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Physics Physics

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Saturday 30 May

Computational Physics · Cross-listed from math.NA

Tensor gradient flow with quasi-entropy for smectic liquid crystals and discretizations keeping coupled physical constraints

Jie Xu and Xiaomei Yao

A gradient flow for the concentration and a $2\times 2$ tensor is constructed to describe smectic liquid crystals. The free energy consists of the entropy term and interaction term involving squared second order spatial derivatives. The entropy term incorporates the concentration in the quasi-entropy originally proposed for the tensor only, which is a strictly convex and lower semicontinuous function imposing coupled constraints between the concentration and the tensor. An evolution equation for the boundary normal derivative of the concentration is proposed in addition to the equations for the concentration and the tensor, giving an energy dissipation system. Numerical schemes are designed with emphases on using the entropy term to keep the coupled constraints, and the discretization of the boundary normal derivatives satisfying summation by parts. Existence, uniqueness, energy dissipation and error estimates are established. Numerical results indicate the efficiency and robustness of the scheme. Configurations of defects different from other layer structures are observed.
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Fluid Dynamics

Linear causality and stability constraints on relativistic second-order magnetohydrodynamics

Yiwei Qiu, Duan She and Defu Hou

In this work, we construct a theoretical framework for relativistic second-order magnetohydrodynamics based on entropy current analysis. The formalism consistently incorporates finite relaxation dynamics of the dissipative fluxes, providing a transient framework suitable for analyzing linear stability and short-wavelength causality. Utilizing linear mode analysis, we investigate the constraints imposed by causality and stability on this anisotropic system. By linearizing the theory around a homogeneous equilibrium state, we identify the magnetosonic, Alfvén, and charge-diffusion sectors, together with their coupling terms. For each sector, we derive asymptotic dispersion relations in both the long-wavelength (small-$k$) and short-wavelength (large-$k$) regimes, validating them against exact numerical roots. Our numerical analysis confirms the accuracy of these asymptotic solutions and uncovers a nontrivial angular dependence, especially near special propagation directions where the ordinary momentum expansion becomes less reliable. By evaluating the large-$k$ behavior of the propagating branches alongside the damping properties of non-hydrodynamic modes, we delineate the corresponding causality constraints. We find that the admissible linear causal domain is governed by the interplay between propagation direction, anisotropic transport coefficients, and relaxation times, with the resulting bounds being intrinsically mode-dependent. These findings provide a systematic theoretical basis for investigating linear stability and short-wavelength causality in relativistic magnetohydrodynamics beyond the first-order approximation.
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Fluid Dynamics

Surrogate-Based Aerodynamic Shape Optimization in Multiscale Flows via the Implicit Unified Gas-Kinetic Scheme

Xiaozhe Xi, Wenpei Long, Wenzhi Guo et al. (+2 more)

While hypersonic glide vehicles such as the HTV-2 continue to be a focal point in aerospace research, their aerodynamic characteristics in complex near-space environments are not yet fully understood. Because traditional continuum assumptions fail to accurately capture multiscale flow features across varying rarefied altitudes, this study investigates the aerodynamic shape optimization of an HTV-2-type aircraft across multiple flow regimes. An automated optimization framework is developed by coupling surrogate-based optimization (SBO) with the implicit unified gas-kinetic scheme (IUGKS). To ensure relevance to practical engineering requirements, both volumetric and center-of-pressure constraints are incorporated into the optimization process. The resulting optimized configurations are subsequently validated through high-fidelity computations, detailed flow-field evaluations, and global sensitivity analyses. Under volumetric constraints, the optimized lift-to-drag ratio ($L/D$) increases significantly at altitudes ranging from 70 km to 100 km. The optimal aerodynamic strategy is shown to shift with altitude: at 70 km, reducing the windward radius ($R_1$) weakens the oblique shock wave, whereas at highly rarefied altitudes, reducing the leeward radius ($R_3$) enhances the expansion wave. Correspondingly, sensitivity analyses confirm that as flow rarefaction increases, aerodynamic dominance shifts toward $R_3$. Furthermore, reducing the wingtip bluntness ($R_2$)yields consistent aerodynamic benefits across the entire flight envelope, ultimately driving the optimized geometries toward a flatter and more slender profile.
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All authors Xiaozhe Xi, Wenpei Long, Wenzhi Guo, Junzhe Cao, Kun Xu

Fluid Dynamics

Lattice Boltzmann Methods for Compressible (Magneto)hydrodynamics

Fedor Bukreev, Adrian Kummerländer and Mathias J. Krause

The simulation of magnetohydrodynamic (MHD) flows presents a highly complex, tightly coupled transport problem that poses severe numerical and computational demands. Towards this, we propose a novel class of Lattice Boltzmann Methods (LBM) schemes capable of solving a wide range of transport equation systems with high computational efficiency and scalability. Our approach exploits the algorithmic structure of kinetic formulations to separately transport all state variables of Strang-splitted conservation equations alongside their characteristics, yielding decoupled, fully local operations. To demonstrate the capability of this framework on complex, numerically demanding multiphysics interactions, we apply it to these MHD flows. Specifically, we discretize ideal compressible and resistive incompressible MHD systems, which naturally encompass hydrodynamic limits such as the compressible Euler and incompressible Navier-Stokes equations. Rigorous performance analysis of the implementation within the platform-transparent multi-physics framework OpenLB demonstrates up to 98.9% of the hardware roofline. We validate our approach against established incompressible and compressible MHD benchmarks across multiple resolutions. Finally, we simulate a moving, surface-resolved magnetized asteroid modeled after 16 Psyche in a supersonic early solar wind flow. This showcases the framework's advanced support for dynamic solid geometries, shifting magnetic fields, and fluid-structure interaction.
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Optics

Möbius-like Real-Space Topology Reshapes Spectral Winding Topology in Hatano-Nelson Rings

Yekai Shen, Shuhang Chen, Zishun Liao et al. (+1 more)

The spectral winding number serves as a bulk topological invariant in non-Hermitian systems, governing the emergence of skin modes and encoding the non-Hermitian bulk-boundary correspondence. However, most existing studies are built on conventional lattice geometries such as linear chains, rings, or planar arrays, leaving the role of real-space topological connectivity as an independent degree of freedom largely unexplored. Here, we construct a Möbius ring system by cutting two parallel Hatano-Nelson (HN) rings and reconnecting them with a half-twist, without altering any local hopping parameter. This topological reconstruction transforms the periodic-boundary spectrum from two disjoint ellipses into a multi-petalled rose curve, and leads to distinct decay lengths for different eigenstates under open boundary conditions. Moreover, the spectral winding number can be driven through discrete winding-number jumps by tuning the coupling strength, with critical values obtained analytically. Our results demonstrate that real-space Möbius connectivity, mediated by the coupling strength, provides an independent and tunable foundation for the systematic control of non-Hermitian topology, with implications for the design of topological devices and sensing schemes.
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All authors Yekai Shen, Shuhang Chen, Zishun Liao, Zhipeng Li

Classical Physics · Cross-listed from cond-mat.soft

Sliding contact creates universal self-affine fractal surfaces

Ruibin Xu, Haohao Ren, Adriane Clerc et al. (+4 more)

Surface roughness evolves during sliding, a process known as run-in, and the resulting topography controls friction, leakage, and failure from machines to geological faults. Yet the physical rule selecting this state remains unclear. We show that metals, rocks, and glasses develop universal self-similar roughness at short wavelengths, while retaining a material-dependent roll-off. A two-process model explains this behavior: junction formation and rupture drive universal roughening, whereas larger-scale deformation and/or fracture limit its growth.
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All authors Ruibin Xu, Haohao Ren, Adriane Clerc, Guilhem Mollon, Wenbo Sheng, Feng Zhou, B.N.J. Persson

Optics · Cross-listed from cond-mat.mes-hall

Non-Hermiticity-induced chirality imbalance of Weyl Landau levels

Sachin Vaidya, Alaa Bayazeed, André Grossi Fonseca et al. (+3 more)

Weyl semimetals obey a global chirality constraint: the net chiral topological charge and any associated chiral spectral flow must vanish, as required by the Nielsen-Ninomiya theorem. Under magnetic fields, this constraint manifests through counter-propagating zeroth Landau levels associated with Weyl nodes of opposite chirality. Here, we experimentally demonstrate how non-Hermiticity can reshape this balance in a synthetic photonic Weyl semimetal. Using engineered gauge fields in one-dimensional multilayer structures, we realize both homogeneous and axial magnetic fields and directly probe the resulting Landau-level spectra. While a homogeneous field produces the expected chirality-balanced zeroth Landau levels, an axial field spatially separates the compensating chiral channels: co-propagating bulk pseudo-Landau levels carry one chirality, whereas the opposite chirality resides in boundary-localized surface states. We show that radiative boundary loss selectively suppresses these surface states, removing them from the long-lived observable spectrum and producing an experimentally accessible chirality imbalance. By reducing boundary loss, we recover the hidden chiral channel and reveal its surface-state origin. These results show that non-Hermiticity, present naturally in photonics, can control and relax fundamental chirality constraints in topological systems, enabling access to otherwise forbidden spectral responses.
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All authors Sachin Vaidya, Alaa Bayazeed, André Grossi Fonseca, Adolfo G. Grushin, Marin Soljačić, Christina Jörg

Biological Physics

Elastohydrodynamic coupling enhances flow generation by coordinated ciliary beating

Shota Nakano, Shinji Deguchi and Daiki Matsunaga

Ciliary arrays pump fluid at low Reynolds number through non-reciprocal beating and phase coordination between neighbouring cilia. Previous studies have demonstrated that antiplectic metachronal waves are more effective than symplectic waves in enhancing transport, and have proposed several physically intuitive explanations for this preference. What remains incomplete is a predictive analytical understanding of how hydrodynamic coupling and beat geometry determine the flow-maximising phase difference. Here, we address this problem in two steps: we first use reinforcement learning to identify flow-maximising coordination in a bead–spring cilia model, and then introduce an analytically tractable reduced model, termed a tilted-slider model, to analyse the weak-coupling limit. Reinforcement learning identifies antiplectic coordination as the flow-maximising state in linear arrays, and shows that the phase difference between neighbouring cilia accounts for most of the flow enhancement. We then use the tilted-slider model to show that a shift of the time-averaged position opposite to the effective-stroke direction enhances fluid transport through its coupling with the elastic restoring force. The reduced model further reveals that antiplectic coordination can be optimal, consistent with previous studies, whereas symplectic coordination can instead become optimal depending on beat geometry. These results identify a simple elastohydrodynamic mechanism underlying flow-maximising metachronal coordination.
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Optics · Cross-listed from quant-ph

Analog photonic simulator for large-scale transport

Mengyu Zhao, Xuezhi Zhu, Nikita Guseynov et al. (+9 more)

Transport equations describe how physical quantities – such as mass, energy, momentum, concentration, probability, or fields – are carried, propagated, or redistributed through space and time, forming a foundational class of partial differential equations across science and engineering. However, high-dimensional partial differential equations are difficult to represent on digital grids because the number of degrees of freedom grows exponentially with dimension. Continuous-variable quantum photonics on the other hand can represent and evolve these large-scale fields without first discretizing space into a discrete grid. We demonstrate a large-scale analog photonic simulator for the constant-coefficient advection equation, a transport equation that is a fundamental benchmark for scientific computing. The solution of a $d$-variable advection equation is encoded into $d$ optical modes, so that the partial differential equation evolution maps directly to programmable phase-space displacements generated by optical quadrature momenta. Using a time-domain continuous-variable quantum photonic platform, we validate programmable control with $20,000$ single-mode squeezed states and $20,000$ two-mode squeezed states, and implement transport dynamics on a $20,000$-mode cluster-state resource. Homodyne measurements then verifies mode-resolved displacement control, which can provide first and second-order moment information of the solution to the advection equation, with final achievable relative error as low as $0.8\%$ and $0.92\%$ for first and second-order moment observables respectively. Our results establish continuous-variable photonics as a suitable programmable analog platform for large-scale advection equations.
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All authors Mengyu Zhao, Xuezhi Zhu, Nikita Guseynov, Yewei Yuan, Na Wang, Meihong Wang, Yunyun Cao, Shi Jin, Nana Liu, Changde Xie, Kunchi Peng, Xiaolong Su

Space Physics · Cross-listed from astro-ph.IM

Prospects for Astrobiology and Technosignature Searches with the Vera C. Rubin Observatory Legacy Survey of Space and Time

Andjelka B Kovacevic, Nigel J. Mason, Aleksandra Ciprijanovic et al. (+4 more)

he Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will repeatedly measure the brightness of billions of astrophysical sources using six colour filters. We test a simple idea: real physical signals tend to appear as coordinated patterns across several measurements, whereas noise does not; we call this behaviour “coherence”. We illustrate the approach with three LSST-like simulations: (i) five Kuiper Belt Object (KBO) surface/activity states, (ii) 648 exoplanet spectra with an injected vegetation-red-edge-like spectral feature, and (iii) 500 multiband light curves. In idealised simulations, a weakly active KBO is strongly separated from its inactive counterpart when all five colours are combined. The injected red-edge-like feature becomes detectable at effective visible-disc coverage of about 13%, and stacking about 150 detections could reach 5$\sigma$. Coherent, natural, and noise-like variability occupy distinct regions. A small Gaia DR3 stellar sample illustrates how colour and stability may help prioritise Galactic search regions.
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All authors Andjelka B Kovacevic, Nigel J. Mason, Aleksandra Ciprijanovic, Becky Long, Dominika Korczakowska, Maia Moore, Juulia Vuolukka

Optics

Robust Radiative Cooling in Functionalizable Silica Microsphere Paints

Jorge Burgos, José Rodrigo Magana, Ares Lladós et al. (+5 more)

Disordered coatings based on silica microspheres provide a scalable and robust platform for passive daytime radiative cooling. While particle-size optimization is often considered critical for enhancing solar scattering, the role of microsphere diameter once a coating operates in the multiple-scattering regime remains unclear. Here, we characterize the radiative cooling performance of disordered, optically thick photonic glass coatings with diameters ranging from 2 to 8 um. Despite measurable differences in microscopic scattering properties, both the spectral radiative response and the net cooling performance are robust to variations in particle diameter when the system operates deep in the diffusive regime. Outdoor thermal measurements reveal nearly identical steady-state temperature reductions across the full size range. These results indicate that radiative cooling in photonic glass coatings is governed by collective light transport, enabling microsphere size to be selected based on surface chemistry or processing constraints without compromising cooling performance.
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All authors Jorge Burgos, José Rodrigo Magana, Ares Lladós, Javier Pascualena Ferré, Sara Núñez-Sánchez, Juliana Jaramillo Fernández, Cefe López, Pedro David García

Classical Physics · Cross-listed from gr-qc

Relativistic transformation of temperature revisited

Soroor Pouryazdan and Babak Vakili

The relativistic transformation of temperature has long remained controversial, with the classical laws of Planck-Einstein, Ott-Eddington-Moller and Landsberg yielding conflicting results. We reexamine this issue from a relativistic thermodynamic and statistical perspective, starting from the energy-momentum tensor of an isotropic system and defining the effective temperature Teff as that inferred by a moving observer from the transformed energy density. Analyses of a photon gas, a relativistic ideal gas and an electron gas show that Teff consistently increases with velocity, supporting the Ott-Eddington interpretation while depending on the system's equation of state. These results indicate that temperature is not a Lorentz-invariant scalar but an observer-dependent quantity. A consistent relativistic description emerges when temperature is related to the inverse-temperature four-vector beta, linking operational and invariant viewpoints within a unified thermodynamic framework.
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Physics and Society

Cycle-resolved explainability of energy storage impacts on whole-system cost and emissions

Zenghui Zhang and Wei He

Grid-scale storage is not intrinsically cost-reducing or emissions-reducing: whether a storage cycle lowers or raises whole-system cost and CO2 depends on when, where, how long, what charges it, and what it displaces. Existing studies often assess storage value in aggregate or through asset-level market response, leaving a blind spot between system value and operational actions. Here we resolve this blind spot by attributing whole-system cost and CO2 consequences to individual charge-discharge cycles across present-day (2023) and planned (2030) UK and EU power systems. We show that aggregate indicators conceal sharply different cycle-level outcomes. In today's systems, commercially rational battery dispatch can reduce cost while increasing emissions, whereas long-duration energy storage more consistently captures infrequent cross-timescale co-benefit cycles that reduce both. Changing the dispatch objective redistributes storage operation within the existing opportunity set, but supply-side decarbonisation shifts that set itself, expanding co-benefit opportunities across technologies. This complementary structure shows that batteries serve recurrent opportunities, while long-duration storage captures stress-period co-benefits. The results identify gaps between market arrangements and whole-system value, and provide a basis for storage portfolio design, siting, and carbon-sensitive market reform that targets the operating regimes through which storage creates public value.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci

Synthesis of single-layered fluorographdiyne nanosheets via selective on-surface 2D covalent polymerization

Chen-Hui Shu, Yi Zheng, Tao Lin et al. (+14 more)

Two-dimensional conjugated polymers (2DCPs) are significant macromolecular materials with intriguing and tunable physicochemical properties that depend on their geometries. Graphdiyne and its derivatives are exemplary 2DCPs featuring sp-sp2 hybridized skeletons. However, achieving single-layered, large-domain/regular graphdiyne and its derivatives on surfaces remains a formidable challenge due to the lack of selective 2D covalent polymerization methods. Here, we report a selective on-surface 2D covalent polymerization method via the combination of cobalt catalysis and coronene templating, achieving the synthesis of single-layered fluorographdiyne nanosheets up to 60*60 nm2 on Au(111) surface. Using scanning probe techniques, we visualize the sequential polymerization process and characterize cobalt-activated coupling intermediates at the atomic level. Experimental and theoretical analyses suggest that strong d-{\pi} coupling between cobalt and alkynyl transforms a robust Csp-Au bond into a weaker Csp2-Au bond, thereby facilitating the demetallization C-C coupling. Besides, the templating effect of coronene suppresses kinetically trapped defects and improves the selectivity of hexagonal-ring formation in the complex 2D covalent polymerization process.
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All authors Chen-Hui Shu, Yi Zheng, Tao Lin, Li-Xia Kang, Zhang Qu, Zhi-Yu Wang, Ying Wang, Zheng-Yang Huang, Qian Liu, Hang Xu, Chong Chen, Yangfan Wu, Longteng Xiao, Mengxi Liu, Xiaohui Qiu, Pei-Nian Liu, Deng-Yuan Li

Instrumentation and Detectors · Cross-listed from quant-ph

Accelerating Surface Radiation Content to Investigate the Impact of Radon Progeny on Superconducting Qubits

Sagar S. Poudel, Dylan J. Temples, Ryan Linehan et al. (+8 more)

Ionizing radiation in the form of $\alpha$, $\beta$, $\gamma$, and additional high-energy particles can induce decoherence via phonon and quasiparticle poisoning in superconducting qubits. Recent studies have explored this effect using cosmic rays or controlled radioactive sources held in the proximity of a qubit package, and have concluded that reductions in such “external” environmental radiation may benefit stable operation of qubit devices. However, the effect of long-lived, unstable daughters of $^{222}$Rn that “plate out” directly on device and packaging surfaces has not been as extensively explored. This plate-out process, well-known to the dark matter direct detection field, occurs throughout the fabrication and testing lifecycle of a device and (separately) its packaging, and produces a local source of $\alpha$-decays which can remain active for decades. As this scales with chip area, understanding and managing this source of ionizing radiation is relevant for successfully scaling quantum computing architectures to larger numbers of qubits in a radiation-robust way. We present a setup capable of accelerating and enhancing radon daughter plateout by a factor of $7\times10^4$ over ambient, in order to study, in situ, the impact of these events on superconducting qubits. We also provide outlook on the potential impact of this source of ionizing radiation on current and future qubit arrays.
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All authors Sagar S. Poudel, Dylan J. Temples, Ryan Linehan, Alejandro Rodriguez, Matthew Hall, Dax Kay, Nathaniel Rodenburg, Daniel Baxter, Enectali Figueroa-Feliciano, Richard W. Schnee, Lauren Hsu

Physics Education

CURE-like, not cure-all: Varying broad relevance in experimentation labs produces similar student outcomes

Elly Markert, Mike Verostek, Matthew Dew et al. (+6 more)

Physics labs that engage students in practices authentic to experimental physics (experimentation-based labs) are being implemented to modernize the undergraduate physics curriculum and broaden participation in physics. Accordingly, prior research has positioned Course-Based Undergraduate Research Experiences (CUREs) as a means to extend the benefits of authentic undergraduate research experiences to more students. However, CUREs are resource-intensive and difficult to implement; a continuous stream of novel research projects adaptable for undergraduate courses is rare. Further, little is known about which specific components of a CURE are crucial to improving student outcomes and which components could be scaled back to improve feasibility for a wider range of class settings. In this study, we aim to isolate the component of broad relevance by running two experimentation-based labs in parallel: one "CURE-like" that increases broad relevance through the use of muon detectors, and one that uses equipment typical to an introductory physics lab and not relevant beyond the classroom. We measure student outcomes for both experimental critical thinking skills and attitudes towards physics labs. We use hierarchical linear modeling to compare student outcomes between the two labs. We find that both experimentation-based labs produce similar student outcomes. Our results suggest that increased levels of broad relevance may not inherently improve gains in student learning or attitudes. Future work should further investigate which components of different experimentation-based lab formats are associated with gains in student outcomes. Although this study did not implement a full CURE, our findings align with a growing body of evidence challenging the idea that CUREs are uniquely positioned to achieve superior student outcomes over other well-designed experimentation-based labs.
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All authors Elly Markert, Mike Verostek, Matthew Dew, Xuan Chen, Mark Lory-Moran, Sofi Padavan, Hissaa Walia, Peter Wittich, N.G. Holmes

Popular Physics · Cross-listed from astro-ph.IM

Some Thoughts on the Future of Technosignature Searches: Constraining the Fermi Paradox

Ian A. Crawford

This paper examines how future technosignature searches may constrain competing resolutions of the Fermi Paradox, with particular attention to the possibility that technologically capable entities (TCEs) are either intrinsically rare or deliberately concealed. I propose a multi-pronged observational strategy comprising expanded radio and optical SETI, spectroscopic searches for biosignatures and technosignatures in exoplanet atmospheres, astronomical searches for large-scale extraterrestrial engineering, and Solar System searches for extraterrestrial artefacts (SETA). The latter is identified as having a distinctive temporal advantage because it can probe evidence accumulated over Solar System (and perhaps even Galactic) history, rather than requiring temporal overlap with TCEs. In this context, I argue that searches for micron-scale interstellar technological debris (Arkhipov particles) in lunar and planetary regoliths may provide an additional constraint on past Galactic technological activity. Additionally, I briefly argue that this programme of scientific exploration should be considered alongside its geopolitical and governance implications.
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Friday 29 May

Computational Physics

Physically Constrained Ensemble Gaussian Process Modelling for Expensive Quantum Systems with Heteroskedastic Noise

Arpan Biswas, Sutirtha Paul, Joseph Agada et al. (+2 more)

Accurate modeling of quantum many-body systems often requires computationally expensive simulations such as Density Matrix Renormalization Group (DMRG) or Quantum Monte Carlo (QMC) calculations. These methods, while precise, impose significant time and resource constraints, limiting their use in exhaustive parameter exploration. Moreover, these expensive simulations can contain variable errors over the large unknown parameter space, which needs to be quantified and propagated. Thus, predictive modelling is required to estimate the functional space accurately over scarcely sampled data with heteroskedastic noise, while preserving the physical relevance of the estimation. Therefore, we present a Physically Constrained Ensemble Gaussian Process (pc-EGP) framework designed to efficiently model complex and noisy quantum systems under physical consistency constraints. The proposed method first enforces physical constraints as a user controlled weighted penalty to the data-driven loss function of the Gaussian Process (GP) surrogates. Then an ensemble of such GP models is trained with variable noisy simulations via numerical quadrature method where these multiple GP(s) at different nodes is integrated as a quadrature weighted average. We first demonstrate the framework on synthetically generated data before applying to quantum systems. In the first case study, we leverage DMRG simulations of the Bose-Hubbard Model to predict the critical interaction parameter Uc governing the superfluid-to-Mott-insulator transition. In the second case study, we demonstrate our method on QMC simulations, of a quantum liquid confined inside a nanoporous silicate with the goal of optimizing a chemical environment to realize a one-dimensional superfluid. Compared to conventional GP, pc-EGP achieves a better balance of accuracy and physically meaningful predictions.
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All authors Arpan Biswas, Sutirtha Paul, Joseph Agada, Matthias Thamm, Adrian Del Maestro

Optics

Real-Space Double Crossing Reveals Symmetry-Driven Dispersion Back-Bending of Surface Phonon Polaritons on {\alpha}-Quartz

Ryoga Odawara, Kotaro Shirahata, Aozora Ohi et al. (+2 more)

Surface phonon polaritons (SPhPs) in anisotropic crystals exhibit direction-dependent propagation and dispersion, yet how their dispersion back-bending manifests in real space has not been quantitatively resolved. Here, using nano-Fourier-transform infrared spectroscopy based on scattering-type scanning near-field optical microscopy, we image SPhP fringes on an $\alpha$-quartz surface for propagation parallel and perpendicular to the optic axis. Near 1160 cm$^{-1}$, the fringe periods for the two directions cross twice, providing a real-space signature of back-bending. Spatial Fourier analysis attributes the dominant fringe to edge-launched SPhPs and enables reconstruction of the intrinsic dispersion. Inverse Fourier analysis further visualizes the spatial attenuation and continuous evolution of the fringe wavelength near the resonance. The reconstructed dispersions reveal that the polarization-selective E-mode phonon produces direction-dependent back-bending and, through its damping, reduces the visibility of the back-bending branch. These results establish how symmetry-controlled dispersion manifests in real-space surface polariton propagation on a bulk anisotropic crystal.
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All authors Ryoga Odawara, Kotaro Shirahata, Aozora Ohi, Shun Hashiyada, Yukio Kawano

Fluid Dynamics · Cross-listed from cs.CE

Streami: An MPI Data-Parallel Library to Compute Field Lines on GPUs

Stefan Zellmann, Milan Jaros, Andrea Paris et al. (+2 more)

We present Streami, an extensible GPU-accelerated library for the computation of field lines in fluid flows on high-performance computers. Streami acts as a thin layer used for both post-hoc or in-situ analysis and can interface with existing MPI applications. We discuss Streami's application programming interface, key design decisions that led to Streami's high performance and extensibility, as well as extensions to support different fluid flow field representations. We also present a sample application for rapid prototyping and interactive seed point placement. Streami is released under a permissive open-source software license.
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All authors Stefan Zellmann, Milan Jaros, Andrea Paris, Ingo Wald, Tatiana von Landesberger

Physics and Society

SF-LIFE: A Large-Scale Simulated Movement Dataset for the San Francisco Bay Area

Chanuka Algama, Taylor Anderson, Henrique Ferraz de Arruda et al. (+14 more)

We introduce SF-LIFE, a large-scale simulated movement dataset designed to accelerate research in transportation, mobility, and machine learning. The dataset contains 3,024,000,000,000 location records capturing complete, noise-free, multi-modality trajectories of 500,000 simulated agents observed at a 1Hz frequency navigating the San Francisco Bay Area network over a 70-day period. The data captures (1) needs-driven daily agendas of individual agents generated by an agent-based simulation of human patterns of life and (2) detailed kinematic trajectories moving agents across the OpenStreetMap representation of San Francisco using data from 40+ transit agencies across 9 counties. SF-LIFE provides unprecedented scale and detail as trajectories are based on real transit infrastructure using San Francisco General Transit Feed Specification (GTFS) data, having agent movements across multiple modalities, including bus, rail, bike, automobile, and walking. For this high-fidelity simulated representation of San Francisco, we provide (1) the full trajectory data annotated with transportation mode labels, (2) reduced-size versions of the trajectory data with reduced temporal frequency, (3) agent activity information describing the causal activity why an agent visits a place, (4) agent demographic data, and (5) the underlying OSM road network and building data. As the first dataset of its scale and level of detail, SF-LIFE overcomes the privacy, noise, and completeness limitations inherent in real-world tracking data, providing a robust and ethically sourced resource for research in transit optimization, human mobility analysis, and urban computing.
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All authors Chanuka Algama, Taylor Anderson, Henrique Ferraz de Arruda, Andrew Crooks, Nathan Holt, Erfan Hosseini Sereshgi, John Hunter, Hamdi Kavak, Lance Kennedy, Yueyang Liu, Dieter Pfoser, Sandro Martinelli Reia, Doug Taylor, Mauryan Uppalapati, Boyu Wang, Carola Wenk, Andreas Züfle

Applied Physics · Cross-listed from cond-mat.mtrl-sci

Data-Driven Discovery of Unconventional Antiferromagnets

Qirui Cui, Chenxu Liu, Anna Delin et al. (+1 more)

Unconventional antiferromagnets combine zero net magnetization with spin-split electronic bands, offering a distinct, important platform for spintronics. Their discovery, however, has so far depended largely on case-by-case studies and on a limited number of compounds with experimentally resolved magnetic structures. Here, we overcome these bottlenecks by resolving magnetic ground states across a broad materials database. We narrow down 37163 magnets from the Materials Project to 189 collinear antiferromagnets by combining physics-informed prescreening, high-throughput exchange calculations and Luttinger-Tisza analysis. Among these, symmetry analysis identifies 36 altermagnets and 11 Luttinger-compensated ferrimagnets (LCFs), including 22 altermagnets and 9 LCFs that have not been reported previously. The identified unconventional antiferromagnets can support nonrelativistic spin Hall effects and doping-tunable spin transport with switchable polarization and giant anisotropy. Our framework converts broad structural databases into a curated, symmetry-classified set of experimentally testable compensated spin-split magnets, establishing a scalable route for the efficient discovery of functional antiferromagnets.
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All authors Qirui Cui, Chenxu Liu, Anna Delin, Kaiyou Wang

Computational Physics · Cross-listed from cond-mat.mtrl-sci

Microscopic origin of polytype-dependent melting in SiC revealed by machine-learning molecular dynamics

Ljiljana Stojanović, Samuel J. Magorrian, Lara Kabalan et al. (+3 more)

Predicting how crystal structure influences high-temperature stability remains a key challenge in materials modelling and design. Silicon carbide (SiC), one of the most thermally and chemically stable materials known, provides an ideal system for studying this problem because its many polytypes preserve similar local tetrahedral bonding while differing in long-range stacking geometry. Here, we combine phase-coexistence machine-learning molecular dynamics with finite-temperature phonon analysis, enabled by a fine-tuned MACE interatomic potential that accurately describes crystalline, high-temperature, and disordered configurations across multiple SiC polytypes. We identify a clear relative stability ordering, 3C > 2H > 9R, reflected consistently in structural disordering, interlayer sliding, and finite-temperature phonon spectra. Across all polytypes, melting initiates through the formation of short C-C contacts and carbon-rich local regions, followed by a progressive loss of tetrahedral Si-C connectivity. The reduced stability of the long-period 9R polytype is traced to low-frequency transverse-acoustic shear modes associated with relative bilayer sliding, which are already present in the 0 K phonon spectra and soften further at high temperature. These modes generate larger lateral bilayer displacements, linking enhanced interlayer sliding to local chemical disordering and ultimately melting. More broadly, our results show that high-temperature stability in polytypic covalent materials is governed not only by local bond strength, but also by stacking-dependent transverse dynamics.
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All authors Ljiljana Stojanović, Samuel J. Magorrian, Lara Kabalan, Richard N. White, Fabian L. Thiemann, Viktor Zólyomi

Computational Physics

Data-Driven Spectral Prediction for Accelerating Large-Scale Electronic Structure Calculations

Abhiram Badrinarayanan, Davor Davidovic, Edoardo Di Napoli et al. (+4 more)

Simulating large molecular systems comprising thousands of atoms requires highly scalable methodologies. While modern Density Functional Theory (DFT) codes exhibit linear scaling, solving the associated large, sparse generalized eigenproblems remains a critical computational bottleneck on exascale architectures. In the context of the LimitX project, we propose a data-driven framework to accelerate these calculations. By shifting the machine learning target from discrete eigenvalues to the coefficients of an interpolating Chebyshev polynomial, and by comparing both all-atom and fragment-based structural representations, we successfully overcome the dimensionality constraints of large-scale spectral prediction. We investigate three machine learning models (Kernel Ridge Regression, Graph Neural Networks, and Random Forests) trained on a novel 2 TB dataset of protein dimers. The predicted spectra provide initial guesses that effectively bypass early Self-Consistent Field (SCF) iterations in BigDFT. Ultimately, these spectral predictors will be deployed to dynamically optimize upcoming rational filter-based eigensolvers, such as FrASE, which is currently in initial development.
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All authors Abhiram Badrinarayanan, Davor Davidovic, Edoardo Di Napoli, Jurica Novak, Luigi Genovese, Gustavo Ramirez-Hidalgo, Xinzhe Wu

Fluid Dynamics · Cross-listed from cond-mat.soft

Impact of viscoelastic polymer solution droplets on a granular bed

Jooyeon Park, Theophile Meiller, Sreeram Rajesh et al. (+1 more)

The impact of polymer solution droplets on granular beds is relevant to powder processing, binder jetting additive manufacturing, and environmental applications involving erosion control or spray deposition, yet most controlled studies of drop–grain interactions have focused on Newtonian liquids. In this study, we experimentally investigate the impact of viscoelastic polyethylene oxide (PEO) droplets on a dry granular bed and compare the resulting cratering dynamics with those of Newtonian liquids over a wide range of impact energies and Ohnesorge numbers. Crater morphology changes with impact energy, and this evolution occurs at lower energies for drops of polymer solution, consistent with their distinct liquid–grain interactions during impact. The crater diameter exhibits two distinct regimes: a low-energy plateau and a power-law growth at higher impact energies. We identify the transition between these regimes and show that, although the plateau size and the power law remain nearly unchanged, viscoelastic droplets reach the transition at lower impact energy than Newtonian droplets. This suggests that viscoelasticity modifies how the impact energy is partitioned between droplet deformation and dissipation in the granular bed.
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All authors Jooyeon Park, Theophile Meiller, Sreeram Rajesh, Alban Sauret

Physics and Society · Cross-listed from astro-ph.IM

Building a Global Astrotourism Community of Practice Through Astronomy for Development

Joyful E. Mdhluli

Astrotourism is an emerging interdisciplinary field situated at the intersection of astronomy, tourism, cultural heritage, and sustainable development. Despite growing global interest, the field remains loosely defined and under-theorized, with limited empirical studies documenting practitioner perspectives and community-led initiatives. This paper presents findings from the first Astrotourism Community Exchange hosted by the International Astronomical Union Office of Astronomy for Development (OAD), which brought together over 150 participants from Africa, Asia, Europe, the Middle East, and Latin America - including practitioners, researchers, educators, tourism processionals, and community developers. Using qualitative thematic analysis of a recorded online community session, we explore how practitioners conceptualize astrotourism, the models being implemented across diverse contexts, and the key challenges shaping the field's development. Five major themes emerged: (1) astrotourism as a tool for community development, (2) cultural heritage and knowledge systems, (3) environmental sustainability and dark sky protection, (4) accessibility and inclusive design, and (5) conceptual and methodological gaps in the field. Across all themes, astrotourism was consistently framed not merely as a form of niche tourism, but as a hybrid socio-cultural and environmental practice with significant implications for sustainable development and science engagement. We argue that astrotourism is evolving into a global community of practice rather than a fixed tourism category, and we highlight the need for further interdisciplinary research, data collection frameworks, and inclusive policy development to support its growth.
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Biological Physics · Cross-listed from cond-mat.dis-nn

Localization of Active Particles on Random Arrays of Parallel Filaments

Owen Santoso and Elena Koslover

Quenched disorder in the environment can fundamentally alter transport dynamics in both active and passive systems. We explore how disordered arrays of filaments govern the distribution of intermittently moving particles which switch between diffusive and processive transport. Motivated by the mixed-polarity arrangements of parallel microtubules observed in mammalian dendrites, we show that such arrays tend to result in localization of particles at regions of convergent filament orientation. In the rapid attachment-detachment limit, the disordered system can be described by a noisy one-dimensional effective energy landscape, whose structure is approximated by a random walk. The depth and width of wells on this landscape are expressed as a function of the transport kinetics and system geometry. Localization is shown to be strongest at intermediate run-lengths, where biased transport persists long enough to sense the quenched filament polarity but not so long as to facilitate escape from local traps. These results demonstrate robust localization of particles moving on random filament networks, highlighting the emergent spatial organization that arises from an interplay of active transport and quenched disorder.
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Atmospheric and Oceanic Physics

Flow Matching for Convective-Scale Precipitation Downscaling

Tom Wetherell

Generative machine learning is an increasingly important complement to dynamical downscaling for producing high-resolution precipitation projections, with diffusion models currently the leading approach. Flow matching is a related generative framework that has recently achieved strong results across image, video and other domains, and shown early promise for downscaling. We train a flow matching model to map daily precipitation from 8 km to 2 km over a convective-scale domain centred on Singapore, and benchmark it against CPMGEM, a score-based diffusion model. Flow matching achieves consistently better spatial skill: higher fractions skill score at every precipitation threshold and neighbourhood scale tested, and tighter structure and amplitude components of the SAL score with comparable location skill. However, flow matching underestimates the upper tail of the precipitation distribution, resulting in a dry bias in the climatological mean. These results suggest that flow matching is a competitive generative framework for convective-scale precipitation downscaling, particularly well suited to capturing spatial structure.
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Physics and Society · Cross-listed from cs.CV

The Harsh Truth: Segment-Level Analysis of Harsh Driving Events in Milan Using Large-Scale Telematics, Street Networks, and Google Street View

Andrea La Grotteria, Paolo Santi, Titus Venverloo et al. (+2 more)

Police-reported crash statistics remain the standard input for urban road-safety assessment, but their incompleteness and reporting lag limit their usefulness for timely, fine-grained intervention design. Harsh acceleration and braking events are widely used as surrogate safety indicators, but have so far been studied only in comparatively small urban samples. This study analyses harsh events across the urban road network of Milan, combining high-resolution telematics from more than 4.2 million vehicles equipped with On-Board Units, segment-level traffic metrics from TomTom, street-network and infrastructure attributes from OpenStreetMap, and visual streetscape features extracted from Google Street View via semantic segmentation using a OneFormer model. We employ an analytical framework combining non-parametric Mann–Whitney U tests of segment-feature distributions between high- and low-harshness groups with supervised machine-learning regressors. We find that, once exposure is controlled for, wider carriageways, crossings and transit stops, and more open visual fields (higher sky- and road-pixel proportions) are associated with higher harsh-event intensity, while denser built frontage is associated with lower intensity. Finally, the cycling-infrastructure case study identifies a gradient in harsh-event intensity across facility types: markings-only cycle lanes are associated with a 19.5% higher harshness score, and mixed-traffic configurations with an 11.5% higher score, relative to physically separated cycle paths, conditional on the included controls. These results support context-specific rather than uniform urban-safety interventions and illustrate how large-scale telematics combined with open geospatial and visual data can inform Vision Zero decision-making at the metropolitan scale.
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All authors Andrea La Grotteria, Paolo Santi, Titus Venverloo, Umberto Fugiglando, Carlo Ratti

History and Philosophy of Physics · Cross-listed from quant-ph

Topics on Foundations of Physics: From the quantum to the (semi) classical, gravity, thermodynamics, and (or beyond) our possible detections

Ricardo Muciño

The work leading to this thesis focuses on assessing and extending quantum theories in order to explore and test their implications across various regimes – including thermodynamics, semiclassical and quantum gravity scenarios, and the in principle detectable predictions of such theories. The general motivation stems from a basic desire to understand the world form its very foundations. For instance, how can we bridge the gap between what we observe or `perceive' and the fundamental quantum nature in our theories. In particular, this work originated from the search to a better understanding of the nature of time according to our physical theories and the common perception that it invariably `flows' to the future, or, in other words, why do we observe distinct natural processes evolving asymmetrically in time? These motivations led to three distinct, yet interconnected and successful, lines of research, presented here in three separate parts: I. On Possible Detections within Physical Theories; II. On Explaining the Approach to Thermodynamic Equilibrium; and III. Relativistic Collapse Theories and a Self-Consistent Model of Semiclassical Gravity.
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2606.00255 · 29 May · Doctoral thesis submitted to the Universidad Nacional Autónoma de México (UNAM). Front page and acknowledgments are in Spanish, the main body is in English. Introductions are in both languages. This version contains typographical and editorial improvements made after the institutional submission: https://hdl.handle.net/20.500.14330/TES01000881995 .(112 pages, 5 figures)

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