. Staunton
Atomic Physics
Tackling the uncertainty of the nuclear-polarization correction to the bound-electron $g$ factor by means of the nuclear Skyrme interaction
Arnab Choudhury and Igor A. Valuev
The Coulomb part of the leading-order
nuclear-polarization correction to the bound-electron $g$ factor of hydrogenlike ions is investigated in a microscopic approach from the
nuclear point of view. To this end, the effective Skyrme force is employed to model nucleon-nucleon interactions, with the energies and the reduced transition probabilities of collective
nuclear excitations being obtained in the Hartree-Fock-based random-phase approximation. These
nuclear parameters serve as input for the
nuclear-polarization correction, evaluated via effective self-energy diagrams where the
photon propagator is modified by a
nuclear-polarization insertion. A diverse set of Skyrme parameterizations is probed for $^{40}\text{Ca}^{19+}$, $^{60}\text{Ni}^{27+}$, $^{90}\text{Zr}^{39+}$, and $^{120}\text{Sn}^{49+}$, and the results are compared to the common approach involving experimental
nuclear data and estimates based on energy-weighted sum rules. As a result, tighter constraints on the theoretical uncertainties of the
nuclear-polarization corrections are obtained, providing key input for high-precision measurements of the bound-electron $g$ factors of heavy hydrogenlike ions.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci
No band gap, no problem: Defects in InAs using a band-avoiding occupation-constrained density functional theory
Peter A. Schultz, Arthur H. Edwards, Evan M. Anderson et al. (+2 more)
Density functional theory (DFT) underestimates the experimental band gap—the infamous band gap problem. As the band gap defines the energy scale of defect levels, this complicates computation of charge transition energies for atomic defects. In the extreme case of narrow-gap
semiconductors, the DFT band gap collapses to zero, seemingly precluding quantitative predictions of defect levels. We present a band-avoiding occupation-constrained DFT (ba-occ-DFT) approach that prevents spurious occupation of band-edge states and enables reliable total energy calculations of atomic defects. Application to indium arsenide (InAs) shows that ba-occ-DFT circumvents the band gap problem, separates band-edge errors from defect level calculations, and enables rigorous defect level predictions in a narrow-gap
semiconductor despite a zero DFT band gap.
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All authors Peter A. Schultz, Arthur H. Edwards, Evan M. Anderson, Anthony C. Knighton, Leopoldo Diaz
Fluid Dynamics
A New Paradigm for 3D Turbomachinery Design: Generative Diffusion Model Based Framework with Direct Geometry Encoding
Yingfan Geng, Jinhong Wang, Lazaros Papachristodoulou et al. (+2 more)
The aerodynamic design of turbomachinery is critical to the performance of the overall energy system, yet it is challenging due to the complex non-linear flow physics and the presence of multiple-target design compromises. Denoising
diffusion model, as one of the leading approaches in generative machine learning, has shown its advantages of high design solution accuracy and diversity in many engineering applications. In this study, we bring it to the 3D inverse design problem of turbomachinery, using centrifugal compressors as a classic representative, to demonstrate the new methodology for complex geometry designs. A
diffusion model-centred design framework has been developed in this study. By specifying the desired design condition (mass flow rate and rotational speed) and targeted performance (pressure ratio and efficiency), the trained
diffusion model returns directly the 3D compressor geometry that satisfies the condition inputs. Compared to traditional deterministic forward design approaches, the proposed method not only generates accurate geometry solutions to inverse design problems, but also enables effective exploration of the entire design space, providing a diverse set of candidate solutions. In addition, this paper presents the first study to directly train on 3D blade geometry coordinates rather than parametrised representations, demonstrating the feasibility of coordinate-based learning while enabling a highly flexible framework applicable to a wide range of designs. The trained
diffusion model achieves excellent design capability, with solution accuracy up to 99% and unfeasible designs less than 1%. Furthermore, the solution diversity of the trained
diffusion model is also quantitatively verified by means of comparing the distribution of the solution sets generated from the
diffusion model and from direct sampling of physical parameters.
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All authors Yingfan Geng, Jinhong Wang, Lazaros Papachristodoulou, Sibo Cheng, Teng Cao
Physics and Society · Cross-listed from q-fin.ST
Where does the criticality live? Early-warning signals are event-heterogeneous across seven crypto-perpetual liquidation cascades
Ramon Marc Garcia Seuma
Do crypto perpetual-futures crashes carry a reproducible early-warning fingerprint of a critical transition, and in which state variable? We study seven major BTC liquidation cascades (2022-2025, including the record 19B USD event of 10 October 2025) using minute-level price and 5-minute leverage/order-flow data. On detrended residuals we compute rolling variance and lag-1 autocorrelation and test their pre-cascade trend with the Kendall-tau statistic, sweeping 39 analysis configurations per variable per event. No variable is event-invariant. Price carries the critical-slowing-down signature in five of seven events but is silent in exactly the two sudden-news (tariff) shocks, suggesting a two-type structure: endogenous-buildup versus exogenous-shock cascades. The October 2025 event, whose in-sample analysis suggests the signature lives in leverage rather than price, turns out to be the outlier, not the rule. The one regularity surviving all events with data is a compression of taker order-flow variance, which passes a 300-onset placebo test (Fisher-combined p ~ 5e-6) but is a population-level precursor, not a per-event alarm. Single-event critical-slowing-down claims in crypto derivatives are therefore fragile by construction. We argue the pattern of failures is itself diagnostic: slowing down is absent exactly where the destabilising mechanism is most abrupt, as one would expect if these cascades are discontinuous, shock-driven transitions rather than critical ones.
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