Plasma Physics
Compact Experimental Negative TriAngUlarity Reactor (CENTAUR): A design study for a compact, affordable breakeven tokamak
The CENTAUR Collaboration, Samuel W. Freiberger, Evan Bursch et al. (+33 more)
This work presents the compact experimental negative triangularity reactor (CENTAUR), a low overnight cost, high-field tokamak, breakeven reactor design, achieving a predicted total fusion power of 40MW and scientific energy gain of 1.3. Ballooning stability calculations confirm that the device's pedestal is within the first stability regime, which is consistent with the expected ELM-free operation associated with negative triangularity (NT)
plasmas. The geometry of the NT divertor allows for high fraction of radiated power (13.5$\%$) between the separatrix and
plasma facing components. Heat transport modeling based on simulations of the edge region show heat loads into
plasma facing components well below material limits. The magnet system employs rare-earth barium copper
oxide (REBCO) high-temperature
superconductors in 18 toroidal field coils, an hourglass-shaped central solenoid, and six poloidal field coils to support high-field ($B_0=10.9$ T)
plasma confinement, shaping, and current drive. Neutronics analysis shows that a 12 cm $B_4C$ shield keeps superconducting magnet heating below the 33~K quench limit during 10 s, 40 MW DT pulses. With this shielding, the modeled fluence indicates HTS components can survive more than ten times the 3000-pulse design lifetime. Iteration of economic analysis in tandem with the technical design process allows CENTAUR to achieve its overnight cost goal of $\$$2B determined using a custom costing model that predicts a total overnight cost of $1.6$B$\pm0.2$B.
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All authors The CENTAUR Collaboration, Samuel W. Freiberger, Evan Bursch, Javier Chiriboga, Hiro J. Farre-Kaga, Eliot Felske, Sophia Guizzo, John Labbate, Shreyas Seethalla, Frederick Sheehan, Jamie L. Xia, Anson Braun, Daniel A. Burgess, Nathaniel Chen, Jacob Halpern, Mohammed Haque, Abdullah Hyder, Alexandra Lachmann, Rohan Lopez, Kian Orr, Kalen Richardson, Melanie Russo, Avigdor Veksler, Christopher J. Hansen, Andreas Holm, Nils Leuthold, Orso Meneghini, Andrew O. Nelson, Matthew Pharr, Tim Slendebroek, Ian G. Stewart, Filippo Scotti, Matthew Tobin, Haley Wilson, C. F. B. Zimmermann, Carlos Paz-Soldan
Optics
Exceptional points in diamond optomechanics
Waleed El-Sayed, Elham Zohari, Joe Itoi et al. (+6 more)
Multimode cavity optomechanical systems allow light to couple otherwise non-interacting mechanical resonators, enabling non-Hermitian phenomena such as exceptional points, where eigenfrequencies and eigenvectors of coupled modes coalesce. Accessing an exceptional point and its nearby parameter space is a first step towards
chiral mode dynamics and topological state transfer. Diamond optomechanical devices support strong coherent optomechanical coupling required to tune resonances to an exceptional point, as well as strain-coupling to
spin-defects for hybrid
quantum technologies, but have not yet been used for multimode non-Hermitian physics. Here we tune to an exceptional point in a diamond optomechanical
crystal, which uses structural
symmetry breaking to produce two high-frequency mechanical resonances coupled to an optical cavity. The exceptional point is reached within a stable operating window below the
phonon-lasing threshold, and we observe asymmetric redistribution of optomechanical damping and anti-damping between hybridized modes. These results establish diamond optomechanical
crystals as a platform for non-Hermitian optomechanics, opening routes to topological mechanical dynamics in hybrid
spin-
phonon interfaces.
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All authors Waleed El-Sayed, Elham Zohari, Joe Itoi, Peyman Parsa, Gustavo de Oliveira Luiz, Joseph E. Losby, Misa Hayashida, Marek Malac, Paul E. Barclay
Fluid Dynamics
A hybrid Volume of Fluid Phase-Field method for Direct Numerical Simulations of soluble surfactant-laden interfacial flows
Ilies Haouche, Benjamin Reichert, Michaël Baudoin et al. (+1 more)
We present a hybrid Volume-of-Fluid (VoF) Phase-Field method for general soluble surfactant-laden interfacial flows. The scheme retains the VoF method for interface tracking and momentum solution, while a diffused Phase-Field serves as a smooth carrier for surfactant transport, enabling consistent coupling between bulk and interfacial concentration fields without computing surface derivatives. Adsorption/desorption kinetics are incorporated through regularized source terms localized at the interface, and surface tension can be specified for general equations of state. The method is fully adaptive via quadtree/octree Adaptive Mesh Refinement, enabling efficient simulations in planar, axisymmetric, and three-dimensional domains with high parallel scalability. Rigorous validation against analytical solutions for surfactant transport on deforming interfaces and for
diffusion-driven adsorption in the no-flow limit confirms accuracy and convergence. We then investigate the buoyancy-driven rise of a bubble in the presence of soluble surfactants, in axisymmetric and three-dimensional configurations. By independently varying the Biot and Damköhler numbers, we recover the correct asymptotic limits corresponding to clean-interface and insoluble-surfactant dynamics, and characterize the intermediate soluble regime. The resulting Marangoni stresses, induced by non-uniform interfacial concentrations, significantly reduce interfacial mobility, leading to measurable reductions in terminal velocity and pronounced modifications of the bubble trajectory. These results demonstrate the robustness of the method in capturing the interplay between hydrodynamics, bulk and interfacial transport, and Marangoni stresses in realistic three-dimensional geometries.
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All authors Ilies Haouche, Benjamin Reichert, Michaël Baudoin, Palas Kumar Farsoiya
Optics
A cavity-less architecture for high-power integrated frequency combs
Mrinmoy Roy, Joshua A. Palacios, Shuva Roy et al. (+2 more)
Photonic chip-based frequency combs have emerged as a transformative platform, enabling compact, scalable, and high-performance multiwavelength sources with far-reaching impact across science and technology. Most commonly, these sources leverage the cavity enhancement of the nonlinearities to produce a spectrum of equidistant frequency lines via cascaded four-wave mixing in high-quality microresonators pumped with a continuous wave tone. While the presence of the resonator inherently enables low-power threshold operation, it also brings intrinsic limitations in efficiency, tunability, and power per line. Here, we propose and demonstrate a cavity-less approach for the generation of optical frequency combs on-chip, which relies on non-degenerate cascaded four wave mixing in dispersion engineered integrated photonic waveguides. The results presented here enable previously inaccessible regimes of pump-to-comb conversion efficiency, wide-range continuous line-spacing tunability, and power per line for coherent comb states. This work opens new research opportunities in nonlinear integrated photonics and pathways toward high-capacity optical interconnects, scalable photonic AI accelerators, and other power-constrained integrated systems.
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All authors Mrinmoy Roy, Joshua A. Palacios, Shuva Roy, Darren D. Hudson, Andrea Blanco Redondo
Computational Physics · Cross-listed from cs.LG
GenSBI: Generative Methods for Simulation-Based Inference in JAX
Aurelio Amerio
Flow and
diffusion generative models have established themselves as widely adopted density
estimators for simulation-based inference (SBI), extending naturally from neural posterior estimation to likelihood and joint density estimation. Their principled optimization objectives and freedom from architectural constraints have driven rapid adoption across the natural sciences. Yet the most widely used SBI libraries remain PyTorch-based, leaving researchers who develop their forward models and analysis pipelines in JAX without a native option. We present GenSBI, an open-source library that implements flow matching, score matching, and denoising
diffusion entirely in JAX. The library offers three
transformer-based architectures - SimFormer, Flux1, and a novel Flux1Joint that extends gate-modulated
transformer blocks to joint density estimation - all interchangeable through a unified interface that decouples generative method, neural backbone, and inference mode. GenSBI provides an end-to-end workflow from training through posterior calibration (SBC, TARP, LC2ST) and supports custom architectures with domain-specific
embedding networks. We validate the framework on standard SBI
benchmarks, achieving near-ideal mean C2ST scores (0.50-0.56, where 0.50 is ideal) on SBIBM tasks with minimal per-task tuning and well-calibrated posterior coverage across all tested configurations. The code is publicly available at https://github.com/aurelio-amerio/GenSBI.
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Chemical Physics
Real-time nuclear-electronic orbital time-dependent density functional theory with a constrained traveling proton basis
Nicholas J. Boyer and Sharon Hammes-Schiffer
Nuclear quantum effects and non-Born–Oppenheimer effects play a vital role in many chemical and biological processes, motivating the incorporation of such effects into dynamical simulations. In real-time
nuclear–electronic orbital time-dependent density functional theory (RT-NEO-TDDFT), the electronic and
nuclear densities are propagated numerically in time according to the time-dependent Schrödinger equation. In this framework, specified
protons are treated
quantum mechanically on the same level as the electrons. The classical
nuclei can be propagated on the instantaneous NEO vibronic surface using Ehrenfest dynamics. A traveling
proton basis (TPB) can be used to describe the dynamics of moving
protons in conjunction with Gaussian-type protonic and electronic basis sets for each
quantum proton. Herein, we present a constrained TPB (c-TPB) approach that ensures each protonic basis function center coincides with the corresponding
proton position expectation value during the dynamics. This approach produces accurate
nuclear–electronic
quantum dynamics and rigorously conserves energy. We demonstrate the accuracy and stability of this approach for computing molecular vibrational frequencies as well as simulating excited-state intramolecular
proton transfer and double
proton transfer in the o-hydroxybenzaldehyde and [2,2$'$-bipyridyl]-3,3$'$-diol molecules. These applications show that the c-TPB method provides accurate dynamics, conserves energy, and is computationally efficient.
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Instrumentation and Detectors
Closed-Form Analytical Charge Response Model for Silicon Photomultipliers with Recursive Correlated Avalanches
Yiqi Liu, Xuewei Liu and Benda Xu
Silicon photomultipliers (SiPMs) have become the preferred photodetectors in next-generation
neutrino experiments, yet no unified closed-form analytical expression free of truncation and numerical convolution has been established for their full charge response spectrum, which must simultaneously capture correlated cross-talk and afterpulsing effects absent in conventional photomultiplier tubes (PMTs). We present a unified closed-form model for the SiPM charge response within the characteristic-function framework, treating pedestal noise, single-electron-response (SER) charge, internal optical cross-talk, and afterpulsing on equal footing. The characteristic-function representation factorises the full charge spectrum into three independent physical components: pedestal, single-electron response (SER), and avalanche count statistics.
Prompt internal optical cross-talk is modelled as a Galton-Watson branching process with Poisson offspring; building on the Generalised Poisson count statistics identified by Vinogradov, we derive a Lambert $W$ closed form for the total-progeny PGF via Lagrange-Bürmann inversion, providing the analytical handle needed for efficient event-level reconstruction. Afterpulsing is modelled as a per-avalanche
geometric chain, derived as the maximum-
entropy Poisson-Gamma mixture: the exponential prior-maximum-
entropy for a positive continuous yield with fixed mean-marginalised over a Poisson count yields the
geometric per-avalanche distribution, whose $N$-avalanche total is Negative Binomial. This naturally encompasses the Poisson afterpulsing limit and recursive afterpulse chains while preserving analytical closure. The resulting eight-parameter expression is further applied to derive an explicit per-channel charge-time likelihood for event-level energy reconstruction without numerical convolution at inference time.
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Accelerator Physics
The Memory Scaling of Reverse-Mode Differentiation in Particle Accelerator Simulations with Space Charge
Arjun Dhamrait, Edoardo Zoni, Axel Huebl et al. (+7 more)
The recent development of differentiable simulation codes for particle accelerators has enabled gradient-based workflows that promise finer control and more realistic modeling of accelerator facilities. However, when using reverse-mode automatic differentiation, the
memory usage continuously increases during the simulation, and can potentially exceed the available hardware
memory – especially when costly space charge computation is included. To study the
memory requirements for differentiable simulations, we have implemented space charge in Cheetah, a PyTorch-based beam tracking code that supports reverse-mode differentiation. We find that the
memory usage for reverse-mode differentiation grows linearly with the number of macroparticles and
cells, and that it is proportional to the number of space charge kicks involved in the simulation. This general scaling can be used to evaluate whether a given differentiable simulation is feasible given hardware
memory constraints.
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All authors Arjun Dhamrait, Edoardo Zoni, Axel Huebl, Ji Qiang, Chad E. Mitchell, Ryan Roussel, Jan Kaiser, Chenran Xu, Jean-Luc Vay, Remi Lehe
Physics and Society
The Structural Case for the Eco-Civilization Paradigm
Lei Zhu and William Zhu
This paper establishes a quantitative and structural framework for civilizational continuity under rapid, non-linear ecological transitions. Utilizing empirical data on Earth's Energy Imbalance (EEI), currently measured at 1.36 W/m^2, we demonstrate that the planetary system is on a deterministic trajectory toward a new ecological
equilibrium, breaching the 1.5 degrees C thermodynamic threshold in less than 6.5 years. We show that mitigating direct anthropogenic waste heat emissions is statistically insufficient, as 35/36-ths of the annual energy imbalance stems from atmospheric radiative forcing rather than localized thermal output. Consequently, preserving legacy centralized socioeconomic frameworks is unfeasible. We present the structural case for the "Eco-Civilization Paradigm" – a decentralized network of autonomous, modular eco-communities engineered to insulate core life-support functions, localized energy networks, and edge computation from cascading macro-system failures. Finally, we outline the systemic requirements for this transition, including the realignment of asset valuation frameworks from geography-dependent to engineering-dependent metrics, the mobilization of youth-driven innovation capital, and the strategic reallocation of global industrial manufacturing capacity to safeguard civilizational survival.
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Atmospheric and Oceanic Physics
Emergent conservation in atmospheric chemical mechanisms
Beatriz Lucia G. Rodriguez, Patrick Obin Sturm, Daniel Getter et al. (+1 more)
Conservation laws are time-invariant properties that constrain many physical systems. For systems of chemical reactions, conservation of mass constrains how atoms flow between chemical species. Here, we demonstrate that chemical reaction networks can display emergent conserved quantities not explained by mass conservation that arise instead from coupled kinetics. While some of these kinetic relationships can be immediately recognizable in simple chemical systems, more complex mechanisms have hidden nontrivial relationships between species. We identify these emergent relationships as a broader class of invariant behavior in atmospheric chemical mechanisms, which we call kinetic invariants. Kinetic invariants emerge when branching reactions with proportional rates cause species concentrations to evolve in lockstep, and can be found across atmospheric chemical mechanisms spanning orders of magnitude in complexity. Identifying kinetic invariants can provide theoretical bounds for exact mechanism reduction and reveal underlying relationships in the atmospheric chemical system.
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All authors Beatriz Lucia G. Rodriguez, Patrick Obin Sturm, Daniel Getter, Sam J. Silva
Chemical Physics
Real-Time Time-Dependent Density Functional Theory for Pump-Probe Spectroscopies
Torsha Moitra
The last decade has witnessed a rapid advancement in
laser technology, enabling the direct monitoring and control of electronic motion on its natural attosecond to sub-femtosecond timescales. Ultrafast processes are conventionally studied using pump-probe spectroscopic techniques, where a pump pulse drives the molecule out of
equilibrium and a time-delayed probe pulse records the response of the coherent non-stationary state. Since, these processes are non-linear and non-perturbative in nature, real-time formalisms provide a suitable theoretical framework for studying ultrafast light-induced dynamics. In addition, relativistic effects can play an important role in such simulations, either because the external field lies in the XUV to soft-X-ray region targeting core-level excitations, or because the molecular system contains heavy elements. In this chapter, we provide an overview of recent developments in real-time time-dependent density functional theory for simulating pump-probe spectroscopies (namely, transient absorption and transient electronic circular dichroism) at both non-relativistic and relativistic
Hamiltonian levels. In order to further interpret these spectroscopic signals, we analyze several spectroscopically relevant time-dependent sub-observables, such as induced electronic densities and induced dipole moments as well as analytical formulations of generalized non-
equilibrium response functions. We provide examples to show that the framework can be used to investigate and design new light-induced phenomena that emerge only in the attosecond regime.
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Atmospheric and Oceanic Physics · Cross-listed from cs.LG
Explainable Comparison of Feature-Based and Deep Learning Models for TROPOMI Methane Plume Screening
Solomiia Kurchaba, Joannes D. Maasakkers, Berend J. Schuit et al. (+1 more)
Continuous and global detection of large methane emissions is a crucial step for global warming mitigation. Satellite observations, such as from S5P/TROPOMI, combined with plume detection
algorithms, can play a key role in this effort. However, not all TROPOMI plume detections that look like methane emission plumes are the result of actual emissions. A significant part of the plume-like features in the data are
retrieval artifacts. Such artifacts could be the result of variations in elevation or albedo gradients, high concentrations of aerosols, coastal lines, water bodies, etc. Previous work approached the problem of plume-artifact classification by means of a Support Vector Machine Classifier (SVC), trained on an extensive set of observation-based scalar features designed by domain experts. However, such an approach limits the information scope received by the
algorithm to what is deemed to be important by the experts, breaks the spatial relationship between pixels, and loses information during the process of statistical aggregation. In this study, we compare feature-based (SVC, Random Forest, XGBoost) and image-based (ResNet-18, ResNet-34) models for methane plume-artifact classification under balanced and imbalanced evaluation settings. To interpret the results, we apply SHAP-based explainability to both model families. Our findings provide practical guidance for model selection in operational methane-screening workflows such as the CAMS Methane Hotspot Explorer.
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All authors Solomiia Kurchaba, Joannes D. Maasakkers, Berend J. Schuit, Ilse Aben
Computational Physics · Cross-listed from astro-ph.CO
A Fast Method to Compute Scalar Induced Gravitational Waves on a Lattice with Primordial Non-Gaussianities
Giovanni Piccoli
Scalar Induced Gravitational Waves (SIGW) are generated at second order in perturbation theory and to achieve observational relevance, inflationary dynamics must evade the standard slow-roll scenario at small scales, generating large
curvature perturbations following strongly non-Gaussian statistics. We propose a method to efficiently compute the SIGW spectrum including arbitrary non-Gaussianities. First, we solve the wave equation adopting semi-analytic methods; this results in an expression involving integrals in
Fourier space which are impossible to solve directly on a
lattice. We overcome this bottleneck by recasting these integrals as a sum of about 50 convolutions, each of which can be computed efficiently with FFT methods. Finally, the power spectrum is measured directly from the
lattice realization. We implement this in FLAN-SIGW, a GPU-accelerated code capable of computing fully non-perturbative, non-Gaussian SIGW spectra in seconds with an error within 10% with modest computational resources. The code is made public at https://github.com/giovannipiccoli99/FLAN-SIGW. In this first implementation, in order to assess the performance of the method, we adopt a standard radiation-dominated background with $w = 1/3$.
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Applied Physics · Cross-listed from cond-mat.mes-hall
Orbital and Spin-Orbit Torque Interplay in Ta/W-based Magnetic Tunnel Junctions with Vertical Non-local Switching
Marco Biagi, Corrado C. M. Capriata, K. Subham Senapati et al. (+6 more)
Spin-orbit torque (SOT) enables ultra-fast, energy-efficient magnetization switching, making it a promising mechanism for introducing MRAMs for cache
memory applications. However, current SOT-MRAM devices face write efficiency limitations, with charge-to-
spin conversion ($\xi_{DL}$) reaching $\sim$ 45%, far below the projected $\sim$ 80% needed to comply with the current delivery of advanced transistor nodes. Recent advances in orbital current physics, evidenced in a wide class of materials, offer a path to enhance $\xi_{DL}$. Here, we study the Ta(3-30 nm)\slash W(1-4 nm) system, revealing a large additional
spin-orbit torque contribution arising from Ta, a four-fold increase compared to the
spin Hall effect in Ta alone, attributed to the orbital
Hall contribution. This system exhibits larger $\xi_{DL}$ than W-based SOT systems with more robust perpendicular
magnetic anisotropy and compatibility with 400$^\circ$C annealing. Leveraging these advantages, we integrate the Ta/W system into 3-terminal SOT-MTJ devices, showing a level of performance similar to that of W-based systems. Our results show that orbital physics can be easily integrated into SOT-MTJ systems, offering a viable strategy to enhance SOT-MRAM efficiency. In addition, we propose and demonstrate a proof-of-concept for vertical non-local switching of SOT-MTJ using orbital torques, simplifying bottom-pinned SOT-MRAM fabrication.
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All authors Marco Biagi, Corrado C. M. Capriata, K. Subham Senapati, Ioannis Trikoilis Koll, Corentin Bouchard, Ricardo C. Sousa, Louis Hutin, Bernard Viala, Kevin Garello
Biological Physics
A Fibonacci-Based Ontogenetic Discretization of Body-Mass Growth Trajectories
Dorilson Silva Cambui
Body-mass growth is usually described by continuous models that represent the gradual increase of mass toward an adult or asymptotic value. In this work, we formulate and test an alternative description based on a Fibonacci-inspired ontogenetic coordinate. The model represents growth through a continuous or discretized developmental index, allowing the trajectory to be organized into fine substages. The main analysis compares the Fibonacci-based model with the ontogenetic growth model of West, Brown, and Enquist using digitized growth data from four species with markedly different body sizes and developmental times. The Fibonacci-based formulation was favored in two of the four cases, while the WBE equation remained favored in the other two. A complementary analysis using rodent growth data showed that the Fibonacci discretized model can also approach the performance of classical continuous models in some
datasets, although not uniformly. These results suggest that a Fibonacci-based ontogenetic coordinate can provide a useful alternative representation of body-mass growth within a biological systems framework.
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Physics and Society · Cross-listed from cs.CY
Queue & AI: When Faster Tasks Slow Down the Workflow
Silvia Bartolucci and Pierpaolo Vivo
Quantifying the workplace productivity effects of Generative Artificial Intelligence is now central to economics, management, and public policy. The deployment of AI tools in customer service, writing, software development, and consulting operations has been reported to generate large per-task productivity gains, typically measured as tasks completed per worker-hour or reductions in mean handle time. We argue that such mean-based metrics can misrepresent AI's effects in workflows where tasks accumulate and compete for scarce human
attention. AI assistance can generate a deceptive productivity signature: average completion times fall because AI tools typically supply a fast first draft, yet workflow-level performance deteriorates when a subset of AI errors escapes review and returns as costly downstream rework. We call this divergence between mean task speed and system-level delay the variance wedge. Depending on the operational parameters, the most time-efficient way to complete a workflow may undergo a transition between two task-processing regimes, a fully AI-assisted and a fully manual one. We formalize the mechanism as a queueing model and derive two main implications analytically. First, under congestion, reviewers rationally raise the risk threshold for checking AI outputs, reducing scrutiny precisely when it would matter the most. Second, AI assistance can stabilize an overloaded workflow only when (i) the fraction of tasks handled by AI exceeds a critical threshold, and (ii) the human
attention required for review and expected rework is lower than the
attention for manual completion, a requirement substantially more stringent than faster draft generation. These results suggest that AI deployment should be evaluated not only by average task speed, but by its overall effects on congestion, rework, and the robustness of human oversight under load.
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Physics and Society
Topological Signatures of Imperial Stress: Persistent Homology of the Eastern Mediterranean Trade Network, 0–400 CE
Jose de Jesus Bernal Alvarado, David Delepine and Carlos Pinedo Guadarrama
We apply persistent homology to the ORBIS Geospatial Network Model of the Roman World in order to quantify the structural resilience of the Eastern Mediterranean trade network between 0 and 400 ce. The network is represented as a weighted transport system whose edges correspond to road, maritime, and riverine routes, each carrying a base cost derived from the ORBIS cost model. To introduce historical dynamics into this static spatial infrastructure, we construct a differential friction model in which edge weights vary by decade and by transport mode according to documented historical perturbations, including epidemic mortality, civil war, military pressure, administrative reorganisation, and imperial reunification. For each decadal snapshot, we compute all-pairs shortest-path distances on the active sub-network and construct a Vietoris–Rips filtration using an adaptive threshold defined by the 90th percentile of finite pairwise distances. The resulting betti number ($\beta_1$) persistent
entropy time series identifies three structurally distinct phases in the Eastern Mediterranean network. Phase~I, from 0 to 200 ce, is a stationary high-redundancy regime consistent with the commercial integration of the early imperial and Antonine periods. Phase~II, from 210 to 280ce, corresponds to recoverable stress during the Crisis of the Third Century: betti number ($\beta_1$)
entropy declines during the crisis but returns to the Phase~I baseline following Aurelianic reunification. Phase~III, from 290 to 400 ce, is qualitatively different: cycle redundancy declines monotonically and does not recover. The main contribution of this study is to show that persistent homology detects a dimension of imperial stress that is not reducible to single economic, military, or political indicators.
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Chemical Physics · Cross-listed from astro-ph.GA
Digging into the Massive Protostar S255IR NIRS3: A Study of Nitrogen-Bearing Molecules and Their Prebiotic Chemistry
Arijit Manna, Sabyasachi Pal, Tapas Baug et al. (+4 more)
The study of complex nitrogen (N)-bearing molecules is essential for probing the physical and chemical
evolution of
star-forming regions. In this paper, we present the identification of rotational emission lines from several complex N-bearing species such as methyl cyanide (CH$_{3}$CN), ethyl cyanide (C$_{2}$H$_{5}$CN), vinyl cyanide (C$_{2}$H$_{3}$CN), cyanamide (NH$_{2}$CN), and formamide (NH$_{2}$CHO) toward the high-mass protostar S255IR NIRS3 using ALMA band 4 observations. In addition, the vibrationally excited transitions of cyanoacetylene (HC$_{3}$N, $\nu_{7}$ = 2) were detected. The column densities and excitation temperatures of these molecules were derived through LTE spectral modelling, yielding excitation temperatures in the range of 175$-$220 K. The high excitation temperatures (175$-$220 K) indicate that the identified N-bearing molecules arise from the warm inner regions ($T \geq 100$ K) of the source. The fractional abundances were further estimated relative to H$_{2}$, CH$_{3}$OH, and CH$_{3}$CN. A Pearson correlation heat map of the abundances reveals a strong positive correlation ($r > 0.7$) among three molecules in the cyanide family, such as CH$_{3}$CN, C$_{2}$H$_{3}$CN, and C$_{2}$H$_{5}$CN, suggesting that these N-bearing molecules may be chemically linked. Comparison with three-phase warm-up chemical models shows that the observed abundances of CH$_{3}$CN, C$_{2}$H$_{5}$CN, C$_{2}$H$_{3}$CN, NH$_{2}$CN, NH$_{2}$CHO, and HC$_{3}$N ($\nu_{7}$ = 2) relative to H$_{2}$ are consistent with model predictions within factors of 1.04, 0.67, 1.28, 0.76, 0.72, and 0.96, respectively. Finally, we discuss the potential formation pathways of the identified N-bearing molecules in the context of gas-grain chemistry within S255IR NIRS3.
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All authors Arijit Manna, Sabyasachi Pal, Tapas Baug, Ariful Hoque, Sandip Dutta, Sekhar Sinha, Sushanta Kumar Mondal
Chemical Physics
Dyck language and fermionic second quantization: II. Applications
Jérémy Morere and Thibaud Etienne
In this work, we establish a direct connection between supplemented Dyck
language and the signed expectation value of chains of second quantization operators relatively to the physical
vacuum and relatively to a one-determinant state. Inspired by the fact that Dyck
language provides an example of the emergence of the Catalan numbers in linguistic framework analysis, we show that these numbers are central when numbering the terms remaining when eliminating vanishing contributions detected by our application of Dyck
language to fermionic second quantization. From the translation of creation and annihilation operator - or of pairs of operators - into a bracket alphabet, we derive simple and intuitive sufficient conditions for the nullity of expectation values that does not require an explicit application of Wick's
theorem. This is done here with respect to the physical
vacuum or relatively to a one-determinant state. We also extend this translation into a diagrammatic framework that allows a visual determination of the signature of fully contracted terms, reproducing the results of Wick's
theorem. This approach has been extended to the case of (nested) commutators of pairs of fermionic second quantization including at least one excitation or deexcitation operator. Our results have been implemented in a software, MobiDyck, whose source code is freely available on the web. The algorithmic approach inspired by our work on Dyck
language is detailed in this paper. Finally, a comparison of our diagrammatic approach with Goldstone diagrams is provided and closes the article.
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Chemical Physics
Dyck language and fermionic second quantization: I. Theory
Jérémy Morere and Thibaud Etienne
This paper proposes a novel framework connecting fermionic second quantization and Dyck
languages. By defining translations of creation and annihilation operators using bracket alphabets, the study establishes nullity criteria for expectation values of chains of second quantization operators. Those translations are designed to reveal sufficient conditions for the nullity of the expectation values relatively to one-determinant states or to the physical
vacuum. The nullity criteria are purely syntactic, and simply reduce to the inspection of sequences of opening and closing brackets. Moreover, numbers and transformations in Dyck
languages can be imported in the context of fermionic second quantization. One of these numbers, the depth, originally absent from second quantization, can be used to introduce more nullity criteria.
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Instrumentation and Detectors · Cross-listed from eess.IV
Unsupervised Deep Image Prior for Sparse-View and Limited-Angle Electron Tomography
Serge Brosset, Daniel del Pozo Bueno, Thomas David et al. (+3 more)
Electron
tomography (ET) plays an important role in the three-dimensional (3D) characterization of nanomaterials. However, under limited-angle and sparse-view conditions, conventional
algorithms produce degraded reconstructions, which compromise the quality and interpretability of resulting 3D data. In this paper, we present deep image prior (DIP), an unsupervised deep learning (DL) approach, for highly degraded
tomography acquisitions and demonstrate, using simulated data, that its performance is comparable to that of supervised approaches requiring training
datasets, even for tilt ranges as limited as 60{\deg} and tilt increments of 10{\deg}. We then apply it to experimental data and show that it enables reliable 3D quantification under both sparse-view and limited-angle conditions, highlighting its potential for a wide range of materials and acquisition modalities.
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All authors Serge Brosset, Daniel del Pozo Bueno, Thomas David, Laure Guetaz, Philippe Ciuciu, Zineb Saghi
Optics · Cross-listed from cond-mat.mtrl-sci
Light-induced Faraday effect from dynamical breakdown of Kleinman symmetry
Niccolò Sellati, Jacopo Fiore and Lara Benfatto
The observation of anomalously large polarization rotations in pump-probe experiments with circularly polarized light has recently challenged the conventional understanding of the inverse Faraday effect. The striking magnitude of these responses implies the generation of effective
magnetic fields orders of magnitude larger than theoretical expectations, raising fundamental questions about the nature of light-induced time-reversal
symmetry breaking. In this work we demonstrate that a static polarization rotation can originate entirely from the antisymmetric component of the third-order optical susceptibility, without generating a macroscopic magnetization of the material. We show that this light-induced Faraday effect is inherently dynamical, emerging when Kleinman
symmetry breaks down. Using a minimal $sp$ tight-binding model on a square
lattice, we demonstrate that the light-induced Faraday response can be sizable even far from dissipative resonances. While the effect emerges at a purely electronic level, we show that resonant coupling with
phonons can significantly enhance the pump-probe response. Finally, we demonstrate that the light-induced Faraday contribution can strongly exceed the magneto-optical response mediated by the inverse Faraday effect in nonmagnetic materials.
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Instrumentation and Detectors
A Levitated Random Telegraph Noise Spectrometer
Molly Message, Bianca C. J. Uy, Katie O'Flynn et al. (+7 more)
Random Telegraph Noise is a ubiquitous process manifesting across technology and the natural world. It is characterized by random jumps between two distinct states with Poissonian waiting times, and is the origin of 1/f noise. Understanding and characterizing this noise is critical for the reliable operation of micro-, nano- and
quantum-technologies. In this work we probe random telegraph noise using a levitated microparticle sensor whose dynamics are driven almost entirely by this non-white source of noise. We observe a startling resonant behaviour, characterized by a thousand-fold increase in the underdamped sensor's position fluctuations, enabling us to measure the spectral properties of the noise over six decades of timescale. This work not only provides a unique way to probe random telegraph noise, but also demonstrates a platform for studying non-
equilibrium stochastic dynamics in the presence of realistic non-white noise, with applications from biology to social behaviour.
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All authors Molly Message, Bianca C. J. Uy, Katie O'Flynn, Yugang Ren, Muddassar Rashid, Jonathan D. Pritchett, Qiongyuan Wu, Hyukjoon Kwon, Benjamin A. Stickler, James Millen
Fluid Dynamics
Quantifying the liquid flow between a soap film and a vertical meniscus
Alexandre Vigna-Brummer, Simon Cox, Médéric Argentina et al. (+2 more)
Fluid exchange between a soap film and its bounding menisci governs film drainage and stability, with direct implications for the lifetime of surface bubbles and
liquid foams. Despite recent advances, a quantitative characterization of this coupling, associated with the phenomenon of marginal regeneration, remains incomplete. The volumetric flux per unit length of contact follows a well-established scaling law involving geometrical parameters such as the film height and the meniscus radius of
curvature. However, the dimensionless prefactor of this relation - the flux coefficient - remains difficult to determine for vertical menisci because of the complex and intermittent flows occurring at the film-meniscus interface. Here, we quantify this flux into the meniscus generated by inserting a solid plate into a vertical soap film. We consider both vertical and inclined plates and further investigate the effects of plate inclination, height, and width. Focusing on the dynamics of the growth of the meniscus driven by
liquid supplied by the film, we analyze both steady and transient regimes resulting from the interplay between capillary pressure,
gravity, and
liquid exchange. Combining experiments, numerical simulations, and theoretical modelling, we determine the flux coefficient using three independent methods and show that it remains constant over the range of parameters explored.
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All authors Alexandre Vigna-Brummer, Simon Cox, Médéric Argentina, Christophe Brouzet, Christophe Raufaste
Popular Physics
A gentle introduction to the cosmological multiverse
Oliver Janssen
We give an introduction to the cosmological multiverse, aimed at an audience of artists. We discuss general relativity – our modern theory of
gravity – and the cosmological constant, which is widely believed to be responsible for the observed accelerated expansion of the universe. We then turn to a big puzzle that the cosmological constant poses, and, eventually, how the multiverse could solve this puzzle. There's no such thing as a free lunch, however: the multiverse can become arbitrarily large and old. The unsolved problem of making unambiguous predictions for observations in eternally accelerating universes is known as the measure problem of eternal inflation.
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Applied Physics · Cross-listed from cond-mat.other
Antisymmetric spontaneous resistivity anisotropy due to hard-axis collapse in polycrystalline Co thin films
Y. Fernandes, J. Geshev, A. M. H. de Andrade et al. (+1 more)
We investigate magnetoresistance phenomena associated with the magnetization hard-axis collapse in polycrystalline Co thin films. Transport measurements reveal that, for specific orientations of the applied
magnetic field, the system exhibits distinct remanent resistance levels in both the in-plane longitudinal and transverse voltage responses. In particular, the planar
Hall resistance shows multiple stable and reproducible levels at room temperature, enabling the identification of at least three remanent states that can be distinguished and used for information storage. These resistance levels originate from non-uniform
magnetic configurations stabilized after the application and removal of the external
magnetic field in the hard-axis region. Since this phenomenon remains largely unexplored, we present an incipient study addressing its potential implications from an applied-physics perspective. The observation of such behavior in polycrystalline Co thin films grown on Si substrates suggests a simple and low-cost platform for spintronic
memory and sensing devices based on the remanent planar
Hall effect.
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All authors Y. Fernandes, J. Geshev, A. M. H. de Andrade, A. D. C. Viegas
Plasma Physics
ITER ECE front-end design, alignment and in-situ calibration
Saeid Houshmandyar, W. L. Rowan, J. P. Ziegel et al. (+1 more)
The electron cyclotron emission (ECE) diagnostics suite at ITER utilizes a front-end quasi-optical (QO) system whose design is fundamentally constrained by a field-stop concept. The field-stop defines the Gaussian beam variation throughout the optical system and within the
plasma, thereby setting the ECE sampling volume and spatial resolution. An in-situ hot calibration source, optimized using Gaussian beam transmission criteria, provides independent and absolute electron temperature measurements. The QO system extends beyond the front-end to include the polarization splitter unit (PSU), transmission lines, and switchyard, forming an integrated optical path to the ECE instruments. Misalignment between the front-end and PSU reduces the effective field-stop size, degrading spatial resolution and measurement fidelity. The oblique ECE view, a key feature of the ITER design, enhances sensitivity to non-thermal electron populations and complements the diagnosis of neoclassical tearing modes. Integrated QO design and
plasma physics understanding are essential for reliable ITER ECE measurements.
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All authors Saeid Houshmandyar, W. L. Rowan, J. P. Ziegel, A. Ouroua
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Molecular Dynamics Study of Defect Evolution Mechanisms in 3C-SiC for Quantum Technologies
Irslan Ullah Ashraf, Gaetano Calogero, Ioannis Deretzis et al. (+4 more)
The migration of point defects and formation of
spin defects in 3C-SiC were investigated using molecular dynamics simulations, with migration barriers obtained from Nudged Elastic Band (NEB) calculations and finite temperature diffusivities evaluated using both mean square displacement (MSD) and jump frequency approaches. While both methods reproduce Arrhenius behavior, the jump frequency formulation exhibits improved statistical stability. Activation energies of 2.12~eV for carbon vacancies and 0.88~eV for carbon interstitials are obtained, consistent with literature. The resulting mobility hierarchy governs defect
evolution and complex formations. Interstitial vacancy recombination competes with vacancy aggregation into divacancies, influencing the stabilization of
spin active defect centers. The study also provides a consistent framework for
diffusion analysis in atomistic simulations.
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All authors Irslan Ullah Ashraf, Gaetano Calogero, Ioannis Deretzis, Giorgio Lo Presti, Damiano Ricciarelli, Elisabetta Paladino, Antonino La Magna
Chemical Physics
Electronic Structure in a Phase Space, non-Born-Oppenheimer Framework: Geometric Forces and Moody-Shapere-Wilzcek Revisited
Mansi Bhati, D. Vale Cofer-Shabica, Jonathan I. Rawlinson et al. (+3 more)
We revisit the three-body problem in
quantum mechanics in two and three dimensions, generating both exact
eigenvalues and eigenvectors of the
Hamiltonian and a series of approximate solutions as calculated with a variety of different schemes to separate heavy ("
nuclear") and light ("electronic") particles. We show that, with minimal extra cost, one can go beyond the Born-Oppenheimer approximation by performing electronic structure calculations parameterized by both the
nuclear position (${\mathbf X})$ and the
nuclear momentum ($\mathbf{P}$), a so-called phase space theory of electronic structure. In particular, we demonstrate that such phase space electronic structure calculations correctly incorporate the non-inertial Coriolis and centrifugal forces felt by electrons in a moving
nuclear frame, thus leading to far more accurate eigenenergies and electronic angular momenta than has been possible before. We also demonstrate that our approach naturally incorporates and generalizes the Moody-Shapere-Wilczek
magnetic monopole for the non-abelian Berry
curvature (now allowing for vibrational motion rather than a diatomic of fixed length). We argue that the resulting approach should be extremely useful for propagating dynamics where angular momentum flows between
nuclei and electrons; in particular, if extended to include
spin degrees of freedom, the present approach will offer a practical means to study
chiral induced
spin selectivity through the lens of
chiral phonons and coupled
nuclear-electronic motion.
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All authors Mansi Bhati, D. Vale Cofer-Shabica, Jonathan I. Rawlinson, Robert G. Littlejohn, Joseph Subotnik, Nadine C. Bradbury
Optics
Probing the Effects of Heat Treatment Atmosphere on the Structural and Electrical Properties of NBT via Eu Photoluminescence
Zongxue Wang, Duanting Yan and Hancheng Zhu
The effect of oxygen partial pressure during the pre-calcination step (high
vacuum, air, nitrogen, and oxygen) on the
crystal structure, microstructure, and electrical properties of Na0.5Bi0.465Sr0.02Eu0.005TiO3
oxide-ion-conducting ceramics was systematically investigated. Dense ceramic samples were prepared by a conventional solid-state reaction route under different atmospheres. The results show that the oxygen partial pressure strongly affects Bi volatilization, grain growth, and oxygen-vacancy concentration. The largest average grain size was obtained for the nitrogentreated sample, whereas the oxygen-treated sample exhibited the finest grains but the highest grain-boundary conductivity. X-ray diffraction and Raman spectroscopy indicate that low oxygen partial pressure enhances structural disorder, while high oxygen partial pressure stabilizes the
lattice and promotes charge-transfer transitions. Eu3+ photoluminescence further reveals the correlation between local structural
evolution and oxygen-vacancy concentration. These findings clarify how oxygen partial pressure regulates grain-boundary behavior and ion-transport mechanisms in NBT-based
oxide-ion conductors, providing guidance for optimizing the total conductivity of polycrystalline electrolytes.
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