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Physics

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Wednesday 16 September

Atmospheric and Oceanic Physics

A more predictable Madden-Julian Oscillation index derived from Koopman spectral analysis

Claire Valva and Edwin P. Gerber

The Madden-Julian oscillation (MJO) is a major source of subseasonal-to-seasonal (S2S) predictability. The MJO is commonly defined and tracked with indices such as the Real-time Multivariate MJO (RMM) index. Although the RMM provides a useful description of the MJO, its evolution can be noisy and difficult to predict. We define an MJO index using a data-driven approximation of the Koopman operator. The Koopman index captures similar tropical circulation and convection patterns to the RMM but evolves more smoothly and predictably. Skillful prediction extends to 46 days for the Koopman index compared to 11 days for the RMM under the same prediction framework. While this new approach does not recover the RMM as well as operational S2S models, which provide skillful forecasts up to 35 days, the Koopman index could complement existing MJO diagnostics in evaluating and developing extended-range forecast systems.
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Nuclear Theory

Long-Lived False-vacuum-Trapped Self-Bound Neutron-rich Droplets

Jingdong Shao and Mei Huang

We propose a novel class of anomalous nuclear matter: self-bound, neutron-rich droplets trapped in false vacuum associated with the nuclear liquid-gas phase transition in heavy-ion collisions. During the early stage of the fireball expansion, strongly correlated local clusters dynamically decouple from the bulk medium and are excited into the liquid phase. As the ambient fireball cools rapidly, these clusters are quenched into metastable anomalous droplets with isospin asymmetry from ambient neutron-enrichment. Mechanical equilibrium among nuclear pressure difference, Coulomb repulsion, and surface tension stabilizes droplets at radii of order $\mathcal{O}(10)$ fm. Isospin asymmetry induces high potential barrier that suppresses decay channels, yielding long lifetimes. These droplets are expected to exhibit characteristic charge-to-mass ratios distinct from conventional neutron-rich nuclei, providing clear experimental signatures for future heavy-ion collision searches.
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Fluid Dynamics

How universal are warm turbulent cascades?

Ben Y. Israeli and Gregory Falkovich

It is often assumed that general stationary solutions to the wave kinetic equation are described solely by conserved fluxes and temperature. The families of solutions parameterized by these quantities are referred to as warm cascades, and are derivable from differential models of wave kinetics. These models rely on the assumption of local interactions, and we demonstrate by a time scale argument that the nonlocal effect of thermal damping on the cascade may result in dependence on an additional parameter, the UV cutoff, calling into question the validity of warm cascade solutions. This is shown for systems with both three-wave and four-wave interactions. We then consider the depletion of the cascade by this damping, and present a numerical demonstration of this nonlocal and nonuniversal behavior.
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Chaotic Dynamics

Ladder of information limits on prediction for reduced-order models

Adrian Lozano-Duran

What can and cannot be predicted by a model when only limited information is available? We answer this question by constructing a ladder of information limits that organizes prediction tasks according to their information requirements: from memoryless and memory-augmented trajectory forecasts to event prediction, stationary statistics, and generative laws. The analysis, which is independent of the model structure or architecture, identifies the minimum attainable error along with the information limitations that give rise to it. The approach distinguishes information hidden in unresolved variables from information recovered through time-delayed observations and connects these contributions to Mori–Zwanzig memory. The ladder also reveals why Lyapunov growth alone cannot characterize reduced-order prediction error, why stationary statistics may remain predictable even when individual trajectories become unpredictable, and why stochasticity can represent (but cannot recover) missing information. Numerical studies of the Kuramoto–Sivashinsky equation and the Lorenz system illustrate these results across the ladder. This unified perspective provides a principled language for understanding the fundamental limitations of ROMs for a given prediction task and for clarifying whether improved predictions require richer observations, greater precision in the input, or additional memory.
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Chemical Physics

Agentic AI for Density-Functional Development: Revisiting r2SCAN

Santosh Adhikari, Kelsey A. Parker, Etinosa Osaro et al. (+2 more)

We demonstrate physics-constrained agentic development of a meta-generalized gradient approximation (meta-GGA) functional using a large language model (LLM) to assist the search and optimization of a band-gap-oriented revision of r2SCAN. No real bonded systems were fitted, preserving r2SCAN's nonempirical philosophy. Across the finalist set, band gaps and several molecular subsets improve relative to r2SCAN; the top finalist, r2SCAN+, reduces the band-gap MAE on a benchmark comprising 24 solids from 1.26 to 0.96 eV and the aggregate MAE on 329 molecular properties from 4.79 to 4.42 kcal/mol. We first curated 78 exchange and 90 correlation candidate correction terms from r2SCAN's dimensionless ingredients, spanning polynomial terms through third degree, exponentials, exponentially damped products, and ratios. Allowing each candidate to combine one to three correction terms from the exchange catalog, the correlation catalog, or both yields about 8 x 10^5 distinct forms, making exhaustive high-throughput screening impractical. We defined the search criteria for the LLM agent using r2SCAN's exact constraints, physical norms, and the targeted iso-orbital derivative response. The agent then combined these criteria with its pretrained knowledge and accumulated search feedback to propose and refine sparse forms, prioritizing terms tied to the iso-orbital response; a second LLM critic screened proposals before deterministic verification. Compared with uniform random search, the workflow learned from prior evaluations, incurred far fewer downstream rejections (0.6% versus 24.6%), and located stronger high-response candidates: 51 agentic candidates exceeded the best random-search response of 1.263, with the overall best reaching 1.331. These results show that agentic search can support density-functional development when flexible hypothesis generation is coupled to automated physical verification.
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All authors Santosh Adhikari, Kelsey A. Parker, Etinosa Osaro, Swagata Roy, Dario Rocca

General Relativity and Quantum Cosmology

Deep Learning Detection of Beyond-General-Relativity Deviations in Gravitational-Wave Signals: A Detection-Threshold Study with Real LIGO Noise

Muhammad Adnan Shahzad

We study machine-learning detection of controlled beyond-General-Relativity (beyond-GR) deviations in gravitational-wave signals, using both synthetic aLIGO-PSD noise and real LIGO H1 detector strain. Three deviation families are applied to General-Relativistic inspiral-merger-ringdown waveforms: amplitude modulation, phase modulation, and frequency modulation, each parameterized by a dimensionless strength coefficient $\beta$. A hybrid classifier combining a one-dimensional convolutional neural network with ten hand-crafted waveform statistics is trained on GR and modified waveforms and tested on a deviation type excluded from training. The central result is a quantitative detectability curve as a function of $\beta$. Using the real GW150914 strain as a template and real H1 detector noise, we find a detection threshold at $\beta \approx 0.25$, with accuracy rising smoothly from chance at $\beta \leq 0.2$ to perfect classification at $\beta \geq 0.5$. The threshold value is specific to the quadratic-in-time modulation form adopted here and should not be interpreted as a generic constraint on beyond-GR parameters. We nevertheless argue that the negative result at small $\beta$ is informative: it establishes a quantitative limit on machine-learning-only beyond-GR searches in real detector noise, in the absence of matched-filter signal extraction.
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Mathematical Physics · Cross-listed from math.CA

Rigorous analysis of giant magnetic vortex strings

Ovidiu Avadanei and Wilhelm Schlag

This paper studies axially symmetric Abrikosov-Nielsen-Olesen vortices in the quartic Abelian Higgs model as the magnetic flux becomes arbitrarily large. The emphasis is on developing the rigorous asymptotic analysis behind the formal large-flux expansions of Hakim, Lemaitre, and Mallick '01 and Dumitrescu, Gaikwad '25. For every coupling constant less than 4 we prove that the radius of the magnetic core is of the size predicted by the physics literature. We identify the interface between then normal and super-conducting regimes with the classical normal-to-superconducting transition layer in Ginzburg-Landau theory. The theorem of Chapman-Howison-McLeod-Ockendon '91 proves its existence, uniqueness and monotonicity. The connection of the Gaussian tail of the scalar field on the left with the interface is made directly with the Weber equation. The core Higgs equation is treated as a semiclassical Sturm-Liouville problem in the left overlap region, where the Higgs field decays like a Gaussian. The exterior region is described perturbatively around modified Bessel functions. A key step is to show that the matching map between the admissible Cauchy data at the two ends of the linearized interface equations has maximal rank.
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Mesoscale and Nanoscale Physics

Multiferroic Quantum Dot in an Artificial van der Waals Heterostructure

Antti Karjasilta, Mohammad Amini, Liwei Jing et al. (+5 more)

Quantum dots (QDs) provide a versatile platform for engineering quantum-confined electronic states with functionalities relevant for optoelectronics, spintronics, and quantum technologies. While substantial progress has been achieved in coupling confined states to spin, valley, topological, or ferroelectric degrees of freedom, the realization of a multiferroic QD in which quantum confinement simultaneously intertwines with magnetism and ferroelectricity remains elusive. Here, we engineer a multiferroic QD in an artificial van der Waals heterostructure grown by molecular beam epitaxy under ultra-high-vacuum conditions. The heterostructure consists of ferroelectric SnTe nanoislands deposited on the layered magnet CrBr$_2$ supported on highly oriented pyrolytic graphite. Combining scanning tunneling microscopy and spectroscopy with ab initio calculations and low-energy tight-binding models, we demonstrate the emergence of spin-polarized discretized electronic states confined within the SnTe islands. Remarkably, the spectroscopic response of the QD strongly depends on the ferroelectric domain configuration of the SnTe nanoislands, demonstrating an interplay between quantum confinement, magnetic exchange, and ferroelectric order at the atomic scale. Our results establish engineered van der Waals heterostructures as a platform for multiferroic quantum confinement and open new routes toward electrically tunable quantum spintronic devices.
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All authors Antti Karjasilta, Mohammad Amini, Liwei Jing, Robert Drost, Jose Lado, Shawulienu Kezilebieke, Peter Liljeroth, Adolfo O. Fumega

Astrophysics of Galaxies

From observing strategies to velocity dispersion bias: forward modeling unresolved binaries in ultra-faint dwarf galaxies

Xiaowei Ou, Andrew B. Pace, Nitya Kallivayalil et al. (+9 more)

Ultra-faint dwarf galaxies (UFDs) in the Milky Way are ideal probes of low-mass galaxy formation and dark matter because they are highly dark-matter dominated. In the lowest-mass systems, however, unresolved binary orbital motion complicates dynamical mass estimates by inflating measured velocity dispersions and biasing the interpretation of the inferred masses. We develop a flexible forward-modeling pipeline, the Binary Observation Simulator, to generate mock multi-epoch radial-velocity observations of binary populations in dwarf galaxies and to quantify how binary-induced biases depend on both galaxy properties and observing strategy. We generate mock samples spanning true velocity dispersion of $\sigma_{\rm true}\sim0.75$-$3.5$ km/sec, binary fractions of $0.1$-$0.9$, and multi-epoch baselines of up to $10$ yr. We find that, while multi-epoch monitoring reduces the binary-induced bias, residual contamination remains significant for low-mass halos: even a $10$-yr baseline can leave $\sim10$-$120\%$ relative bias for systems with $\sigma_{\rm true}\lesssim1$ km/sec. We also note that small sample sizes ($\lesssim20$) introduce substantial stochastic scatter in the recovered dispersions, sometimes masking the expected improvement from longer observational baselines. Applying the framework to the real $\sim17$-yr Bootes I observing record reproduces the literature velocity dispersions, yields an empirical correction conditioned on that cadence, and shows that redistributing the same observations onto half the number of stars would have removed roughly half of the residual binary bias. These results emphasize that robust dispersion estimates for the faintest dwarfs require forward modeling of both binary populations and survey cadence.
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All authors Xiaowei Ou, Andrew B. Pace, Nitya Kallivayalil, Amery Gration, Christopher T. Garling, Nathan R. Sandford, Lina Necib, Niusha Ahvazi, Andres Almeida, Kaia R. Atzberger, Yanbo Pan, Jack T. Warfield

Quantum Physics

Fifty Years of the GKLS Master Equation: Foundations and Early Developments

Fabio Benatti, Dariusz Chruściński and Saverio Pascazio

The year 2026 marks the fiftieth anniversary of the two seminal papers in which Gorini, Kossakowski, and Sudarshan, and independently Lindblad, characterized the generators of completely positive quantum dynamical semigroups. We revisit the conceptual and historical route leading to the Gorini-Kossakowski-Lindblad-Sudarshan (GKLS) master equation and examine several of its early developments and consequences. Our aim is to show how several initially separate mathematical and physical ideas converged in the GKLS structure theorem, imme- diately opening the way to manifold consequences for the description of dissipative quantum phenomena and how that theorem, fifty years later, remains both a foundational result and an active framework for open quantum dynamics.
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Physics Education

Calculating a journey to Mars with introductory physics

Jorge Pinochet

The problem of a crewed mission to Mars provides a compelling and realistic context for teaching introductory physics. In this work, we present a coherent set of calculations describing a round-trip journey between Earth and Mars, using only mathematical tools accessible at the high-school level. The treatment integrates key topics that are typically taught separately -such as Newtonian gravitation, energy, circular motion, and basic astrodynamics- into a single coherent framework. The analysis includes Hohmann transfer orbits, travel times, launch conditions, and mission constraints, illustrating how a complex real-world problem can be transformed into an effective classroom resource. This work aims to support teachers and students in exploring interplanetary travel as an accessible and motivating application of fundamental physics.
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High Energy Physics (Theory)

Current Reconstruction and Higher Interactions in Gauge Theory

Carolina Matté Gregory

We revisit Deser's current reconstruction in first-order Yang–Mills theory with an independent two-form. We fix the quadratic auxiliary sector and the first gauge correction, and ask whether a prescribed curvature interaction can be added without higher-order action terms. For a compact semisimple gauge algebra, requiring the mixed Noether identity to close without a $gh$ action term fixes the algebraic auxiliary representative to the tangent representative, up to linear curvature and dual-curvature terms on each simple ideal. For the analytic radial class $U=\Phi(f\cdot f)$, with first nonlinear term $c_p(f\cdot f)^p$, no allowed representative avoids a third-order action correction when all second-order action coefficients vanish. A free-field scaling argument inside a root $\mathfrak{su}(2)$ subalgebra establishes this result for every compact semisimple gauge algebra. Ordinary covariantization and an auxiliary-field shift give an explicit completion. For $p=2$, its seven-gluon contact term cancels a nonzero tree-level Ward contraction at real nonsingular kinematics. We also study an affine star-gauge sector motivated by Seiberg–Witten maps, where strict current feedback and second-order action truncation select different representatives. Together these results show how the prescribed auxiliary data determine which interactions are required by current reconstruction.
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Physics Education

From Prompts to Physical Laws: A Generative AI Workflow for Engineering Physics Education

Laura B. Alvarado-Cruz, Josep Ll. Suñer, Pedro Yuste et al. (+3 more)

This work explores the use of generative artificial intelligence (AI) as a source of synthetic experimental content for introductory physics courses in engineering education. Using PixVerse.ai, Grok Imagine, and Pippit, three video scenarios were generated to represent distinct resistive force regimes: constant friction, linear drag, and quadratic drag. Kinematic data were extracted from the generated videos using Tracker, an open-source video analysis tool, and subsequently fitted to the corresponding analytical models through non-linear least-squares regression in Microsoft Excel. The results show good agreement between the synthetic data and the classical kinematic equations derived from Newton's Second Law. From the fitted parameters, physically meaningful quantities were recovered in each case, with values broadly consistent with those reported in the literature under the assumed conditions. A recurring observation is that the physical plausibility of the generated motion depends on the level of detail included in the text description used to generate the videos. More specific descriptions tend to produce more coherent dynamical behaviour, suggesting that the formulation of input prompts plays a relevant role in shaping the resulting physical consistency and can be regarded as an integral component of the experimental design process. The integration of generative AI, video-based motion tracking, and curve fitting provides a complete workflow that mirrors key stages of experimental practice, from model construction to quantitative validation. The proposed methodology engages students in experimental design, data acquisition, parameter estimation, and model evaluation, promoting key engineering competencies in modelling of physical models using widely available tools. Overall, the proposed methodology demonstrates the potential of generative AI to support physics education
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All authors Laura B. Alvarado-Cruz, Josep Ll. Suñer, Pedro Yuste, Juan C. Castro-Palacio, Juan A. Monsoriu, Francisco M. Muñoz-Pérez

Nuclear Experiment

Measurements of $\gamma_v p \to \pi^+ \pi^-p'$ Cross Sections with the CLAS12 Detector for $Q^2$ from 2.4-8.0 GeV$^2$ and $W$ from 1.4-2.1 GeV

K. Neupane, R.W. Gothe, D.S. Carman et al. (+145 more)

This paper reports exclusive cross sections for the $ep \to e'\pi^+\pi^-p'$ reaction using the CLAS12 detector at Jefferson Laboratory. The extractions of fully integrated and nine single-differential cross sections are presented for the first time for photon virtualities $Q^2$ from 2.4 to 8.0 GeV$^2$ and center-of-mass energies $W$ from 1.4 to 2.1 GeV, which covers a large part of the nucleon resonance region. These data considerably extend the kinematic reach of previous measurements from CLAS that covered $Q^2$ up to 5.0 GeV$^2$. Exclusive $\gamma_v p \to \pi^+ \pi^-p'$ cross section measurements are of particular importance for the extraction of $\gamma_vpN^*$ resonance electrocouplings across the $N^*$ spectrum, especially in the mass range above 1.6 GeV where several resonances decay preferentially to the $\pi\pi N$ final states. The electrocouplings with extended $Q^2$ coverage expected from these new data will enable an improved understanding of the emergence of $N^*$ mass and structure in the transition from the strongly coupled toward the perturbative QCD regime.
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All authors K. Neupane, R.W. Gothe, D.S. Carman, V.I. Mokeev, A.G. Acar, P. Achenbach, J.S. Alvarado, W.R. Armstrong, H. Avakian, N.A. Baltzell, L. Barion, M. Bashkanov, M. Battaglieri, F. Benmokhtar, A. Bianconi, A.S. Biselli, A. Biswas, F. Bossù, S. Boiarinov, M. Bondi, K.-Th. Brinkmann, W.J. Briscoe, W.K. Brooks, J. Bryce, N.L. Bucuru R., V.D. Burkert, T. Cao, A. Celentano, P. Chatagnon, V. Chesnokov, H. Chinchay, G. Ciullo, E.W. Cline, P.L. Cole, M. Contalbrigo, A. D'Angelo, N. Dashyan, R. De Vita, A. Deur, S. Diehl, C. Dilks, C. Djalali, R. Dupre, H. Egiyan, M. Ehrhart, A. El Alaoui, L. El Fassi, L. Elouadrhiri, C. Fanelli, M. Farooq, S. Fegan, I.P. Fernando, E. Ferrand, A. Filippi, M. Filippini, C. Fogler, S. Frantzen, K. Gates, G.P. Gilfoyle, D.I. Glazier, Y. Gotra, S. Gramigna, B. Gualtieri, K. Hafidi, F. Hauenstein, T.B. Hayward, D. Heddle, T. Hellstern, M. Hoballah, M. Holtrop, Y. Ilieva, D.G. Ireland, E.L. Isupov, H.S. Jo, T. Kageya, M. Kerr, V. Klimenko, A. Kripko, V. Kubarovsky, C. Lama, L. Lanza, S. Lee, P. Lenisa, X. Li, D. Martiryan, V. Mascagna, M. Masud, B. McKinnon, A. Mehta, R.G. Milner, R. Milton, M. Mirazita, E.F. Molina Cardenas, C. Munoz Camacho, P. Nadel-Turonski, T. Nagorna, S. Niccolai, G. Niculescu, M. Osipenko, A. Osmond, P. Pandey, M. Paolone, L.L. Pappalardo, R. Paremuzyan, E. Pasyuk, C. Paudel, S.J. Paul, N. Pilleux, L. Polizzi, J. Poudel, Y. Prok, A. Radic, K. Ramage, B.A. Raue, M. Ripani, M. Ronayette, P. Rossi, A.A. Rusova, C. Salgado, S. Schadmand, A. Schmidt, Y.G. Sharabian, S. Shrestha, U. Shrestha, E. Sidoretti, Iu.A. Skorodumina, N. Sparveris, S. Stepanyan, I.I. Strakovsky, S. Strauch, M. Tenorio, F. Touchte Codjo, N. Tyler, R. Tyson, M. Ungaro, S. Vallarino, C. Velasquez, L. Venturelli, H. Voskanyan, E. Voutier, Y. Wang, D.P. Watts, U. Weerasinghe, X. Wei, N. Wuerfel, Z. Xu, Z.W. Zhao, M. Zurek

Quantum Physics

Transformers as Intrinsic Optimizers for Quantum Approximate Optimization Algorithm

Kuan-Cheng Chen, Xiaotian Xu, Hiromichi Matsuyama et al. (+3 more)

The Quantum Approximate Optimization Algorithm (QAOA) is a leading variational framework for combinatorial optimization on noisy intermediate-scale quantum hardware, but its practical performance depends strongly on the classical optimizer used to train its variational parameters. This outer-loop optimization is often nonconvex, initialization-sensitive, and costly when repeated across large families of related problem instances. In this work, we propose a Transformer-based intrinsic optimization framework for QAOA, in which the optimizer itself is learned and embedded directly into the hybrid quantum-classical loop. The proposed graph-conditioned Transformer processes problem structure, current QAOA parameters, measurement feedback, and recent optimization history to predict the next variational-parameter update, thereby reformulating instance-wise classical optimization as an amortized learned policy. We develop a mathematical formulation of this intrinsic-optimization perspective and evaluate the method on QAOA-based MaxCut benchmarks across multiple problem settings, with comparisons against representative classical and learned optimization baselines. The results demonstrate that Transformer-based intrinsic optimization can provide a structured and transferable mechanism for improving the classical component of hybrid quantum optimization algorithms.
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All authors Kuan-Cheng Chen, Xiaotian Xu, Hiromichi Matsuyama, Wei-Hao Huang, Haomu Yuan, Yu Yamashiro

Chemical Physics

Machine-Learned Dynamical Representations for Accelerated RiteWeight Convergence

Sagar Kania

The increasing use of generative models has made ensembles of short molecular dynamics trajectories increasingly common, creating a growing need for methods that can recover physically meaningful steady-state populations and kinetics from improperly weighted conformational ensembles. Randomized Iterative Trajectory Reweighting (RiteWeight) addresses this problem through repeated random clustering and iterative reweighting, without requiring the fixed Markovian discretization used in conventional Markov state models (MSM). However, the choice of reduced feature space in which RiteWeight performs random clustering has not been systematically investigated. Here, we compare two machine-learned representations, DeepTICA and SPIB-VAE, with linear TICA for recovering steady-state observables from flawed distributions. DeepTICA learns nonlinear coordinates by targeting slow transfer-operator eigenmodes, whereas SPIB-VAE compresses configurations into a low-dimensional latent space while retaining information predictive of future metastable states. DeepTICA provided a comparatively robust RiteWeight representation under limited hyperparameter exploration, whereas SPIB-VAE benefited more strongly from broader optimization. Moreover, a kinetic score computed from a coarse MSM at a resolution comparable to that used for RiteWeight random clustering provided a useful criterion for efficiently selecting reduced representations and their hyperparameters for RiteWeight.
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Superconductivity

Multiple Andreev Reflection Spectroscopy of Spin-Resolved Proximity States

A.A. Golubov and M.Yu. Kupriyanov

We predict a coherent multiple Andreev reflection regime in superconducting nanoconstrictions with parallel proximity-induced exchange fields in the electrodes. The subharmonic gap structure is controlled by reconstruction of the spin-resolved electrode spectra, rather than by a rigid displacement of BCS gap edges. This produces split and redistributed anomalies governed by the interval between the outer gap edge and a shifted exchange induced density of states singularity. The effect survives channel transparency averaging and provides a direct transport probe of spin-resolved proximity states.
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Mesoscale and Nanoscale Physics

Displacement field stabilizes even-denominator and partonic fractional quantum Hall states in the $\mathcal{N}{=}2$ Landau levels of Bernal-stacked bilayer graphene

Rakesh K. Dora, Udit Khanna and Ajit C. Balram

Bernal-stacked bilayer graphene (BLG), in which a graphene layer is stacked atop another and laterally shifted by a lattice constant, offers remarkable tunability in its single-particle states under applied magnetic and displacement fields. Owing to this tunability, recent transport and scanning tunneling microscopy experiments in the presence of a perpendicular magnetic field and finite interlayer displacement fields have observed even-denominator fractional quantum Hall (FQH) states at half-filling in the first excited, namely, $\mathcal{N}{=}2$, Landau level (LL) of BLG. In contrast, at zero displacement field, a gapless composite fermion Fermi liquid (CFFL) is realized at half-filling of the $\mathcal{N}{=}2$ LL. Motivated by these experiments, we compute the phase diagram as a function of the displacement field in the half-filled $\mathcal{N}{=}2$ LL of BLG by studying the competition between the CFFL and the Moore-Read state—a candidate even-denominator FQH state—by calculating their thermodynamic energies in this setting. We find that the modified effective Coulomb interaction, induced by changes in the single-particle states with increasing displacement field, softens the inter-electronic repulsion at short distances, thereby stabilizing the Moore-Read state over the CFFL in the $\mathcal{N}{=}2$ LL of BLG. We also study the nature of FQH states at fillings $2/5$, $3/7$, $4/9$, and $6/13$ in the $\mathcal{N}{=}2$ LL of BLG. Our results suggest that, with increasing displacement field, the Jain composite-fermion states at $3/7$, $4/9$, and $6/13$ transition into states with distinct topological order that are well-captured by parton wave functions.
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Applied Physics

Static-to-dynamic field conversion in a temporally switched Lorentz medium

Alazar G. Salfore and Mario J. Mencagli

We investigate static-to-dynamic electromagnetic field conversion in a temporally switched Lorentz medium initially subjected to an electrostatic field. An abrupt change of the oscillator strength drives the material away from its initial equilibrium, while the polarization retains memory of the pre-switch state and acts as the source of the resulting transient. We formulate the resulting initial-value problem in the Laplace domain and derive an analytical representation of the generated field in terms of the poles of the finite Lorentz slab. Material dispersion gives rise to a richer modal structure than in the nondispersive case, including families of slab-mode poles that accumulate toward the singularities associated with the Lorentz polarization dynamics. We further show that material memory governs the earliest stage of the transient, producing a smooth field onset and setting the velocity of the earliest propagating disturbance through the high-frequency permittivity. Because the temporal switch generates broadband spectral content, the transient samples positive-, near-zero-, and negative-permittivity regions of the post-switch material response, leading to qualitatively different spatial field distributions. These results reveal how material dispersion and memory fundamentally shape the generation and evolution of radiation produced from an initially static electromagnetic state.
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Astrophysics of Galaxies

Characterizing the hierarchical structure of filaments I. On the origin of the length-mass (L-M) scaling relation

Rahul Patel, Daniel Seifried and Alvaro Hacar

Aims. Filamentary structures in molecular clouds are widely recognized as fundamental components of star formation. Observations report a length-mass relation of the form $L \propto M^\alpha$ with $\alpha \simeq 0.5$. We characterize this relation in simulated molecular clouds and investigate the influence of hierarchical fragmentation and spatial resolution. Methods. We apply a two-step filament identification method to high-resolution 3D hydrodynamical and magnetohydrodynamical simulations from the SILCC-Zoom project, combining the Rolling Hough Transform with dendrogram-based segmentation for hierarchical decomposition. We analyze the resulting structures across multiple spatial resolutions. Results. The identified structures span column densities of $\sim 10^{21}$–$\sim 10^{23}\,\mathrm{cm}^{-2}$. Across multiple resolutions and, separately, the full hierarchical decomposition at the highest resolution, the ensemble exhibits a sub-linear $L-M$ relation close to $L \propto M^{0.5}$. When individual structures are traced across resolutions, the slopes remain sub-linear ($\alpha \simeq 0.45$–$0.70$), consistent with the geometric prediction $L \propto M^{0.5}$ of a fragmentation-driven random walk. In contrast, decomposing individual structures at the highest resolution yields a wide range of slopes ($\alpha \simeq 0.2$–$3$), peaking at $\alpha<1$. A simple toy model shows that this diversity arises from differences in the internal column-density distribution and segmentation geometry. Conclusions. Taken together, these results indicate that the average sub-linear length-mass relation with $\alpha \simeq 0.5$ is a robust property of the hierarchical structure and fragmentation occurring in molecular clouds.
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Astrophysics of Galaxies

Star clusters as tracers of the perturbed southern outer disk of the Large Magellanic Cloud

Matías Chiarpotti, Andrés E. Piatti, Denis M.F. Illesca et al. (+1 more)

The complex interaction history between the Large and Small Magellanic Clouds (L/SMC) has left significant imprints on their structural and chemical evolution. In this work, we use a sample of 70 star clusters located in the southern outer disk of the LMC ($R > 5^{\circ}$) to trace the magnitude of these tidal perturbations. Using deep $g,i$ photometry from the SMASH DR2 survey and the Automated Stellar Cluster Analysis (ASTeCA) code, we provide a homogeneous determination of cluster ages, metallicities, and heliocentric distances. Our results show a population with ages ranging from 1.02 to 3.34 Gyr and metallicities between -0.70 and -0.07 dex. We find that clusters at greater heliocentric distances are predominantly located toward the western regions, facing the SMC. Analysis of the vertical distribution reveals an oscillatory variation in the mean height ($\langle Z \rangle$) relative to the LMC mid-plane and an increase in intrinsic vertical dispersion ($W$) toward the West. These geometric features are consistent with a corrugated disk structure induced by recent tidal encounters with the SMC. Chemically, the clusters follow the age-metallicity relationship typical of the LMC and are well-represented by a bursting-type formation model. The lack of chemically distinct clusters suggests that while the interaction was sufficient to dynamically deform and corrugate the outer disk, it did not lead to significant cluster capture from the SMC. We conclude that the southern outer disk remains structurally and chemically part of the LMC, despite being heavily perturbed by tidal forces.
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All authors Matías Chiarpotti, Andrés E. Piatti, Denis M.F. Illesca, Roberto Butrón

Astrophysics of Galaxies

Sub-arcsecond imaging of HCN and CN in the Orion Bar. UV-driven warm Nitrogen chemistry in dense environments

M. Zannese, J. R. Goicoechea, S. Cuadrado et al. (+3 more)

Rotationally excited HCN and CN lines, due to their high critical densities, are often used as tracers of gas densities. ALMA, with its high spectral and spatial resolution, provides unique access to the spatial morphology and kinematics of HCN and CN emission to study the substructures of the molecular cloud edges. We present new sub-arcsecond imaging of HCN 4-3 and CN 3-2 lines to probe the density structure in the Orion Bar. We study their spatial distribution and compare them to other existing tracers inside the PDR. We complemented these data with multiple J lines observed with the IRAM 30m and Herschel telescopes to study HCN and CN excitation near the dissociation front (DF). We find that HCN and CN emission are more spatially extended toward the more UV-shielded cloud than C2H and H2. However, they both peak very close to the DF, in disagreement with previous lower-angular-resolution observations. This morphology can be explained by the enhanced UV-driven chemistry. In dense and irradiated environments, HCN is efficiently formed via H2+CN. Hence, its emission can also probe warmer gas near the DF. CN emission is observed in the atomic PDR, not accounted by stationary gas-phase chemistry due to the very low H2 abundances. We interpret this as photoprocessing of CN-bearing PAHs. We derive high densities near the DF when comparing observations with RADEX and Meudon PDR Code models. Finally, we do not find evidence of small-scale high-density clumps and argue that the observed density gradient could explain the variation of excitation between the different tracers. We resolve two velocity components in HCN emission: 10.5 km/s (velocity of the Bar) and 11.5 km/s. The very structured emission of HCN observed in this redshifted emission component is more compatible with the signature of the propagation of a UV-induced shock compressing the gas than clumps.
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All authors M. Zannese, J. R. Goicoechea, S. Cuadrado, J. Pety, M. Gerin, E. Chapillon

Materials Science

Pressure-dependent melting and crystallization of B2-NiAl from neural-network molecular dynamics

A. S. Onegin, P. R. Levashov and N. M. Chtchelkatchev

We investigate pressure-dependent melting of ordered B2-NiAl using neural-network molecular dynamics with a Deep Potential interatomic model. Melting temperatures are determined from two-phase solid-liquid coexistence simulations over a broad pressure range, yielding the melting curve $T_m(P)$. Relative to available experimental and previous molecular-dynamics results, the present calculations predict a stronger increase of the melting temperature with pressure at elevated compression. To assess the thermodynamic consistency of the calculated melting line, we evaluate the enthalpy and volume changes upon melting and compare the Clapeyron slope with the derivative of the fitted $T_m(P)$ curve. The two estimates are in good agreement over most of the investigated pressure range, supporting the internal consistency of the coexistence results. To probe the character of melting, we perform a layer-resolved composition analysis of the coexistence configurations and find that the coexisting liquid remains essentially equiatomic at all studied pressures, with deviations of the aluminum fraction from the stoichiometric value not exceeding $5\times10^{-3}$. This provides direct atomistic evidence that melting of B2-NiAl remains congruent within the present model. Together, these results establish a thermodynamically consistent pressure-dependent melting description of B2-NiAl and clarify the character of its melting under compression.
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Geophysics

Vertical Attenuation of Thermoremanent Magnetic Anomalies: Implications for Drone-Borne Archaeological and Shallow Geophysical Surveys

Alexandru Hegyi, Kristoffer Aalstad, Arne Anderson Stamnes et al. (+6 more)

Magnetic surveys are widely used in archaeology to reveal buried features by detecting variations in the Earth's magnetic field caused by past human activities. However, as sensor height increases, magnetic anomalies produced by subsurface sources weaken and broaden, posing challenges for both ground-based and aerial (UAV) surveys. This study quantifies that altitude-dependent loss of signal and spatial definition using a fully synthetic model of a uniformly magnetized circular kiln together with upward continuation of measured fluxgate data from the Storbekken 1 iron-production site in central Norway. The synthetic experiment shows that a 2 m diameter, 1 m thick magnetized cylinder buried 0.3 m below ground retains only about 11% of its near-surface (0.2 m) peak amplitude at 2 m sensor height and about 3% at 4 m. In the hybrid experiment, composite furnace anomalies of several hundred nanoteslas collapse to tens of nanoteslas by 2 to 3 m, while distinct lobes merge into broad, low-contrast features. The results show that UAV-borne magnetometry can remain effective for site detection and delineation at elevations where detailed intra-site morphology is already strongly degraded. For small or subtle archaeological targets, sub-metre to low-metre sensor heights provide substantially greater interpretative detail. Recent field evidence on UAV-system noise further indicates that practical detectability will depend not only on source-distance attenuation but also on platform configuration and acquisition strategy. The resulting attenuation curves and morphological observations provide transferable guidance for planning archaeological and shallow-geophysical UAV magnetic surveys.
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All authors Alexandru Hegyi, Kristoffer Aalstad, Arne Anderson Stamnes, Luc Girod, Sebastian Westermann, Diaa Sheishah, Enas Abdelsamei, Michał Pisz, Norbert Pirk

Optics

Time-resolved topology of aperiodically driven systems

Justin T. Cole, Christina Jörg, Terry A. Loring et al. (+1 more)

Topological phases of periodically driven systems are commonly classified through Floquet Hamiltonians, whose definition relies on a repeated driving cycle. However, this framework breaks down for systems whose realized evolution is aperiodic or nonlinear, even when robust topological phenomena appear to persist. Here, we introduce an evolution-history spectral localizer framework that classifies Chern topology directly from a system's finite-time unitary evolution operator. The method produces a time-resolved local Chern marker and an associated local gap, allowing topology and its protection to be tracked during the actual dynamics of a driven system. We demonstrate this approach in quasiperiodically driven and nonlinear photonic models, where it identifies transient topological protection, its subsequent loss, and the recovery of topology after nonlinear excitations disperse. The developed framework provides a route for analyzing driven photonic systems whose topological behavior depends on finite-time dynamics rather than an idealized Floquet cycle.
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All authors Justin T. Cole, Christina Jörg, Terry A. Loring, Alexander Cerjan

Solar and Stellar Astrophysics

Extragalactic Multi-Band Exploration of Red Supergiants (EMBERS): Pipeline, Source Classification, and Bolometric Properties of 101,219 Red Supergiants from James Webb Space Telescope Imaging

Aswin Suresh, Charles D. Kilpatrick, Wen-fai Fong et al. (+6 more)

The evolution of red supergiants (RSGs), especially in their final stages before exploding as hydrogen-rich Type II supernovae (SNe), remains poorly understood, owing to small samples of well-characterized stars in the Local Group. We present the largest population study of RSGs to date using $\sim10^5$ stars with bolometric parameters inferred from archival James Webb Space Telescope/Near-Infrared Camera (NIRCam) imaging of 15 galaxies within 20 Mpc. We also present jwst123, a newly-developed general-purpose NIRCam reduction and photometry pipeline, and its application to our set of 15 galaxies. We build a simulation-based parameter inference framework to rapidly fit multi-band photometry of $\sim1.5$ million luminous stars in milliseconds per source. Using clustering in the effective temperature ($T_{\rm eff}$)-luminosity ($\log L/L_{\odot}$)-dust optical depth ($\tau_V$) phase space, we introduce a novel method to select RSGs with high completeness and purity. Leveraging the scale of our catalog, we find that the dustiest RSGs prefer metal-rich hosts, and RSG luminosities correlate with host specific star formation rate, suggesting that environment shapes RSG evolution. While most selected RSGs agree with theoretical stellar evolution tracks, we identify a new population of 1,669 RSGs that are heavily dust-enshrouded ($\tau_V>4$), overluminous ($\log(L/L_{\odot})>5.55$), or anomalously cool ($T_{\rm eff}<3000\,{\rm K}$), including analogs of known SN progenitors. Our catalog provides a population-scale baseline for understanding massive stellar evolution and connecting field RSGs to dusty progenitors of Type II SNe.
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All authors Aswin Suresh, Charles D. Kilpatrick, Wen-fai Fong, Maria R. Drout, Daichi Hiramatsu, Luca Izzo, Wynn V. Jacobson-Galán, Armin Rest, Samaporn Tinyanont

Solar and Stellar Astrophysics

A Grid of Contribution Functions to Help the Interpretation of Time-resolved Observations of Brown Dwarfs

Myrla Phillippe, Theodora Karalidi, Elena Manjavacas et al. (+4 more)

We present a grid of thermal emission contribution functions and their corresponding atmospheric spectra model for cloudy and cloud-free brown dwarfs, spanning effective temperatures $T_{\rm eff} \in [500, 2000]$ K, surface gravities $\log g = [3.5, 5.5]$ [cgs], sedimentation efficiencies $f_{\rm sed} = 1, 2, 3, 4$ and 8, and eddy diffusion coefficients $\log K_{\rm zz} = [6, 11]$. We use temperature-pressure profiles from the Sonora Diamondback models in conjunction with the picaso radiative transfer code and the cloud modeling code virga, to explore how different atmospheric parameters influence the vertical distribution of emitted radiation for atmospheres in chemical equilibrium. We confirm that cloud opacity significantly impacts atmospheric emission depth in prominent molecular features such as CH$_4$, H$_2$O, CO, NH$_3$, CO$_2$, and atomic features Na and K. The atmospheric emission depth varies most notably in the $J$-band, and at mid-resolution spectra in the Na and K doublets. Our analysis highlights pressure-wavelength differences between cloudy and cloud-free atmospheres for characterizing L, L/T transition, and T-type brown dwarfs and demonstrates how contribution functions can guide targeted spectroscopic investigations. To facilitate observational planning, we provide an accessible database and web-based application that enable the community to compare observational data with our model grid of spectra and contribution functions with a wavelength range of 0.5 - 30 $\mu$m.
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All authors Myrla Phillippe, Theodora Karalidi, Elena Manjavacas, Natalia Oliveros-Gomez, Daniel Apai, Jonathan Fernandez, Kieran M. Manjrawala

Materials Science

Electron $g$-value comparison of paramagnetic muonium and hydrogen centers in rutile TiO$_2$

T. U. Ito, W. Higemoto and A. Koda

Muonium (Mu) is widely used as a model for isolated hydrogen in condensed matter, but whether its electronic state is truly equivalent to that of hydrogen remains to be tested with an orbital-sensitive probe. Here we use double electron-muon resonance to determine the electron $g$ values of the paramagnetic Mu center in rutile TiO$_2$ for magnetic fields along [100], [110], and [001] directions. The obtained $g$ values closely follow those of the H-related Ti$^{3+}$ paramagnetic center in both magnitude and anisotropy. This agreement tests the Mu–H correspondence at the level of the Ti $3d$ electronic state and supports a common localized Ti$^{3+}$ electronic core for the two centers.
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Applied Physics

Si- and C-Induced Modifications in Vapor-Solid-Grown InGaAs Nanowires: From Crystal Structure to Carrier Dynamics

Hamidreza Esmaielpour, Leopold Rothmayer, Thomas Trinkl et al. (+5 more)

Determining the impact of dopants in ternary III-V nanowires (NWs) is crucial for their applications in next-generation optoelectronic and photonic devices; however, the interplay between dopant species, crystal structure, and carrier dynamics in vapor-solid-grown InGaAs NWs remains underexplored. In this study, the influence of silicon (Si) and carbon (C) doping on the structural, morphological, and optical properties of catalyst-free, selective-area grown InGaAs NWs fabricated by molecular beam epitaxy is investigated. Scanning electron microscopy demonstrates that C-doping increases the NW aspect ratio by over 100% compared to undoped NWs, while a concomitant decrease in their planar defect density is observed, indicating enhanced crystal quality with C-doping. Despite their superior crystal quality, the C-doped NWs present a diminished photoluminescence intensity, due to point defects and increased surface recombination velocity. This is further supported by time-resolved photoluminescence spectroscopy, revealing accelerated non-radiative recombination in the C-doped NWs. Lastly, hot-carrier effects in these nanostructures are studied, and their signatures remain observable, albeit with reduced intensity in both Si- and C-doped NWs. This comprehensive study establishes clear correlations between doping parameters and the resulting material characteristics and carrier dynamics, offering valuable insights into the fundamental mechanisms governing the VS-grown InGaAs NWs and their implications in optoelectronic devices.
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All authors Hamidreza Esmaielpour, Leopold Rothmayer, Thomas Trinkl, Laura Niermann, Tore Niermann, Michael Lehmann, Jonathan J. Finley, Gregor Koblmüller

Fluid Dynamics

Fredholm Backstepping with Heymann Pre-Feedback for Linearized Navier–Stokes 2D Channel

Miroslav Krstic

We stabilize the linearized 2-D Poiseuille channel flow at arbitrary Reynolds numbers, and assign the decay of every wavenumber to any user-prescribed rate. The actuation is as in Vazquez–Krstic (IEEE TAC, 2007), VK'07 below: the two velocity components at only one wall. This is the first Fredholm backstepping design for a Navier–Stokes system. In VK'07 the wall-normal input renders the plant spatially causal, after which the tangential input closes a Volterra backstepping loop. Here the normal input carries a finite-rank feedback of arbitrarily small gain, whose sole role, in the sense of Heymann's lemma (TAC, 1968), is to give the plant simple spectrum and make every mode controllable from the tangential velocity. The tangential input then applies a stabilizing feedback, obtained through an invertible Fredholm transform to a Stokes target PDE, shifted left by an arbitrary decay. No simplicity of eigenvalues of the Orr–Sommerfeld operator is assumed and the exclusions of plant coefficient values that have accompanied Fredholm backstepping are removed. We state the comparison with the Volterra design without embellishment: the Fredholm architecture is powerful, but its gain is spectral where VK'07 is closed-form, the simpler of the two, and one from which the Fredholm approach takes its model, its actuation, and its target. What is demonstrated here is the reach of the Fredholm method on its most demanding plant to date. The feedback is tested at Reynolds number $30000$, with the dominant part of the closed-loop spectrum assigned so that it amounts to slowing the flow about twentyfold.
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