Peer Revenue Past citations are no guarantee of future returns

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Physics

physics Watch Physics

Friday 26 June

Instrumentation and Detectors · Cross-listed from astro-ph.IM

In-flight calibration of the Wide-field X-ray Telescope on board the Einstein Probe

Huaqing Cheng, Hai-Wu Pan, Yuan Liu et al. (+14 more)

By utilizing novel lobster-eye optics, the Wide-field X-ray Telescope (WXT) onboard the Einstein Probe (EP) satellite achieves an unprecedented combination of a large instantaneous field-of-view (FoV) and high sensitivity for monitoring the dynamic X-ray sky. In this paper, we present the in-orbit calibration results of the WXT during its first two and a half years of operations. By conducting observations of standard celestial sources–including the Crab Nebula, Scorpius X-1, and Cassiopeia A–we systematically characterized key instrumental properties. Our analysis demonstrates that the in-orbit performance of the WXT agrees with prelaunch ground calibrations well. The spatial resolution, denoted by the full width at half maximum (FWHM) of the focal spot, typically ranges from $3'$ to $6'$ across $\sim$90% of the FoV, with a median of $\sim 4.3'$. The post-calibration source positioning accuracy achieves $1.3'$ (at the 90% confidence level). The in-orbit effective area is consistent with model predictions and ground measurements, exhibiting an overall systematic uncertainty of $\lesssim 10\%$ (90% C.L.) in the 0.5-4 keV band. While the vast majority of the detectors remain highly stable, a noticeable long-term degradation at the low-energy end ($\sim30\%$-$40\%$, 0.4-0.6 keV) is observed in a few specific modules. Furthermore, spectral evaluations using Cas A confirm the stability of the energy scale and spectral resolution of the focal-plane Complementary Metal-Oxide Semiconductor (CMOS) detectors. All derived calibration products have been incorporated into the WXT calibration database (CALDB). These results comprehensively verify the instrumental capabilities of the WXT, providing a solid foundation for the reliable analysis of scientific observations.
Read the full abstract

All authors Huaqing Cheng, Hai-Wu Pan, Yuan Liu, Jingwei Hu, Haonan Yang, Donghua Zhao, Zhixing Ling, Yifan Chen, Xiaojin Sun, Longhui Li, Ge Jin, Wenxin Wang, Xue Yang, He-Yang Liu, Chen Zhang, Shuang-Nan Zhang, Weimin Yuan

Atomic Physics · Cross-listed from quant-ph

Single Electrons in a Dual-Plane Printed-Circuit-Board Penning Trap

Zirui Fang, Benedict A. D. Sukra and Xing Fan

We demonstrate single-electron trapping and detection in a two-dimensionally scalable dual-plane printed-circuit-board Penning trap. We characterize deterministic electron loading, axial damping, axial temperature, and collision-induced magnetron-radius growth at low magnetic fields. These results establish a practical platform for planar Penning traps and identify key next steps toward applications in quantum information science.
Read the full abstract

Biological Physics

Active diffusion enhances plankton carbon capture and phycosphere radius

Maggie Liu and Arnold J. T. M. Mathijssen

Plankton fix about 40 gigatons of carbon annually, using photosynthesis to convert $\text{CO}_2$ into $\text{O}_2$ and carbohydrates. These solutes are exchanged with the ocean in a diffusive boundary layer around the organism called the phycosphere. Here, we study how organisms can increase their carbon influx and outflux by actively mixing the surrounding fluid. By developing exact analytical expressions validated by stochastic simulations, we determine the enhanced diffusivity of phycosphere particles as a function of mixing activity, and their resulting fluxes and concentration fields. Hence, we find that plankton can significantly increase their uptake and photosynthetic turnover. Moreover, we find that the phycosphere radius is enlarged both by increased metabolism and by increased diffusive transport further from the organism. These results provide new biophysical insights into marine microbial ecology, with important implications for global carbon capture and climate change.
Read the full abstract

Atomic and Molecular Clusters · Cross-listed from cond-mat.mes-hall

Determining Electron Beam Lateral Coherence in a Scanning Electron Microscope Using Electron Diffraction

Evelijn Akerboom, Fatemeh Kiani, Giulia Tagliabue et al. (+4 more)

We develop and characterize scanning transmission electron microscopy (STEM) capabilities within a scanning electron microscope (SEM) to investigate the effective lateral coherence of the electron beam (e-beam) in the specimen plane. Using single-crystalline Au flakes and a sample composed of a monolayer of graphene, we obtain high-quality selected-area electron diffraction (SAED) maps and convergent-beam electron diffraction (CBED) patterns, validating the systems ability to probe crystallographic information at an acceleration voltage of 30 keV. Building on these capabilities, we implement a method, which is adapted from techniques traditionally used in transmission electron microscopy, to measure the degree of lateral coherence of the e-beam in the specimen plane of the SEM. By analyzing interference between electrons with two different wave vectors separated by 0.031 per angstrom, we extract a lower limit for the degree of lateral coherence over 5% of the e-beam diameter of approximately 60%. These coherence values are sufficient to enable quantum-coherent electron-light-matter interaction experiments in the SEM.
Read the full abstract

All authors Evelijn Akerboom, Fatemeh Kiani, Giulia Tagliabue, Wiebke Albrecht, Joanne Etheridge, F. Javier García de Abajo, Albert Polman

Instrumentation and Detectors · Cross-listed from astro-ph.IM

The performance of the TA$\times$4 surface detector array: 4.3 years of the first-half expansion

Telescope Array Collaboration: R.U. Abbasi, T. Abu-Zayyad, M. Allen et al. (+126 more)

The Telescope Array (TA) experiment aims to reveal the origin of ultra-high-energy cosmic rays (UHECRs) by observing air showers using surface detectors (SDs), which spread over an area of approximately 700 km$^2$, and fluorescence detectors (FDs) viewing the skies above the SD array. The TA experiment has been observing UHECRs since 2008, and has reported an indication of clustering in the arrival directions of cosmic-ray events with energy greater than 57 EeV. To improve the exposure for anisotropy studies of UHECRs, the TA$\times$4 upgrade was designed to expand the observational area by approximately 2,000 km$^2$ with 500 additional SDs. Half of the planned upgrade, consisting of 257 SDs, was completed, and the newly installed array began operation in 2019. In addition to the expanded SD array, two FD stations were constructed for the TA$\times$4 experiment. In this paper, we present a study of the performance of the expanded SD array, including the energy resolution, angular resolution, and effective aperture, over the first 4.3 years of data acquisition. While the effective aperture varied initially due to changing detector states, it has stabilized since June 2023 with more than 90% operational SDs. Furthermore, a new inter-tower trigger system was implemented to connect six new communication towers to form two geographically separated arrays, increasing the effective aperture. The time variation of this effective aperture, the resulting total exposure of approximately 3,500 km$^2$ sr yr, and a comparison with the original TA SD array are presented to demonstrate the performance of the expanded array.
Read the full abstract

All authors Telescope Array Collaboration: R.U. Abbasi, T. Abu-Zayyad, M. Allen, J.W. Belz, D.R. Bergman, F. Bradfield, I. Buckland, W. Campbell, B.G. Cheon, K. Endo, A. Fedynitch, T. Fujii, K. Fujisue, K. Fujita, M. Fukushima, G. Furlich, A. Gálvez Ureña, Z. Gerber, N. Globus, T. Hanaoka, W. Hanlon, N. Hayashida, H. He, K. Hibino, R. Higuchi, D. Ikeda, D. Ivanov, S. Jeong, C.C.H. Jui, K. Kadota, F. Kakimoto, O. Kalashev, K. Kasahara, Y. Kawachi, K. Kawata, I. Kharuk, E. Kido, H.B. Kim, J.H. Kim, J.H. Kim, S.W. Kim, R. Kobo, I. Komae, K. Komatsu, K. Komori, A. Korochkin, C. Koyama, M. Kudenko, M. Kuroiwa, Y. Kusumori, M. Kuznetsov, Y.J. Kwon, K.H. Lee, M.J. Lee, B. Lubsandorzhiev, J.P. Lundquist, H. Matsushita, A. Matsuzawa, J.A. Matthews, J.N. Matthews, K. Mizuno, M. Mori, S. Nagataki, K. Nakagawa, M. Nakahara, H. Nakamura, T. Nakamura, T. Nakayama, Y. Nakayama, K. Nakazawa, T. Nonaka, S. Ogio, H. Ohoka, N. Okazaki, M. Onishi, A. Oshima, H. Oshima, S. Ozawa, I.H. Park, K.Y. Park, M. Potts, M. Przybylak, M.S. Pshirkov, J. Remington, C. Rott, G.I. Rubtsov, D. Ryu, H. Sagawa, N. Sakaki, R. Sakamoto, T. Sako, N. Sakurai, S. Sakurai, D. Sato, K. Sekino, T. Shibata, J. Shikita, H. Shimodaira, H.S. Shin, K. Shinozaki, J.D. Smith, P. Sokolsky, B.T. Stokes, T.A. Stroman, H. Tachibana, K. Takahashi, M. Takeda, R. Takeishi, A. Taketa, M. Takita, Y. Tameda, K. Tanaka, M. Tanaka, M. Teramoto, S.B. Thomas, G.B. Thomson, P. Tinyakov, I. Tkachev, T. Tomida, S. Troitsky, Y. Tsunesada, S. Udo, F.R. Urban, M. Vrábel, D. Warren, K. Yamazaki, Y. Zhezher, Z. Zundel, J. Zvirzdin

Plasma Physics

On the Relationship Between Plasma and Tritium Fuel Cycle Through Matter Injection and Particle Exhaust

Samuele Meschini and Matteo Moscheni

This work identifies an inconsistency between plasma operating scenarios and tritium fuel cycle (TFC) requirements, calling for a re-examination of the traditional reactor-led design approach. The key point is simple: in current TFC architectures, fuel puffing must contain tritium. Moscheni et al. (2026 Nucl. Fusion 66 026008) investigated fuel puffing rates in detached operation. Expanding that database, puffing is shown to exceed core fuelling by about an order of magnitude, from present-day tokamaks to next-step stellarators. Though not unknown in the plasma community, TFC models instead assumed core fuelling to dominate. The implications are severe. In recent TFC architectures, direct internal recycling (DIR) is intended to minimise tritium inventory, but assumes near-50:50 D:T composition. This assumption may become self-defeating: a substantial fraction of the puffed fuel must be tritium. Tritium inventory, doubling time, required breeding ratio, and pump sizing therefore become critical once puffing is properly accounted for. Mitigation is assessed by extending the models of Meschini et al. (2023 Nucl. Fusion 63 126005). For a notional plant, realistic TFC requirements can be met with D-rich, T-lean puffing, at the cost of about 10% lower fusion power. Alternatively, for near-50:50 D:T puffing, reduced fuel puffing with stronger impurity seeding can maintain detachment while alleviating TFC constraints, albeit with higher core contamination. Combined use of these strategies enables scenarios that minimise tritium inventory and throughput while balancing competing requirements. Ultimately, these results place renewed emphasis on the TFC as a central element of reactor design. A viable fusion reactor requires joint optimisation of core plasma, edge plasma, and TFC, implying unavoidable trade-offs across all three.
Read the full abstract

Optics

Broadband on-chip Half Maxwell Fisheye

Xin Zheng, Quan Yue, Jean-René Coudevylle et al. (+4 more)

In this article, we report on the design and the experimental evidence of a Half Maxwell Fish Eye (HMFE), for Silicon Photonics and working at telecommunication wavelength. It is designed by implementing a Graded Photonic Crystal operating in the non-resonant metamaterial regime. The results of 3D Finite-Difference Time-Domain simulations (FDTD) show an excellent broadband focusing capacity. It has been urther fabricated via the Silicon On Insulator (SOI) platform for its compatibility with CMOS technology. Experimentally, its performances are firstly investigated by the means of a fan-shaped set output waveguides. Next, Scanning Near-Field Optical Microscopy (SNOM) characterisation confirms the wavefront curving inside the HMFE lens. Quantitative analysis of the SNOM results demonstrates its excellent focusing performances: the Full Width Half Maximum (FWHM) is $0.466\lambda_0$ at $\lambda_0=1550$nm, while the thickness of the lens is $3.18\lambda_0$.
Read the full abstract

All authors Xin Zheng, Quan Yue, Jean-René Coudevylle, Aziz Benamrouche, Ségolène Callard, Anatole Lupu, Éric Akmansoy

Physics and Society

Indecision and accuracy under social information across groups sizes

Andrew M Bate, Charlie Pilgrim and Richard P. Mann

Observing the decisions and actions of others provides social information that can inform decisions such as whether to follow. We consider a model where agents simultaneously gather stochastic private information, each deciding once sufficiently confident. Observed decisions and indecision provide social information that triggers discrete waves of collective response: a first decision causes others to update and potentially follow, whose decisions in turn provide further social information, generating successive waves. We explore this model across a range of group sizes and report three main findings. First, social information leads to faster and more accurate decisions than individual decision-making, but agent-level accuracy is maximised at a finite optimal group size. This contrasts with the accuracy of the majority choice, which increases monotonically with the number of agents. Second, waves frequently fail to resolve collective indecision, particularly for smaller groups and when the first decision is incorrect, leaving a subgroup of agents unconvinced. Third, these remaining undecided agents are systematically biased and make less accurate subsequent decisions, with this inaccuracy growing with group size.
Read the full abstract

Chemical Physics

FMO-xTB: Fragment molecular orbital method with GFN1-xTB for large-scale quantum-mechanical simulations

Richard Einsele and Roland Mitric

We present the fragment molecular orbital method (FMO) combined with the GFN1-xTB extended tight-binding approach (FMO-xTB) for efficient quantum-mechanical calculations of large molecular systems. Both the two-body (FMO2) and three-body (FMO3) expansions are formulated, and fully analytic energy gradients including the response contribution from the self-consistent embedding potential are derived and implemented. The FMO-xTB method inherits the broad element coverage of GFN1-xTB, which employs element-specific rather than atom-pair-specific parameters and is parameterized for all spd-block elements up to radon(Z = 86), representing a significant practical advantage over FMO- DFTB approaches. The accuracy of FMO-xTB is systematically benchmarked against non-fragmented xTB calculations for water clusters, anthracene aggregates, and pentacene supercells. FMO3-xTB reproduces the reference energies with deviations on the order of 10^-4 Hartree for organic semiconductor systems. The covalent bond fragmentation capability using the hybrid orbital projection (HOP) boundary treatment is also implemented with fully analytic gradients and validated for polyalanine alpha-helices and B-DNA double helices, yielding FMO3-xTB energy deviations on the order of 10^-6 Hartree for polyalanine and in the millihartree range for B-DNA. Near-linear scaling is achieved with effective scaling exponents between b= 1.06 and b= 1.28, compared to cubic scaling for non-fragmented xTB. Parallelization over multiple CPU cores yields significant speed ups, and a complete energy and gradient evaluation of a pentacene supercell containing 23760 atoms is feasible within minutes on a single computing node, enabling routine molecular dynamics simulations of systems with tens of thousands of atoms. The method is implemented in the DIALECT software package.
Read the full abstract

Fluid Dynamics

Multiscale Cavitation Sub-Grid Modeling via Population Balances as Linear Stochastic Process

Fynn Jerome Aschmoneit

A multiscale sub-grid cavitation model is developed in which the bubble size distribution evolves as a linear stochastic process in radius space. Starting from the integrated Rayleigh–Plesset equation, the population balance is recast as a hyperbolic transport equation for the number density per radius, whose method-of-characteristics solution, projected onto a discrete histogram basis, yields a column-stochastic Markov chain governing the bubble counts per size bin. The transition matrix factors into a precomputable, mesh-only geometric part and a local, pressure-dependent shift, isolating the coupling to the surrounding flow into a single dimensionless vector per cell. The framework recovers classical homogeneous-mixture cavitation closures in the limit of a single representative scale.
Read the full abstract

Fluid Dynamics

Effects of thermochemical modelling on a hypersonic shock-wave/turbulent boundary-layer interaction

Marco Fratini, Pedro Stefanin Volpiani and Matteo Bernardini

Thermochemical non-equilibrium can alter the structure, loads, and time scales of hypersonic shock-wave/turbulent boundary-layer interactions, yet its role in fully turbulent configurations remains largely unquantified. The present work addresses this issue by performing three direct numerical simulations of an oblique shock impinging on a turbulent high-enthalpy boundary layer at edge Mach number $M_e=6.4$ and stagnation enthalpy $H_e=16.9$ MJ/kg. The simulations share identical geometry and freestream conditions, but employ a hierarchy of progressively simplified thermochemical descriptions: a finite-rate reactive case, a single-species thermally perfect gas model, and a single-species calorically perfect model. The reactive simulation shows that the shock-induced temperature rise substantially enhances chemical activity relative to the incoming boundary layer, with peak concentrations of dissociation products attained downstream of the interaction. Thus, the thermal and chemical responses are not synchronised: the composition lags the rapid thermal forcing imposed by the shock system, and turbulent Damköhler numbers reach values of order unity within the recirculation region, indicating non-negligible turbulence-chemistry interaction. The comparison among the three models shows that thermally and calorically perfect descriptions yield similar predictions, whereas finite-rate chemistry produces systematic differences: a smaller separation bubble, lower post-interaction wall heat flux, lower mean and fluctuating temperatures, and a less inclined reflected shock. In the present regime, the dominant modelling distinction is therefore between frozen and chemically reacting descriptions, with caloric-model effects playing only a secondary role.
Read the full abstract

Accelerator Physics

Diagnosing Ghost Bunches with the Upstream Extinction Monitor in the Mu2e Experiment

R. Hensley, E. Prebys and A. Gaponenko

The Mu2e experiment has a stringent requirement for extinction of the pulsed proton beam, referring to the elimination of particles between proton bunches to a relative level of 10$^-10$, which means a single out-of-time particle in the inter-pulse gaps for every 250 complete proton pulses. As the construction of the Mu2e experiment nears completion, it is crucially important to make an early measurement of the beam extinction in its current condition. Hence the upstream extinction monitor was constructed and operated to probe for problems in the proton pulse structure or a higher than expected incidence rate of out-of-time particles. The analysis in this work comes from data taken in March 2026. The long data run showed a significant presence of out-of-time particles from ghost bunches in the Delivery Ring approximately 388 ns after the centers of the main proton pulses. These are hypothesized to be the result of a combination of a RF frequency mismatch, particle space charge, and machine impedance during the rebunching sequence in the Recycler Ring, which can lead to particles leaking into adjacent buckets, but further studies and simulations are needed to confirm this
Read the full abstract

Fluid Dynamics

Flow dynamics in a wavy channel filled with anisotropic porous material under the effect of wall slip

Shyamal Kumar Mondal, Sougata Mandal and Sukhendu Ghosh

In this study, a theoretical and graphical analysis is conducted to examine the effects of wall-velocity slip, anisotropic ratio, and porosity parameter on a two-dimensional, viscous, laminar, and incompressible flow through a wavy channel filled with anisotropic porous media. The flow is assumed to be steady and symmetric, with a constant volumetric flow rate imposed along the channel walls. The governing equations are described using the Darcy-Brinman model coupled with the continuity equation, while the tangential velocity at the wavy boundaries is represented through Navier slip conditions. An analytical solution is obtained using a perturbation approach under physically consistent boundary conditions. The effects of key parameters, including anisotropic ratio, Darcy number, and slip parameter, on flow characteristics such as axial velocity, pressure gradient, shear stress, and streamline patterns are examined in detail and presented graphically. The results indicate that wall velocity slip significantly reduces flow reversal, enhances near-wall velocity, and decreases the center-line velocity. For a fixed non-zero slip, a decrease in the Darcy number leads to a pronounced modification in the velocity profile, while increased slip further strengthens near-wall flow and weakens the core flow. Additionally, the streamline analysis reveals that velocity slip plays an important role in controlling flow separation near the crest of the wavy wall. In the case of isotropic porous media with a large amplitude wavy channel, flow separation can also be effectively regulated. Overall, the study demonstrates that velocity slip provides a powerful mechanism for controlling flow behavior by altering the shear distribution within the perturbed flow, with potential applications in technological, geophysical, and biophysical transport systems.
Read the full abstract

Biological Physics · Cross-listed from cond-mat.stat-mech

Nonextensive Statistical Signatures of the Bilaterian Transition in Proteome Length Distributions

Sertac Eroglu

Protein length distributions across the tree of life carry a quantitative signature of organismal complexity. Nonextensive statistical mechanics, through the Tsallis generalized entropy formalism, provides a natural framework for describing complex systems characterized by long-range correlations, scale invariance, and hierarchical organization – features that classical Boltzmann-Gibbs statistics cannot accommodate. In this work, the complementary cumulative distribution function (CCDF) of protein lengths is analyzed within this framework for the reference proteomes of 22 fully sequenced organisms spanning the domains Archaea, Bacteria, and Eukarya, with deliberate sampling across the animal transition zone from sponges and cnidarians to higher bilaterians. Maximum likelihood (MLE) fitting of truncated discrete q-exponential distributions, with bootstrap 95% confidence intervals (CIs) reveals that the entropic index q resolves into three statistically distinct regimes: superextensive (q < 1) for prokaryotes, unicellular and non-animal multicellular eukaryotes, and basal animals; a boundary regime (CI on spanning unity) for the two cnidarians studied and the basal bilaterian C. teleta; and subextensive (q > 1) for all higher bilaterians, with q increasing monotonically across the four deuterostomes sampled from S. purpuratus (1.033) to H. sapiens (1.147). The q-exponential outperforms the ordinary exponential distribution across all 22 proteomes and becomes progressively more competitive against alternative two-parameter distributions as proteome complexity increases. These results identify the Tsallis entropic index as a continuous, physically interpretable indicator of proteome organizational complexity and extend the applicability of nonextensive statistical mechanics to proteomic systems.
Read the full abstract

Biological Physics · Cross-listed from q-bio.PE

Reconstructability of evolutionary intermediates in generative epistatic landscapes

Roberto Netti and Martin Weigt

Evolutionary intermediates connect observed proteins, but the sequence of steps that produced them is rarely recoverable from extant data alone. Here we ask what can, and cannot, be inferred about such intermediates from the endpoints. Using generative sequence landscapes as controlled models of protein-family evolution, we benchmark data-driven reconstruction against ground-truth simulated trajectories. We find that the best point prediction is not necessarily the most faithful evolutionary reconstruction: maximum-likelihood intermediates can be residue-wise accurate yet statistically atypical, whereas conditional sampling better captures the ensemble of plausible histories. Predictability is limited by the topology of the landscape. Constrained, low-mutability regions preserve information about the path, while permissive high-mutability regions open many alternative routes and erase path-specific memory. We also show that sequence divergence alone is an insufficient measure of elapsed evolutionary time; incorporating endpoint mutability provides a more reliable way to place intermediates in the landscape. These results recast intermediate reconstruction as a calibrated probabilistic problem. Rather than seeking a single "true" sequence, data-driven models should identify when endpoints contain evolutionary information, and return realistic ensembles.
Read the full abstract

Fluid Dynamics · Cross-listed from cond-mat.stat-mech

A Finite Element Method for Fluctuating Navier–Stokes Equations

Dimitrios Gourzoulidis, Mirko Gallo, Soumaya Elkantassi et al. (+2 more)

We introduce a finite-element framework for simulating thermal fluctuations in compressible fluids governed by the fluctuating Navier-Stokes equations. The method is designed to preserve the fundamental fluctuation-dissipation balance at the discrete level. This is achieved by defining the stochastic forcing term in the weak formulation, ensuring its covariance is proportional to the discrete viscous dissipation operator. A nodal quadrature rule is employed to eliminate unphysical mesh-scale correlations. The time integration is performed using the Crank-Nicolson scheme to maintain numerical stability and accuracy. The proposed approach is numerically validated in one, two, and three spatial dimensions, demonstrating its capability to correctly capture equilibrium fluctuation statistics across various discretisation parameters.
Read the full abstract

All authors Dimitrios Gourzoulidis, Mirko Gallo, Soumaya Elkantassi, Toby Kay, Serafim Kalliadasis

Physics and Society

SimPol: Simulating polarisation in political belief networks in European countries

Isabela Burattini Freire, Hongryol Cha, Irina Epure et al. (+7 more)

Here we combine empirical network analysis with agent-based modelling to understand how different ways of structuring belief systems may affect the polarisation drive, and how the diversity of belief systems in Europe may result in different polarisation trajectories. Using the 2016 European Social Survey, we infer belief networks across 23 European countries via a Bayesian algorithm, revealing that belief systems are predominantly organised around immigration, LGBT rights, and economic interventionism, reflecting the influence of populist discourse across the continent. We further verify a Western-Eastern divide across the national belief networks: in Western European countries, left-right self-identification is a more reliable predictor of broader belief alignment, whereas in Eastern Europe this relationship breaks down. By applying these empirical belief networks into a sociologically grounded agent-based model, we further show that polarisation is amplified by high individual belief rigidity and low susceptibility to social influence, and that cross-country differences in polarisation levels mirror the same geographic divide observed in belief network topology. These findings establish belief networks topologies as a structural driver of political polarisation, with implications for understanding and anticipating polarisation dynamics across diverse European contexts. We find that populations are not polarised when little attention is placed on maintaining internal coherence and polarisation levels are moderate when high attention is placed in both keeping internal coherence and agreement in beliefs with others.
Read the full abstract

All authors Isabela Burattini Freire, Hongryol Cha, Irina Epure, Sara Filippini, Karan K.H. Manjunatha, Chethan Kavaraganahalli Prasanna, Ivan Samoylenko, Niels Van Santen, Adarsh Prabhakaran, Guillermo Romero Moreno

Physics and Society

From streaks to synergies: A multi-scale analysis of performance and scoring in the NBA

Malvina Bozhidarova, Yanpei Cai, Ricardo M.S. Carvalho et al. (+7 more)

Modern play-by-play data make it possible to test long-standing intuitions about basketball with the same statistical rigour now routinely applied to other professional sports. Using play-by-play data from 7,054 regular-season and 504 playoff NBA games spanning the 2020-2025 seasons, we provide quantitative insights into scoring patterns and the performance of individual players and teams through methods from statistics, network science, and complexity science. Our findings offer an evidence-based perspective on in-season and in-game performance that can inform coaching strategies, player evaluation, and tactical decision-making.
Read the full abstract

All authors Malvina Bozhidarova, Yanpei Cai, Ricardo M.S. Carvalho, Daniele Cirulli, Quentin Dehaene, Martin Diaz, Alexandra Krasnokutskaya, Bernardo Pereira, Onkar Sadekar, Federico Battiston

Physics and Society

Linking the "inner" and "outer" self to mental health and brain networks

Cosimo Agostinelli, Ivan Casanovas, Lochan Chaudhari et al. (+8 more)

How are psychosocial profiles, mental health, and brain functional connectivity related? Studies have been dedicated to unraveling the associations of social support perception and neural functional connectivity. Additionally, personality traits have been explored by examining brain networks. Research on mental health has been developed using a broad range of methods and different approaches. However, little attention has been devoted to understanding how personality traits and social variables are related, and to what extent these components are reflected in brain functional connectivity and mental health outcomes. In this work, we aim to address these complex relations by using data from the Human Connectome Project, both from surveys and resting-state fMRI. The survey data includes personality traits measures and self-reported social support-related variables, which we will refer to as inner- and outer-self, respectively. It also includes data on mental health outcomes. Using z-score standardized measures, we analyze correlation matrices to evaluate the association between the inner- and outer-self domains. Our results show that the social indicators are more evidently grouped by impact on social experience than by the duality of inner-outer selves. Using a $k$-means clustering algorithm, we separate individuals into two groups according to social profiles. When confronting these results with the mental health outcomes, we show that the more socially desirable cluster exhibited a higher score on positive aspects such as life satisfaction and purpose in life. In the functional brain connectivity, we observe that the cluster with a more socially beneficial profile exhibits lower interconnectivity, especially in the default mode network. The pipeline we present uses a combined analysis of both fMRI and psychosocial variables, which could open the path for more extensive analysis.
Read the full abstract

All authors Cosimo Agostinelli, Ivan Casanovas, Lochan Chaudhari, Arda Ergin, Pablo Estévez-Gutiérrez, Akanksha Gupta, Juliane T. Moraes, Mario Edoardo Pandolfo, Carlos Gershenson, Haily Merritt, Andreia Sofia Teixeira

Physics and Society · Cross-listed from cs.CY

AI Persuasive Framing in Collective Dilemmas

Anders Giovanni Møller, Alessia Galdeman, Arianna Pera et al. (+1 more)

AI agents are promising tools that can act as flexible behavioral nudges to enhance human cooperation in addressing large-scale societal problems. However, evidence on whether AI agents can effectively boost cooperation remains mixed. We recruited 1,283 participants to play iterated Collective Risk Games in small groups, testing whether AI assistants could nudge participants toward cooperation. By using persuasive framing personalized to each player's Social Value Orientation profile, the AI interventions significantly increased contributions and group success rates. These cooperative effects were short-lived, however, fading after the first few rounds. Strikingly, when the AI treatments were reconfigured to promote selfish behavior through exculpatory framing, the negative effects on contributions and group success were larger and substantially more persistent, particularly for personalized interventions. This asymmetry between prosocial and antisocial persuasion highlights the dual-use risks of AI systems designed to influence group behavior in collective action settings.
Read the full abstract

All authors Anders Giovanni Møller, Alessia Galdeman, Arianna Pera, Luca Maria Aiello

Biological Physics · Cross-listed from q-bio.BM

Towards coevolution-aware ancestral sequence reconstruction

Alya Zeinaty, Leonardo di Bari, Saverio Rossi et al. (+3 more)

Ancestral sequence reconstruction (ASR) is a powerful approach for studying molecular evolution and the emergence of protein function. Yet most ASR methods assume that sites evolve independently, neglecting the epistatic constraints that shape protein structure, stability, and function. This simplification affects both ancestral inference and its evaluation: maximum-a-posteriori reconstructions may over-concentrate probability into a single over-idealized sequence, whereas independent posterior sampling can generate implausible or poorly functional ancestors. Here, we introduce a coevolution-aware ASR framework that combines standard phylogenetic inference with Direct Coupling Analysis (DCA), thereby preserving site-wise ancestral uncertainty while enforcing residue-residue constraints learned from extant protein families. To benchmark the method, we develop a controlled forward-evolution framework based on a DCA evolutionary sampler, allowing reconstructed ancestors to be compared with known ground-truth sequences generated under realistic epistatic constraints. Applied to beta-lactamases and DNA-binding domains, the approach improves reconstruction when ancestral states are epistatically constrained, and yields ensembles of candidate ancestors that are both phylogenetically consistent and statistically compatible with natural protein families. This framework bridges the gap between single-sequence MAP reconstruction and unconstrained posterior sampling, providing a practical route toward ancestral reconstructions that better reflect the coupled nature of protein evolution.
Read the full abstract

All authors Alya Zeinaty, Leonardo di Bari, Saverio Rossi, Pierre Barrat-Charlaix, Francesco Zamponi, Martin Weigt

Physics and Society

Students using GenAI lag behind in problem-solving competence: an agent-based study of classroom networks

Lorenzo Betti, Iacopo Caporossi, Carsten Källner et al. (+8 more)

The development of problem-solving competence (PSC) among high school students is foundational for preparing resilient and adaptive citizens. Generative artificial intelligence (GenAI) can support this process, but it may also encourage students to offload part of the cognitive work that is necessary for deep learning. While the individual effects of GenAI use are increasingly studied, its collective consequences for competence development within classroom environments remain underexplored. In this study, we use an agent-based model to simulate the evolution of PSC in a high school physics classroom, where students complete tasks individually, in collaboration with peers, or with the support of GenAI. By comparing classrooms with and without access to GenAI across different peer-network structures, we show that GenAI use can diminish competence development and increase the share of students remaining in lower competence tiers. These results suggest that the educational impact of GenAI should be assessed not only through individual learning outcomes but also through its effects on collective competence dynamics.
Read the full abstract

All authors Lorenzo Betti, Iacopo Caporossi, Carsten Källner, Karolina Levanaitė, Chenyu Li, Xuan-Chen Liu, Giulia Lorenzini, Vittoria Socci, Michele Re Fiorentin, Ilaria Stanzani, Marta Baratto

Physics and Society

Preferentiality and bandwidth drive tie activity in online and offline ego networks

Gamal Adel, Shrichand Bhuria, Alessandro Catalano et al. (+7 more)

Ego networks capture the variety of structural patterns in the social interactions of individuals. Recently it has been shown that ego networks in online settings display universal patterns of tie strength distributions, but it is unclear how constraints such as spatial proximity and bounded social bandwidth affect such generic behaviour in offline settings. Here, we analyse the time evolution of interaction activity in ego networks constructed from offline face-to-face and colocation data, compare them to online communication networks, and explore simple cumulative advantage models that capture the varying preferentiality of individuals for specific social ties. We find that patterns of preferentiality at the population level are similar for online and face-to-face networks, but not for colocation data, suggesting that the latter is a poor proxy of social network structure. We also provide evidence that empirical ego networks exhibit a bandwidth in the way communication events are allocated across connections. A model implementing this notion uncovers evidence of universal scaling between the tie preferentiality and bandwidth of individuals, common to all online and offline systems explored. Our findings strengthen our understanding of the fundamental mechanisms governing human communication and help disentangle the internal and external factors shaping tie evolution across social contexts.
Read the full abstract

All authors Gamal Adel, Shrichand Bhuria, Alessandro Catalano, Liber Dorizzi, Leonardo Federici, Theodora Moldovan, Berné Nortier, Chara Deanna Punzal, Giulia de Meijere, Gerardo Iñiguez

Computational Physics · Cross-listed from hep-th

$\texttt{SMaSH}$ : Simplify Massive Spinor Helicity

Aakash Kumar, Arnab Rudra and Rahul Shaw

We present $\texttt{SMaSH}$, a $\texttt{Mathematica}$ package to do spinor helicity computations in four spacetime dimensions $\href{https://github.com/aakash-kmr/SMaSH}{\text{(github)}}$. It can handle massive spinor helicity computations with explicit little group indices which is a novel feature. It can also handle massless as well as off-shell spinor helicity variables. It is designed to compute perturbative computations; it comes with predefined three point amplitudes and propagators for any masses and spins (arXiv:1709.04891). It can implement the high energy limit over an expression, check the discrete $\tt{C,P,T}$ transformations, compute contact terms and impose gauge invariance for any scattering process. We have shown the usage of such functions for computing gauge invariant Weinberg minimal amplitudes (arXiv:2506:12431, arXiv:2504:06343). The package can also generate both real and complex numerical kinematics for any $n$-point scattering for arbitrary masses and energy scales by implementing the $\tt{RAMBO}$ algorithm. It is also rich with basic spinor helicity manipulations like Schouten simplification, Clifford algebra manipulation, conversion between spinor helicity and Lorentz vectors, derivative w.r.t. spinors and their scalars, helicity scaling etc.
Read the full abstract

Fluid Dynamics

Effect of an aligned current on the stability of oscillatory incompressible flow past a circular cylinder

Geng Chen, Lian Gan and Philip H. Gaskell

The stability of incompressible flow past a circular cylinder under collinear steady and oscillatory forcing is investigated within a two-dimensional Floquet framework. The flow is parameterised by the Keulegan-Carpenter number $KC \in [4,12]$, the steady-to-oscillatory velocity ratio $m \in [0,1]$, and the oscillatory Reynolds number $Re_m \in [20,100]$. The loci of the leading Floquet multipliers, and hence case-specific bifurcation modes, are examined by progressively reducing $Re_m$ to subcritical values for prescribed $m$. A steady current with $m > 0.5$ gives rise to a period-doubling subharmonic bifurcation that does not occur in purely oscillatory flow, where only synchronous and quasi-periodic modes arise. For $Re_m = 100$, three key features are discernible. First, the neutral stability curve in $(KC,m)$ space is strongly non-monotonic in $m$, separating intrinsically stable regions from those with single unstable modes; a sub-region of striking mode re-stabilisation appears beyond $m \approx 0.9$, where the flow recovers a $Z_2$-symmetric state at peak Reynolds number $\approx 190$, despite the steady and oscillatory components each being individually unstable. Second, a distinct regime supports the coexistence of two unstable modes of different types. Third, complementary direct numerical simulations show that, for a single unstable mode, the linear analysis successfully predicts the saturated nonlinear state even when $Re_m = 100$ substantially exceeds the critical Reynolds number, whereas under mode coexistence the quasi-periodic attractor tends to dominate the developed dynamics.
Read the full abstract

Optics

Bound States in the Continuum and Unidirectional Guided Resonances Enabled by Competing Fourier Harmonics near the Fourth Stop Band

Sun-Goo Lee and Wook-Jae Lee

Bound states in the continuum (BICs) and unidirectional guided resonances (UGRs) are singular radiative eigenstates in planar photonic lattices characterized by complete or directional suppression of out-of-plane radiation, respectively. Here, we show that, near the fourth stop band, the formation of BICs and UGRs can be understood within a unified two-pathway radiation model, in which the Bloch eigenmode radiates through indirect and direct pathways mediated by the first and second Fourier harmonics of the dielectric modulation, respectively. In vertically symmetric photonic lattices, when the two radiation components cancel each other out in both the upward and downward directions, BICs emerge. The model yields an analytical BIC condition that can be satisfied by tuning a single lattice parameter, the duty cycle $\rho$, and is confirmed by finite-element simulations. By contrast, in vertically asymmetric photonic lattices, the upward and downward radiation-cancellation conditions no longer coincide, allowing UGRs to arise when the cancellation condition is satisfied in only one direction. We introduce a zero-contrast grating (ZCG), in which the upper protruding grating region produces pronounced up-down asymmetry, and show that two off-$\Gamma$ UGRs emerge and can be merged at the $\Gamma$ point by tuning the lattice parameters.
Read the full abstract

Optics

Quantum frequency comb with pump-selectable bin pairing and extraction-aware loading in a lithium niobate microresonator

Mohamad Reza Nurrahman, Hyeon Hwang, Nuri Han et al. (+6 more)

Integrated quantum photonics requires bright, high-fidelity photon-pair sources capable of spectral multiplexing, correlation control, and circuit-compatible extraction. Cavity-enhanced spontaneous parametric down-conversion (SPDC) increases pair generation, but triply resonant operation imposes stringent pump-signal-idler spectral-alignment constraints. Moreover, the trade-off between intrinsic generation and coincidence-to-accidental ratio (CAR) does not capture the usable output flux, which depends on photon extraction. Here, we demonstrate a single-pass-pumped, resonator-enhanced quantum frequency comb (QFC) source based on a periodically poled lithium niobate photonic-crystal Fabry-P$\'e$rot microresonator. The device yields intrinsic and loaded brightnesses of 69.9 and 1.88 MHz/$\mu$W, respectively, and a maximum CAR of 16,000. Frequency-resolved measurements reveal 461 cavity-defined bins spanning 1495-1570 nm, and loaded spectral brightness approaching $4.29\times10^9$ pairs/(s$\cdot$mW$\cdot$nm). Heralded autocorrelation measurements yield a second-order autocorrelation $g_H^{(2)}(0)$ as low as $4.0\times10^{-4}$ for a selected high-CAR cavity-defined bin pair. In particular, tuning the single-pass pump deterministically selects correlated frequency-bin pairings within the fixed QFC grid while preserving brightness and pairwise coincidence rates. We further separate intrinsic generation from output photon-pair flux, revealing the loaded-brightness-CAR relation. Together, pump-selectable bin pairing and extraction-aware loading point to tailored SPDC QFCs as chip-integrated nonclassical light resources for multichannel quantum-state transport and information processing.
Read the full abstract

All authors Mohamad Reza Nurrahman, Hyeon Hwang, Nuri Han, Guhwan Kim, Hong-Seok Kim, Kiwon Moon, Jung Jin Ju, Hansuek Lee, Min-Kyo Seo

Computational Physics

Mosaic: A Benchmark Suite for Differentiable Physics Solvers

Andrin Rehmann, Heiko Zimmermann and Dion Häfner

Differentiable partial differential equation (PDE) solvers underpin solver-in-the-loop ML training, gradient-based optimal control, and inverse problems, yet the practical cost of obtaining correct, usable gradients from a given solver on a given problem is largely undocumented. Integration effort, computational cost, gradient accuracy, and numerical conditioning vary widely across solvers and are discoverable only by trial and error. We introduce Mosaic, an extensible benchmarking framework for differentiable PDE solvers that standardizes access to solver gradients. Each solver is packaged as a containerized component (Tesseract) exposing a uniform gradient API regardless of language or automatic differentiation (AD) strategy, enabling researchers to evaluate, compare, and build on non-trivial physical solvers. Our evaluation of 14 solvers across fluid dynamics, structural mechanics, and heat transfer demonstrates that the benchmark surfaces practically relevant differences: order-of-magnitude variation in computational cost and Jacobian conditioning, alongside structural incompatibilities that eliminate solvers from realistic tasks entirely. Despite this variation, all solvers that produce gradients converge to similar optima, indicating that the practical barriers are memory limits, numerical stability, and setup compatibility rather than gradient accuracy alone. Mosaic is open-source and available at https://github.com/pasteurlabs/mosaic.
Read the full abstract

Optics

Vibrational high-harmonics and period-doubling bifurcation probed by time-resolved electron diffraction

Alexander Schröder, Kai Nettersheim, Ferdinand Evers et al. (+1 more)

Nanoscale mechanical oscillators exhibit a plethora of nonlinear phenomena with promising applications for the sensing and clocking of processes down to atomic length scales. Oscillator dynamics are typically probed by electrical or optical means, providing only limited access to the spatial profile of the oscillator motion. Here, we introduce event-based convergent beam electron diffraction for the spatio-temporal mapping of nanoscale mechanical resonators in ultrafast transmission electron microscopy. Employing an optically driven silicon membrane resonator at various driving strengths, we gain access to nonlinear processes with increasing complexity, ranging from a simple Duffing behavior to nonlinear multimode coupling and period-doubling bifurcations. The time-resolved diffraction probing approach supports a spatial resolution down to a few nanometers and a temporal resolution of 5 ns and provides quantitative information on the local membrane bending. Because the diffraction signal responds to local displacement gradients, which become more pronounced as resonators shrink, this approach offers a route toward probing nonlinear nanomechanics at the atomic scale.
Read the full abstract

All authors Alexander Schröder, Kai Nettersheim, Ferdinand Evers, Sascha Schäfer

Plasma Physics

Electrons with Anomalous Energy Generated in Gas-Filled and Vacuum Diodes

Victor F. Tarasenko, Vasily Yu. Kozhevnikov, Andrey V. Kozyrev et al. (+2 more)

It is shown that, when high-voltage pulses (with a voltage amplitude exceeding 100 kV in centimeter gaps) with a leading edge duration of 1 ns or shorter are applied to gas-filled and vacuum electric discharge diodes, electrons with kinetic energies nominally exceeding the amplitude of the applied voltage are detected. In the experiments, electron beam attenuation curves were measured in absorbers consisting of Al foil of varying thicknesses. These curves were used to reconstruct the electron beam energy spectrum by regularizing the solution of an integral equation based on deep machine learning. The obtained spectra contain electrons with anomalously high energies, the proportion of which, depending on the conditions, can reach 25 percent. A control experiment with a long voltage pulse on a large-area vacuum diode (voltage 150 kV, pulse duration 35 microseconds, vacuum gap 12 cm, electrode area 75 x 15 cm2) showed that the proportion of electrons with anomalous energies is less than 0.2 percent. Experiments have shown that the main mechanism for generating electrons with anomalous energy is the spatio-temporal synchronism of the motion of fast electrons in the enhanced field formed in the gap by space charge.
Read the full abstract

All authors Victor F. Tarasenko, Vasily Yu. Kozhevnikov, Andrey V. Kozyrev, Evgenii Kh. Baksht, Maxim S. Vorobyov