Plasma Physics
Enhanced Hot Electron Preheat Observed in Magnetized Laser Direct-Drive Implosions
M. Cufari, M. Gatu Johnson, C.K. Li et al. (+5 more)
Hard x-ray emission, associated with hot electron preheat, in direct-drive implosions was observed to be enhanced by a factor of $1.5\pm0.1$ by application of a $10$ T
magnetic field. The applied
magnetic field reaches a quasi steady-state aligned with the ablation flow prior to the onset of
laser-
plasma instabilities in the corona. Hot electrons that would otherwise escape the corona and lead to capsule charging in unmagnetized implosions are confined in a mirror-mode of the
magnetic field in magnetized implosions. These hot electrons are shown to subsequently pitch-angle scatter from the mirror onto the capsule, thereby leading to the observed hard x-ray generation in magnetized implosions. Consequently, the energy of charged-fusion products, associated with the capsule charging, are observed to decrease when the implosion is magnetized. These results intensify the need to mitigate
laser-
plasma instabilities – particularly for magnetized implosions – to maximize fusion gain and implosion efficiency.
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All authors M. Cufari, M. Gatu Johnson, C.K. Li, J.A. Frenje, P.W. Moloney, A.J. Crilly, P.V. Heuer, J.R. Davies
Optics
MxDiffusion: A Physics-Aware Maxwells Law-Guided Diffusion Model Strategy for Inverse Photonic Metasurface Design
Sujoy Mondal, Taehyuk Park, Sudipta Biswas et al. (+2 more)
We introduce MxDiffusion, a hybrid physics- and data-driven
diffusion-based framework that enables efficient and highly accurate generation of photonic structures from target optical properties. The improved accuracy is achieved through a two-stage generation strategy, in which the first
diffusion model is explicitly trained with Maxwells equation-based loss to embed physical insight directly into the inverse design process, while the second model maps the physically consistent intermediate representation to the final structural geometry with significantly higher fidelity than solely data-driven approaches. The performance of MxDiffusion is validated on two representative applications: gold nanostructures patterned on a silica substrate and a highly tunable bandpass filter based on phase change material. In both cases, the proposed framework consistently outperforms a conventional data-driven
diffusion model
benchmark, particularly for out-of-training-distribution design targets and highly constrained resonance conditions. These results demonstrate the efficacy and superiority of MxDiffusion as a general physics-guided inverse design paradigm.
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All authors Sujoy Mondal, Taehyuk Park, Sudipta Biswas, Alan X. Wang, Wenshan Cai
Instrumentation and Detectors
Performance of the Endcap Time-of-Flight detector in the STAR beam-energy scan
Mathias C. Labonté, Daniel Cebra, Zachary Sweger et al. (+16 more)
The
STAR experiment at RHIC at Brookhaven National Laboratory completed the installation of an endcap time-of-flight subsystem (eTOF) in February 2019. The eTOF subsystem provided essential mid-rapidity particle identification (PID) for the fixed-target (FXT) portion of phase II of the beam energy scan (BES II). The FXT program allowed BES II to include center-of-mass energies from $\sqrt{s_{_{NN}}} = 3.0$ GeV to $\sqrt{s_{_{NN}}} = 7.7$ GeV, not accessible by colliding beams. The eTOF detectors and readout electronics were designed for the CBM experiment at FAIR and adapted for use at
STAR. In this paper, we describe the details of the system in terms of geometrical layout, acceptance, calibration, hit reconstruction, and particle identification. The system achieved a time resolution of about 70 ps and a PID efficiency of about 70%, meeting the design goals of the project.
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All authors Mathias C. Labonté, Daniel Cebra, Zachary Sweger, Geary Eppley, Frank Geurts, Yannick Söhngen, Norbert Herrmann, Esteban Rubio, Philipp Weidenkaff, Ingo Deppner, Pierre-Alain Loizeau, Jochen Frühauf, David Emschermann, Florian Seck, David Tlusty, Dongdong Hu, Yongjie Sun, Tonko Ljubicic, Yi Wang
Atomic Physics · Cross-listed from hep-ph
Probing Ultralight Dark Matter at the Mega-Planck Scale with the Thorium Nuclear Clock
Jason Arakawa, Jack F. Doyle, Elina Fuchs et al. (+10 more)
Ultralight dark matter is expected to induce oscillations of
nuclear parameters. These oscillations are characterized by extremely weak couplings or high suppression scales, with the Planck scale - the characteristic scale of
quantum gravity - serving as a natural
benchmark. Probing this phenomenon requires systems with exceptional sensitivity to shifts in
nuclear energies. The uniquely low-energy
nuclear isomeric transition in ${}^{229}$Th provides such sensitivity: it directly probes the
nuclear interaction and, owing to a near cancellation between electromagnetic and
nuclear contributions, its response to changes in
nuclear structure is greatly amplified. We devise and perform a new type of ultrasensitive search for dark matter which uses the precision
nuclear spectroscopy at JILA to set the strongest bounds in the mass range $10^{-21}\,{\rm eV} \lesssim m_{\rm DM} \lesssim 10^{-19}\,{\rm eV}$. Our results probe effective interaction scales exceeding $10^6$ times the Planck scale (the Mega-Planck scale) and establish the ${}^{229}$Th system as the leading probe of dark matter couplings to the
nuclear sector.
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All authors Jason Arakawa, Jack F. Doyle, Elina Fuchs, Jacob S. Higgins, Fiona Kirk, Kai Li, Tian Ooi, Gilad Perez, Wolfram Ratzinger, Marianna S. Safronova, Thorsten Schumm, Jun Ye, Chuankun Zhang
Plasma Physics
Operational measurement of relativistic equilibrium from stochastic fields alone
Ira Wolfson
The inverse-temperature four-vector $\beta^\mu = u^\mu/(k_B T_0)$ has been the theoretically accepted description of relativistic
equilibrium since van Kampen and Israel, yet no experiment has ever reconstructed $\beta^\mu$ as a single observable. All existing methods – Thomson scattering, spectral fitting, blast-wave models – infer rest-frame temperature and flow velocity from separate measurements. We propose the first protocol that extracts both components of $\beta^\mu$ from the same passive observable: electromagnetic fluctuation correlations emitted by a drifting medium. A dimensionless $E$-$B$ cross-spectral ratio yields the drift velocity from Lorentz mixing of the field-strength tensor, while angle-resolved noise power governed by the covariant fluctuation-dissipation
theorem provides the rest-frame temperature via a ratio method that cancels absolute amplitude. Together, these reconstruct $\beta^\mu$ without external probes, spectral lines, or absolute radiometric calibration. The protocol enables the first direct experimental test of whether the thermal state of a relativistic medium transforms as a four-vector – a question unresolved since the Planck–Ott-Landsberg controversy of 1907. Monte Carlo simulations parameterized to the HIGGINS dual 100\,TW
laser-
plasma facility demonstrate sub-percent temperature recovery for $\gamma = 1.05$-$10$, with robustness to additive noise at SNR~$\gtrsim 10$.
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Classical Physics
Asymptotic Effects of Incident Angle and Lateral Conduction in Electromagnetic Skin Heating
Ulises Jaime-Yepez, Hongyun Wang, Shannon E. Foley et al. (+1 more)
Previously we derived the leading term asymptotic solution of temperature distribution in skin heating by an electromagnetic beam at an arbitrary incident angle. The asymptotic analysis is based on that the penetration depth of the beam into skin is much smaller than the size of beam cross-section. It allows arbitrary incident angle. We expand the temperature in powers of the small depth to lateral scale ratio. The incident angle affects all terms in the expansion while the lateral heat conduction appears only in terms of positive even powers. The previously obtained leading term solution captures only the main effect of incident angle. The main effect of lateral heat conduction is contained in the second order term, which is mathematically negligible in the limit of small depth to lateral scale ratio. At a moderate length scale ratio (e.g., 0.1), however, the contribution from lateral conduction is quite significant and needs to be included in a meaningful approximate solution. In this study, we derive closed form analytical expressions for the first order and the second order terms in the asymptotic expansion. The resulting asymptotic solution is capable of predicting the temperature distribution accurately including the effects of both incident angle and lateral heat conduction even at a moderate length scale ratio.
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All authors Ulises Jaime-Yepez, Hongyun Wang, Shannon E. Foley, Hong Zhou
Chemical Physics · Cross-listed from cond-mat.str-el
Ab Initio Auxiliary-Field Quantum Monte Carlo in the Thermodynamic Limit
Jinghong Zhang, Meng-Fu Chen, Adam Rettig et al. (+5 more)
Ab initio auxiliary-field
quantum Monte Carlo (AFQMC) is a systematically improvable many-body method, but its application to extended solids has been severely limited by unfavorable computational scaling and
memory requirements that obstruct direct access to the thermodynamic and complete-basis-set limits. By combining tensor hypercontraction with $\mathbf{k}$-point
symmetry, we reduce the computational and
memory scaling of ab initio AFQMC for solids to $\mathcal O(N^3)$ and $\mathcal O(N^2)$, respectively, with an arbitrary basis, comparable to
diffusion Monte Carlo. This enables direct and simultaneous thermodynamic-limit and complete-basis-set AFQMC calculations across insulating, metallic, and strongly correlated solids, without
embedding, local approximations, empirical finite-size corrections, or composite schemes. Our results establish AFQMC as a general-purpose, systematically improvable alternative to
diffusion Monte Carlo and coupled-cluster methods for predictive ab initio simulations of solids, enabling accurate energies and
magnetic observables within a unified framework.
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All authors Jinghong Zhang, Meng-Fu Chen, Adam Rettig, Tong Jiang, Paul J. Robinson, Hieu Q. Dinh, Anton Z. Ni, Joonho Lee
Accelerator Physics
FLUKA-Based Optimization of Muon Production Target Design for a Muon Collider Demonstrator
Ruaa Al-Harthy
This study investigates how target geometry and material influence pion and
muon production from an 8 GeV
proton beam, in support of target-system design for a
muon collider demonstrator. A 2 m long, 0.7 m radius solenoid with a 5 T peak
magnetic field is used to capture secondary particles, with the target positioned at its center. We examine how variations in target radius, length, and material affect secondary-beam yield and emittance at the solenoid exit. In parallel, we evaluate temperature rise within the target to assess material limitations and guide future work on thermal and structural survivability. The results provide initial intuition for optimizing both particle yield and target durability in
muon collider front-end systems.
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Optics
Operator based propagation of Whittaker and Helmholtz Gauss beams
M. A. Jacome Silva, I. Julian Macias, F. Soto Eguibar et al. (+4 more)
We introduce a compact operator-based technique that solves the paraxial wave equation for a broad class of structured light fields. Using the spatial
evolution operator to propagate two families of physically apodized inputs, Gaussian apodized Whittaker integrals and Gaussian apodized Helmholtz fields, we derive closed form expressions that retain the Gaussian width and therefore describe finite energy beams. The method unifies and extends the Helmholtz Gauss families and readily generalizes to nonseparable nondiffracting architectures. Experiments on superposed Bessel Gauss beams confirm the predicted transverse rotations, demonstrating that this operator approach is a fast, transparent, and practical alternative to standard diffraction ntegral treatments
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All authors M. A. Jacome Silva, I. Julian Macias, F. Soto Eguibar, U. Ruiz Corona, I. Ramos Prieto, D. Sanchez de la Llave, H. M. Moya Cessa
Computational Physics · Cross-listed from cond-mat.dis-nn
Optimizing p-spin models through hypergraph neural networks and deep reinforcement learning
Li Zeng, Mutian Shen, Tianle Pu et al. (+5 more)
p-
spin glasses, characterized by frustrated many-body interactions beyond the conventional pairwise case (p>2), are prototypical disordered systems whose ground-state search is NP-hard and computationally prohibitive for large instances. Solving this problem is not only fundamental for understanding high-order disorder, structural glasses, and topological phases, but also central to a wide spectrum of hard combinatorial optimization tasks. Despite decades of progress, there still lacks an efficient and scalable solver for generic large-scale p-
spin models. Here we introduce PLANCK, a physics-inspired deep reinforcement learning framework built on hypergraph neural networks. PLANCK directly optimizes arbitrary high-order interactions, and systematically exploits gauge
symmetry throughout both training and inference. Trained exclusively on small synthetic instances, PLANCK exhibits strong zero-shot generalization to systems orders of magnitude larger, and consistently outperforms state-of-the-art thermal annealing methods across all tested structural
topologies and coupling distributions. Moreover, without any modification, PLANCK achieves near-optimal solutions for a broad class of NP-hard combinatorial problems, including random k-XORSAT, hypergraph max-cut, and conventional max-cut. The presented framework provides a physics-inspired algorithmic paradigm that bridges statistical mechanics and reinforcement learning. The
symmetry-aware design not only advances the tractable frontiers of high-order disordered systems, but also opens a promising avenue for machine-learning-based solvers to tackle previously intractable combinatorial optimization challenges.
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All authors Li Zeng, Mutian Shen, Tianle Pu, Zohar Nussinov, Qing Feng, Chao Chen, Zhong Liu, Changjun Fan
Fluid Dynamics
Axisymmetric cavities in hypersonic flow
Soumya R. Nanda, T. V. Krishna, S. K. Karthick et al. (+1 more)
A detailed experimental campaign is conducted to investigate the shear layer characteristics of an axisymmetric open cavity exposed to a Mach $6$ freestream. Experiments are performed in a Ludwieg tunnel for varying Reynolds numbers ($23000\leq Re_D \leq 74000$) based on cavity depth ($D$). The effects of geometry are examined through length-to-depth ratios ($[L/D]=[2,4,6]$) and non-dimensional rear-face height differences ($[\Delta h/D]=[-0.5,-0.25,0,0.25,0.5]$). Shear layer
evolution is interpreted using qualitative schlieren and Planar
Laser Rayleigh Scattering (PLRS) along with quantitative unsteady pressure measurements. For all $[L/D]$, the shear layer remains laminar at low $Re_D$ and develops Kelvin-Helmholtz (K-H)
vortices as $Re_D$ increases. For the longest cavity ($[L/D]=6$), transition to
turbulence occurs at the highest $Re_D$ due to a longer K-H growth length. Spectral analysis of pressure signals and PLRS intensity shows a shift in dominant frequency from the first Rossiter mode to higher modes for $[L/D]=6$. Except for $[L/D]=6, [\Delta h/D]=0$, dominant frequencies agree with Rossiter predictions and remain largely Reynolds-number independent. Variation of $[\Delta h/D]$ leads to mode switching identified using POD of PLRS snapshots. Negative $[\Delta h/D]$ favors K-H modes (5th-6th Rossiter), whereas positive values promote a strong flapping mode (1st Rossiter) due to pressure build-up inside the cavity. At $[\Delta h/D]=0$, both modes may coexist depending on $Re_D$. Azimuthal measurements indicate dominant axisymmetric behavior in flapping cases and weaker correlation for K-H dominated shear layers.
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All authors Soumya R. Nanda, T. V. Krishna, S. K. Karthick, J. Cohen
Plasma Physics
Nonlinear Frequency Shifts due to Phase Coherent Interactions in Incompressible Hall MHD Turbulence
Erik C. Hansen, Prerana Sharma and Swadesh M. Mahajan
Turbulence in the magnetized
plasma is well understood to be the consequence of wave interactions. When the
Hall effect is added to the minimum magnetohydrodynamics (MHD), the MHD waves become dispersive and different nonlinear interactions are expected. The emergent turbulent state will thus be expected to be different. For incompressible
Hall MHD we develop a reduced model for wave-wave interactions concentrating on those processes that will lead to phase coherent modifications to the linear dispersion of a given wave. We show that these special interactions provide an amplitude-dependent contribution to the linear dispersion relation, which yields nonlinear frequency shifts. The resonance-driven frequency shifts are dominant and add damping or growth to the linear dispersion. The damping/growth rates represent the nonlinear time scales for energy redistribution and can be used in conjunction with a
conjecture like the "critical balance" to estimate the energy spectral content.
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Atomic Physics
Ultracold atoms in a dipole trap in microgravity
Julien Le Mener, Clement Metayer, Vincent Jarlaud et al. (+2 more)
Most cold atoms experiments in microgravity platforms or in Space are achieved using atom chips, leading to limitations in terms of optical access and inhomogeneous
magnetic fields. Optical dipole traps do not have these drawbacks but have difficulties producing atomic samples with a large number of atoms at ultra low temperature in the absence of
gravity. Here, we report on an efficient evaporative cooling in two-crossed
laser beams during
parabolic flights. Time-averaged potentials combine the advantages of large capture volume and trap compression, increasing the initial phase space density and collision rate to favor the evaporative process. With this technique we demonstrate the production of an ultra cold gas of $2.5\times 10^4$ rubidium atoms at a temperature below 100 nK in less than 4 seconds. Our experiment paves the way for the development of
quantum sensors applied to fundamental physics and geodesy as well as the study of ultracold atomic physics in Space.
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All authors Julien Le Mener, Clement Metayer, Vincent Jarlaud, Celia Pelluet, Baptiste Battelier
Biological Physics · Cross-listed from stat.ML
Enhanced Diffusion Sampling: Efficient Rare Event Sampling and Free Energy Calculation with Diffusion Models
Yu Xie, Ludwig Winkler, Lixin Sun et al. (+10 more)
The rare-event sampling problem has long been the central limiting factor in molecular dynamics (MD), especially in biomolecular simulation. Recently,
diffusion models such as BioEmu have emerged as powerful
equilibrium samplers that generate independent samples from complex molecular distributions, eliminating the cost of sampling rare transition events. However, a sampling problem remains when computing observables that rely on states which are rare in
equilibrium, for example folding free energies. Here, we introduce enhanced
diffusion sampling, enabling efficient exploration of rare-event regions while preserving unbiased thermodynamic
estimators. The key idea is to perform quantitatively accurate steering protocols to generate biased ensembles and subsequently recover
equilibrium statistics via exact reweighting. We instantiate our framework in three
algorithms: UmbrellaDiff (umbrella sampling with
diffusion models), MetaDiff (a batchwise analogue for metadynamics), and $\Delta$G-Diff (free-energy differences via tilted ensembles). Across toy systems,
protein folding landscapes and folding free energies, our methods achieve fast, accurate, and scalable estimation of
equilibrium properties within GPU-minutes to hours per system-closing the rare-event sampling gap that remained after the advent of
diffusion-model
equilibrium samplers.
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All authors Yu Xie, Ludwig Winkler, Lixin Sun, Sarah Lewis, Adam E. Foster, José Jiménez Luna, Tim Hempel, Michael Gastegger, Yaoyi Chen, Iryna Zaporozhets, Cecilia Clementi, Christopher M. Bishop, Frank Noé
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Understanding the influence of yttrium on the dominant twinning mode and local mechanical field evolution in extruded Mg-Y alloys
Chaitali Patil, Qianying Shi, Abhishek Kumar et al. (+2 more)
Twinning is a primary deformation mechanism in Mg
alloys. This study focuses on tension twins during uniaxial compression of Mg-Y
alloys, with three key aspects: the orientation specificity of twin grains, the relative
evolution of CRSS with increasing Y content, and the local stress and strain
evolution at twin sites. Experimental characterization and
crystal plasticity modeling were performed. In Mg-7wt.%Y, TT2-{112-1} tension twins were observed in addition to the common TT1-{101-2} twins. Increasing Y suppressed TT1 formation while promoting TT2 activity. A previously unreported group of crystallographic orientations with a higher global Schmid factor for <c+a> slip was identified, which exhibited TT1 twinning with increasing compression strain. To elucidate Y effects on twin activity and local mechanical fields, both TT1 and TT2 tension twin modes were incorporated into PRISMS-Plasticity, an open-source, finite element-based
crystal plasticity solver. Four binary Mg-Y
alloys were modeled under compression, and statistical analysis was conducted to correlate initial orientations, stress-strain distributions, and twin activities as functions of Y concentration. The plasticity analysis revealed that increasing Y decreases the CRSS ratio of prismatic and pyramidal slip relative to TT1 twinning, while the slip-to-twin CRSS ratio for TT2 increases, thereby serving as a potential indicator of differential twin activity with Y addition in Mg
alloys. Additionally, despite their small volume fraction, TT2 twin sites were predicted higher local strain accumulation locally, relative to the representative volume element and TT1 twins, suggesting their potential influence on localized phenomena such as recrystallization or twin nucleation. These findings provide insight into local mechanical behavior in Mg
alloys and support
alloy design for advanced engineering applications.
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All authors Chaitali Patil, Qianying Shi, Abhishek Kumar, Veera Sundararaghavan, John Allison
Plasma Physics
Measurement of the Saturation Length of the Self-Modulation Instability
A. Clairembaud, M. Turner, M. Bergamaschi et al. (+8 more)
The self-modulation (SM) instability transforms a long charged particle bunch traveling in
plasma into a train of microbunches that resonantly drives large-amplitude wakefields. We present the first determination of the saturation length of SM using experimental and numerical results. The saturation length is the distance over which wakefields reach their maximum amplitude along the
plasma. By varying the
plasma length and measuring the radius of the transverse distribution of the bunch, we find that the saturation length of SM decreases with
plasma density and initial field amplitude, e.g., when seeding. The saturation length is a fundamental parameter of the instability, and these results are key for understanding SM and designing
plasma wakefield accelerators driven by long bunches, such as AWAKE, or by long
laser pulses for radiation production.
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All authors A. Clairembaud, M. Turner, M. Bergamaschi, L. Ranc, F. Pannell, J. Mezger, H. Jaworska, N. van Gils, J. Farmer, P. Muggli, the AWAKE Collaboration
Fluid Dynamics · Cross-listed from eess.SP
WindDensity-MBIR: Model-Based Iterative Reconstruction for Wind Tunnel 3D Density Estimation
Karl J. Weisenburger, Gregery T. Buzzard, Charles A. Bouman et al. (+1 more)
Experimentalists often use wind tunnels to study aerodynamic
turbulence, but most wind tunnel imaging techniques are limited in their ability to take non-invasive 3D density measurements of
turbulence. Wavefront
tomography is a technique that uses multiple wavefront measurements from various viewing angles to non-invasively measure the 3D density field of a turbulent medium. Existing methods make strong assumptions, such as a spline basis representation, to address the ill-conditioned nature of this problem. We formulate this problem as a
Bayesian, sparse-view tomographic reconstruction problem and develop a model-based iterative reconstruction
algorithm for measuring the volumetric 3D density field inside a wind tunnel. We call this method WindDensity-MBIR and apply it using simulated data to difficult reconstruction scenarios with sparse data, small projection field of view, and limited angular extent. WindDensity-MBIR can recover high-order features in these scenarios within 10% to 25% error even when the tip, tilt, and piston are removed from the wavefront measurements.
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All authors Karl J. Weisenburger, Gregery T. Buzzard, Charles A. Bouman, Matthew R. Kemnetz
Chemical Physics
Fluctuation-induced acceleration of inter-ligand exciton transfer in bis(dipyrrinato)Zn(II) complex
Hiroki Uratani and Hirofumi Sato
Exciton transfer dynamics between chromophores depends on excitonic coupling, which is governed by relative orientation between the chromophores. While the excitonic coupling is treated as a static parameter in many cases, structural dynamics can introduce time-dependence on the excitonic coupling. However, influence of the dynamics of excitonic coupling on the
exciton transfer has been scarcely understood. In the present study,
exciton transfer under dynamical fluctuation in excitonic coupling was investigated via combined use of non-adiabatic molecular dynamics simulations,
exciton density analysis, and a simple two-state model, for inter-ligand
exciton transfer in bis(dipyrrinato)Zn(II) as the example case. The reaction coordinate for the
exciton transfer was obtained a posteriori via regression analysis where the target and explanatory variables are diabatic energy gaps and atomic displacements, respectively. The results suggest that dynamical angular fluctuation between the two dipyrrinato ligands breaks the
symmetry to incidentally increase the excitonic coupling, accelerating the
exciton transfer between the ligands.
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Chemical Physics · Cross-listed from math.AG
On the Coupled Cluster Doubles Truncation Variety of Four Electrons
Fabian M. Faulstich, Vincenzo Galgano, Elke Neuhaus et al. (+1 more)
We extend recent algebro-
geometric results for coupled cluster theory of
quantum many-body systems to the truncation varieties arising from the doubles approximation (CCD), focusing on the first genuinely nonlinear doubles regime of four electrons. Since this doubles truncation variety does not coincide with previously studied varieties, we initiate a systematic investigation of its basic algebro-
geometric invariants. Combining theoretical and numerical results, we show that for $4$ electrons on $n\leq 12$ orbitals, the CCD truncation variety is a complete intersection of degree $2^{\binom{n-4}{4}}$. Using representation-theoretic arguments, we uncover a Pfaffian structure governing the quadratic relations that define the truncation variety for any $n$, and show that an exact tensor product factorization holds in a distinguished limit of disconnected doubles. We connect these structural results to the computation of the beryllium insertion into molecular hydrogen ({Be$\cdots$H$_2$ $\to$ H–Be–H}), a small but challenging bond formation process where multiconfigurational effects become pronounced.
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All authors Fabian M. Faulstich, Vincenzo Galgano, Elke Neuhaus, Irem Portakal
Applied Physics · Cross-listed from cs.LG
AIFL: A Global Daily Streamflow Forecasting Model Using a Deterministic LSTM Pre-trained on ERA5-Land and Fine-tuned on IFS
Maria Luisa Taccari, Kenza Tazi, Oisín M. Morrison et al. (+7 more)
Reliable global streamflow
forecasting is essential for flood preparedness and water resource management, yet data-driven models often suffer from a performance gap when transitioning from historical reanalysis to operational forecast products. This paper introduces AIFL (Artificial Intelligence for Floods), a deterministic LSTM-based model designed for global daily streamflow
forecasting. Trained on 18,588 basins curated from the Caravan
dataset, AIFL utilises a two-stage transfer-learning strategy to bridge the reanalysis-to-forecast domain shift. The model is first pre-trained on 40 years of ERA5-Land reanalysis (1980-2019) to capture robust hydrological processes, then fine-tuned on operational Integrated
Forecasting System (IFS) forecasts (2016-2019) to adapt to the specific error structures and biases of operational numerical weather prediction. Ablation experiments confirm that this two-stage approach outperforms both a naive IFS-only baseline and a mixed-forcing single-stage alternative. To our knowledge, this is the first global model trained end-to-end within the Caravan ecosystem. On an independent temporal test set (2021-2024), AIFL achieves high predictive skill with a median modified Kling-Gupta Efficiency (KGE') of 0.66 and a median Nash-Sutcliffe Efficiency (NSE) of 0.53. Benchmarking results show that AIFL achieves comparable accuracy to current state-of-the-art global systems. The model provides a streamlined and operationally robust baseline for the global hydrological community.
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All authors Maria Luisa Taccari, Kenza Tazi, Oisín M. Morrison, Andreas Grafberger, Juan Colonese, Corentin Carton de Wiart, Christel Prudhomme, Cinzia Mazzetti, Matthew Chantry, Florian Pappenberger
Optics
Piezoelectric MEMS Phase Modulator for Silicon Nitride Platform in the Visible Spectrum
Firehun T. Dullo, Paul C. Thrane, Nikhil Jayakumar et al. (+4 more)
Active photonic integrated
circuits (PICs) in the visible spectrum are essential for on-chip applications, requiring low-loss waveguides with broad transparency and efficient, low-power phase modulation. Here, we demonstrate a compact, ultra-low-power phase modulator based on a silicon nitride (Si$_3$N$_4$) waveguide integrated with thin-film lead zirconate titanate (PZT) that actuates a bridge-type MEMS. The suspended actuator exploits PZT's strong piezoelectric effect to induce mechanically driven phase shifts, enabling efficient modulation in a Mach–Zehnder interferometer. For 3~mm and 5~mm modulators, phase shifts of $1.45\pi$ and $2.5\pi$ are achieved at 10~V, corresponding to a scalability metric ($V_{\pi}\cdot L$) of 2.25~V$\cdot$cm at 635~nm. This represents an order-of-magnitude improvement in scalability over stress-optic PZT modulators. The devices also exhibit ultralow power consumption ($\sim 12\,\mathrm{nW}$), $\sim 5\,\mathrm{ms}$ rise time, and optical loss $< 0.75\,\mathrm{dB/cm}$. Furthermore, we demonstrate on-chip beam shaping.
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All authors Firehun T. Dullo, Paul C. Thrane, Nikhil Jayakumar, Zeljko Skokic, Christopher A. Dirdal, Jo Gjessing, Balpreet S. Ahluwalia
Fluid Dynamics
Multifluid Hydrodynamic Simulation of Metallic-Plate Collision Using the VOF Method
Fedor Belolutskiy, Elena Oparina and Svetlana Fortova
The present study is concerned with a one-dimensional problem in explosive welding that pertains to the collision of lead and steel plates. The metal plates and the surrounding air are represented as separate immiscible phases governed by independent equations of state. A multifluid Godunov-type (finite-volume) computational
algorithm, based on the mechanical-
equilibrium Euler equations and incorporating pressure relaxation, is used to numerically describe the
evolution of the waves resulting from the collision. The position of the interface (contact discontinuity) between immiscible phases is tracked by means of the volume-of-fluid (VOF) method. The numerical model allows one to account for the existence of tensile stresses in metal and registers them as regions of negative pressure. The computed arrival time of the unloading wave at the interface between the plates agrees with the experimental data and with simulation results obtained via different methods.
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Space Physics
Scattering and sputtering on the lunar surface; Insights from negative ions observed at the surface
Romain Canu-Blot, Martin Wieser, Umberto Rollero et al. (+6 more)
Context. Airless planetary bodies are directly exposed to
solar wind ions, which can scatter or become implanted upon impact with the regolith-covered surface, while also sputtering surface atoms. Aims. We construct a semi-analytical model for the scattering of ions of hundreds of eV and the sputtering of surface atoms, both resulting in the emission of negative ions from the lunar surface. Our model contains a novel description of the scattering process that is physics-based and constrained by observations. Methods. We use data from the Negative Ions at the Lunar Surface (NILS) instrument on the Chang'e-6 lander to update prior knowledge of ion scattering and sputtering from lunar regolith through
Bayesian inference. Results. Our model shows good agreement with the NILS data. A precipitating
solar wind
proton has roughly a 22% chance of scattering from the lunar surface in any charge state, and about an 8% chance of sputtering a surface hydrogen atom. The resulting ratio of scattered to sputtered hydrogen flux is eta_sc / eta_sp = 1.5 for a
proton speed of 300 km/s. We find a high probability (7-20%) that a hydrogen atom leaves the surface negatively charged. The angular emission distributions at near-grazing angles for both scattered and sputtered fluxes are controlled by surface roughness. Our model also indicates significant inelastic energy losses for hydrogen interacting with the regolith, suggesting a longer effective path length than previously assumed. Finally, we estimate a surface binding energy of 5.5 eV, consistent with the observations. Conclusions. Our model describes the scattering and sputtering of particles of any charge state from any homogeneous, multi-species surface. Using NILS data, we successfully applied the model to update our understanding of
solar wind interacting with lunar regolith, and the emission of negative hydrogen ions.
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All authors Romain Canu-Blot, Martin Wieser, Umberto Rollero, Thomas Maynadié, Stas Barabash, Gabriella Stenberg Wieser, Aibing Zhang, Wenjing Wang, Chi Wang
Classical Physics
Continuous and discontinuous realizations of first-order phase transitions
Matthias Hempel
First-order phase transitions are commonly associated with a discontinuous behavior of some of the thermodynamic variables and the presence of a latent heat. In the present study it is shown that this is not necessarily the case. Using standard thermodynamics, the general characteristics of phase transitions are investigated, considering an arbitrary number of conserved particle species and coexisting phases, and an arbitrary set of state variables. It is found that there exist two different possible types of realizations of a phase transition. In the first type, one has the immediate replacement of a single phase with another one. As a consequence, some of the global extensive variables indeed behave discontinuously. In the second type, one has instead the gradual (dis-) appearance of a single phase over a range of the state variables. This leads to a continuous behavior of the (global) basic thermodynamic variables. Furthermore, in this case it is not possible to define a latent heat in a trivial manner. It is derived that the latter (former) case happens if the number of extensive state variables used is larger or equal (lower) than the number of coexisting phases. The choice of the state variables thus place a crucial role for the qualitative properties of the phase transition.
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Plasma Physics
Laboratory observation of collective beam-plasma instabilities in a relativistic pair jet
J W D Halliday, C D Arrowsmith, A M Goillot et al. (+37 more)
We report on a measurement of collective behavior in a relativistic electron-positron pair
plasma produced in the laboratory. Using the Fireball platform at CERN's HiRadMat facility, 440 GeV
protons were used to generate an ultra-relativistic, charge-neutral electron-positron pair beam that propagated through an ambient RF discharge
plasma.
Magnetic-field amplification due to a beam-
plasma instability was diagnosed using a high-sensitivity Faraday-rotation probe, supported by detailed characterization of the diagnostic impulse response. The measured path-integrated
magnetic field agrees quantitatively with predictions from particle-in-
cell simulations. The results provide a critical
benchmark for models of relativistic beam-
plasma interactions in astrophysical contexts such as blazar jets and
pulsar-wind nebulae.
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All authors J W D Halliday, C D Arrowsmith, A M Goillot, P J Bilbao, P Simon, V Stergiou, S Zhang, P Alexaki, M Bochmann, A F A Bott, S Burger, H Chen, F D Cruz, T Davenne, A Dyson, A Ebn Rahmoun, I Efthymiopoulos, D H Froula, J T Gudmundsson, D Haberberger, T Hodge, S Iaquinta, E E Los, G Marshall, F Miniati, S Parker, B Reville, P Rousiadou, S Sarkar, A A Schekochihin, K G Schlesinger, L O Silva, T Silva, R Simpson, E Soria, R M G M Trines, T Vieu, N Charitonidis, R Bingham, G Gregori
Optics
Metasurface-encoded optical neural network wavefront sensing for high-speed adaptive optics
Arturo Martin Jimenez, Dylan Brancato, Marc Baltes et al. (+3 more)
Free-space optical communications with moving targets, such as satellite terminals, demand ultrafast wavefront sensing and correction. This is typically addressed using a Shack-Hartmann sensor, which pairs a high-speed camera with a lenslet array, but such systems add significant cost, weight, and power demands. In this work, we present a hybrid opto-electric neural network (OENN) wavefront sensor that enables ultra-high-speed operation in a compact, low-cost system. Subwavelength diffractive metasurfaces efficiently encode the incoming wavefront into tailored irradiance patterns, which are then decoded by a lightweight multilayer perceptron (MLP). In simulation and experiment, the hybrid approach achieves average Strehl ratio (SR) improvements exceeding 60% and 45%, respectively, for unseen wavefronts compared to purely electronic sensors with few-pixel inputs. Although larger MLPs allow purely electronic sensors to match the hybrid's SR under static conditions, transient atmosphere modeling shows that their added latency leads to rapid SR degradation with increasing Greenwood frequency, while the hybrid system maintains performance. These results highlight the potential of hybrid OENN architectures to unlock scalable, high-bandwidth free-space communication systems and, more broadly, to advance optical technologies where real-time sensing is constrained by electronic latency.
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All authors Arturo Martin Jimenez, Dylan Brancato, Marc Baltes, Jackson Cornelius, Neset Akozbek, Zachary Coppens
Accelerator Physics · Cross-listed from cond-mat.mtrl-sci
Thermal Decoherence and Population Transfer of MeV Channeling Electrons in Diamond
Tadas Paulauskas
Channeling radiation from MeV-regime electrons is governed by transitions between quantized transverse bound states, but experimental spectra are strongly modified by thermal diffuse scattering. To capture these open-system dynamics, a frozen-
phonon multislice framework is combined with bound-state projection analysis to construct depth-dependent reduced density
matrices in selected transverse
manifolds. Beyond reproducing experimental channeling-radiation transition energies, this approach separates thermal population transfer, intra-
manifold decoherence, and cross-
manifold coherence loss. Applied to 16.9 MeV axial electron channeling in $\langle100\rangle$ diamond, the results show approximately exponential population decay from the initially occupied states, accompanied by strongly channel-dependent feeding among low-lying
manifolds. Starting from a coherent superposition within the degenerate 2p
manifold,
stochastic symmetry breaking by thermal displacements drives the intra-
manifold purity toward the maximally mixed limit, indicating rapid phase scrambling. Under 1s initialization, population transferred into the 2p and 3d
manifolds remains internally close to maximally mixed, yet a weak residual 2p-3d cross-
manifold coherence persists. This framework goes beyond static mean-field thermal broadening and provides a microscopic basis for evaluating population dynamics and coherence lifetimes in strongly quantized channeling-radiation systems.
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Chemical Physics
Fragment-Based Configuration Interaction: Towards a Unifying Description of Biexcitonic Processes in Molecular Aggregates
Johannes E. Adelsperger, Coen de Graaf and Merle I. S. Röhr
Biexcitonic states govern singlet fission, triplet-triplet and
exciton-
exciton annihilation, yet a unified understanding of how these processes compete within a shared electronic
manifold remains elusive. We outline a conceptual framework based on fragment-based configuration-interaction that systematically constructs diabatic
Hamiltonians spanning the full one-particle (LE, CT) and two-particle (LELE, CTCT, TT, CTX with X = LE, CT, or T)
manifolds from monomer-local building blocks, preserving physical interpretability throughout. SymbolicCI provides analytic
Hamiltonian matrix elements for efficient large-scale calculations; NOCI-F delivers
benchmark-quality couplings. The resulting diabatic
Hamiltonians can be coupled to
quantum dynamics simulations. Applications to ethylene aggregates and the anthracene
crystal reveal CTX configurations as electronic gateways bridging excitonic
manifolds, with CT-mediated relaxation pathways competing with conventional annihilation. In H-type aggregates, LECT admixture stabilizes a "bi-excimer" analogous to one-particle excimers. By providing first-principles access to biexciton formation, separation, and transport, we hope to stimulate further exchange between electronic structure and
quantum dynamics communities toward a predictive understanding of multiexcitonic photophysics.
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Geophysics
Generative deep learning improves reconstruction of global historical climate records
Zhen Qian, Teng Liu, Sebastian Bathiany et al. (+7 more)
Accurate assessment of anthropogenic
climate change relies on historical instrumental data, yet observations from the early 20th century are sparse, fragmented, and uncertain. Conventional reconstructions rely on disparate statistical interpolation, which tends to smooth local features and create unphysical artifacts, often leading to an underestimation of intrinsic variability and extremes. While recent machine learning approaches have improved reconstruction accuracy, they remain confined to purely spatial inpainting of coarse-resolution fields. Here, we present a unified, probabilistic generative deep learning framework that overcomes these limitations and reveals previously unresolved historical
climate variability back to 1850. Leveraging a learned generative prior of Earth system dynamics, our model performs probabilistic inference to estimate spatiotemporally consistent historical temperature and precipitation fields from sparse observations. Our approach preserves the higher-order statistics of
climate dynamics, transforming reconstruction into a robust uncertainty-aware assessment. We demonstrate that our reconstruction mitigates the smoothing effects inherent in widely used historical reference products, including those underlying IPCC assessments, especially regarding extreme weather events. Notably, we uncover higher early 20th-century global warming levels compared to existing reconstructions, primarily driven by more pronounced polar warming, with mean Arctic warming trends exceeding established
benchmarks by 0.15–0.29C per decade for 1900–1980. Conversely, for the modern era, our reconstruction indicates that the broad Arctic warming trend is likely overestimated in recent assessments, yet explicitly resolves previously unrecognized intense, localized hotspots in the Barents Sea and Northeastern Greenland.
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All authors Zhen Qian, Teng Liu, Sebastian Bathiany, Shangshang Yang, Philipp Hess, Nils Bochow, Christian Burmester, Maximilian Gelbrecht, Brian Groenke, Niklas Boers
History and Philosophy of Physics · Cross-listed from gr-qc
General formalism, classification, and demystification of the current warp-drive spacetimes
Hamed Barzegar, Thomas Buchert and Quentin Vigneron
We critically examine proposals for the so-called warp-drive spacetimes and classify these models based on their various restrictions within the framework of General Relativity. We then provide a summary of general formalism for each class, and in the process, we highlight some misconceptions, misunderstandings, and errors in the literature that have been used to support claims about the physicality and feasibility of these models. On the way, we prove several new no-go
theorems. Our analysis shows that when the principles of General Relativity are applied correctly, most claims regarding physical warp drives must be reassessed, and it becomes highly challenging to justify or support the viability of such models, not merely due to the violation of energy conditions.
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