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Friday 7 August

Mathematical Physics

Effective mass density for wave propagation in periodic layered media in the elasto-acoustic transition

Gabriel Núñez, William J. Parnell and Raphaël C. Assier

This article investigates the effective mass density for acoustic and elastic wave propagation in layered media, with emphasis on its transition between these regimes. Conventionally, it is possible to recover the governing equations of acoustics from those of elasticity via the no-shear limit. However, when considering an effective medium, the anisotropic effective mass density typically obtained for acoustics differs from the isotropic one found in elasticity. Furthermore, direct investigation of this limit is hindered by the fact that the effective mass density is independent of the shear modulus $\mu$. To tackle this problem, a transfer matrix approach is combined with Bloch's theorem to derive the effective wavenumber for a periodic material whose unit cell consists of two layers with different densities. The effective mass density is obtained analytically from the wavenumber, allowing for its evaluation in both regimes. Moreover, for the first time, a description of the transition from isotropic elastic to anisotropic acoustic effective density in a periodic layered medium is provided. Additionally, the existence of band structure in $\mu$-space is demonstrated, along with exceptional points, where compressional and shear modes coalesce and waves become evanescent, which heavily affects the behaviour of the effective density in the elasto-acoustic transition.
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Physics and Society

Coordinated incentives in AI-generated misinformation governance

Qin Li, Gui Zhang, Minyu Feng et al. (+2 more)

With the rapid diffusion of AI-generated content, AI-driven misinformation is becoming increasingly pervasive and difficult to govern, undermining information credibility and social trust. This study models the strategic interdependence among a government regulator, an AI enterprise, and users through a three-party evolutionary game that incorporates heterogeneous rewards and punishments. From the resulting replicator equations, we characterize the evolutionary stability of competing governance and production strategies. The analysis indicates that neither unilateral regulation nor market incentives alone can effectively curb misinformation. Instead, an evolutionarily stable regime of real-information production arises only when regulatory rewards and punishment intensity, enterprise reputation loss, and user adoption incentives collectively surpass critical thresholds. The findings highlight the need for coordinated and adaptive policy mixes that align regulatory instruments with enterprise behavior and user uptake while managing governance costs.
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All authors Qin Li, Gui Zhang, Minyu Feng, Matjaz Perc, Attila Szolnoki

High Energy Astrophysical Phenomena

Constraining Circum-burst Environments of GRBs with Jet Break Features in X-ray Afterglows

Si-Ji Xin, Yu-Qi Zhou, Sheng-Jin Sun et al. (+6 more)

The nature of the circum-burst medium serves as a key diagnostic for probing the progenitor systems and the physics of relativistic jet propagation in gamma-ray bursts (GRBs). In this work, we systematically infer the density profile index $k$ (where $n \propto r^{-k}$) from the change in the temporal decay index at the jet break ($\Delta\alpha$). Within the framework of the uniform jet model, the two quantities are linked by the relation $\Delta\alpha = (3 - k)/(4 - k)$. We apply this diagnostic to a substantial and uniformly selected sample of 170 GRBs with clear jet breaks, identified from over 1,400 Swift/XRT X-ray afterglows observed from 2004 to 2024. By fitting the light curves with a broken power-law model, we obtain $\Delta\alpha$ for each burst and subsequently derive the corresponding $k$ value. We then use the derived $k$ values to classify the circum-burst environment of each GRB. Our results reveal a near-even split: 82 bursts ($\sim48\%$) are consistent with a constant-density interstellar medium (ISM, $k \approx 0$), while 88 bursts ($\sim52\%$) favor a wind environment ($k \approx 2$). For the 35 bursts with optical data, our X-ray-based classifications are generally consistent with independent multi-band analyses. Additionally, we derive jet opening angles and true beaming-corrected energies for bursts with known redshifts.
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All authors Si-Ji Xin, Yu-Qi Zhou, Sheng-Jin Sun, Cheng-Jie Sun, Shuang-Xi Yi, Yuan-Chuan Zou, Yu-Peng Yang, Yan-Kun Qu, Fa-Yin Wang

Soft Condensed Matter

Active Brownian motion in a single-relaxation viscoelastic fluid

Sanatan Halder and Manas Khan

Active Brownian particles (ABPs) in viscoelastic (VE) media exhibit fascinating dynamical phenomena set by self-propulsion, thermal fluctuations, and fluid viscoelasticity. We extend our model, in which the Brownian dynamics within a slowly diffusing harmonic well emulates that in a single-relaxation VE fluid, to study active Brownian motion in such media. Consequently, the resultant dynamics is governed by the interplay of the characteristic timescales of the systems: the crossover and equilibration times of the VE fluid, $\tau_k$ and $\lambda$, respectively, and the persistence time of the ABP, $\tau_{\mathrm{R}}$. Following analytical predictions and simulations, we study two practically relevant regimes where the dynamics is dominated by the persistence of active motion and the elastic confinement of the VE fluid, with a phoretically active Pt-coated Janus colloid in a dynamic optical trap, and show quantitative agreement with the simulations. This approach provides a VE environment with tunable VE properties that remain unaffected by the strength of self-propulsion, allowing us to systematically investigate active Brownian motion in VE media in ways that are not otherwise possible with physical VE fluids.
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Optics

Characterising Interleaver Length in a Turbulent Deployed Terrestrial Free-Space Optical Link

Kadir Gümüş, Vincent van Vliet, Menno van den Hout et al. (+3 more)

We investigate the correlation between interleaver length and turbulence for a deployed terrestrial free-space optical link spanning 4.6 km. Using 24 hours of measurements, we show an indicative distribution of interleaver length for capacities up to 350 Gb/s/pol and outage probabilities down to $10^{-4}$.
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All authors Kadir Gümüş, Vincent van Vliet, Menno van den Hout, Thomas Bradley, Eduward Tangdiongga, Chigo Okonkwo

Mesoscale and Nanoscale Physics

Magneto-optical signal from $\mathrm{Co_2Mn}$-based Heusler thin films in MOKE and BLS

Anna Maria Friedel, Nicolas Fermon, Tobias Böttcher et al. (+3 more)

$\mathrm{Co_2Mn}$-based Heusler compounds offer a versatile, composition-tunable platform for magnonics and spintronics. Among them, the half-metallic $\mathrm{Co_2MnSi}$ is of particular interest for magnonics owing to its ultralow Gilbert damping, yet its weak magneto-optical response in the visible challenges optical probing such as Brillouin light scattering (BLS). We study the magneto-optical response of epitaxial $\mathrm{Co_2Mn}X$ films ($X = \{\mathrm{Al}_x\mathrm{Si}_{1-x}, \mathrm{Ga}_x\mathrm{Ge}_{1-x}, \mathrm{Sn}\}$) by magneto-optical Kerr effect (MOKE) spectroscopy and BLS. Angle-resolved MOKE resolves a significant, wavelength-dependent quadratic MOKE (QMOKE) only for $\mathrm{Co_2MnSi}$, whereas $\mathrm{Co_2MnAl}$, $\mathrm{Co_2MnGa}$ and $\mathrm{Co_2MnSn}$ respond dominantly linearly. Comparing BLS intensities of thermal magnons at two wavelengths, $\mathrm{Co_2MnSi}$ gives the weakest signal at 532 nm yet among the strongest at 457 nm, tracking the spectral dependence of its Kerr angle. These results emphasise the relation between the two magneto-optical techniques, guiding the choice of probing wavelength for $\mathrm{Co_2Mn}$-based Heusler compounds.
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All authors Anna Maria Friedel, Nicolas Fermon, Tobias Böttcher, Sébastien Petit-Watelot, Stéphane Andrieu, Philipp Pirro

Applied Physics

Roadmap on UV-C photodetectors: materials, applications and industry perspectives

Fabien Massabuau, Drew Riley, Paul Meredith et al. (+44 more)

UV-C photodetectors are poised to play an increasingly important role in future photonic technologies, driven by the rapid emergence of UV-C light sources and new wide bandgap semiconductors. These advances are enabling new levels of spectral selectivity, radiation hardness, sensitivity, and device integration, while opening opportunities across a broad range of applications. This roadmap provides a comprehensive overview of the current landscape of UV-C photodetection, spanning established and emerging material platforms (Ga2O3, AlGaN, BN, diamond, MgZnO, 2-dimensional materials, metal halide perovskites, micro-electromechanical systems), and their applications in metrology, astronomy, communications, environmental monitoring, fire detection, missile warning, gas sensing, and medical diagnostics. By identifying opportunities, bottlenecks, and future directions, this roadmap aims to support both newcomers and established researchers, with the aim of accelerating the translation of UV-C photodetectors into impactful technologies.
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All authors Fabien Massabuau, Drew Riley, Paul Meredith, Tilman Weiss, Damanpreet Kaur, Yuichi Oshima, Robert W. Martin, Eva Monroy, Le Chen, Hongwei Liang, Hong Yin, Keyun Gu, Meiyong Liao, Yaonan Hou, Fa Cao, Xiaosheng Fang, Ruiheng Li, Guoqiang Peng, Zhiwen Jin, Lijie Li, Nasim Zarrabi, Sebastian Wood, Jesper Skottfelt, Susan E. S. Spesyvtseva, Jonathan McKendry, Christopher G. Leburn, Daniel K. L. Oi, Ryan Pereira, Graeme Moore, Tom Lendrem, Christoph Wagner, David Maestre, Emilio Nogales, David J. Rogers, Eric Sandana, Michel Chamberlin, Ferechteh H. Teherani, Bianchi Méndez, Yana Suchikova, Marina Konuhova, Anatoli I. Popov, Luís F. da Silva, Eduard Llobet, Sangjin Yoon, Dohyung Kim, Sangwoo Hong, Seung Hwan Ko

Solar and Stellar Astrophysics

Euclid Early Release Observations of the Barnard 30 dark cloud I. Brown dwarfs and planetary mass candidate members at the core of the association

D. Barrado, H. Bouy, E. L. Martin et al. (+8 more)

This study aims to identify very low-mass members within the Barnard 30 dark cloud, with a particular focus on detecting objects in the substellar domain, including those within the planetary-mass regime. We employed deep photometric observations using data from the Euclid mission, incorporating advanced data processing techniques, in particular the DeNeb tool for optimized source detection. We also analyze multi-wavelength ancillary observations and perform a Spectral Energy Distribution analysis for each candidate member. In addition, low-resolution near-infrared spectroscopy was obtained for one candidate to further assess its nature and properties. Our initial photometric analysis yielded a initial sample of nearly one hundred candidate members in the substellar mass range. A subsample of 23 probable members, located close to the 3 Myr isochrone, has been identified. Thus, we have substantially expanded the known population of faint, cool sources associated with the region. Low resolution near-IR spectroscopic analysis of one candidate reveals an L2 spectral type with low gravity, consistent with a young ultra-cool dwarf. If its membership is confirmed, its estimated mass lies in the range 15-20 Mjup. These findings validate the reliability of our multi-wavelength photometric selection methodology. These results offer valuable insights into the low-mass end of the initial mass function (IMF) and demonstrate the effectiveness of Euclid in identifying brown dwarf and planetary-mass candidates in nearby, densely packed star-forming regions.
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All authors D. Barrado, H. Bouy, E. L. Martin, J.-C. Cuillandre, N. Huélamo, M. Žerjal, C. Dominguez-Tagle, S. Muñoz Torres, J.-Y. Zhang, E. Bertin, J. Olivares

General Relativity and Quantum Cosmology

Entropy-geometry correspondence as effective nonlocal gravity

Kimet Jusufi and Ankit Anand

We develop an operator formulation of the entropy-geometry correspondence for static, spherically symmetric gravity. Starting from a generalized entropy, we reconstruct an effective nonlocal form factor, its coordinate-space source, the associated cumulative mass profile, and the resulting spacetime geometry. The construction is worked out for the Bekenstein-Hawking, Rényi, Tsallis-Cirto, Barrow, Kaniadakis entropies, logarithmically/exponentially corrected entropy and LQG inspired entropy. The operator representation provides a direct relation between generalized entropy, nonlocal gravitational dressing, and a scale-dependent effective mass or Newton coupling. We analyze the reconstructed sources and their infrared and ultraviolet behavior, discuss their physical consistency, and identify the limits in which the standard Schwarzschild description is recovered. We show that the generalized entropy exactly reproduces the area law with the reconstructed running Newton coupling, $\dd S=\dd A/4G_S(r_+)$, ensuring thermodynamic consistency. Since horizon entropy is determined by the action, this favors entropy corrections in the gravitational sector. We also derive the conditions for the reconstructed horizon to be an event horizon with positive temperature.
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Cosmology and Nongalactic Astrophysics

Revisiting 2D and 3D Dainotti Correlations for GRBs Using Bayesian Neural Networks

Nilanjana Bagchi Aurpa, Abha Dev Habib and Nisha Rani

Gamma-ray bursts (GRBs) are promising cosmological probes, but their use as standard candles is limited by the circularity problem, necessitating model-independent calibration of GRB luminosity correlations. We revisit the two-dimensional (2D) and three-dimensional (3D) Dainotti correlations using Bayesian Neural Networks (BNNs) trained on the updated Observational Hubble Data (OHD) and Pantheon+ Type Ia Supernova sample. The reconstructed luminosity distances are used to calibrate the Platinum and Narendra et al. GRB samples. We constrain the parameters of the 2D Dainotti relation and the 3D fundamental plane, and examine the impact of calibration datasets and GRB sample selection. Calibration achieved using Pantheon+ yields tighter constraints than OHD, while the 3D correlation exhibits lower intrinsic scatter than the 2D relation. Our results demonstrate that BNNs provide a robust framework for model independent calibration of GRB luminosity correlations with reliable uncertainty propagation. Further, the underlying distance probe is a key factor in model-independent calibration, determining both the size of the GRB samples and the precision of the resulting constraints.
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Mesoscale and Nanoscale Physics

Out-of-equilibrium spin-valley dynamics of ferromagnets in topological Chern bands

J. James, I. Krastilevskiy, F. Pichler et al. (+8 more)

Understanding quantum matter far from equilibrium is a central goal of modern physics. Twisted MoTe2 bilayers constitute a promising platform for exploring this frontier by combining strong Coulomb interactions, nontrivial band geometry, and optical control. Here, we exploit this setting to investigate the role of topology and many-body correlations in the out-of-equilibrium dynamics of ferromagnets in Chern bands. Using a focused circularly polarized light pulse, we create a local magnetic domain oriented opposite to an external magnetic field and directly image its subsequent spin-valley relaxation in spatially and time-resolved low-temperature experiments. We demonstrate that in the vicinity of both integer and fractional Chern insulating states, the dynamics is governed by qualitatively different mechanisms than in ferromagnetic metals. Whereas metallic domains collapse by shrinking, Chern domains melt via thermal activation, resulting in drastically different temporal spin evolution and orders-of-magnitude longer relaxation times. These findings demonstrate the influence of topology and strong correlations on far-from-equilibrium collective spin phases, opening new opportunities for dynamical control of ferromagnets in the quantum Hall regime.
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All authors J. James, I. Krastilevskiy, F. Pichler, L. Wang, A. Iafarova, F. Menzel, K. Watanabe, T. Taniguchi, C. Kuhlenkamp, M. Knap, T. Smoleński

Quantum Physics

Multimode phonon-mediated enhancement of entanglement and competing synchronization in cavity magnomechanics

Z.Imara, Jia-Xin Peng, E.K. Berinyuy et al. (+2 more)

The generation of quantum correlations in hybrid quantum systems remains a central challenge due to the intrinsic limitations of linear interactions. In cavity magnomechanical platforms, the cavity-magnon coupling gives rise to hybridized cavity-magnon polaritons (CMPs). However, as a beam-splitter-type interaction, it does not by itself generate entanglement between the polariton modes in the absence of additional nonlinear or parametric processes. Here, we propose a mechanism based on multimode phonon mediation, in which multiple vibrational modes act as parallel scattering channels that couple the polaritons through Stokes and anti-Stokes processes. We show that , in the parameter regime explored here, the presence of multiple phonon modes leads to a monotonic enhancement of steady-state entanglement, thereby going beyond the limitations of conventional single-mode schemes. Furthermore, we demonstrate that quantum synchronization between the polariton modes originates from the same underlying scattering processes responsible for entanglement generation, yet exhibits an opposite scaling behavior with increasing phonon number for the phase quadrature, while the amplitude synchronization reveals collective squeezing that grows with the number of phonon channels. Our results provide new insights into the role of multimode interactions in shaping quantum correlations and establish a viable pathway for controlling entanglement and collective dynamics in hybrid magnomechanical platforms.
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All authors Z.Imara, Jia-Xin Peng, E.K. Berinyuy, S.K. Singh, A. El Allati

General Relativity and Quantum Cosmology

Numerical Simulation of Black Hole Images from photon trajectories in Schwarzschild Geometry

Alin Galea and Victor E. Ambrus

With the arrival of advanced telescopes such as the Event Horizon Telescope (EHT), direct imaging of a black hole's shadow became a reality. Simulations play an important role in reproducing their appearance and constraining physical parameters of the black hole. We present a simple framework of simulating images of Schwarzschild black holes surrounded by thin, rotating accretion disks, accounting for gravitational and Doppler redshifts. A ray tracing algorithm based on integrating the photon geodesic equations with a 4th-order Runge-Kutta scheme is used for imaging. The accuracy of the numerical method is verified by convergence tests. A brief discussion of the validity of the weak field approximation is included and a qualitative comparison between the simulated images and the EHT image of M87* is presented.
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Physics and Society · Cross-listed from cs.LG

Hyperbolic Graph Embedders for Link Prediction and Topology Reconstruction

Robert Jankowski, Maksim Kitsak and Dorota Celińska-Kopczyńska

Hyperbolic embeddings provide compact geometric representations of complex networks in hyperbolic spaces, but systematic comparisons of methods developed in machine learning, network science, and algorithmics remain rare. We benchmark 13 unsupervised hyperbolic graph embedders under a unified protocol for link prediction and topology reconstruction on synthetic and empirical networks. The protocol captures both missing-link recovery and the preservation of local and global network structure. Maximum-likelihood and representation-learning-based approaches, including hybrid variants, achieve the strongest overall performance, although no method dominates across all tasks and structural regimes. Performance is more strongly associated with embedding paradigm than with disciplinary origin. We identify the network regimes in which different paradigms succeed or fail and provide practical guidance for method selection in downstream applications.
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Mathematical Physics · Cross-listed from math.DG

Monte Carlo methods on compact symplectic manifolds

Yuri A. Kordyukov

We build an unbiased Monte Carlo estimator of the integral of any $C^1$ function on a prequantized compact symplectic manifold against a smooth Riemannian volume form, taking for quadrature nodes the determinantal point process associated with an appropriate spectral projection of the Bochner-Schrödinger operator. We show that the estimator satisfies a central limit theorem, and the decay rate of the mean squared error reaches the optimal worst-case rate investigated by Bakhvalov in Euclidean spaces. These results extend previous results of Lemoine and Bardenet on Monte Carlo methods on compact complex manifolds.
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Strongly Correlated Electrons

Local magnetic properties of the rare-earth intermetallics $R$Mn$_2$Ge$_2$ ($R$=Ce, Pr, Nd)

N. P. Bentley, T. L. Breeze, A. Hernández-Melián et al. (+9 more)

We present an investigation of the rare-earth intermetallic materials, $R$Mn$_2$Ge$_2$ ($R$=Ce, Pr, Nd), reported to host a lattice of skyrmionic bubbles at room temperature. The magnetism of all three materials is characterised by the onset of local fluctuations as the magnetic state changes from a conical magnetic structure to a collinear antiferromagnetic one as temperature $T$ is increased. In this $T$ regime, where skyrmion-bubble textures have been reported, we see dynamics similar to those observed in other skyrmion-hosting materials. The level of disorder above this transition increases across the series from $R$=Ce to Nd. At low temperatures the magnetism is affected by the ordering of the rare-earth ions, resulting in distinct behaviour for the different members of the series.
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All authors N. P. Bentley, T. L. Breeze, A. Hernández-Melián, M. J. Pearce, T. J. Hicken, M. T. F. Telling, B. M. Huddart, G. D. A. Wood, D. A. Mayoh, G. Balakrishnan, S. J. Clark, T. Lancaster

Nuclear Experiment

Measurement of the Electron capture of $^{76}$As into the first excited state of $^{76}$Ge

Hans F. R. Hoffmann, Björn Lehnert and Kai Zuber

The neutrinoless double beta decay of $^{76}$Ge is searched for in the large-scale experiment LEGEND. The measurement of the half-life of this process would give access to the neutrino mass using the nuclear matrix element. Experimentally the contribution of the $^{76}$As ground state to the nuclear matrix element can be investigated via the branching ratios of its $\beta^-$ and electron capture decay. While energetically, the electron capture of $^{76}$As into the first excited state of $^{76}$Ge is possible and was measured once before this work, the electron capture into the $^{76}$Ge ground state was not observed yet. The present study investigates the branching of $^{76}$As that is produced via $^{75}$As(n,$\gamma$) on a thin As$_2$O$_3$ sample. A silicon drift detector measures characteristic X-rays emitted by the germanium atoms caused by an inner vacancy after the electron capture. A high-purity germanium detector is used to measure the 562.9$\,$keV $\gamma$-rays emitted after electron capture into the excited state. Investigation of coincident signals in both detectors leads to the branching ratio of the $^{76}$As electron capture into the first excited state of $^{76}$Ge of $\nu_{\mathrm{EC}^\ast} = (0.0572 \pm 0.0029 (\mathrm{stat.}) \pm 0.0074(\mathrm{syst.}))\%$. This is the first measurement with the full uncertainty budget quantified.
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Cosmology and Nongalactic Astrophysics

Cosmography for a General Spacetime Centred at Arbitrary Redshift

Jonas Broe Bendtsen, Asta Heinesen and Sofie Marie Koksbang

With upcoming surveys providing large volumes of highly precise observational data across a wide range of redshifts, it is increasingly important to have tools that can translate observational data into geometric and dynamical information without imposing a predetermined cosmological model. General cosmographic expansions centred at arbitrary redshift provide exactly such a tool. We here present the formalism for general cosmographic expansions centred at an arbitrary redshift, valid for 4-dimensional Lorentzian spacetimes. We then apply the expansion formalism to test its ability to reproduce the redshift-distance relation in two examples of large-scale cosmic structures (an underdensity and an overdensity) modelled by the Lemaître-Tolman-Bondi metric, where we examine the effect of choosing different redshift intervals for the cosmographic series expansions. This quantifies the extent to which cosmographic coefficients inferred from redshift-distance observations retain their interpretation as local geometric and dynamical quantities, as is expected in standard FLRW cosmology. Similarly to earlier results, we here find that in more general spacetimes the coefficients instead become effective parameters reflecting the finite observational range probed. Lastly, we discuss possible strategies for using the expansions to constrain dynamical and geometric quantities.
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Biological Physics · Cross-listed from q-bio.MN

Simulating is not always understanding: When model complexity obscures biology

Lendert Gelens, Alejandro Fábregas-Tejeda, Grant Ramsey et al. (+2 more)

In cell biology, computational models of biological systems range from minimal representations with a handful of parameters to whole-cell simulations tracking thousands of molecular species across a complete cell cycle. While these models span a continuum of detail, increasing complexity changes what they capture and are able to explain, what they can predict, and how they can fall short. A model contributes to understanding only when it makes novel predictions, reveals an unexpected coupling between processes, or fails in a way that identifies missing parameters. We contend that what is important for understanding is not the number of components or spatial dimensions a model contains, but the ratio of free parameters to the experimental constraints available to pin them down, and whether we can see why it produces the behaviors it does. Large-scale agent-based models of cytoskeletal dynamics or tissue mechanics that are built on a small number of physically grounded rules can reveal rich self-organization behavior precisely because their parameter spaces are small enough to explore systematically. By contrast, when free parameters grow faster than the data available to constrain them, models become progressively harder to interpret – and even disprove –regardless of their biological scope. We argue that the field needs to reconsider the goal of complex models. We should move away from trying to include as many parameters as possible and instead aim for systematic comparisons with simpler representations, dynamical analysis, and explicit model hierarchies that trace how cellular behavior emerges from its parts.
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All authors Lendert Gelens, Alejandro Fábregas-Tejeda, Grant Ramsey, Sylvia Wenmackers, Bart Smeets

Quantum Physics

Fugacity-Resolved Stabilizer Entropy in Critical Quantum Chains: Discrete Selberg Sums and Exactly Solvable Rényi Indices

Reyhaneh Khasseh and M. A. Rajabpour

Stabilizer Rényi entropy quantifies the nonstabilizerness of a quantum state through Rényi moments of its Pauli expectation-value distribution. Its standard form sums over Pauli-string degrees and retains only the total Rényi weight. We introduce a fugacity-resolved partition function for the critical transverse-field Ising chain that resolves this degree in the balanced Majorana representation and generates its full counting statistics. This Ising problem extends beyond a single model: exact decimation identities and the correspondence with the half-filled \(XX\) chain establish it as a common finite-size building block for stabilizer and computational-basis Shannon–Rényi entropies. We map the fugacity-resolved all-minors sum, for every positive Rényi index, to a checkerboard-weighted discrete Selberg ensemble on a half-filled doubled root lattice. For positive integer indices, it reduces to a finite aliased Dyson constant term. At \(\alpha=\tfrac12,1,2\), determinant and Pfaffian compressions yield product formulas. At \(\alpha=4\), the generic-fugacity problem admits an exact inverse Jack–Kostka representation, while at unit fugacity a complementary middle-minor identity relates it to the square of the \(\alpha=2\) result. These generating functions determine the balanced-degree statistics. Complement symmetry makes the distribution symmetric about \(k=L/2\), with an index-dependent width. It is exactly binomial at \(\alpha=1\), has variance proportional to \(L\) at \(\alpha=\tfrac12\), and develops an \(L\log L\) enhancement at \(\alpha=2\). After variance rescaling, the centered distributions converge to Gaussian limits at all three indices. Beyond these solvable cases, finite-size numerics reveal an evolution from a central peak to a symmetric bimodal profile and eventually to endpoint dominance as the Rényi index increases.
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Atomic Physics

An ionic clock qubit inside a circular Rydberg atom

Fabian Thielemann, Aaron Götzelmann, Marius Thomas et al. (+4 more)

Neutral atoms trapped in optical tweezers and excited to Rydberg states, together with trapped ions, are among the most advanced platforms for quantum simulation and quantum computing. Current experiments often rely on additional atoms in neighboring traps to encode ancilla qubits for local manipulation and readout. Here, we demonstrate a dual ion-Rydberg system comprising two qubits encoded in two individually controlled electrons of the same alkaline-earth atom. The first, a microwave qubit, is encoded in a pair of circular Rydberg states, while the second, an optical qubit, is encoded on a narrow quadrupole transition of the Rydberg atom's ionic core. We demonstrate coherent control of the optical qubit and achieve coherence times of several hundred microseconds under dynamical decoupling. Furthermore, we realize coherent coupling between the two electrons via electrostatic quadrupole interactions over the large separation between the Rydberg electron and the ionic core, and map out its angular tunability. Finally, we demonstrate a two-qubit operation, reminiscent of a Mølmer-Sørensen gate, that evolves through an entangled state of the two qubits driven by the quadrupole coupling. Our work opens a pathway to exploit a pair of individually controlled electronic qubits with tunable coupling for quantum simulation and quantum metrology.
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All authors Fabian Thielemann, Aaron Götzelmann, Marius Thomas, Einius Pultinevicius, Armin Humić, Christian Hölzl, Florian Meinert

Optics

Real-Time Dynamic Crosstalk Tracking and Compensation via Photonic Blind Source Separation

Dongliang Wang, Yikun Nie, Dingqian Zhao et al. (+4 more)

Space-division multiplexing in few-mode fibers can substantially increase optical-link capacity, but its practical deployment is hindered by dynamically varying inter-modal crosstalk induced by environmental perturbations. Although silicon photonic reconfigurable mode processors have been widely demonstrated, continuous adaptation during high-speed intensity-modulation direct-detection (IM/DD) transmission remains challenging. Here, we experimentally demonstrate real-time tracking and compensation of dynamically varying inter-modal crosstalk using a hybrid photonic–electronic framework that combines an integrated silicon photonic processor with an FPGA-based control backend. The photonic processor performs signal separation in the optical domain, while the FPGA extracts signal statistics and implements a blind source separation (BSS)-based feedback algorithm without requiring dedicated training sequences. A two-stage optimization strategy combines rapid crosstalk suppression with stable continuous tracking under dynamic channel variations. We demonstrate photonic blind source separation for signals up to 100 GBaud and FPGA-enabled continuous adaptation for two 64 GBaud data channels in a few-mode-fiber transmission system. The system maintains bit-error rates below $10^{-4}$ under dynamic crosstalk, with a per-update control latency of 4 ms. These results establish a practical route toward low-latency, hardware-efficient adaptive photonic front ends for dynamic high-speed IM/DD space-division-multiplexed links.
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All authors Dongliang Wang, Yikun Nie, Dingqian Zhao, Dan Yi, Gaolei Hu, Hon Ki Tsang, Chaoran Huang

High Energy Physics (Phenomenology)

Leptogenesis via Resonant Sequential Dominance and TBC3 Mixing in a Type-I Seesaw Model

Michael Fodroci and Teruyuki Kitabayashi

We demonstrate how phenomenological model construction assuming Sequential Dominance can be extended to cases with degenerate right-handed neutrino masses. Because this framework accommodates resonant leptogenesis, we designate it as Resonant Sequential Dominance. We then investigate Dirac mass matrix textures compatible with current neutrino data within Resonant Sequential Dominance, utilizing a novel neutrino mixing matrix ansatz termed TBC3, proposed in this work. Additionally, we present an $A_4 \times (Z_3)^4 \times (Z_2)^2$-symmetric Lagrangian that is consistent with neutrino oscillation data and successfully drives resonant leptogenesis. Lastly, we find that accounting for the observed baryon asymmetry of the Universe requires the lightest right-handed neutrino mass to lie in the range $0.13\text{ TeV} \le m_{N_1} \le 230\text{ TeV}$.
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Chaotic Dynamics

The Belousov-Zhabotinsky reaction reveals two regimes of non-Arrhenius temperature scaling in relaxation oscillators

Simen Jacobs, Nikita Frolov, Panna Farkas et al. (+3 more)

The period of biological and chemical oscillators scales with temperature in a characteristic way. Some oscillators are very well described by an Arrhenius law, while others show systematic deviations. Several frameworks have been proposed to explain such deviations, but they are either phenomenological, focus on activation energy imbalances in specific circuits, or restrict themselves to sequential processes. Here we develop a mechanistic account of the temperature scaling of relaxation oscillators, using the Belousov-Zhabotinsky (BZ) reaction as a model system. We distinguish two typical scenarios by their temperature-scaling signatures. In the first, an Arrhenius-dependent timescale separation parameter produces a biphasic Arrhenius scaling of the period as the oscillator approaches a Hopf bifurcation. In the second, Arrhenius-dependent nullclines hide the same bifurcation behind a canard explosion, yielding apparent single-line Arrhenius scaling. Measuring the electrode potential of a classical and an uncatalyzed BZ reaction, over a very wide temperature range ({\approx} 100 {\deg}C), and comparing to dynamical models, we find that the two reactions represent these two distinct scenarios. Furthermore, we show that a single parameter characterizing the waveform asymmetry between fast and slow phases quantitatively predicts the temperature scaling of three other observables close to the Hopf bifurcation: the period, amplitude, and phase noise. This analysis also recovers elementary activation energies of the BZ mechanism, including a new estimate for the autocatalytic step. We discuss how this framework and its waveform-based diagnostics apply to the analysis of general biochemical relaxation oscillators
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All authors Simen Jacobs, Nikita Frolov, Panna Farkas, István Lagzi, István Szalai, Lendert Gelens

Astrophysics of Galaxies

Smoothed particle magnetohydrodynamics for simulations of galaxy and cosmic structure formation

Orestis A. Karapiperis, Matthieu Schaller, Nikyta Shchutskyi et al. (+2 more)

We introduce a novel formulation of cosmological smoothed particle magnetohydrodynamics (SPMHD), designed to model magnetic field physics in a vast array of nonlinear astrophysical systems, and which we have implemented in the highly-parallel, entirely modular, and open-source simulation code SWIFT. Our numerical scheme is designed to offer optimal performance at a minimal computational cost, keep a low memory footprint, and most notably couple robustly to effective sub-resolution recipes of galaxy formation. This is achieved through expressing our evolution equations in a density-energy conservative form, and augmenting them with discontinuity-capturing terms tailored to high dynamic range simulations, which are further modulated by adaptive switches that drastically improve coupling to sub-grid models and limit spurious dissipation. We moreover present novel suggestions for the two major regularisation techniques used in modern SPMHD, namely a tensile instability correction and mixed hyperbolic/parabolic divergence-cleaning scheme, to ensure code stability in highly dynamical scenarios. We evaluate the performance of our method on a series of problems of increasing complexity, culminating in three astrophysical applications which have historically proven challenging for mesh-less methods: we study jet launching from a forming proto-stellar core, dynamo amplification in a massive galaxy cluster and magnetic field evolution in a Milky Way-like disk galaxy; the latter constitutes the first reported coupling of the EAGLE galaxy formation model to a magnetohydrodynamics solver. Keeping model hyperparameters fixed across our test suite to provide a transparent picture of our method's capabilities in production, we demonstrate sound performance and convergence with resolution on standard `laboratory' numerical experiments, as well as competitive capabilities in realistic applications.
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All authors Orestis A. Karapiperis, Matthieu Schaller, Nikyta Shchutskyi, Federico A. Stasyszyn, Maarten Elion

Mathematical Physics · Cross-listed from math.NA

A model and a finite element approximation of the mixed-dimensionality diffusion problem

Ignacio Romero and David Portillo

We present the formulation of a boundary value problem that models the coupled behavior of a three-dimensional diffusive solid with one-dimensional diffusive fibers embedded inside it. We introduce a variational statement of the problem that identifies the linked diffusive fields as energy minimizers under a coupling constraint. This saddle-point problem is proved to be well posed. Then, we introduce a finite element discretization of the proposed boundary value problem, and we prove the convergence of the finite element solution to the exact one. The most significant feature of this approximation is that the meshes of the bodies need not be conforming. Numerical examples confirm the theoretical results
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Quantum Physics

Single-qubit detection by collective phase imprinting

Kritsana Srakaew, Pascal Weckesser, Daniel Adler et al. (+4 more)

The amplification of quantum information carried by a single quantum excitation is a recurring challenge across diverse quantum platforms. The coupling between a single qubit and a mesoscopic ensemble of spins, for example, can be leveraged to realize non-destructive detection of the qubit state. However, realizing robust couplings between such systems is experimentally challenging and typically requires programmable quantum gates or native long-range interactions. Here, we introduce a platform that couples a single qubit, encoded in the ground-to-Rydberg transition of a control atom, to a Rydberg-dressed target ensemble of ground-state atoms trapped in an optical lattice. We show that the state of the control qubit can be coherently mapped onto the ensemble via a qubit-controlled collective phase shift. By Rydberg-dressing the ensemble, the controlled phase shift per target atom becomes independent of the number of target atoms, making the protocol intrinsically insensitive to atom-number fluctuations and atom loss, which are the dominant experimental imperfections in our system. Exploiting the collective response of up to eight target spins, we demonstrate the efficacy of the scheme by realizing non-destructive detection of a single Rydberg excitation with a state-assignment fidelity of $\mathcal{F} = 99.81^{+0.17}_{-1.47}\,\%$. Our approach demonstrates the key ingredients for high-fidelity transfer of quantum information from a single qubit to a mesoscopic ensemble, opening a route to non-destructive mid-circuit readout of Rydberg states and to efficient interfaces between single qubits and photonic modes.
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All authors Kritsana Srakaew, Pascal Weckesser, Daniel Adler, Suchita Agrawal, David Gröters, Immanuel Bloch, Johannes Zeiher

Physics and Society

How a shared state is described determines whether AI agents synchronize

Takahiro Ezaki, Naoto Imura and Katsuhiro Nishinari

Language-model agents increasingly act in populations, where the outcome that matters is collective: whether they align, split or fail to coordinate. Each acts not on the world but on a text description of it, a choice usually fixed in software. Using synchronization, the canonical probe of how interaction rules produce collective order, we show that this choice can decide the outcome. Agents on a circle chose to advance, stay or move back after reading the others' relative positions, in 507,112 valid responses across matched populations, controlled inputs and three model families. In GPT, numerical summaries aligned every matched population at both positive couplings, whereas histograms aligned none; Claude showed the reverse at the stronger coupling. Re-describing identical states shifted action probabilities in all three families, even between histograms carrying the same information. No single directional coefficient explained the outcome: state descriptions are part of the interaction rule that turns individual responses into collective order.
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Materials Science

Spin-group theory on Edelstein effect and spin-orbit torque in Collinear Ferromagnets

Yizhuo Song, Qing Zhang, Jiahao Shentu et al. (+2 more)

Current-induced spin-orbit torques (SOTs) are central to the electrical manipulation of magnetic order in spintronic devices. In transition-metal/collinear ferromagnet bilayers, field-like and damping-like torques have been described only phenomenologically via the spin or orbital Hall effect, lacking a rigorous symmetry-based foundation. The precise role of spin-orbit coupling (SOC) in both the Edelstein effect and SOTs has remained unresolved. Here we develop a spin-group symmetry theory for the Edelstein effect and SOTs in collinear ferromagnets, treating SOC as a symmetry-breaking perturbation. For 4mm (C4v) point group symmetry, we derive the full forms of field-like and damping-like torques, which arise predominantly from first- and second-order SOC. We further show that SOTs in both orbital-Hall-dominated Ti/Ni and spin-Hall-dominated Pt/CoFe bilayers originate at first-order SOC. Taking the 3m (C3v) torque as a paradigmatic example, we elucidate the role of second- and higher-order SOC torques in field-free switching of perpendicular magnetic anisotropy. Remarkably, in PtMnSb, we demonstrate that SOTs under certain point group symmetries deviate from the conventional form: zeroth- and first-order SOC contributions vanish identically, with the leading SOT emerging at second order. All symmetry-based predictions from spin-group theory are in excellent quantitative agreement with first-principles calculations. Our work establishes a unified symmetry framework for the microscopic understanding of the Edelstein effect and current-induced spin torques in ferromagnetic systems.
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All authors Yizhuo Song, Qing Zhang, Jiahao Shentu, Jie Li, Jia Zhang

High Energy Physics (Phenomenology)

Probing dark matter through charged Higgs pair production at future multi-TeV muon colliders: A machine-learning analysis

Khiem Hong Phan and Quang Hoang-Minh Pham

Probing dark matter (DM) via charged Higgs pair production at future multi-TeV muon colliders is investigated within the Inert Doublet Model (IDM). The viable parameter space of the IDM is first updated by incorporating theoretical constraints and current experimental data. Based on the allowed parameter space, we evaluate DM relic density and compare the results with the latest constraints from direct DM detection experiments. The resulting parameter points consistent with all DM constraints are subsequently employed to study charged Higgs pair production at future multi-TeV muon colliders, including the subsequent decays of the charged Higgs bosons into Standard Model (SM) particles in association with DM candidate. In particular, we study the following production processes: $\mu^- \mu^+ \to \nu_{\mu} \bar{\nu}_{\mu} H^{\pm} H^{\mp} \to \ell^+ \ell^- + \nu_{\mu} \bar{\nu}_{\mu} \nu_{\ell} \bar{\nu}_{\ell} HH$, $\mu^- \mu^+ \to \nu_{\mu} \bar{\nu}_{\mu} H^{\pm} H^{\mp} \to \ell^\pm + 2\,\text{jets} + \nu_{\mu} \bar{\nu}_{\mu} \nu_{\ell} HH$ and $\mu^- \mu^+ \to \nu_{\mu} \bar{\nu}_{\mu} H^{\pm} H^{\mp} \to 4\,\text{jets} + \nu_{\mu} \bar{\nu}_{\mu} HH$ for $\ell =e, \mu$. The signal significance is evaluated against the corresponding SM backgrounds using both cut-based and machine-learning (ML) approaches. We find that ML framework substantially enhances the sensitivity to the signal processes compared with the conventional cut-based analysis. Furthermore, our results indicate that the DM signals through charged Higgs pair production can be indirectly probed with a statistical significance exceeding $5\sigma$ for several viable benchmark points at future multi-TeV muon colliders.
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