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Physics

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Friday 21 August

Computational Physics

Resolving positive semi-definiteness in physics-informed kernels for scientific machine learning

J. Moser, C. Albert and S. Ranftl

Many modern machine learning models can be understood as kernel-based function-space models, including Gaussian processes and neural tangent kernels. In scientific machine learning, differential operators are increasingly used to encode physical structure directly into such models. However, it has remained unclear under which conditions these constructions are valid machine learning models, i.e. preserve positive semi-definiteness, and whether observed instabilities arise from ill-posed modeling or numerical effects. Here, we establish a simple and sufficient condition for positive semi-definiteness: for linear differential operators of order m, the base kernel must be m-times continuously differentiable. Crucially, this guarantee holds for operators with non-constant and even discontinuous coefficients. Examples are ubiquitous in physical systems, including diffusion, material elasticity, wave propagation in inhomogeneous media, and quantum systems. We conclude that remaining instabilities are attributable to numerical issues, providing a unifying validity foundation for operator-informed kernel methods.
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Quantum Physics

A Classification of Translation-Invariant Quantum Codes in Any Dimension

Andrew Li and Dominic J. Williamson

Quantum error-correcting codes with two-dimensional translation invariance are known to be equivalent to copies of the two-dimensional toric code. Such a simple classification is not possible for quantum codes with higher dimensional translation invariance due to the existence of multiple types of toric codes and infinite families of fracton codes. Here, we focus on D-dimensional translation-invariant quantum codes based on length-D chain complexes. This includes multivariate multicycle codes where the number of variables equals the number of cycles. We show that such codes are equivalent to copies of D-dimensional toric codes. This directly generalizes the classification result for two-dimensional translation-invariant codes.
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Soft Condensed Matter

Polymer Genome in the Age of Artificial Intelligence

Jifeng Wang and Ying Wang

Artificial intelligence (AI) is redefining the landscape of polymer science. Although numerous AI applications have been introduced in this field, the roles of polymer encoding strategies and different applications of AI models in polymer design remain insufficiently understood. Here, we build upon the foundation of polymer databases to critically examine the performance and applicability of current encoding strategies across different use cases. We then focus on two major AI application domains, property prediction and inverse design, to evaluate the strengths, weaknesses and suitable scenarios for various model architectures. Finally, we emphasize the significance of the online platforms for promoting data accessibility and accelerating the migration from experience-based discovery toward AI-driven innovation in polymer science and engineering. Through these discussions, we aim to provide practical guidance for future research and development in AI-assisted polymer design.
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Materials Science

Quasi-one-dimensional topological band structure and van Hove singularities in monolayer TaIrTe$_4$ from laser $\mu$-ARPES

Honey Boban, Tanguy Prongué, Amarjyoti Choudhury et al. (+9 more)

Recent transport experiments reported a quantum spin Hall insulator phase in monolayer 1T-TaIrTe$_4$ gated away from charge neutrality. This phase is not predicted by band structure calculations and has been attributed to an electronic instability induced by strong correlations at a putative van Hove singularity. Here, we investigate the electronic structure of exfoliated monolayer 1T-TaIrTe$_4$ using micro-focus laser angle resolved photoemission. We find a strongly anisotropic band structure susceptible to density wave instabilities. Our data further reveal a saddle point singularity in the density of states. However, we find that the saddle point lies at a density for which transport experiments found no anomalies. Moreover, the quasiparticle line widths suggest weak electron correlations only. This points to a secondary role of van Hove singularities and electron correlations in the transport phase diagram of monolayer 1T-TaIrTe$_4$.
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All authors Honey Boban, Tanguy Prongué, Amarjyoti Choudhury, Dario Marchiani, Andrés Bareño, Felix Eder, Enrico Giannini, Fabian O. von Rohr, Alberto F. Morpurgo, Marco Gibertini, Anna Tamai, Felix Baumberger

General Relativity and Quantum Cosmology

Conformal flatness selects a universal isothermal attractor in pure Lovelock gravity

Sudan Hansraj

We determine the complete solution set of the conformally flat isotropic pure Lovelock field equations for every order $N\ge2$ and every admissible dimension $d\ge2N+1$. Conformal flatness and pressure isotropy combine into a single identity that factorises exactly, splitting the solutions into two branches. The first is the constant-density Schwarzschild interior, which persists at every order with both metric potentials keeping their Einstein form. The second has no Einstein counterpart and is governed by the single dimension–order parameter $k=(d-2N)/[4(1-N)]$; we obtain its physically admissible orbit in explicit closed parametric form, both potentials included. A phase-space analysis on the projective line shows that no solution of this branch has a pressure-free boundary at finite radius, so only the Schwarzschild branch can describe a bounded star. The second instead loses all memory of its central data and relaxes onto a pure Lovelock isothermal sphere with $\rho\propto r^{-2N}$, a higher-curvature analogue of the singular isothermal halo, which we show to be the attractor of the whole family, approached at the closed-form rate $\lambda_*=-(d-2)/(d-2N)$ and with limiting equation of state fixed by $(d,N)$ alone. We prove that $p/\rho$ increases monotonically outward there, and that of the two regular-centre orientations only one is admissible. Since $k$ is rational the spatial potential is algebraic of degree $u+v$, where $2k=-u/v$; radical inversion is guaranteed for degree at most four, while four representative cases have full symmetric Galois group.
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Materials Science

Scalable Cyclic Olefin Copolymer Encapsulation for High Optical Quality of TMD Monolayers

Suprova Das, Md Tarik Hossain, Zlata Fedorova et al. (+8 more)

Monolayer transition metal dichalcogenides (TMDs) combine a direct bandgap, strongly bound excitons, and pronounced second-order optical nonlinearity, which makes them promising materials for ultrathin optoelectronic and nanophotonic devices. However, their optical performance is often degraded by environmental exposure and substrate-induced charge trapping, motivating the development of scalable encapsulation strategies. Here, we investigate spin-coated cyclic olefin copolymer (COC) as a scalable encapsulant for TMDs. Room-temperature and cryogenic optical spectroscopy reveal enhanced photoluminescence and second-harmonic generation, accompanied by excitonic linewidth narrowing and an increased exciton-to-trion ratio. In addition, COC encapsulation induces an excitonic peak splitting and an overall spectral blueshift. First-principles calculations attribute these spectral modifications to local symmetry breaking at the chalcogen interface and macroscopic compressive strain, respectively. These findings establish spin-coated COC as an effective, scalable encapsulation strategy and a potential platform for post-growth excitonic and band-structure engineering.
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All authors Suprova Das, Md Tarik Hossain, Zlata Fedorova, Zifei Zhang, Axel Printschler, Begimai Adilbekova, Honey Jayeshkumer Shah, Stefan Velja, Caterina Cocchi, Andrey Turchanin, Isabelle Staude

Computational Physics · Cross-listed from eess.AS

Training DeepFilterNet with Accurate Room Acoustic Simulations Improves Single-Channel Speech Enhancement

Alessia Milo, Georg Götz, Steinar Gu{\dh}jónsson et al. (+3 more)

We investigate how the realism of synthetic room impulse response (RIR) datasets affects the training of DeepFilterNet3 for single-channel speech enhancement. We compare a DNS4 image-source-method (ISM) RIR dataset with a higher-acoustic-fidelity dataset generated using hybrid wave-based and geometrical acoustics simulation. Rather than isolating individual simulation factors, we compare complete RIR generation pipelines while keeping the enhancement model unchanged. Models are evaluated on unseen measured RIRs using objective speech enhancement metrics and downstream automatic speech recognition (ASR). Training with the higher-fidelity dataset consistently yields modest improvements in objective metrics and substantially lower ASR word error rates than the ISM dataset. Although the experiments do not attribute these gains to individual modelling components, they show that increasing the overall realism of synthetic acoustic training data improves the generalization of DeepFilterNet3 to unseen measured environments.
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All authors Alessia Milo, Georg Götz, Steinar Gu{\dh}jónsson, Daniel Gert Nielsen, Jesper Pedersen, Finnur Pind

Optics

Direction-Selective Wave Freezing and Amplification at a Hyperbolic Time Interface

Zhao Wang, Ai Gang, Xinghong Zhu et al. (+3 more)

Hyperbolic media are well known for converting high k-components that are evanescent in conventional dielectrics into propagating bulk waves through their open equifrequency contours. Here, we reveal a complementary temporal effect: after a sudden transition into an effectively nondispersive hyperbolic state, conservation of the full wavevector causes the indefinite dispersion to partition momentum space into real-, zero-, and purely imaginary-frequency regimes. Consequently, p-polarized waves undergo conventional temporal scattering, critical magnetic-field freezing, or exponential growth and decay, depending solely on their conserved wavevector direction, whereas s-polarized waves remain in the real-frequency regime. A second temporal boundary releases the frozen or amplified fields into propagating waves at original frequency. Analytical temporal boundary theory, k-space pulse reconstruction, and finite-difference time-domain simulations corroborate these dynamics. These results establish hyperbolic temporal boundaries as a compact route to direction-selective imaginary frequency dynamics and wave amplification without Floquet periodicity.
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All authors Zhao Wang, Ai Gang, Xinghong Zhu, Hongru Ma, Wen Xiao, Huanyang Chen

Materials Science

Broken Inversion Symmetry via a Magic Methyl Effect

Calum J Gibb, Jordan Hobbs, Caitlin O Brien et al. (+4 more)

Polar liquid crystals - fluid phases in which molecular dipoles organise into ferro- or antiferroelectric states - present a highly constrained molecular design space, where small changes can entirely suppress polar organisation. Here we demonstrate, contrary to expectations, that installation of a methyl group in the 5-position of a 1,3-dioxane ring substantially increases the onset temperature of polar order. Remarkably, this effect proves transferable across several liquid-crystal families, including examples where the methylated derivative exhibits a polar phase whereas its parent compound does not. Across 8 matched pairs, we find that a 5-methyl group can enhance the onset temperature of polar order in 1,3-dioxane materials by up to 120 {\deg}C. These findings establish a simple and general molecular design strategy for enhancing and enabling spontaneous dipolar ordering in liquid crystals.
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All authors Calum J Gibb, Jordan Hobbs, Caitlin O Brien, Kate Hille, Benji Maher, Christopher M Pask, Richard J Mandle

Chaotic Dynamics

Identifying the structure of dynamical transitions in logistic map

Aswin Balaji, Shruti Tandon, Shwetha Viswesh et al. (+3 more)

Nonlinear dynamical systems manifest rich variety of dynamical states and transitions driven by fluctuations. To understand the pattern of fluctuations during dynamical transitions, we investigate the structural features of chaos to order transition in logistic map. We determine fluctuations as amplitude jumps and encode them onto a complex network where nodes represent amplitude levels and links represent transitions between distinct amplitude bins. We discover that global network measures identify points of period doubling, regimes of periodicity and chaos, including interior crises events. Using local network measures, we also unravel novel peculiar parabolic-shaped patterns in the orbit diagram that we show are reminiscent of the distribution of stable and unstable periodic points in the bifurcation diagram.
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All authors Aswin Balaji, Shruti Tandon, Shwetha Viswesh, Norbert Marwan, Juergen Kurths, R. I. Sujith

Quantum Physics

Tools for Reducing Service Time in Near-Term Quantum Networks

Jake Smith, Thomas R. Beauchamp, Scarlett Gauthier et al. (+2 more)

Architectures have been proposed to control entanglement generation in multi-user quantum networks. To allow time for local operations and classical communication at end nodes, these architectures insert fixed separations between consecutive batches of entanglement generation attempts. This reduces network utilization when attempts fail, leaving the network idle during the scheduled separation. To address this limitation, we propose a novel method to reclaim this idle time by shortening the scheduled separation between attempts while respecting hardware constraints. The method uses an analytical execution model to optimize the separation and reduce the total network service time of an application. Evaluations within the Arqon architecture show network service time reductions of up to 42 minutes (7.6%) for single applications and 16-29 minutes (26-30%) per application when co-scheduled. The approach applies broadly to quantum network architectures that share hardware between entanglement generation and local operations, and the method can be used online by network schedulers.
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All authors Jake Smith, Thomas R. Beauchamp, Scarlett Gauthier, Oumayma Bouchmal, Stephanie Wehner

Fluid Dynamics

A Low-Fidelity Method for Aerofoil Shape Optimisation for Curvilinear Blade Kinematics

Benjamin Irwin, David Toal and Swathi Krishna

This study develops a low-fidelity framework for aerofoil shape optimisation under curvilinear blade kinematics, using a hovering cyclorotor as a representative case. Aerofoil optimisation can improve cyclorotor efficiency by suppressing leading-edge vortex separation during dynamic stall, but conventional approaches rely on computationally expensive CFD-based optimisation. The proposed method uses a single-streamtube model to estimate the rotor throughflow and optimises the aerofoil camberline using separate leading- and trailing-edge criteria. Assessed across configurations with varying blade counts and chord lengths, the framework consistently identifies aerofoils that improve hover efficiency, quantified by Figure of Merit. For the baseline four-bladed configuration, the low-fidelity optimum achieves 77% of the Figure of Merit improvement obtained using high-fidelity optimisation at a fraction of the computational cost. The analysis also reveals an additional torque-minimising design family at increased chord lengths, highlighting the influence of trailing-edge loading. Aerofoil optimisation is also compared to blade-pitch kinematics optimisation, which improves the efficiency through similar control of the leading-edge vortex separation. While both approaches produce comparable improvements in efficiency, the optimised kinematics substantially reduces thrust. Aerofoil optimisation may therefore be more practical, as maintaining a target thrust with optimised pitch kinematics would require higher rotational speeds, potentially introducing structural and noise issues.
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Earth and Planetary Astrophysics

The impact of tidal locking on Earth-like planetary dynamos

J. P. Hidalgo and D. R. G Schleicher

We investigate how tidal locking affects the planetary dynamo and the magnetospheres of Earth-like planets orbiting the habitable zones of M dwarfs. We couple an empirical stellar wind model with two distinct planetary dynamo paradigms, direct rotational scaling and energy-flux scaling, using a Constant Time Lag (CTL) model to simulate continuous tidal spin-down until synchronization. We model two hypothetical planets based on a highly dissipative Modern Earth and a less dissipative, rapidly rotating Early Earth representative of the Paleoarchean. Our results show that tidal locking acts as a severe negative feedback on planetary magnetism across both paradigms, where the dipolar field frequently collapses before full tidal synchronization is reached. Essentially, a shielded atmospheric environment around M dwarfs requires a host massive enough ($\geq 0.32 M_\odot$) to place the HZ at wider orbital distances, sparing the planet from the sub-Alfvénic environment, and the internal tidal dissipation of the planet must be sufficiently low to prevent rapid rotational decay. For mid-to-late M dwarfs, the inevitable tidal locking and the extreme stellar wind pressures result in a total collapse of the magnetic shield, reducing the likelihood of atmospheric protection to essentially zero across the habitable zone.
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Atmospheric and Oceanic Physics

A Graph Neural Network Framework for Characterizing Rainfall Variability Regimes across India

Pradyumnan Raghuveeran, Gaurav Chopra, Ajay Bankar et al. (+1 more)

The Indian Summer Monsoon shows significant spatial variation. While prior work primarily focused on forecasting rainfall amounts, little attention has been given to how consistently a location's seasonal rainfall trajectory repeats from year to year. We introduce a graph-based machine learning framework to classify locations across India by this inter-annual consistency. Using 2001 to 2022 GSMaP ISRO data (excluding 2012), we constructed graphs for 29,026 grid points where nodes represent individual years and edges denote cosine similarity. A Graph Convolutional Network classified locations as either consistent or erratic with 96.8% accuracy. Applied to the Indian landmass, the model successfully identified the Western Ghats, Northeast India, and parts of central India as consistent regions. This classification was rigorously validated through statistical testing and temporal stability analysis, showing 93.6% agreement across two independent timeframes. Crucially, the results reveal a previously unreported coupling: regions with higher rainfall volumes are also the most temporally repeatable year-to-year, demonstrating an emergent, spatially coherent structure.
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All authors Pradyumnan Raghuveeran, Gaurav Chopra, Ajay Bankar, R. I. Sujith

Nuclear Theory

Fresh Look at Polarized Deuterons at the Nuclotron/NICA & HIAF and Beyond

B. Gou, V.P. Ladygin, N.N. Nikolaev et al. (+3 more)

Being a spin-1 particle, the deuteron, when polarized, offers access to a wide range of interesting tensor observables. A quest for tensor asymmetries is at the heart of the spin physics with polarized deuterons at future colliders, and calls for frequent tensor polarization flips in storage rings or in deuterium targets. Here we focus on the JEDI developed technique of the Fourier analysis of the horizontal polarization oscillations under continuous radiofrequency driven spin flips. The so generated time-stamped oscillating helicity of stored particles paves the way to the nucleon/nucleus spin structure studies and to the search for the parity violation. Simultaneously a whole set of tensor spin asymmetries, including the off-diagonal ones needed for searches for the T-violation beyond the Standard Model, will be produced. A crucial ingredient is a long polarization lifetime, and we report the first analytic treatment of decoherence of the tensor polarization under continuous radiofrequency spin flips. Our principal conclusion is that at low- and intermediate-energy accelerators the deuteron polarization lifetime could be in the ballpark of several hours, making the oscillating polarization approach viable at Nuclotron/NICA and HIAF. We comment on a utility of the flattop spin-tensor dichroism via oscillations in the cross section of interaction of deuterons in the internal target as a monitor of the tensor polarization. Simultaneously, the dichroism effect can be used for measuring the spin precession frequences and as a comagnetometer to synchronize spin phases of colliding bunches in a collider.
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All authors B. Gou, V.P. Ladygin, N.N. Nikolaev, F. Rathmann, A.J. Silenko, Y.N.Uzikov

Mathematical Physics · Cross-listed from cs.CV

LHMCF-Net: A Learned Hyperbolic Mean Curvature Flow Network for Medical Images Segmentation

Shuangshuang Duan, Chunlei He, Shoujun Huang et al. (+1 more)

Motivated by the classical Chan-Vese model and the ability of deep priors to capture complex spatial structures, we develop a segmentation model that leverages learned hyperbolic mean curvature flow (LHMCF) as a mathematical foundation for integrating feature space data fidelity and deep structural priors within a unified high-dimensional framework. The proposed LHMCF model is governed by a second-order dissipative hyperbolic PDE, where the introduction of a velocity field provides inertia and momentum to the evolving interface. This hyperbolic mechanism enables the contour to bypass noise-induced local minima and propagate coherently through low-contrast or ambiguous regions, addressing limitations inherent to first-order parabolic flows. To solve the continuous LHMCF model, we construct a deep unfolding network, named LHMCF-Net, which maps the iterative numerical procedure of the PDE into a sequence of discrete evolution stages. Each stage corresponds to one physically interpretable update of the underlying dynamical system, allowing the network to inherit the stability and geometric consistency of the PDE while supporting end-to-end optimization. Comprehensive experiments on three publicly available medical segmentation datasets demonstrate that LHMCF-Net achieves superior performance, particularly in challenging scenarios with low contrast and unclear boundaries. These results highlight the effectiveness of embedding hyperbolic geometric evolution into deep unfolding architectures and underscore the potential of physically inspired models for robust medical image segmentation.
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All authors Shuangshuang Duan, Chunlei He, Shoujun Huang, Dexing Kong

Mesoscale and Nanoscale Physics

Interedge backscattering in quantum spin Hall-based NS and SNS junctions

Cajetan Heinz, Patrik Recher and Fernando Dominguez

We investigate the microscopic conditions that allow for the coupling between opposite quantum spin Hall (QSH) edges in hybrid junctions with superconductors. Using a microscopic Bernevig–Hughes–Zhang model and the Bogoliubov–de Gennes formalism, we model a potential barrier along the NS interface and identify the parameter regimes in which the QSH edges are coupled. In normal–superconductor junctions, such coupling manifests as deviations from the quantized zero-bias Andreev conductance $G=4e^2/h$. These deviations are controlled by the induced gap in the barrier, the barrier geometry, the interface transparency, orbital and Fermi-velocity mismatch, and disorder strength as well as the bias voltage leading to a zero-bias peak. We then analyze the impact of this interedge-coupling mechanism in Josephson junctions at equilibrium and show that it hybridizes the edge-resolved Andreev branches, opens gaps at the time-reversal-invariant phase differences $\varphi=0$ and $\varphi=\pi$, and modifies the superconducting quantum interference pattern. In a reflection-symmetric geometry, the relative sizes of the two gap openings provide complementary information about the interedge dynamical phase, which also determines the parity of the suppressed lobes in the magnetic interference pattern. This investigation sheds light on the microscopic details that control the coupling of helical edge states in actual devices and the resulting consequences for superconducting hybrid systems.
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Chaotic Dynamics

Data-Driven Characterisation of Wave-Forced Turbulence Using Time-Resolved Forecast-Error Growth

Raj Jyoti Baishya, Joychen Kenglang, Andrei Velichko et al. (+1 more)

Periodic surface-wave forcing can reorganise turbulent flows through coherent spectral response, synchronization, intermittency, and changes in short-term predictability, so its dynamical effect need not vary monotonically with forcing frequency. We reanalyse laboratory acoustic Doppler velocimetry records obtained at constant discharge under four conditions (0, 0.5, 0.67, and 1~Hz) using one common KNN–GMAE forecast-error-growth protocol. A distance-weighted $k$-nearest-neighbour predictor generates out-of-sample forecasts over multiple horizons, and the slope of the early quasi-linear region of $\ln(\mathrm{GMAE})$ versus physical forecast time is reported as a finite-horizon forecast-error-growth rate, $\lFEG$. For the full 120-s records, $\lFEG$ is 5.68, 0.85, 3.39, and 4.11~s$^{-1}$ for 0, 0.5, 0.67, and 1~Hz, respectively. The ordering 0~Hz $>$ 1~Hz $>$ 0.67~Hz $>$ 0.5~Hz is preserved in all seven nearby parameter configurations, indicating that the comparative result is not an artefact of a single KNN setting. A 40-s sliding-window analysis with a 10-s step reveals substantial temporal structure. The no-wave condition remains predominantly high and the 0.5-Hz condition predominantly low, whereas the 1-Hz record has weaker local support for a single exponential-growth regime: only 3 of 9 windows satisfy the adopted early-fit criterion $\RFEG\geq0.90$, compared with 8/9, 7/9, and 7/9 for 0, 0.5, and 0.67~Hz.
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All authors Raj Jyoti Baishya, Joychen Kenglang, Andrei Velichko, Bimlesh Kumar

Other Condensed Matter

Artificial spin ice systems on single edge length tilings

Ellie Weightman and Sam Coates

Artificial spin ices (ASIs) are decorations of single domain nanomagnets on geometric lattices allowing for study of magnetic interactions on easily varied lattice geometries. We extend the study of ASIs on single rhomb tilings by simulating an ASI with the aperiodic hexagonal $H_{\frac{1}{2}\frac{1}{2}}$ tiling as the base structure, and the periodic dice lattice for additional comparison. Using a point dipole metropolis Monte Carlo approach, we cool our arrays of nanoislands to form a low energy configuration, assessing individual vertex excitations as identified through complementary micromagnetic simulations. Using the energy and charge landscape of final spin states, we propose a potential ground state spin configuration for the aperiodic system.
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High Energy Physics (Theory)

Finite Weyl polynomials and the approach to Tsirelson's bound in relativistic scalar quantum field theory

J. G. A. Caribé, M. S. Guimaraes, I. Roditi et al. (+1 more)

We construct four bounded Hermitian operators, each one a finite polynomial in the unitary Weyl operators, for the Bell-CHSH inequality in a free massive scalar field in $1+1$ dimensions. The operators are localized in complementary wedges. Odd Weyl harmonics provide two exactly anticommuting axis observables in each wedge, while normalizable packets with compact support in the spectrum of the boost generator give exact modular inner products at nonvanishing bandwidth. The resulting Bell-CHSH correlator is a finite double sum. An operator with six Weyl terms per axis already gives $2.14885$. Using normalized Fejér approximants of $\operatorname{sgn}(\cos(x))$, we show that the supremum over the finite-polynomial family equals $2\sqrt{2}$, although no finite member attains it; a degree-$511$ example gives $2.80027$. We also point out that, in a centered quasifree state, a Bell-CHSH test whose four final settings are bounded functions of individual quadratures admits one common Gaussian representation and therefore stays below $2$. The finite-Weyl construction avoids this restriction because Bob's final settings mix two noncommuting axis observables.
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All authors J. G. A. Caribé, M. S. Guimaraes, I. Roditi, S. P. Sorella

Optics

High-Resolution Speckle-based Single-Pixel Imaging using Silicon Photonic Non-Redundant Optical Phased Array

Keita Hirashima, Taichiro Fukui, Kento Komatsu et al. (+3 more)

Optical phased arrays (OPAs) are promising wavefront controlling devices for imaging applications due to their compact and high-speed nature. However, conventional periodic OPAs have a limited spatial resolution, which scales only linearly with the number of optical antennas $N$. Here, we experimentally demonstrate high-resolution imaging using a non-redundant OPA (NR-OPA). Due to the non-redundant antenna layout of NR-OPA based on the Costas array, the resolution scales quadratically with $N$. Combined with the speckle-based single-pixel imaging (SSPI) scheme, which avoids the need for precise phase calibration, we experimentally achieve a large number of resolvable imaging points exceeding 10,000 using a silicon photonic NR-OPA chip with only $N=127$ without sweeping the wavelength. The demonstrated scheme provides a promising route toward mega-pixel imaging by a compact OPA chip with reduced number of phase shifters.
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All authors Keita Hirashima, Taichiro Fukui, Kento Komatsu, Chun Ren, Yoshiaki Nakano, Takuo Tanemura

High Energy Astrophysical Phenomena

Hyperonic compact stars with vector portal dark matter

Prafulla K. Panda, Deepak Kumar, Hiranmaya Mishra et al. (+1 more)

The appearance of hyperons in the core of neutron stars generally softens the equation of state (EOS), posing a longstanding challenge to the existence of observed two-solar-mass compact stars. We investigate whether repulsive interactions mediated by a dark-sector vector portal can provide an additional source of high-density pressure and thereby modify the structure of hyperonic compact stars. The baryonic sector is described within the modified quark-meson coupling (MQMC) model, in which the octet baryons are treated as confined relativistic constituent-quark systems interacting self-consistently through the $\sigma$, $\omega$, and $\rho$ fields within a mean field approximation. The dark sector consists of a fermionic dark matter coupled to baryonic matter through a neutral vector mediator $Z^\prime$, generating an additional repulsive contribution to the dense-matter EOS. We investigate the resulting equation of state, mass–radius relation, tidal deformability, and moment of inertia. The resulting mass–radius relations satisfy the observational bounds from massive pulsars, including PSR J0740 + 6620, with maximum neutron star masses reaching approximately $2 M_{\odot}$. The resulting changes in tidal and rotational observables provide additional avenues for testing the dark-sector interaction through multimessenger observations.
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All authors Prafulla K. Panda, Deepak Kumar, Hiranmaya Mishra, Sudhanwa Patra

Disordered Systems and Neural Networks

The Trachenko-Zaccone equation: nonlinear relaxation from glasses to complex systems

Alessio Zaccone, Valeriy V. Ginzburg, Oleg V. Gendelman et al. (+2 more)

The Trachenko-Zaccone equation provides a compact nonlinear dynamical framework for describing non-Debye relaxation in disordered condensed matter. Originally developed to rationalize stretched- and compressed-exponential relaxation in liquids and glasses from the dynamics of interacting local relaxation events, the same equation has subsequently appeared in broader contexts, including polymer relaxation and nonlinear models of global population dynamics. This review retraces the conceptual development of the equation, with particular emphasis on its physical origin in Kostya Trachenko's feed-forward interaction mechanism, its mathematical structure, and its possible generalizations. We also include personal recollections of the work with Kostya Trachenko at Queen Mary University of London in August 2019, during which the equation emerged in essentially its present form. After reviewing applications to stress relaxation, glassy materials, polymer relaxation and population dynamics, we discuss future directions including time-dependent feedback parameters, coupled order parameters, heterogeneous and spatially resolved formulations, flux terms, network versions and stochastic extensions. The central theme of the review is that the Trachenko-Zaccone equation should be viewed not only as a model of glassy relaxation, but as a general nonlinear feedback equation with potential applications across complex systems.
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All authors Alessio Zaccone, Valeriy V. Ginzburg, Oleg V. Gendelman, Sofia F. Mauro, John C. Mauro

Chemical Physics

Orbital-Optimized Quasi-Variational Distinguishable Cluster Doubles Method

Fangcheng Wu and Daniel Kats

We present the orbital-optimized quasi-variational distinguishable cluster doubles (OQVDCD) method, obtained by applying the distinguishable cluster (DC) approximation to orbital-optimized quasi-variational coupled cluster doubles (OQVCCD). The resulting method retains a Hermitian-like energy functional, is size-extensive, obeys the generalized Hellmann-Feynman theorem at a stationary point, is exact in the isolated two-electron and two-hole limits, and scales as O(o2v4), like coupled cluster singles and doubles (CCSD). For the tested closed-shell reaction energies, it is shown that OQVDCD reduces the mean absolute deviation relative to OQVCCD from 1.20 to 0.81 kcal/mol, bringing the errors close to distinguishable cluster singles and doubles (DCSD). In the strongly correlated examples considered here, OQVDCD shifts the OQVCCD energies toward the benchmark, although the convergence remains somewhat less robust than for DCSD.
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Astrophysics of Galaxies

Ultra-Deep imaging of the starless galaxy candidate Cloud-9

Ignacio Trujillo, Ignacio Ruiz Cejudo, Sergio Guerra Arencibia et al. (+1 more)

We report the non-detection of stellar light associated with the dark galaxy candidate Cloud-9. Ultra-deep imaging obtained with HiPERCAM at the Gran Telescopio Canarias (GTC) reaches surface-brightness limits of 31.4 and 31.0 mag/arcsec$^2$ in g and r, respectively, approximately ten times deeper than previous deep imaging of the region. No stellar emission is detected within the central 1'$\times$1' ($\sim$1.3$\times$1.3 kpc) region of Cloud-9. Assuming an old, metal-poor stellar population, these limits imply a stellar surface mass density of no more than $\sim$0.01 M$_\odot$/pc$^2$ and an upper limit on the total stellar mass of 1.6$\times$10$^4$ M$_\odot$. This independent constraint from integrated light complements previous limits based on resolved-star counts and strengthens the case for Cloud-9 as a candidate starless galaxy.
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All authors Ignacio Trujillo, Ignacio Ruiz Cejudo, Sergio Guerra Arencibia, Mireia Montes

Solar and Stellar Astrophysics

The DIRECD coronal mass ejection direction catalog: three-dimensional propagation inferred from coronal dimmings

Shantanu Jain, Tatiana Podladchikova, Karin Dissauer et al. (+2 more)

Coronal mass ejections (CMEs) are among the primary drivers of space weather disturbances at Earth, yet their early propagation in the low corona remains poorly constrained owing to occultation and projection effects inherent to coronagraph observations. Coronal dimmings offer an alternative diagnostic to infer CME propagation direction directly from the low corona. We present the DIRECD CME Direction Catalog, a unified dataset of three-dimensional CME propagation directions derived via the DIRECD (Dimming Inferred Estimation of CME Direction) method, which reconstructs CME cone geometry from SDO/AIA 211 Å\ coronal dimming observations. The catalog comprises 64 events spanning 2010-2026, combining 31 Solar Cycle 25 (2021-2026) events with 33 events from prior studies. For each event we report the 3D propagation direction, 2D inclination angles, angular width, and cone height. Statistical analysis reveals a systematic asymmetry in low-coronal CME propagation: meridional inclinations exhibit a systematic tendency toward latitude-dependent deflection, with poleward deflections more pronounced at higher source latitudes, while equatorial inclinations show no significant dependence on source longitude. This is consistent with low-coronal CME trajectories being governed primarily by local active-region magnetic topology, with the large-scale coronal field and heliospheric current sheet assuming a progressively dominant role at greater heliocentric distances. Incorporating DIRECD-derived propagation directions into CME arrival forecasts improves predictions of geomagnetic storm intensity, raising the correlation with observed storm strength from r = 0.58 to r = 0.70 when combined with CME speed. The DIRECD software, catalog, and all associated data products are publicly available to support space weather research.
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All authors Shantanu Jain, Tatiana Podladchikova, Karin Dissauer, Astrid Veronig, Amaia Razquin

Materials Science

Systematic and accurate anharmonic formation free energies of metastable defects via a constrained Bayesian Adaptive Biasing Force framework

Clovis Lapointe, Anruo Zhong, Manuel Athènes et al. (+1 more)

Computing the formation free energies of metastable defects at finite temperature remains challenging due to anharmonicity, the multiplicity of basins and the frequent occurrence of migration events. Using the previously introduced constrained Bayesian Adaptive Biasing Force method (BABFc), we establish a practical thermodynamic integration framework for computing restricted anharmonic formation free energies associated with individual metastable defect basins. We demonstrate that BABFc can be exploited as a robust, systematic and numerically efficient tool for addressing a long standing bottleneck in atomistic materials science: the finite temperature thermodynamic characterization of metastable defects in complex, highly anharmonic energy landscapes. The proposed workflow requires only a reference local minimum and a confinement strategy and does not rely on defect specific collective variables. It therefore provides a general route to assign well-defined free energies to individual metastable basins, even when these basins are separated by low barriers and embedded in a dense landscape of competing configurations. In this setting, BABFc enables stable, bias corrected free energy estimates with statistical accuracies at the meV/atom level and a very low failure rate, including for systems containing approximately one thousand atoms. We demonstrate this capability through thousands of independent free energy calculations covering hundreds of four-interstitial and four-vacancy configurations in bcc $\alpha$-Fe over a broad temperature range, using both a traditional empirical potential and a data driven force field.
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All authors Clovis Lapointe, Anruo Zhong, Manuel Athènes, Mihai-Cosmin Marinica

Plasma Physics

Reinforcement learning for vertical position control on the EXL-50U spherical tokamak

Lei Xing, Huicong Ma, Changquan Yu et al. (+14 more)

Vertical position control is essential for sustaining high-performance operation in spherical tokamaks, where increased plasma elongation introduces stringent requirements on fast and robust stabilization. This work presents an experimentally validated reinforcement-learning(RL)-based vertical position control framework for the EXL-50U spherical tokamak. A high-fidelity discharge-reconstructed simulation environment is developed by integrating physics-based plasma-circuit models with experimental equilibrium information, enabling systematic controller synthesis and sim-to-real evaluation. Within this framework, RL is benchmarked in simulation against operational proportional–integral–derivative (PID) and model-based linear quadratic regulator (LQR) controllers under identical plant dynamics, actuator constraints, and measurement imperfections.Simulation results show that RL achieves tracking accuracy comparable to PID with consistently lower vertical-stabilization coil effort, while lightweight integral compensation improves robustness against residual model–plant mismatch. The RL controller is subsequently deployed on EXL-50U for closed-loop experiments. Across more than ten discharges with RL takeover, stable vertical regulation is achieved within the controlled windows. For seven representative discharges, RL maintains millimetre-scale tracking accuracy comparable to the operational PID controller (MAE typically ~ 1-5 mm) while consistently reducing actuator effort. These results demonstrate the feasibility of learning-based plasma control on a real spherical tokamak and establish a practical pathway toward future fusion control systems.
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All authors Lei Xing, Huicong Ma, Changquan Yu, Xuanhe Wang, Jiayi Zhi, Pei Guo, Mengyao Li, Zhengyuan Chen, Yapeng Zhang, Guoyang Shi, Dongkai Qi, Xiang Gu, Siqi Ding, Yong Liu, Jianguo Chen, Tianyuan Liu, the EXL-50U Teama

Instrumentation and Methods for Astrophysics

EXPO: a quantum leap in fast, wide-band X-ray polarimetry for astrophysics

Paolo Soffitta, Sebastien Guillot, Ian Hutchinson et al. (+137 more)

The Enhanced X-ray Polarimetry Observatory (EXPO) is a mission concept proposed to ESA as an M8 candidate, with a prospective launch in 2041. Building on the scientific success of IXPE, EXPO is designed to overcome its two main limitations, the narrow 2-8 keV energy band and the very slow repointing time, and to enable new scientific capabilities. A wide energy band and fast repointing are essential for investigating the hard X-ray emission of magnetars and black-hole binaries, particle acceleration in supernova remnants and pulsar-wind nebulae, radiative transfer in highly magnetized plasmas, X-ray reflection in accretion flows and active galactic nuclei, and the prompt and afterglow emission of gamma-ray bursts and magnetar flares. EXPO comprises five focusing X-ray telescopes and gas photoelectric polarimeters based on the Timepix ASIC family with InGrid amplification, enabling three-dimensional track imaging and operation in the 2-35 keV band through optimized low- and medium-energy detector configurations. The mirror modules use proven electroformed nickel technology with Au-C coatings and an XMM-like focal length of 7.5 m. The polarimeters are complemented by a coded-mask Wide Field Instrument (WFI), derived from SVOM/ECLAIRs for continuous monitoring of a 2 sr field of view; a Spectral Imaging Camera (SIC), based on stacked CMOS and CdTe detectors for broadband imaging spectroscopy and accurate spectro-polarimetric decomposition; and an Instrument Control Unit (ICU) for payload management, onboard WFI image reconstruction, transient identification, and autonomous spacecraft repointing requests. These capabilities extend X-ray polarimetry into the hard X-ray domain and open a new observational window on fast transients, time-domain astrophysics, and multi-messenger astronomy.
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All authors Paolo Soffitta, Sebastien Guillot, Ian Hutchinson, Fabio Muleri, Mark Pearce, Andrea Santangelo, Daniele Spiga, Ivan Agudo, Gino Bruno Amata, Jaroslaw Bakala, Elisabetta Baracchini, Stefano Basso, Jorg Bayer, Benedikt Bergmann, Jaroslaw Borek, Enrico Bozzo, Soren Krinstian Brandt, Carl Budtz-Jorgensen, Vadim Burwitz, Stefano Cesare, Jerome Chenevez, Enrico Costa, Elisa Costantini, Vincenzo Cotroneo, Walter Cugno, Riccardo Ferrazzoli, Nicolas De Angelis, Desiree Della Monica Ferreira, Klaus Desch, Giorgio Dho, Giuseppe Di Persio, Sergio Fabiani, Davide Fiorina, Szymon Gburek, Markus Gruber, Allan Hornstrup, Jennifer Jones, Jochen Kaminski, Mozsi Kiss, Irfan Kuvvetli, Carlo Lefevre, Hannah Lerman, Honghui Liu, Pasqualino Loffredo, Niels Lund, Hemanth Manikantan, Melissa McHugh, Paul O'Brien, Stephane Paltani, Giovanni Pareschi, Stefano Piacentini, Vladislavs Plesanovs, John Rankin, Ajay Ratheesh, Selina Ringsborg Howalt Owe, Alda Rubini, Miguel Andres Sanchez Carrasco, Emanuele Scalise, Konrad R. Skup, Gianpiero Tagliaferri, Chris Tenzer, Berend Winter, Silvia Zane, Lorenzo Amati, Alessio Anitra, Maria Cristina Baglio, Thibault Barnouin, Stefano Bianchi, Fabrizio Bocchino, Markus Boettcher, Niccolo Bucciantini, Sara Capecchiacci, Fiamma Capitanio, Martina Cardillo, Eugene Churazov, Stefano Covino, Filippo D'Ammando, Laura Di Gesu, Alessandro Di Marco, Tiziana Di Salvo, Michal Dovciak, Lorenzo Ducci, Hua Feng, Giorgio Galanti, Giancarlo Ghirlanda, Vittoria Elvezia Gianolli, Andrea Gnarini, Emanuele Greco, Jeremy Heyl, Adam Ingram, Svetlana Jorstad, Philip Kaaret, Ildar Khabibullin, Fabian Kislat, Henric Krawczynski, Josefin Larsson, Ioannis Liodakis, Frederic Marin, Andrea Marinucci, Lorenzo Marra, Alan Marscher, Herman Marshall, Giorgio Matt, Marco Miceli, Riccardo Middei, Romana Mikusincova, Alexander Mushtukov, Kirpal Nandra, Lara Nava, Giuseppe Maria Oppedisano, Salvatore Orlando, Simone Pagliarella, Alessandro Papitto, Pierre-Olivier Petrucci, Oleh Petruk, Jakub Podgorny, Juri Poutanen, Arne Rau, Agata Roszanska, Felix Ryde, Vincenzo Sapienza, Patrick Slane, James Steiner, Valery Suleimanov, Jiri Svoboda, Daniele Tagliacozzo, Antonella Tarana, Fabrizio Tavecchio, Roberto Taverna, Francesco Tombesi, Sergey Tsygankov, Youli Tuo, Roberto Turolla, Francesco Ursini, Alexandra Veledina, Jacco Vink, Martin C. Weisskopf, Fei Xie, Haocheng Zhang, Menglei Zhou

Cosmology and Nongalactic Astrophysics

Probing cosmological phase transitions with SKAO through nano-Hz gravitational-wave portal

Roman Pasechnik and António P. Morais

The recent evidence for a stochastic gravitational wave (GW) background at nano-Hz frequencies from pulsar timing arrays (PTAs) provides a strong science case for exploring cosmological histories and phase transitions at the Square Kilometer Array Observatory (SKAO). The latter cosmological events are of primary interest for physics of the early Universe associated with out-of-equilibrium and relaxation phenomena in the vicinity the quantum chromodynamics (QCD) epoch as well as those originating from dark sectors or other phenomena beyond the Standard Model of particle physics. Such a novel GW portal provides a complimentary access to particle physics phenomena that have so far escaped detection at particle colliders, and also probes fundamental aspects of out-of-equilibrium dynamics beyond the perturbation theory and their cosmological implications. This chapter aims at elucidating most interesting physics cases, theoretical models and approaches, as well as cosmological scenarios that are of particular relevance for future GW measurements at SKAO. We elaborate on how such measurements can deepen our understanding of particle interactions and violent processes in the early Universe, and discuss possible competitive advantages and complementarity of SKAO in this research compared to other experiments.
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