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Physics Physics

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Tuesday 23 December

Optics · Cross-listed from cs.NI

CBA: Communication-Bound-Aware Cross-Domain Resource Assignment for Pipeline-Parallel Distributed LLM Training in Dynamic Multi-DC Optical Networks

Dianxuan Fu, Xiaomin Liu, Yihao Zhang et al. (+3 more)

We propose a communication-bound-aware cross-domain resource assignment framework for pipeline-parallel distributed training over multi-datacenter optical networks, which lowers iteration time by 31.25% and reduces 13.20% blocking requests compared to baselines.
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All authors Dianxuan Fu, Xiaomin Liu, Yihao Zhang, Shikui Shen, Weisheng Hu, Qunbi Zhuge

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

Gauge-Invariant Long-Wavelength TDDFT Without Empty States: From Polarizability to Kubo Conductivity Across Heterogeneous Materials

Christian Tantardini, Quentin Pitteloud, Boris Yakobson et al. (+1 more)

Electromagnetic response is commonly computed in two languages: length-gauge molecular polarizabilities and velocity-gauge (Kubo) conductivities for periodic solids. We introduce a compact, gauge-invariant bridge that carries the same microscopic inputs-transition dipoles and interaction kernels-from molecules to crystals and heterogeneous media, with explicit SI prefactors and fine-structure scaling via $(\alpha_{\rm fs})$. The long-wavelength limit is handled through a reduced dielectric matrix that retains local-field mixing, interfaces and 2D layers are treated with sheet boundary conditions (rather than naïve ultrathin films), and length-velocity equivalence is enforced in practice by including the equal-time (diamagnetic/contact) term alongside the paramagnetic current. Finite temperature is addressed on the Matsubara axis with numerically stable real-axis evaluation (complex polarization propagator), preserving unit consistency end-to-end. The framework enables predictive, unit-faithful observables from radio frequency to ultraviolet-RF/microwave heating and penetration depth, dielectric-logging contrast, interfacial optics of thin films and 2D sheets, and adsorption metrics via imaginary-axis polarizabilities. Numerical checks (gauge overlay and optical $(f)$-sum saturation) validate the implementation. Immediate priorities include compact, temperature- and salinity-aware kernels with quantified uncertainties and operando interfacial diagnostics for integration into multiphysics digital twins.
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All authors Christian Tantardini, Quentin Pitteloud, Boris Yakobson, Martin Andersson

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

Dielectric and gate metal engineering for threshold voltage modulation in enhancement mode monolayer MoS2 field effect transistors

Lixin Liu, Han Yan, Leyi Loh et al. (+8 more)

Excellent gate electrostatics in field effect transistors (FETs) based on two-dimensional transition metal dichalcogenide (2D TMD) channels can dramatically decrease static power dissipation. Energy efficient FETs operate in enhancement mode with small and positive threshold voltage (Vth) for n-type devices. However, most state-of-the-art FETs based on monolayer MoS2 channel operate in depletion mode with negative Vth due to doping from the underlying dielectric substrate. In this work, we identify key properties of the semiconductor/dielectric interface (MoS2 on industrially relevant high dielectric constant (k) HfO2, ZrO2 and hBN for reference) responsible for realizing enhancement-mode operation of 2D MoS2 channel FETs. We find that hBN and ZrO2 dielectric substrates provide low defect interfaces with MoS2 that enables effective modulation of the Vth using gate metals of different work functions (WFs). We use photoluminescence (PL) and synchrotron X-ray photoelectron spectroscopy (XPS) measurements to investigate doping levels in monolayer MoS2 on different dielectrics with different WF gate metals. We complement the FET and spectroscopic measurements with capacitance-voltage analysis on dielectrics with varying thicknesses, which confirm that Vth modulation in ZrO2 devices is correlated with WF of the gate metals - in contrast with HfO2 devices that exhibit signatures of Vth pinning induced by oxide/interface defect states. Finally, we demonstrate FETs using a 2D MoS2 channel and a 6 nm of ZrO2 dielectric, achieving a subthreshold swing of 87 mV dec-1 and a threshold voltage of 0.1 V. Our results offer insights into the role of dielectric/semiconductor interface in 2D MoS2 based FETs for realizing enhancement mode FETs and highlight the potential of ZrO2 as a scalable high-k dielectric.
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All authors Lixin Liu, Han Yan, Leyi Loh, Kamal Kumar Paul, Soumya Sarkar, Deepnarayan Biswas, Tien-Lin Lee, Takashi Taniguchi, Kenji Watanabe, Manish Chhowalla, Yan Wang

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

Microscopic and spectroscopic evidences for multiple ion-exchange reactions controlling biomineralization of CaO.MgO.2SiO2 nanoceramics

R. Vahedifard and E. Salahinejad

This study is focused on the mechanism of in vitro biomineralization on the surface of CaO.MgO.2SiO2 (diopside) nanostructured coatings by scanning electron microscopy, energy-dispersive X-ray spectroscopy and inductively coupled plasma spectroscopy assessments. A homogeneous diopside coating of almost 2 um in thickness was deposited on a medical-grade stainless steel by coprecipitation, dipping and sintering sequences. After soaking the sample in a simulated body fluid (SBF) for 14 days, a layer with the thickness of 8 {\mu}m is recognized to be substituted for the primary diopside deposit, suggesting the mineralization of apatite on the surface. Investigations revealed that the newly-formed layer is predominantly composed of Ca, P and Si, albeit with a biased accumulations of P and Si towards the surface and substrate, respectively. The variations in the ionic composition and pH of the SBF due to the incubation of the sample were also correlated with the above-interpreted biomineralization. In conclusion, the multiple ion-exchange reactions related to Ca, Mg, Si and P were found to be responsible for the in vitro bioactivity of nanodiopside.
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Medical Physics

Fabrication, drug delivery kinetics and cell viability assay of PLGA-coated vancomycin-loaded silicate porous microspheres

N. Zirak, A. Maadani, E. Salahinejad et al. (+2 more)

Porous ceramic microspheres are a desirable substance for bone tissue reconstruction and delivery applications. This study focuses on Mg-Ca silicate microspheres encapsulated in biodegradable poly (lactic-co-glycolic acid) (PLGA) to serve as a biocompatible carrier for the controlled release of vancomycin hydrochloride. In this regard, diopside (MgCaSi2O6), bredigite (MgCa7Si4O16) and akermanite (MgCa2Si2O7) powders were synthesized by sol-gel and subsequent calcination methods. Then, porous akermanite, diopside and bredigite microspheres of 700-1000 um in diameter were fabricated by using carbon porogen, droplet extrusion and sintering, then loaded with the drug and eventually coated with PLGA. The bare microspheres showed a considerable burst release mode of the drug into a physiological medium, whereas PLGA coating of the microspheres reduced the burst release level. To investigate effective mechanisms governing in the drug release from the carriers, the contribution of burst, degradation, and diffusion was analyzed by the sequential quadratic programming algorithm method. It was found that the relative contribution of diffusion to bioresorption is ranked as diopside > akermanite > bredigite, whereas PLGA coating dominates the diffusion mechanism. The dental pulp stem cells cytocompatibility MTT assay of the microspheres also showed that the drug loading deteriorates but PLGA coating improves the cell biocompatibility significantly. Comparatively, the biocompatibility of the PLGA-coated microspheres was ranked as akermanite > diopside > bredigite, as a result of a compromise between the release of the constituting ions of the ceramic carriers and vancomycin molecules. It was eventually concluded that PLGA-coated Mg-Ca silicate microspheres are promising candidates for drug-delivery bone tissue engineering and dental bone grafting applications.
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All authors N. Zirak, A. Maadani, E. Salahinejad, N. Abbasnezhad, M. Shirinbayan

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

Stress analysis of dilute particle suspensions in non-Newtonian fluids with efficient evaluation in the weakly non-Newtonian limit

Arjun Sharma and Donald L. Koch

We present a semi-analytical framework to compute the suspension stress in dilute particle-laden non-Newtonian fluids, separating Newtonian and non-Newtonian contributions. The ensemble-averaged stress includes both the particle-induced non-Newtonian stress (PINNS) and an interaction stresslet arising from surface tractions due to the non-Newtonian stress and its induced Newtonian flow. Using a generalized reciprocal theorem, we express this interaction stresslet entirely in terms of the non-Newtonian stress, for a general constitutive model. For weakly non-Newtonian fluids, a regular perturbation expansion combined with the method of characteristics yields all leading-order stress contributions from the Newtonian velocity field alone, avoiding the need to solve coupled partial differential equations. This generalizes the method of Koch et al. (Phys. Rev. Fluids 1, 013301 (2016)) beyond polymeric fluids to any weakly non-Newtonian medium driven by velocity and its gradients. We apply the method to two systems: (i) spheres suspended in a fluid of smaller spheroids, where the interaction stress becomes negative for sufficiently anisotropic shapes due to orientation misalignment of the spheroids; and (ii) suspensions in weakly anisotropic nematic liquid crystals. In the latter, assuming a uniform director field fixed by an external field, PINNS vanishes while interaction stresslets remain, either opposing or enhancing background anisotropic stress. These results demonstrate the utility of our framework in capturing first-order particle-microstructure interactions across a broad class of non-Newtonian fluids.
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Optics

All-optical 3-input OR and 2-input AND/NIMPLY logic gates in a linear planar three-core optical fiber coupler

J. P. T. Rodrigues, F. L. B. Martins and J. C. do Nascimento

Most all-optical logic processing devices reported in the literature rely on nonlinear effects to achieve logical discrimination, which typically results in increased implementation complexity, higher optical power requirements, and limited scalability over larger optical circuits. Here, we present the numerical modeling and analysis of two all-optical logic gates based on a fully linear, dispersion-free planar symmetric three-core optical fiber coupler. The proposed devices operate with low-powered amplitude-modulated pulses and require no nonlinear materials, material doping, or optoelectronic components. By exploiting only the fiber geometry and coupled-mode theory, we demonstrate two logic processing functionalities: a 3-input OR gate and a configurable gate that performs either the AND or the NIMPLY operation based on a control signal. Logical discrimination is measured using a contrast-based performance metric, showing clear separation between logic levels for all input combinations. The simplicity of the proposed linear structure, combined with its scalability and compatibility with different fiber technologies, favor compact implementation and integration into larger photonic signal processing and optical computing systems.
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Physics and Society

Verification of the Outer Space Treaty with Cosmic Protons

Areg Danagoulian

The Outer Space Treaty (OST) was opened to signatures in 1967, and since then 117 countries, including China, the United States, Russia, have become part of it. Among other stipulations the treaty bans the placement of nuclear weapons in outer space. Recently the US government has raised worries that Russia is testing nuclear-armed anti-satellite weapon components, with the possibility that it will place a nuclear weapon in space. Such a device, if detonated, would destroy most of the satellites in the Low Earth Orbit. This danger is compounded by the lack of a verification mechanism for the OST. No methodologies of verification have been proposed in the open peer reviewed literature. This study presents a concept and a feasibility study for verifying a satellite's compliance to the OST by observing the neutrons induced by spallation from the $\sim$GeV protons in the inner Van Allen radiation belts. The calculations show that a 9U CubeSat sized detection platform can identify a thermonuclear weapon from the distance of 4~km in approximately one week of observation. This conceptual study will stimulate and inform future research and development of verification platforms for OST.
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Computational Physics

Molecular Dynamics Investigation of Mass Transport During Evaporation for the Binary System of n-Dodecane and Nitrogen

Suman Chakraborty, Bongseok Kim and Li Qiao

The study of interfacial fluxes under evaporative or condensation processes are ubiquitous in thermal systems, propulsion devices, and many other engineering applications. Most continuum scale models fail to capture the true nature of thermodynamic property variation across the interface, particularly under high-temperature and high-pressure conditions. An improvement over the sharp interface assumption of such continuum scale models is the consideration of a diffused interface and using Kinetic Boundary Conditions (KBCs) to model the mass-transport across the liquid vapor interface. Prior studies on KBCs mainly address monoatomic fluids. Two of the main ingredients required to form KBCs are: density and mass flux. Here, we study a Type-III binary mixture of n-dodecane and nitrogen using non-equilibrium molecular dynamics at near-critical temperatures. Interfacial properties such as thickness, density gradient, and surface tension were analyzed. A key result is the temporal evolution of the evaporation and reflected mass fluxes across the vapor-liquid interface. We observe that both the evaporation and reflection fluxes increase with increasing temperature, indicating enhanced molecular activity and mass transport across the interface at higher Tr. In contrast, the evaporation coefficient alpha_evap decreases from about alpha approximately 0.978 at Tr equals 0.70 to alpha approximately 0.905 at Tr equals 0.95 because the reflected-out flux increases along with the evaporation flux, which reduces the net efficiency of molecular evaporation across the interface. To the authors' knowledge, this is one of the very few studies estimating mass transport coefficients for Type-III binary systems, laying the foundation for KBCs in hydrocarbon and nitrogen mixtures.
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Classical Physics · Cross-listed from math-ph

Eversion Buckling of Toroidal Shells: Mechanism, Bifurcation, and Applications in Energy Absorption

Junjie Liu, Aijie Tang, Mingchao Liu et al. (+2 more)

Thin shells can store and release elastic energy through large geometric transformations, but their post-deformation stability is often highly sensitive to geometry and loading direction. Here, we study the eversion of open toroidal shells generated by revolving a meridional arc about an external axis and identify a geometry-controlled instability, which we define as eversion buckling. After eversion, the shell may either remain in an axisymmetric everted state or spontaneously collapse into a non-axisymmetric configuration. We show that this transition is governed by the competition between bending and membrane energies. A scaling analysis leads to a dimensionless geometric parameter that predicts the onset of eversion buckling, namely, the spontaneous loss of stability of the axisymmetric everted configuration after unloading. Finite element simulations and experiments confirm that this parameter collapses the stability data for shells with different geometries, including circular and semi-elliptical generating curves. The loss of axisymmetric stability is consistent with a pitchfork-like symmetry-breaking transition, in which the collapsed state has no preferred in-plane direction because of the axisymmetry of the everted shell. When the axisymmetric everted configuration is stable, a finite perturbation can trigger rapid snap-through toward a lower-energy collapsed equilibrium, accompanied by substantial volume contraction and a triggering response that is relatively insensitive to boundary constraints. We further show that assemblies of these shells behave as granular energy-absorbing systems, exhibiting a stable stress plateau, delayed densification, and substantial frictional dissipation during collective rearrangement. These results provide a mechanics-based route for designing shell assemblies with robust, direction-insensitive energy absorption.
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All authors Junjie Liu, Aijie Tang, Mingchao Liu, Xiaoding Wei, Qingsheng Yang

Optics

Multifunctional tapered fiber-based micro-waveguide for optical ultrasound microsensors

Mengyue Zhang and Changhui Li

Various optical ultrasound microsensors have been developed with size ranging from tens to hundreds of micrometers. However, it becomes challenging to further minimize these sensors' size. In this work, we proposed a method that use a tapered fiber-based micro-waveguide (TFMW) attaching to the optical microsensor to bypass this challenge. The TFMW not only serves as the waveguide to transport ultrasound, but can also deliver light and actively excite ultrasound. In this study, we proposed the design and analyzed its performance using theoretical analysis and simulation.
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Atomic Physics

Time-domain measurement of Auger electron dynamics in xenon atoms after giant resonant photoionization

Mahmudul Hasan, Jingsong Gao, Hao Liang et al. (+7 more)

Time-resolved measurement of Auger-Meitner (AM) decay [Nature 419, 803 (2002)] marked a milestone in the development of attosecond science. To date, the time constants for the AM decay processes obtained from the time-domain experiments were found to be consistent with the values deduced from conventional energy-domain measurements. One of the main factors limiting the temporal resolution of these studies is the unlocked carrier-envelope-phase (CEP) of the laser pulses used to probe the electronic dynamics triggered by inner-shell photoabsorption. In this work, we report time-resolved inner-shell electron spectroscopy of xenon and krypton using attosecond soft X-ray (atto-SXR) pulses centered at 130 eV in combination with CEP-stabilized few-cycle Yb laser pulses. We observed that the N$_{4,5}$OO Auger electrons from xenon exhibit a clear streaking pattern, but with an unexpected time shift of $\sim$ 1.32 fs relative to the 4$d$ photoelectrons. Furthermore, the energy-integrated yield of streaked Auger electrons from xenon exhibits a pronounced minimum at a pump-probe time delay of 4 fs. Neither of these observations can be explained by current streaking theories and both are inconsistent with lifetimes inferred from energy-domain measurements. The M$_{4,5}$NN Auger electrons from krypton partly overlap in energy with the 3$d$ inner-shell photoelectrons and do not show these anomalous features. This study offers new insights into the inner-shell electron dynamics of heavy atoms in the giant dipole resonance region, laying the groundwork for attosecond soft X-ray spectroscopy of molecular systems containing iodine or bromine atoms.
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All authors Mahmudul Hasan, Jingsong Gao, Hao Liang, Yiming Yuan, Zach Eisenhutt, Ming-Shian Tsai, Ming-Chang Chen, Hans Jakob Wörner, Artem Rudenko, Meng Han

Fluid Dynamics

Energy-conserving finite difference scheme for compressible magnetohydrodynamic flow at low Mach numbers using nonconservative Lorentz force

Hideki Yanaoka

In magnetohydrodynamic (MHD) flows, incompressibility is assumed for low Mach numbers. However, even at low Mach numbers, the Mach number influences flow and magnetic fields. Therefore, it is necessary to develop a method that can stably analyze low Mach number compressible MHD flows without using the incompressible assumption. This study constructs an energy-conserving finite difference method to analyze compressible MHD flows at low Mach numbers with the nonconservative Lorentz force. This analysis method discretizes the Lorentz force so that the transformation between conservative and nonconservative forms holds. This scheme simultaneously relaxes velocity, pressure, density, and internal energy, and stable convergence solutions can be obtained. In this study, we analyze four types of models and verify the accuracy and convergence of this numerical method. In the analyses of two- and three-dimensional ideal periodic inviscid MHD flows, it is clarified that momentum, magnetic flux density, and total energy are conserved discretely. The total energy is conserved even in a nonuniform grid. Even without correction for the magnetic flux density, the divergence-free condition of the magnetic flux density is satisfied discretely. Analysis of a Taylor decaying vortex under a magnetic field clarifies that the present numerical method can be applied to incompressible flows and can accurately predict the trend of energy attenuation. In the Orszag-Tang vortex analysis, an increase in Mach number reduces the magnitude of vorticity and current density. In addition, compression work increases more than expansion work, and the influence of compressibility appears. An increase in Mach number slightly delays the transition to turbulent flow. This numerical method has excellent energy conservation properties and can accurately predict energy conversion.
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History and Philosophy of Physics · Cross-listed from cond-mat.supr-con

The Nobel Prize in physics and the contribution of Ukrainian scientists to the understanding of quantum phenomena, in particular the behavior of macroscopic systems (The 2025 Nobel Prize in Physics)

O. G. Turutanov

The Nobel Prize in Physics 2025 has been awarded to John Clarke, John Martinis, and Michel Devoret for "the discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit". Their achievements open up possibilities for developing the next generation of quantum technologies, including quantum cryptography, quantum computers, and quantum sensors. This article explains physical grounds of these discoveries and describes the role of earlier studies of weak superconductivity and macroscopic quantum systems by other scientists, highlighting the contribution of researchers from the B.I. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, who obtained pioneering results in this field. The paper includes short biographies of the Nobel laureates.
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Optics

Dynamic Imaging of Periodic Structures using Extreme Ultraviolet Scatterometry

Brendan McBennett, Michael Tanksalvala, Emma E. Nelson et al. (+10 more)

Dynamic scattering and imaging with coherent, ultrafast, extreme ultraviolet (EUV) light sources can resolve charge, phonon and spin processes on their intrinsic length and time scales. However, full field coherent diffraction imaging requires scanning of the sample combined with computational phase retrieval, making it challenging to quickly acquire a large series of dynamic frames. In this work, we demonstrate a technique for extracting dynamic 1D images of the average unit cell in a periodic sample from traditional EUV scatterometry data by analyzing the changing intensities of the far field diffracted orders. Starting from a system of equations relating small changes in far field diffraction to phase and amplitude perturbations at the sample plane, it is shown that under certain conditions, changes to the $n$th diffracted order map exclusively onto the $n$th Fourier component of the perturbation via a closed-form relation. We show through rigorous coupled-wave analysis simulations that our method can provide a good approximation even outside the scalar diffraction theory framework in which it is derived. Finally, we experimentally demonstrate this reconstruction method by exiting 1D nickel nanowires on a diamond substrate using an infrared laser pump pulse, and measuring their relaxation using a time-delayed EUV probe pulse, to visualize nanoscale phonon dynamics.
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All authors Brendan McBennett, Michael Tanksalvala, Emma E. Nelson, Theodore H. Culman, Yunhao Li, Jiayi Liu, Ethan Berk, Albert Beardo, James Harford, Justin Shaw, Henry C. Kapteyn, Margaret M. Murnane, Joshua L. Knobloch

Monday 22 December

Fluid Dynamics · Cross-listed from cs.DC

SPUMA: a minimally invasive approach to the GPU porting of OPENFOAM

Simone Bnà, Giuseppe Giaquinto, Ettore Fadiga et al. (+2 more)

High Performance Computing (HPC) on hybrid clusters represents a significant opportunity for Computational Fluid Dynamics (CFD), especially when modern accelerators are utilized effectively. However, despite the widespread adoption of GPUs, programmability remains a challenge, particularly in open-source contexts. In this paper, we present SPUMA, a full GPU porting of OPENFOAM targeting NVIDIA and AMD GPUs. The implementation strategy is based on a portable programming model and the adoption of a memory pool manager that leverages the unified memory feature of modern GPUs. This approach is discussed alongside several numerical tests conducted on two pre-exascale clusters in Europe, LUMI and Leonardo, which host AMD MI250X and NVIDIA A100 GPUs, respectively. In the performance analysis section, we present results related to memory usage profiling and kernel wall-time, the impact of the memory pool, and energy consumption obtained by simulating the well-known DrivAer industrial test case. GPU utilization strongly affects strong scalability results, reaching 65% efficiency on both LUMI and Leonardo when approaching a load of 8 million cells per GPU. Weak scalability results, obtained on 20 GPUs with the OpenFOAM native multigrid solver, range from 75% on Leonardo to 85% on LUMI. Notably, efficiency is no lower than 90% when switching to the NVIDIA AmgX linear algebra solver. Our tests also reveal that one A100 GPU on Leonardo is equivalent 200-300 Intel Sapphire Rapids cores, provided the GPUs are sufficiently oversubscribed (more than 10 million of cells per GPU). Finally, energy consumption is reduced by up to 82% compared to analogous simulations executed on CPUs.
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All authors Simone Bnà, Giuseppe Giaquinto, Ettore Fadiga, Tommaso Zanelli, Francesco Bottau

Physics and Society

The Transformation of Broadband Demand: From Discretionary Service to Essential Infrastructure (2010-2024)

Samir Orujov, Ilgar Ismayilov and Jeyhun Huseynzade

Has broadband become a necessity good immune to price changes? Using a 15-year panel of 33 European countries (2010–2024) and two-way fixed effects with Driscoll–Kraay standard errors, we document a fundamental transformation in broadband demand. Pre-COVID, Eastern Partnership countries exhibited highly elastic demand ($\varepsilon = -0.61$, p$<$0.001) – a 10% price reduction increased subscriptions by 6% – while EU countries showed moderate elasticity ($\varepsilon = -0.12$, p$<$0.05). By 2020–2024, both regions converged to near-zero elasticity, with price changes having no detectable effect on adoption. Crucially, placebo tests reveal this transformation began in 2015, not 2020, indicating a decade-long digital integration process rather than a COVID-19 shock. We further demonstrate that price measurement critically affects inference: income-relative prices (as % of GNI) yield significant results in 100% of specifications, compared to only 25% for PPP-adjusted prices. These findings have immediate policy relevance: as broadband transitions from discretionary service to essential utility, policy emphasis must shift from affordability subsidies to universal infrastructure deployment.
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Popular Physics

The Universe in four letters: a bedtime history

Pedro Bargueño

One evening, a father tells his three daughters, Lucía, Inés, and Ana, a bedtime story unlike any other. It is a tale of four silent architects ($c$, $\hbar$, $G$, and $\Lambda$) whose presence or absence shapes the very fabric of reality. By imagining worlds where each constant is removed, they explore realms from the quantum gravity of the Planck scale to the stretching cosmos of de Sitter space, from the mass of the observable Universe to the surprising link with the proton's whisper. Woven with the insights of great scientists, this narrative reveals how these fundamental constants write the story of everything, from the smallest particle to the vast cosmic horizon, suggesting a beautiful and hidden unity in the architecture of our world.
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General Physics

Emergent Gravity from a Spontaneously Broken Gauge Symmetry: a Pre-geometric Prospective

Andrea Addazi

We explore the paradigm of pre-geometric gravity, where spacetime geometry and the gravitational field are not fundamental but emerge from the spontaneous symmetry breaking (SSB) of a larger gauge symmetry. Specifically, we consider a gauge theory based on the de Sitter $SO(1,4)$ or anti-de Sitter $SO(3,2)$ group, formulated on a manifold without a prior metric structure. General covariance is maintained by constructing Lagrangian densities using the Levi-Civita symbol. The SSB is triggered by an internal vector field $\phi^A$, which reduces the symmetry to the Lorentz group $SO(1,3)$ and dynamically generates a spacetime metric. We analyze two specific models: the MacDowell-Mansouri formulation, which yields the Einstein-Hilbert action plus a cosmological constant and a Gauss-Bonnet term, and the Wilczek model, which produces a pure Einstein-Hilbert action with a cosmological constant. In both cases, the observed Planck mass and the small cosmological constant emerge from a see-saw mechanism dependent on the symmetry-breaking scale. We then present the Hamiltonian formulation of this pre-geometric theory, demonstrating that it possesses three number of physical degrees of freedom, corresponding to a massless graviton and a massive scalar. Integrating out the massive scalar, the Arnowitt-Deser-Misner Hamiltonian of General Relativity is obtained after SSB. This establishes a foundational bridge between pre-geometric theories and canonical quantum gravity approaches like Loop Quantum Gravity, and allows for the formulation of a pre-geometric Wheeler-DeWitt equation.
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Fluid Dynamics

GIMLET: Generalizable and Interpretable Model Learning through Embedded Thermodynamics

Suguru Shiratori, Elham Kiyani, Khemraj Shukla et al. (+1 more)

We develop a data-driven framework for discovering constitutive relations in models of fluid flow and scalar transport. Under the assumption that velocity and/or scalar fields are measured, our approach infers unknown closure terms in the governing equations as neural networks. The target to be discovered is the constitutive relations only, while the temporal derivative, convective transport terms, and pressure-gradient term in the governing equations are prescribed. The formulation is rooted in a variational principle from non-equilibrium thermodynamics, where the dynamics is defined by a free-energy functional and a dissipation functional. The unknown constitutive terms arise as functional derivatives of these functionals with respect to the state variables. To enable a flexible and structured model discovery, the free-energy and dissipation functionals are parameterized using neural networks, while their functional derivatives are obtained via automatic differentiation. This construction enforces thermodynamic consistency by design, guaranteeing monotonic decay of the total free energy and non-negative entropy production. The resulting method, termed GIMLET (Generalizable and Interpretable Model Learning through Embedded Thermodynamics), avoids reliance on a predefined library of candidate functions, unlike sparse regression or symbolic identification approaches. The learned models are generalizable in that functionals identified from one dataset can be transferred to distinct datasets governed by the same underlying equations. Moreover, the inferred free-energy and dissipation functions provide direct physical interpretability of the learned dynamics. The framework is demonstrated on several benchmark systems, including the viscous Burgers equation, the Kuramoto–Sivashinsky equation, and the incompressible Navier–Stokes equations for both Newtonian and non-Newtonian fluids.
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All authors Suguru Shiratori, Elham Kiyani, Khemraj Shukla, George Em Karniadakis

Applied Physics · Cross-listed from cond-mat.mes-hall

Pyroelectric effects in hybrid semiconductor-lithium niobate quantum devices

Manas Ranjan Sahu, Suraj Thapa Magar, Yadav Prasad Kandel et al. (+1 more)

Hybrid quantum devices using surface acoustic waves show promise as key elements of quantum information processors. We report measurements of integrated flip-chip devices consisting of semiconductor quantum dots and surface acoustic wave resonators in lithium niobate. We observed that the pyroelectric effect in lithium niobate inhibited the operation of quantum dots in the integrated devices. GaAs/AlGaAs devices suffered from unintentional carrier depletion, and Si/SiGe devices suffered from electrostatic discharge. Our results highlight the importance of mitigating pyroelectric effects in semiconductor-lithium niobate hybrid devices for continued progress in quantum interconnects and transducers.
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All authors Manas Ranjan Sahu, Suraj Thapa Magar, Yadav Prasad Kandel, John M. Nichol

Instrumentation and Detectors

Optimization and Performance Characterization of the Second Generation Fermilab Constant Fraction Discriminator Readout ASIC

Artur Apresyan, Shuoxing Wu, Si Xie et al. (+5 more)

We present the optimization and performance characterization of the second-generation Fermilab Constant Fraction Discriminator ASIC (FCFD), designed for the readout of AC-coupled low-gain avalanche detector (LGAD) strip-sensors. The FCFD is explicitly engineered to be insensitive to signal-amplitude variations, thereby removing the need for time-walk correction that is required in other LGAD time-stamping readout ASICs. This updated version, referred to as FCFD1.1, incorporates several enhancements over the first iteration to address key challenges in AC-coupled LGAD front-end design. We outline the primary readout-ASIC design considerations for these applications, describe the methodology used to evaluate critical sensor and system parameters, and summarize the additionally implemented features. Performance measurements using injected charge signals and minimum-ionizing particles in test-beams demonstrate a time resolution of approximately 40 ps and a position resolution of roughly \SI{15}{\micro\meter} when tested with beam particles uniformly over the active area of the sensor.
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All authors Artur Apresyan, Shuoxing Wu, Si Xie, Cristián Peña, Tom Zimmerman, Sergey Los, Todd Zenger, Zhenyu Ye

Computational Physics · Cross-listed from math.NA

Hybrid Weight Window Method for Global Time-Dependent Monte Carlo Particle Transport Calculations

Caleb A. Shaw and Dmitriy Y. Anistratov

This paper presents a new Monte Carlo (MC) algorithm for time-dependent particle transport problems with global variance reduction based on automatic weight windows (WWs). The centers of WWs at a time step are defined by the solution of an auxiliary hybrid MC / deterministic problem formed by the low-order second-moment (LOSM) equations. The closures for the hybrid LOSM equations are calculated by the MC method. The LOSM equations are discretized by a scheme of the second-order accuracy in time and space. Filtering techniques are applied to reduce noise effects in the LOSM closures. The WWs defined with the auxiliary solution give rise to sufficiently uniform MC particle distribution in space on each time step. The algorithm is analyzed by means of an analytic transport benchmark. We study performance of the MC algorithm depending on a set parameters of WWs. Figure of merit and relative error results are presented, demonstrating the performance of the hybrid MC method and quantifying its computational efficiency.
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Fluid Dynamics

Dynamics of jet formation and collapse for axisymmetric surface gravity waves: coupled 3D potential flow and SPH simulations

Taiga Kanehira, Peter K. Stansby, Benedict D. Rogers et al. (+3 more)

Axisymmetric waves occur across a wide range of scales. This study analyses large-scale gravity-dominated axisymmetric waves, with jet heights of up to 6 m, for which surface-tension effects are negligible. The Bond number is O(10^5) and the Weber number ranges from O(10^4) to O(10^6). Our aim is to clarify the dynamics of highly nonlinear axisymmetric jet formation, cavity collapse and the consequent generation of secondary jets. The newly developed three-dimensional framework OceanSPHysics3D, combining unsteady potential flow with smoothed particle hydrodynamics, enables full simulation of jet initiation and collapse. The computed free-surface elevations and jet evolution agree well with the experiments of McAllister et al. (Journal of Fluid Mechanics, 2022) and with an analytical jet-tip-angle formulation by Longuet-Higgins (Journal of Fluid Mechanics, 1983). The simulations elucidate how the falling primary jet induces a secondary jet. The mechanisms forming the pre-jet trough and the post-jet cavity are fundamentally different. The pre-jet trough arises geometrically from directional focusing of the constituent waves, yielding a self-similar shape when appropriately scaled. In contrast, the post-jet cavity is formed inertially by the falling continuous jet and lacks both spatial and temporal self-similarity. Its collapse also differs: the cavity pinches off at the neck to generate upward and downward secondary jets, with local accelerations reaching approximately 150 times gravity. The primary jet scale governs the ensuing secondary-jet dynamics, including vortex-ring formation and strong vertical mixing. These findings illustrate the complexity of axisymmetric jet dynamics and demonstrate the ability of the present framework to reproduce the key coupled processes in such extreme free-surface events.
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All authors Taiga Kanehira, Peter K. Stansby, Benedict D. Rogers, Mark McAllister, T. S. van den Bremer, Samuel Draycott

Atomic Physics

Synthesis of a high intensity, superthermal muonium beam for gravity and laser spectroscopy experiments

Jesse Zhang, Aldo Antognini, Marek Bartkowiak et al. (+8 more)

The universality of free fall, a cornerstone of Einstein's theory of gravity, has so far only been tested with neutral composite states of first-generation Standard Model (SM) particles, such as atoms or neutrons, and, most recently, antihydrogen. Extending these gravitational measurements to other sectors of the SM requires the formation of neutral bound states using higher-generation, unstable particles. Muonium, the bound state of an antimuon ($\mu^+$) and an electron ($e^-$), offers the possibility to probe gravity with second-generation (anti)leptons, in the absence of the strong interaction. However, the short $\mu^+$ lifetime ($\tau_{\mu}\approx 2.2~\mu$s) and the existing diffuse thermal muonium sources rendered such measurements unfeasible. Here, we report the synthesis of a high-brightness muonium beam, extracted from a thin layer of superfluid helium by exploiting its chemical potential and unique transport properties. The mean longitudinal velocity (${v}\approx 2180~\rm{m/s}$) and narrow distribution (${\Delta v}< 150 ~\rm{m/s}$) of the atoms characterise a superthermal beam, while yields are similar to the highest intensity diffuse sources. This new beam is expected to enable muonium interferometry and a percent-level measurement of its gravitational acceleration, providing the first direct test of the Weak Equivalence Principle with second-generation (anti)matter. Its unprecedented brightness also opens the way to sub-kHz 1S-2S spectroscopy, enabling precise determination of the muon mass and stringent tests of bound-state quantum electrodynamics.
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All authors Jesse Zhang, Aldo Antognini, Marek Bartkowiak, Klaus Kirch, Andreas Knecht, Damian Goeldi, David Taqqu, Robert Waddy, Frederik Wauters, Paul Wegmann, Anna Soter

Optics

Inverse-Designed Superchiral Hot Spot in Dielectric Meta-Cavity Toward Ultra-Compact Enantioselective Detection

Anastasia Romashkina, Omer Yesilurt, Vahagn Mkhitaryan et al. (+8 more)

Chiral nanophotonic structures have garnered considerable interest in recent years due to their potential to enhance the efficacy of chirality-sensitive biomolecular detection. Designing metaplatforms to enhance chiroptical signals under linearly polarized excitation is particularly appealing due to the minimal chiral background and the ease of controlling excitation polarization. Here, a novel two-step inverse design scheme for dielectric lossless metasurfaces with superchiral hot spots is proposed. The method extends the local density of field enhancements for non-chiral fields into the chiral regime and significantly surpasses previous enhancements in superchiral field generation. It has been demonstrated that by leveraging the excitation of high quality factor modes with small mode volumes, it is theoretically possible to convert linearly polarized plane waves into a superchiral hot spot with record-high enhancement in the near-field optical chirality up to 10^4. A prototype is successfully implemented using advanced nanofabrication technologies. The optical characterization of the prototype demonstrates a 10^2-fold enhancement in optical chirality. The findings of this study unveil novel prospects for chiral spectroscopy with ultra-compact devices, underscoring the role of machine learning and physics-based inverse design in the development of cutting-edge, functional photonic structures.
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All authors Anastasia Romashkina, Omer Yesilurt, Vahagn Mkhitaryan, Owen Matthiessen, Min Jiang, Evgeny Lyubin, Bayarjargal N. Tugchin, Isabelle Staude, Jer-Shing Huang, Thomas Pertsch, Alexander V. Kildishev

Plasma Physics · Cross-listed from astro-ph.HE

Superluminal Wave Activation at Relativistic Magnetized Shocks

Jens F. Mahlmann, Logan Eskildsen, Arno Vanthieghem et al. (+2 more)

Fast radio bursts (FRBs) are extremely energetic radio transients, some are generated in magnetar magnetospheres and winds. Despite a growing number of observations, their emission mechanisms remain elusive. It has recently been proposed that Alfvénic perturbations can convert into superluminal O-modes at magnetized shocks and propagate downstream as a radio signal. We validate this superluminal wave activation mechanism using pair-plasma theory and particle-in-cell simulations. Theory predicts two different downstream modes: nonpropagating Alfvénic perturbations and propagating superluminal O-modes. Superluminal wave activation occurs if the frequency of upstream perturbations in the shock frame exceeds the downstream plasma frequency. 1D particle-in-cell simulations confirm wavenumber and frequency jumps across the shock for upstream perturbations with frequencies well above the plasma frequency. Our simulations model both monochromatic upstream waves and broadband spectra with the downstream plasma frequency acting like a high-pass filter for superluminal O-modes. We discuss implications for FRB generation in relativistic magnetized winds.
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All authors Jens F. Mahlmann, Logan Eskildsen, Arno Vanthieghem, Dawei Dai, Lorenzo Sironi

Fluid Dynamics

Exact Coherent Structures of Sheared Double-Diffusive Convection

Van Duc Nguyen and Chang Liu

The interaction between shear and double-diffusive convection (DDC) in the diffusive regime (cold fresh water on top of hot salty water) plays an important role in the heat and mass transport of polar region oceans. This study computes exact coherent structures (ECS) of diffusive-regime DDC with a uniform background shear in a vertically wall-bounded flow layer. We focus on the shear-influenced regime and present two-dimensional (2D) ECS consisting of steady-state solutions and periodic orbits. The steady-state solutions include tilted convective rolls with various horizontal wavenumbers, and they are invariant under horizontal translation. All tilted convective roll states undergo saddle-node bifurcation, leading to a stable upper branch and an unstable lower branch, suggesting that they originate from the subcritical bifurcation of conduction base states. Hopf bifurcations appear on the stable upper branch of tilted convective rolls, leading to periodic orbits. Bifurcation diagrams for dimensionless parameters, including the Rayleigh number, the Prandtl number, and the diffusivity ratio, are established, suggesting subcritical behavior. Increasing shear strength stabilizes the 2D tilted convective roll, while these tilted convective rolls continue to exist in the limit of zero density ratio corresponding to sheared Rayleigh-Bénard convection. Extension to the three-dimensional (3D) domain leads to 3D streamwise-elongated roll solutions; one of them originates from a subcritical bifurcation of the corresponding 2D roll solution. Chaotic solutions from direct numerical simulations generally visit neighborhoods of these steady or periodic solutions, and these visits leave an imprint on the flow statistics.
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Chemical Physics · Cross-listed from quant-ph

Dissipative quantum algorithms for excited-state quantum chemistry

Hao-En Li and Lin Lin

Electronic excited states are central to a vast array of physical and chemical phenomena, yet accurate and efficient methods for preparing them on quantum devices remain challenging and comparatively underexplored. We introduce a general dissipative algorithm for selectively preparing ab initio electronic excited states. The key idea is to recast excited-state preparation as an effective ground-state problem by suitably modifying the underlying Lindblad dynamics so that the target excited state becomes the unique steady state of a designed quantum channel. We develop three complementary strategies, tailored to different types of prior information about the excited state, such as symmetry and approximate energy. We demonstrate the effectiveness and versatility of these schemes through numerical simulations of atomic and molecular spectra, including valence excitations in prototypical planar conjugated molecules and transition-metal complexes. Taken together, these results provide a new pathway for advancing quantum simulation methods for realistic strongly correlated electronic systems.
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Geophysics

Climate change impacts on supra-permafrost soil and aquifer hydrology: broader, deeper, and longer activity

Neelarun Mukherjee, Bo Gao, Ethan T. Coon et al. (+6 more)

The thermal dynamics and hydrology of active layer soils and supra-permafrost aquifers determine the fate of the vast pool of carbon that they hold. In permafrost watersheds of Arctic Alaska, air temperature has warmed by up to 3.5 {\deg}C and snowfall has increased by up to ~40 mm from 1981 to 2020. How these changes impact the seasonal to decadal hydrological activity of the carbon-rich aquifers is mostly unknown. Observation-informed thermal hydrology modeling of a hillslope drained by a headwater stream (Imnavait Creek) within continuous permafrost showed profound changes from 1981 to 2020. Warmer summer temperatures deepened annual thaw depths. Steadily warming winter air temperatures, heavier snowfall, and stored energy from summer increased annual water outflow from the hillslope aquifer to the stream, warmed soil temperatures, and expanded and prolonged zero-curtain (stable at 0 {\deg}C) zones. In 2017-2018, zero-curtain areas with liquid water persisted through winter. Our findings reveal that both summer and winter warming drive year-round aquifer dynamics, creating conditions that amplify the permafrost-carbon-climate feedback.
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All authors Neelarun Mukherjee, Bo Gao, Ethan T. Coon, Pin Shuai, Devon Hill, Bethany T. Neilson, George W. Kling, Jingyi Chen, M. Bayani Cardenas