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Physics Physics

physics Watch Physics

Thursday 16 April

Fluid Dynamics

A data-driven approach for 2D vorticity PDF equations by a new conditional average estimation

Qian Huang, Simon Görtz, Paul Hollmann et al. (+3 more)

We consider the statistics for the vorticity field in two-dimensional homogeneous isotropic turbulence (HIT). First, we exploit the invariance properties to derive dimensionally reduced governing equations for the one-point and two-point probability density functions (PDFs). These take the form of linear kinetic transport equations, but with an unclosed operator in terms of a conditional average. To solve the PDF equation numerically we suggest a hybrid data-driven method that relies on carefully selected samples of DNS data and a sampling estimator for the conditional average. The method is applied to DNS data for both decaying and forced HIT, demonstrating good agreement with the direct evaluation of the PDFs using the DNS data.
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All authors Qian Huang, Simon Görtz, Paul Hollmann, Johannes Conrad, Christian Rohde, Martin Oberlack

Optics

Incoherence-assisted mode excitation in non-Hermitian resonant systems

Amin Hashemi, Vinzenz Zimmermann, Armando Perez-Leija et al. (+1 more)

We introduce and experimentally demonstrate an approach for selective mode excitation in non-Hermitian resonant systems using incoherent light. This method eliminates the need for precise phase control that is often required in coherent excitation schemes. Using this technique on a silicon photonic platform with coupled ring resonators, we successfully excite the topological edge state of a non-Hermitian Su-Schrieffer-Heeger (SSH) model. Our work shows that incoherence-assisted excitation is a robust and passive strategy for topological state preparation, which broadens the scope of non-Hermitian topological photonics thereby providing a practical and experimentally viable tool for selective mode excitation.
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All authors Amin Hashemi, Vinzenz Zimmermann, Armando Perez-Leija, Andrea Blanco-Redondo

Atomic Physics · Cross-listed from nucl-ex

The Proton Radius Puzzle

Gerald A. Miller

Pohl et al. measured the energy difference between the 2P and 2S states of muonic hydrogen and used it to determine a precise value of the proton radius. The result disagreed significantly from values extracted from electronic hydrogen and elastic electron-proton scattering. This discrepancy was exciting because it indicated a breakdown of Coulomb's law. In more technical terms, the discrepancy indicated that a fundamental property of the Standard Model, known as lepton universality, could be violated. This chapter explains the origins, meaning and significance of the puzzle. A resolution, based on very recent experiments, is stated. The proton radius puzzle is no more.
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Plasma Physics

Ion-motion-driven enhancement of energy coupling and stability in relativistic laser-microchannel interaction

K. Weichman, M. VanDusen-Gross, G. Bruhaug et al. (+5 more)

For sufficiently short relativistic-intensity laser pulses, the disparity in time scales for electron and ion motion causes ions to behave as a fixed, neutralizing background. As the pulse duration or intensity is increased, ion motion becomes important, leading to instability in uniform plasmas but more complex, and potentially desirable behavior in structured targets. In this work, we introduce a new self-organized regime in laser-driven microchannels wherein ion motion facilitates stronger peak fields and high charge and photon conversion efficiency. 3-D particle-in-cell simulations demonstrate that the qualitative laser-microchannel interaction regime is governed by similarity parameters relating the pulse duration, spot size, and intensity to channel scales. The observed similarity suggests that lower-intensity experiments can inform designs for next-generation facilities, where the high-field, highly-radiative properties of the self-organized regime are especially desirable.
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All authors K. Weichman, M. VanDusen-Gross, G. Bruhaug, J. P. Palastro, M. Wei, A. Haid, A. V. Arefiev, H. G. Rinderknecht

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

Universal Loop Statistics from Active Extrusion with Kinetic Barriers

A. Chervinskaya, R. Metzler and K. E. Polovnikov

We develop a kinetic theory of cohesin-driven loop extrusion on a disordered chromatin track with transient barriers. In the stationary state, the mean loop size is shown to obey a universal law determined by the bare processivity and a renormalized obstacle density. Beyond the mean, one-sided extrusion always yields a single-exponential loop-length distribution, whereas two-sided extrusion produces a finite sum of exponential modes and, generically, a peaked distribution. Experimental CTCF-anchored loop statistics exhibit such a peak, thereby providing a direct discriminator of extrusion symmetry. The theory therefore establishes a unified framework for disorder-limited loop extrusion and supports a scenario in which both cohesin arms actively operate in living cells.
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Atomic Physics · Cross-listed from hep-ph

Lorentz and CPT violation and the hydrogen and antihydrogen molecular ions III – rovibrational spectrum and the non-minimal SME

Graham M Shore

Rovibrational transitions in the hydrogen and antihydrogen molecular ions $H_2^+$ and $\overline{H}_2^-$ offer the possibility of testing Lorentz and CPT symmetry to extremely high precision, in principle attaining $O(10^{-17})$. In this paper, the third in a series, we give a comprehensive derivation of the rovibrational spectrum of $H_2^+$ and $\overline{H}_2^-$ in the SME, an effective quantum field theory incorporating Lorentz and CPT violation. New developments described here include a complete analysis of the molecular dynamics from first principles in terms of the spherical tensor representation of the SME couplings, the systematic extension of our previous results to the non-minimal SME, a full description of the quantum number dependence of the rovibrational energy levels in the spherical tensor formalism with both high and low background magnetic fields, and an extended discussion of sidereal and annual variations of transition frequencies arising from both rotations and Lorentz boosts. The resulting sensitivity of the rovibrational spectrum to an extended range of SME couplings, together with the ability to isolate their individual effects using the quantum number dependence of the transition frequencies, enhances the opportunities to detect Lorentz and CPT symmetry breaking through rovibrational spectroscopy of $H_2^+$ and $\overline{H}_2^-$.
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Fluid Dynamics · Cross-listed from cond-mat.soft

Formation of cylindrical shells via sphere packing from fluidized beds

Vinícius Pereira da Silva Oliveira, Danilo da Silva Borges, Erick de Moraes Franklin et al. (+1 more)

The results of a numerical investigation of fluidized beds of spherical particles in a narrow vertical cylindrical pipe, with particular attention to the spontaneous settling along the wall, are reported. Starting from a steady fluidized state, the particles fluctuate because of fluid-particle, particle-particle, and particle-wall interactions. The particles are heavier than the fluid, with diameters d yielding ratios of pipe to particle diameters D/d=4.3 and 4.7. For given ranges of flow velocities and bed sizes, particles settle on the wall, with a decrease in the bed height and particle fluctuations. Either a glass- or crystal-like shell forms along the pipe wall, in qualitative agreement with previous experiments. The polydispersity and the particle-particle friction are varied to test the stability of the particulate shell formation. The shell structure is analyzed by unwrapping it in a plane and locating all particles and their contact points, and we find that it exhibits a hexagonal lattice with a defects density that increases with polydispersity. The shell formation is hindered by polydispersity, and there exists a critical point for polydispersity above which a crystal-like shell is unstable. In a particular case of bidisperse beds, the crystal-like shell only appears when the particle-particle friction is high enough. Finally, we compute the contact forces within particle-particle chains and in particle-wall contacts, which sustain the cylindrical shell, highlighting the dominant role of particle-particle forces.
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All authors Vinícius Pereira da Silva Oliveira, Danilo da Silva Borges, Erick de Moraes Franklin, Jorge Manuel Peixinho

Optics

End-to-End Physical Design Automation Flow for Yield-Optimized Inverse-Designed Large-Scale Electronic-Photonic Integrated Circuits

Hongjian Zhou, Haoyu Yang, Haoxing Ren et al. (+2 more)

As AI systems scale to multi-chiplet and wafer-level architectures, the demand for ultra-high bandwidth and system scalability has outpaced the capabilities of electrical interconnects and computing units. Large-scale heterogeneous electronic-photonic integrated chiplets (EPICs) provide a promising solution, but their practical adoption is limited by the lack of a unified, fabrication-aware physical design automation stack. At the same time, inverse-designed ultra-compact photonic devices offer orders-of-magnitude improvements in spatial and spectral density, yet remain constrained by insufficient design-for-manufacturing support and yield optimization. In this work, we present OptoSynthesizer, an end-to-end physical design automation flow for yield-optimized, inverse-designed EPICs. It integrates three key components across the physical design pipeline: (1) OptoSynthesizer-InvDes, a physical-AI-augmented, digital-twin-assisted photonic inverse design and photonics-aware inverse lithography framework; (2) OptoSynthesizer-Place, a GPU-accelerated routing-informed EPIC placer for large-scale routability-optimized layout; and (3) OptoSynthesizer-Route, a hierarchical curvy-aware waveguide router with global-planning-assisted electrical-optical co-routing. Together, these toolkits form a seamless flow from EPIC netlists to fabrication-ready, yield-robust GDS layouts. We demonstrate how this framework enables compact large-scale photonic tensor cores and high-bandwidth interconnect fabrics for heterogeneous EPIC platforms, providing a practical foundation for manufacturable large-scale EPICs in next-generation AI systems.
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All authors Hongjian Zhou, Haoyu Yang, Haoxing Ren, Joaquin Matres, Jiaqi Gu

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

Divergence of detachment forces in the finite Voronoi model

Wei Wang and Brian A. Camley

Detachment and fracture are central to many tissue-level processes, but they are challenging to simulate with Voronoi-type models that typically assume a confluent tissue. Here we analyze the finite Voronoi model, a nonconfluent extension of conventional Voronoi models, in which cell boundaries are composed of straight Voronoi edges and circular arcs of fixed radius $\ell$. When the line tension on cell-medium interfaces exceeds the tension on cell-cell contacts, we find that the model exhibits a strong time-step dependence in the fracture timescale of initially intact active clusters: decreasing $\Delta t$ can unphysically suppress cluster rupture events. We trace this behavior to a divergence of detachment forces in the finite Voronoi model and introduce a simple regularization. We then compare the finite Voronoi model's near-detachment mechanics to a deformable polygon model and propose two potential calibration strategies. Finally, we examine the fracture–no-fracture transition in nonconfluent tissues and show that it is governed by detachment mechanics: the calibration can even determine the sign of the transition's dependence on cell shape. Our results show that, for studies focused on fracture or intercellular adhesion in nonconfluent monolayers, a physically motivated calibration of near-detachment mechanics in the finite Voronoi model is essential.
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Medical Physics

Fractal geometry-governed oxygen diffusion: Tumors vs. Normal Tissues

Neda Valizadeh, Robabeh Rahimi and Ramin Abolfath

Purpose: To develop a geometry-governed diffusion framework that explains differential tissue response under FLASH ultra-high dose rate (UHDR) irradiation by explicitly accounting for structural heterogeneity and anomalous transport in biological tissues. Methods: We formulate a generalized diffusion–reaction model on fractal substrates to describe molecular transport in heterogeneous media. Tissue architecture is characterized by a fractal (Hausdorff) dimension \(D\), while scale-dependent transport inefficiency and memory effects are captured by a fractional parameter \(\theta\). Analytical solutions for radially symmetric geometries are derived and compared with classical normal (Euclidean) diffusion and a Gaussian reference model under identical physical conditions. Transport behavior is quantified through transient probability distributions and steady-state spatial profiles. Results: The model reveals systematic suppression of long-range transport and enhanced localization as tissue structural complexity increases. Increasing \(\theta\) leads to subdiffusive dynamics, reduced effective diffusion lengths, and persistent non-Gaussian concentration profiles, even in the steady state. While increasing \(D\) alone enhances spatial accessibility, fractional dynamics dominate transport behavior when \(\theta>0\), counteracting geometric connectivity. These effects produce a separation between regimes characterized by efficient inter-track overlap and rapid homogenization, and regimes marked by isolated, long-lived reactive domains.
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Optics

Quantum-Well-Metasurface to Maximize Nonlinear Polarization

Pernille Undrum Fathi, Irene Occhiodori, Patrick Devaney et al. (+12 more)

Nonlinear frequency conversion unlocks technologies ranging from telecommunications to quantum computation; however, weak nonlinearities and architectures that resist miniaturization currently limit devices. Here, we combine a bandstructure-engineered GaAs/AlGaAs heterostructure with a high quality factor dielectric metasurface to simultaneously tailor the intrinsic nonlinear susceptibility and optimize the electromagnetic field within the heterostructure. By engineering a resonant interband transition, we realize a large second-order nonlinear tensor element, 1.6 nm/V at 1.57 um wavelength. We then make it free-space-accessible and boost the effective nonlinearity to ~ 14 nm/V using a metasurface patterned on the material. Our proof-of-concept experiment establishes that interband transition engineering and metasurfaces accessing otherwise unusable nonlinear tensor elements enable giant effective nonlinearities in the near-infrared to visible spectrum. This addresses material and device-level constraints in nonlinear photonics, providing a scalable route to compact, efficient devices.
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All authors Pernille Undrum Fathi, Irene Occhiodori, Patrick Devaney, Amberly Ricks, Rithvik Ramesh, Yiwei Ju, Moaz Waqar, Theodore P. Letsou, Christina M. Spägele, Hyunseung Jung, Igal Brener, Xiaoqing Pan, Marcus Ossiander, Seth R. Bank, Federico Capasso

Fluid Dynamics

Component-Based Reduced-Order Modeling Framework for Rocket Combustion Dynamics in Multi-Injector Configurations

Brody Gatza and Cheng Huang

Even with the most advanced computational capabilities, high-fidelity (e.g., large-eddy) simulations of large-scale rocket engines remain far out of reach. In the current work, we develop and establish a component-based reduced-order modeling (CBROM) framework to enable accurate and efficient parametric modeling of large-scale rocket engines by geometrically decomposing a single domain into a combination of several representative components, including injectors, combustor and nozzle. Individual component-based reduced-order models (ROMs) are trained for each component with fabricated system-level responses enforced through carefully formulated boundary conditions during the training, which only require high-fidelity simulations of a much smaller computational domain, thereby significantly reducing the costs of ROM training. The trained component-based ROMs are then coupled together to enable full-system simulations. Specifically, we pursue an advanced adaptive ROM formulation leveraging a model-form preserving least-squares with variable transformation (MP-LSVT) projection to construct the component-based ROMs. The CBROM framework is evaluated using a seven-injector model rocket combustor configuration that exhibits self-excited combustion dynamics with distinct characteristics that vary with flow condition and geometric variations. The framework is demonstrated to provide accurate parametric predictions of the changes in dynamic behaviors, expressed in the spectra from dynamic mode decomposition (DMD) analysis and features in the time-averaged and RMS fields of target state variables.
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Computational Physics · Cross-listed from cs.CE

A shifted interface approach for internal discontinuities in poroelastic media

David Michael Riley, Guglielmo Scovazzi and Ioannis Stefanou

Porous media containing cracks, fractures, or internal discontinuities arise throughout subsurface geomechanics, biomechanics, and materials science. Numerical simulation of the coupled hydromechanical response is inherently challenging because the pressure and displacement fields are tightly coupled through the Biot equations, requiring stable mixed formulations. These difficulties are compounded when cracks are present, because standard mesh-conforming approaches require costly, labor-intensive, body-fitted meshing, while unfitted methods often require cut-cell integration, enrichment functions, or additional stabilization. In this work, we use an alternative approach, we adapt the shifted interface method to coupled transient poroelasticity with embedded interfaces. The method replaces the true crack by a surrogate approximation where interface conditions are transferred through local expansions. A unified derivation yields shifted forms for both hydraulic transmission and mechanical traction coupling. Two enforcement strategies are extensively compared: a weak (integral) enforcement and a strong (pointwise) enforcement. Four test cases of increasing geometric complexity (offset mesh-aligned, boundary-intersecting angled, embedded angled, and multi-crack configurations) validate the formulation. Away from crack tips, interface residuals converge as O(h); near tips, localized post-processing artifacts degrade the global rate, but first-order convergence is recovered when a small tip region is excluded. A multi-crack demonstration with four simultaneously embedded cracks of distinct geometry and interface properties confirms the practical applicability of the framework. These results support the shifted interface method as a practical framework for poroelastic crack modeling on non-body-fitted meshes with geometrically complex embedded interfaces.
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Computational Physics · Cross-listed from cond-mat.dis-nn

The Phase Transitions in a $p$ spin Glass Model: A Numerical Study

Prerak Gupta, Auditya Sharma, Bharadwaj Vedula et al. (+2 more)

We investigate the balanced $M=4$, $p=4$ spin-glass model for a one-dimensional long-range proxy for the finite dimensional short-range $p$-spin glass model to examine the nature of the glass transition beyond mean-field theory. We perform large-scale Monte Carlo equilibrated simulations for both fully connected and power-law diluted versions of the model. The critical temperatures extracted from the finite-size scaling (FSS) analysis of spin-glass susceptibility are in good agreement with theoretical predictions for $\sigma = 0, 0.25$, and 0.55. For these values of the long-range exponent $\sigma$ (which is the power of the decrease of the interactions between the spins with their separation), one might have expected that mean-field theory would provide a good description of the system. However, the spin-overlap distribution and the value of the $\lambda$-parameter do not provide numerical evidence for a one-step replica symmetry breaking (1RSB) phase transition. Instead, our results indicate a direct transition from the paramagnetic state to a full replica symmetry broken phase, with a renormalized value of $\lambda\equiv \omega_2/\omega_1 < 1$ suggesting a continuous FRSB transition, despite this ratio being equal to 2 at mean-field level. A value of $\lambda > 1$ is required for the discontinuous 1RSB transition. We argue that strong finite-size effects and closely spaced transition temperatures remove the expected 1RSB transition for the system sizes which we can study. For values of the exponent $\sigma = 0.85$, which roughly corresponds to a three dimensional system, we find that the renormalized value of $\lambda$ is again less than 1, with no signs of either the 1RSB transition or the continuous FRSB transition, suggesting that the Kauzmann temperature $T_K$ in three dimensions might be zero and the complete absence of phase transitions in structural glasses.
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All authors Prerak Gupta, Auditya Sharma, Bharadwaj Vedula, J. Yeo, M.A. Moore

Optics · Cross-listed from cond-mat.str-el

Ultrastrong Coupling Signatures in Photon Statistics from Terahertz Higgs-Polaritons

Spenser Talkington, Benjamin Kass and Martin Claassen

The ultrastrong coupling regime of cavity photons and quantum materials has emerged as a pathway to modify materials properties, however definitive signatures of ultrastrong coupling remain elusive. Focusing on the quantum photon statistics of light transmitted through a cavity-embedded superconductor, we show that a two-photon Higgs polariton at strong coupling realizes a photonic nonlinearity at the single terahertz photon level. We find that as light-matter coupling increases, the photon statistics show pronounced changes due to the formation of a hybrid photon-matter dark-cavity state with finite photon occupancy, producing testable signatures of ultrastrong coupling. We derive a non-Markovian input output relation and study the cavity-embedded superconductor 2H-NbSe2 as it approaches ultrastrong light-matter coupling. Our results reveal a diagnostic for ultrastrong coupling in the two-photon coincidence statistics that is absent in total counts.
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Classical Physics

Optical Theorem for Measuring the Acoustic Extinction Cross Section of Helmholtz Resonators

Vladimir Igoshin, Daniil Klimov, Yuri Utkin et al. (+5 more)

The optical theorem is a powerful tool of scattering theory that directly relates the extinction cross section of a scatterer to its forward scattering amplitude. While widely used in electromagnetism and optics, its application in acoustics has remained limited, primarily due to experimental challenges. These include the finite size of practical sound sources and the stringent requirements for detecting weak scattered signals. In this work, we analyze these limitations and develop a robust methodology for measuring the acoustic extinction cross section under realistic conditions, including non-ideal anechoic environments. The approach is applied experimentally to a Helmholtz resonator in an imperfect anechoic environment with standing-wave resonances. The retrieved extinction cross section exhibits a single pronounced resonance near 2000 Hz. The resonance position, peak magnitude, and spectral lineshape are consistent with full-wave numerical simulations. The results demonstrate that, when combined with appropriate data processing, the optical theorem provides a simple and reliable tool for characterizing acoustic resonators, opening new opportunities for quantitative analysis of acoustic scattering and absorption phenomena.
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All authors Vladimir Igoshin, Daniil Klimov, Yuri Utkin, Sergey Ermakov, Mikhail Kuzmin, Andrey Bogdanov, Yong Li, Mihail Petrov

Data Analysis and Statistics · Cross-listed from cs.LG

PRL-Bench: A Comprehensive Benchmark Evaluating LLMs' Capabilities in Frontier Physics Research

Tingjia Miao, Wenkai Jin, Muhua Zhang et al. (+19 more)

The paradigm of agentic science requires AI systems to conduct robust reasoning and engage in long-horizon, autonomous exploration. However, current scientific benchmarks remain confined to domain knowledge comprehension and complex reasoning, failing to evaluate the exploratory nature and procedural complexity of real-world research. In this work, we present research-oriented evaluations in theoretical and computational physics, a natural testbed with comprehensive domain knowledge, complex reasoning, and verifiable end-to-end workflows without reliance on experiments. Here we introduce PRL-Bench (Physics Research by LLMs), a benchmark designed to systematically map the capability boundaries of LLMs in executing end-to-end physics research. Constructed from 100 curated papers from the latest issues of Physical Review Letters since August 2025 and validated by domain experts, PRL-Bench covers five major theory- and computation-intensive subfields of modern physics: astrophysics, condensed matter physics, high-energy physics, quantum information, and statistical physics. Each task in the benchmark is designed to replicate the core properties of authentic scientific research, including exploration-oriented formulation, long-horizon workflows, and objective verifiability, thereby reconstructing the essential reasoning processes and research workflows of real physics research. Evaluation across frontier models shows that performance remains limited, with the best overall score below 50, revealing a pronounced gap between current LLM capabilities and the demands of real scientific research. PRL-Bench serves a reliable testbed for accessing next generation AI scientists advancing AI systems toward autonomous scientific discovery.
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All authors Tingjia Miao, Wenkai Jin, Muhua Zhang, Jinxin Tan, Yuelin Hu, Tu Guo, Jiejun Zhang, Yuhan Wang, Wenbo Li, Yinuo Gao, Shuo Chen, Weiqi Jiang, Yayun Hu, Zixing Lei, Xianghe Pang, Zexi Liu, Yuzhi Zhang, Linfeng Zhang, Kun Chen, Wei Wang, Weinan E, Siheng Chen

Instrumentation and Detectors

SHIELD: A Reference Gas-Driven Permeation Platform for Hydrogen Permeation Studies

James Dark, Colin Weaver, Remi Delaporte-Mathurin et al. (+2 more)

A gas-driven permeation (GDP) platform, SHIELD (Salt-compatible Hydrogen barrier Investigation and EvaLuation for fusion Devices), has been developed to measure hydrogen transport properties in structural materials under controlled thermal and pressure conditions. The system is designed to minimise experimental uncertainties associated with leaks, temperature instability, and pressure measurement, while providing reproducible conditions for permeation experiments. The rig operates in a static GDP configuration with independent upstream and downstream volumes, enabling precise control of driving pressure and accurate measurement of downstream pressure rise. An openly documented data acquisition and processing framework is implemented to ensure data traceability and reproducibility. The platform's performance is demonstrated by hydrogen permeation measurements on 316 stainless steel and AISI 1018 low-carbon steel over the temperature range of \SIrange{100}{600}{\degreeCelsius}. Steady-state permeation fluxes are extracted from linear downstream pressure rise and used to determine permeability. The measured permeability exhibits Arrhenius behaviour and agrees well with published literature data for both materials. Permeability measurements are shown to be robust and reproducible. These results demonstrate that SHIELD provides a reliable reference platform for hydrogen permeation measurements and is well-suited to evaluating permeation barrier coatings and advanced materials for fusion applications.
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All authors James Dark, Colin Weaver, Remi Delaporte-Mathurin, Sara Ferry, Kevin B. Woller

Instrumentation and Detectors

The nEXO Radioassay Program

R. MacLellan, P. Acharya, B. Aharmim et al. (+148 more)

Material radioactivity compilations, such as the one presented here, are important enablers of science. They are useful for the selection of radiopure materials used in the design and construction of low-energy rare-event search experiments. They allow researchers developing such experiments to save time on material studies and avoid costly duplication of effort. The data presented here were generated in support of the planned nEXO double-beta decay search. This work contains among the most restrictive constraints on the natural radioactivity content of materials of general interest to the low-radioactivity community, found in any tabulation of this kind. In this study, various techniques were employed; they are described here.
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All authors R. MacLellan, P. Acharya, B. Aharmim, S. Alcantar Anguiano, A. Anker, I. J. Arnquist, D. Auty, T. Bhatta, D. Chernyak, J. S. Choe, B. Cleveland, J. Daughhetee, A. Der Mesrobian-Kabakian, Y. Y. Ding, M. L. di Vacri, J. Farine, A. D. French, O. Gileva, R. Gornea, K. Harouaka, K. P. Hobbs, E. W. Hoppe, L. K. S. Horkley, M. Hughes, L. Kieser, A. Larson, I. Lawson, E. K. Lee, D. S. Leonard, K. M. Melby, B. Mong, O. Nusair, D. Pacesila, A. Piepke, N.D. Rocco, R. Saldanha, A. B. M. R. Sazzad, T. D. Schlieder, K. S. Thommasson, R. H. M. Tsang, V. Veeraraghavan, C. Vivo-Vilches, J. Vuilleumier, L. J. Wen, J. Zhao, A. Amy, A. Atencio, J. Bane, V. Belov, A. Bolotnikov, P. A. Breur, J. P. Brodsky, E. Brown, T. Brunner, B. Burnell, E. Caden, G. F. Cao, L. Q. Cao, D. Cesmecioglu, M. Chiu, R. Collister, E. Coulthard, T. Daniels, L. Darroch, M. J. Dolinski, B. Eckert, A. Emara, N. Fatemighomi, W. Fairbank, B. Foust, D. Gallacher, N. Gallice, A. Gaur, G. Giacomini, W. Gillis, F. Girard, A. Gorham, G. Gratta, C. A. Hardy, M. Heffner, E. Hein, J. D. Holt, A. Iverson, A. Karelin, D. Keblbeck, I. Kotov, A. Kuchenkov, K. S. Kumar, M. B. Latif, S. Lavoie, B. G. Lenardo, K. K. H. Leung, H. Lewis, X. Li, Z. Li, C. Licciardi, R. Lindsay, S. Majidi, C. Malbrunot, M. Marquis, C J. Masbou, M. Medina-Peregrina, S. Mngonyama, D. C. Moore, X. E. Ngwadla, K. Ni, A. Nolan, J. C. Nzobadila Ondze, A. Odian, J. L. Orrell, G. S. Ortega, C. T. Overman, L. Pagani, A. Pena-Perez, H. Peltz Smalley, A. Pocar, E. Raguzin, R. Rai, H. Rasiwala, D. Ray, A. M. Remnant, G. Richardson, V. Riot, R. Ross, P. C. Rowson, S. Sangiorgio, D.R. Seiner, S. Sekula, T. Shetty, L. Si, K. Skarpaas, V. Stekhanov, X. L. Sun, S. Thibado, A. Todd, T. Totev, S. Triambak, O. A. Tyuka, T. Vallivilayil John, E. van Bruggen, S. Viel, Q. D. Wang, M. Watts, W. Wei, S. Wilde, X. M. Wu, H. Xu, H. B. Yang, L. Yang, M. Yu, O. Zeldovich

History and Philosophy of Physics

The Metric Fossil: Emergent Spacetime from Asymmetric Projection

Jonathon Sendall

This paper develops a conditional framework for understanding the emergence of measurable physical structure from a pre-metric domain. Contemporary physics provides powerful and precise descriptions of relations among already-defined observables, yet offers comparatively little on the prior question of how observability, separability, and metric structure themselves arise. I propose that if three-dimensional spacetime is the result of an asymmetric projection from a non-orientable pre-geometric regime grounded in a minimal invariant, then a determinate and internally constrained set of consequences follows. These include: time reinterpreted as projection asymmetry rather than as a dimension or entropy gradient; matter as stabilised residue of projection rather than ontological primitive; quantum correlation as pre-separable unity dissolved by non-orientable topology; black holes as regimes of projection saturation rather than information sinks; dark matter as structured lag in the projection process rather than undetected particle species; and gravity as metric tension at sites of high projection density. The framework does not claim empirical confirmation. Its claim is that the proposal is internally coherent, structurally constrained, capable of generating non-trivial research directions, and that several phenomena currently treated as anomalous or paradoxical become expected consequences of the architecture rather than problems requiring additional postulates. An annex presents candidate formal objects and identifies research obligations for each consequence.
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Fluid Dynamics

Endwall and leading-edge film cooling of turbine blades in a hydrogen-fueled rotating detonation combustor-turbine coupled system

Yeqi Zhou, Songbai Yao, Jingtian Yu et al. (+3 more)

This study performs a three-dimensional numerical simulation of the coupled flow field in a hydrogen-air rotating detonation combustor (RDC)-turbine system to evaluate the effectiveness of different film cooling strategies for the turbine blades. The results demonstrate that combining the endwall cooling with leading-edge film cooling effectively reduces blade surface temperatures while improving turbine flow field stability and blade protection. For endwall cooling, numerical simulations compare circular and slot hole configurations. Circular holes consume less cooling air than slot holes while maintaining comparable cooling performance, making them the preferred choice. For the leading-edge film cooling, both the vertical and the vertical-inclined schemes are examined. The vertical-inclined scheme demonstrates higher cooling efficiency and improved secondary flow attachment, ensuring greater stability under the oscillatory effects of the detonation flow. Additionally, the flow fields of film-cooled turbine blades with and without the propagation of the rotating detonation wave are compared, revealing that the upstream rotating detonation flow field facilitates the downstream diffusion of secondary film cooling jets.
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All authors Yeqi Zhou, Songbai Yao, Jingtian Yu, Weijia Qian, Ping Wang, Wenwu Zhang

General Physics

Equations of motion of the mass centers in a scalar theory of gravity with a preferred frame

Mayeul Arminjon

The theory considered interprets gravity as a pressure force. Thus, the scalar gravitational field defines the gravity acceleration field. However, it also determines the relation between the flat “background metric” and a curved “physical metric”. Here we derive the equations of motion of the mass centers of a system of weakly gravitating bodies in the second version of that theory. We use the framework which was built and used for the first version. Namely, we use an asymptotic scheme of post-Newtonian (PN) approximation to derive the local (field) PN equations, and by integration inside the bodies we deduce from those local equations the equations of motion of the mass centers, using also an asymptotic framework for the good separation between the different bodies.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Atomic-scale order enables high thermal boundary conductance at $\beta$-Ga$_2$O$_3$/4H-SiC interfaces

Hongao Yang, Yongtao Yang, Yuanbin Liu et al. (+8 more)

Thermal boundary conductance (TBC) at dissimilar interfaces imposes a fundamental limit on electronic device performance, yet predicting and understanding heat transport across realistic, disordered boundaries remains elusive. Here, we develop a computational framework that combines machine-learned interatomic potentials with lattice dynamics to address the long-standing problem of how interfacial structure, from disordered to atomically sharp, affects thermal transport in the technologically important $\beta$-Ga$_2$O$_3$/4H-SiC heterostructure. By explicitly accounting for phonon wave-particle duality, we show that interfacial disorder introduces additional interfacial phonon modes that facilitate vibrational impedance matching between the two highly dissimilar crystals, yet it simultaneously disrupts interfacial phonon coherence and limits the potential heat-transport benefit. Our atomistic simulations further indicate that restoring atomic-scale order preserves coherence and yields markedly higher conductance. These insights motivate the controlled epitaxial growth of $\beta$-Ga$_2$O$_3$/4H-SiC heterostructures with systematically tuned interfacial order. Experimental measurements validate our predictions, achieving a record-high TBC of 231 MW m$^{-2}$ K$^{-1}$ at atomically sharp junctions. Beyond the immediate implications for $\beta$-Ga$_2$O$_3$-based power electronics, our results establish the preservation of interfacial phonon coherence as an effective strategy for mitigating thermal bottlenecks in mismatched systems.
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All authors Hongao Yang, Yongtao Yang, Yuanbin Liu, Tao Ding, Yang Shen, Jiawei Huang, Weigang Ma, Linfeng Fei, Zhenping Wu, Gábor Csányi, Bingyang Cao

Fluid Dynamics

Superstatistical Approach to Turbulent Circulation Fluctuations

Henrique S. Lima, Rodrigo M. Pereira, Luca Moriconi et al. (+2 more)

Recent investigations of turbulent circulation fluctuations have uncovered substantial insights into the statistical organization of flow structures and revealed unexpected geometric features of turbulent intermittency. Of particular interest here is the observation that circulation probability distribution functions admit a superstatistical representation, namely a description based on "ensembles of Boltzmann-Gibbs ensembles". A fundamental phenomenological ingredient of this approach, which serves as a natural starting point for modeling, relies on the strong correlation between the dissipation field and the spatial distribution of elementary circulation-carrying structures, i.e., small-scale vortices. Within the language of superstatistics, this corresponds to characterizing circulation statistics through an appropriate choice of conditioned (Boltzmann-like) distributions and mixing distributions. We show that the superstatistical class of q-exponentials, known to have broad applicability in a wide range of multiscale and non-equilibrium systems, provides an accurate description of the observed circulation statistics in homogeneous and isotropic turbulence. This finding opens avenues for exploring the statistical structure of the turbulent cascade in the context of non-extensive statistical mechanics, rooted in the concept of non-additive entropies.
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All authors Henrique S. Lima, Rodrigo M. Pereira, Luca Moriconi, Katepalli R. Sreenivasan, Constantino Tsallis

Physics and Society · Cross-listed from math.AT

Motif-based filtrations for persistent homology: A framework for graph isomorphism and property prediction

Meritxell Vila-Miñana, Robert Jankowski, Aina Ferrà Marcús et al. (+3 more)

Determining whether two graphs are isomorphic is a fundamental problem with practical applications in areas such as molecular chemistry or social network analysis, yet it remains a challenging task, with exact solutions often being computationally expensive. We address this task using persistent homology built on motif-based filtrations of graphs, a method from topological data analysis that summarizes the shape of data by tracking the persistence of structural features along filtrations. Specifically, we use edge-weighting schemes based on the densities of triangles, chordless squares, and chordless pentagons, which have been shown to be effective for detecting network dimensionality. Our cycle-density filtrations distinguish non-isomorphic graphs perfectly or nearly perfectly across four demanding graph families, many of which exhibit symmetries. We outperform curvature-based, degree-based, and Vietoris–Rips filtrations, and match or exceed the accuracy of egonet-distance methods while incurring a lower computational cost. The expressive power of our filtrations goes beyond isomorphism testing: because they capture rich structural information from graphs, they consistently achieve top performance on property prediction tasks using real-world data, and exhibit high sensitivity to edge rewiring and removal. Together, these findings establish cycle-density filtrations as an effective and computationally tractable framework for graph comparison and characterization, bridging topological data analysis and network science.
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All authors Meritxell Vila-Miñana, Robert Jankowski, Aina Ferrà Marcús, Rubén Ballester, M. Ángeles Serrano, Carles Casacuberta

Instrumentation and Detectors

Studies of the Modular COsmic Ray Detector (MCORD) using an automatic temperature control loop to maintain constant gain parameters of semiconductor SiPM photomultipliers

M. Bielewicz, M. Kiecana, A. Bancer et al. (+10 more)

The MCORD detector is a modular scintillator-based system employing silicon photomultipliers (SiPMs) and FPGA-based digital signal processing, designed for applications such as cosmic muon detection, veto systems, and detector calibration support. In this work, we investigate the influence of ambient temperature variations on detector performance, with particular emphasis on SiPM gain stability. Several automatic temperature compensation loops were implemented to stabilize the operating voltage of the sensors. Based on controlled laboratory measurements, we evaluate the effectiveness of different control strategies, including variations in temperature averaging time and threshold response criteria. The performance of each approach is compared in terms of gain stability and response dynamics. We identify the optimal temperature control configuration for planned MCORD measurements and present recent modifications to the detector electronics, including updated software for AFE control. Additionally, we describe modifications made to the detectors electronics since the previous publication, including new software developed to control the AFE electronics.
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All authors M. Bielewicz, M. Kiecana, A. Bancer, J. Grzyb, M. Grodzicka-Kobylka, T. Szczesniak, K. Kopanski, W. Noga, L. Kazmierczak, G. Saworska, A. Broslawski, P. Mazerewicz, E. Jaworska

Biological Physics · Cross-listed from math-ph

Blocking of 2D bistable reaction-diffusion fronts by obstacles

J.-G. Caputo, G. Cruz-Pacheco, J. Gatlik et al. (+1 more)

We investigate numerically the blocking of two-dimensional bistable reaction diffusion fronts by geometric obstacles. Our goal is to derive quantitative criteria for front propagation in the presence of spatial heterogeneities. Using a conservation law approach, we show that the integral of the reaction term acts as an effective driving force for the front. Combining this insight with the exact one-dimensional traveling wave solution, we construct a reduced analytical model that predicts blocking thresholds. In particular, we obtain explicit conditions for front propagation in a waveguide connected to a conical region of angle theta, valid for widths w less than 4. The model captures the influence of both geometry and nonlinearity, and shows good agreement with numerical simulations. Finally, we extend the analysis to more complex geometries, including checkerboard-like obstacles, and derive simple heuristic rules governing front propagation. ~
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All authors J.-G. Caputo, G. Cruz-Pacheco, J. Gatlik, B. Sarels

Applied Physics

3D Finite Element-Based Multiphysics Simulation of a Shape Memory Alloy Hybrid Composite Module

Lukas Handl, Max Kaiser, Miro Duhovic et al. (+1 more)

Shape adaptive shape memory alloy hybrid composites (SMAHCs) are composites that incorporate shape memory alloys (SMAs) to realize shape transformation. Despite the availability of numerous analytical and finite element models for predicting the transient response of SMAHCs, many approaches exhibit limitations with respect to the thermomechanical coupling and comprehensive experimental validation. Therefore, this paper presents a coupled, multiphysics, 3D finite element approach for the simulation of a SMAHC actuator, integrating mechanical, thermal and electromagnetic solvers in the Finite Element Code ANSYS LS-DYNA. The proposed approach employs a micromechanical constitutive model implemented in ANSYS LS-DYNA, to accurately capture the complex thermomechanical phase transformation of SMAs. A key feature of the model is the ability to prescribe a defined martensitic pre-strain through a preceding simulation step, in which an initially scaled SMA wire is mechanically loaded and stretched to its nominal length. This procedure enables partial detwinning of the martensitic microstructure and provides a physically motivated initialization of the material state. Joule heating of the SMA wires, as well as varying mechanical loads and ambient temperature conditions, are explicitly considered. The simulation results are validated against experimental data and a fully coupled transient staggered scheme model to assess the predictive capability of the 3D approach. The results show good qualitative agreement, reproducing the characteristic hysteresis of actuator deflection as a function of temperature. Quantitatively, the predicted deflections are of the correct order of magnitude, although marginally outside the 95 % experimental confidence interval. Overall, a consistent trend between simulation and experiment is observed, giving rise to possibility of simulating more complex SMAHC systems.
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All authors Lukas Handl, Max Kaiser, Miro Duhovic, Martin Gurka

Optics

Picometer-Scale Spatial Symmetry Breaking in Active Transmissive Metasurfaces

Martin Thomaschewski, Ruzan Sokhoyan, Elisabetta Schneider et al. (+1 more)

Active transmissive metasurfaces are central building blocks for future compact, cascadable optical systems, enabling the stacking of multiple functional layers for advanced dynamic beam shaping, photonic neural networks, depth sensing, and holography. We present a transmissive electro-optic metasurface based on silicon-on-lithium-niobate, where an array of silicon waveguides with periodic perturbations, individually controlled at the 100 pm scale, supports well-defined high-Q (>2000) guided-mode resonances (GMRs). We incorporate interdigitated push-pull electrodes between subwavelength-spaced GMR elements to locally tune the refractive index in the lithium niobate substrate, thereby shifting the GMR resonance and enabling opposite phase and amplitude modulation between neighboring radiative elements. In a geometrically symmetric metasurface, this effect introduces electro-optic beam splitting via diffraction, with diffraction efficiencies as high as 3%. By introducing controlled passive resonance detuning via 100 pm scale perturbation shifts, we realize a Vernier-type enhancement mechanism through geometrical symmetry breaking, thereby increasing the efficiency of amplitude modulation six-fold , and achieving modulation depths of 40% at $\pm$30 V. This work demonstrates the potential of active and passive resonance control enabled by high-Q GMR structures for efficient electro-optic modulation or multifunctional sensing.
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All authors Martin Thomaschewski, Ruzan Sokhoyan, Elisabetta Schneider, Harry Atwater

Optics

Minimum energy and photon content in PT symmetric metamaterials

J. B. Pendry and S. A. R. Horsley

In the context of waves in space time modulated materials, we ask two questions how much energy does it cost to break time reversal symmetry and transition to a PT symmetric state. and can a PT symmetric system have a ground state in the sense that no photons are present. Our model system is a periodic metamaterial set in virtual motion with velocity cg to become a space-time crystal. We find that the expectation of energy content is always increased on breaking symmetry. At the same time breaking T symmetry introduces photon-pairs even when we start from a T symmetric ground state empty of photons, except in certain pathological examples which we describe. For a range of velocities, PT symmetry is broken so that energy must be continuously invested to preserve motion, creating a trail of photon pairs. Here energy must be continuously invested to preserve motion. We make an analogy with acoustic radiation generated from breaking the sound barrier.
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