Physics and Society
Shannon entropy and complex network community detection to study electoral coalition behaviour at municipal scale
Andrea Lo Sasso
Traditional electoral analyses often rely on aggregate sociopolitical indicators or on macroscopic models grounded in statistical physics that treat election data at national level; however, these models have rarely been applied to local-level voting data, where the analytical complexity is substantially higher. In this study, we propose a framework rooted in statistical physics and complex network theory to investigate the fine-grained architecture of voting behaviour at the local scale. Leveraging a granular
dataset from the 2024 municipal and 2025 regional elections in Bari, Italy, we represent the urban electoral landscape as a complex network, in which polling sections are modelled as nodes connected by links that encode statistically significant correlations based on vote expression. For each coalition participating in the elections, community detection reveals geographically proximal clusters that transcend administrative boundaries. Furthermore, in order to quantify whether a coalition exhibits territorially homogeneous voting behaviour or, instead, is fragmented into distinct voting blocs, we adapt latent-ideology estimation and the information-theoretic Shannon
entropy $H$ to the intra-coalition scale. Our results indicate that winning coalitions exhibit significantly higher territorial fragmentation, and these findings suggest that, at the local level, electoral success is not driven by the maintenance of geographically uniform consensus rather than by the capacity to aggregate diverse and non-homogeneous voting blocs. This scalable, data-driven framework moves beyond simple geographic accounting, providing a robust tool for uncovering the structural dynamics of political idea clustering and coalition fragmentation in complex urban environments.
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Quantum Physics
Redesigning the linear–quadratic–Gaussian cost function for feedback cooling of a quantum harmonic oscillator
Shuma Sugiura, Koki Shiraishi and Masahito Ueda
Linear–quadratic–Gaussian (LQG) control is optimal only with respect to a prescribed cost function, the choice of which dictates the physical objective of the control. We consider feedback cooling of a continuously monitored
quantum harmonic oscillator by shifting the minimum of its trapping potential. In this setting, the physically relevant cooling objective can be defined as minimizing the oscillator's energy relative to the feedback-shifted potential. In contrast, conventional LQG control evaluates the energy from a fixed origin and thus fails to directly optimize this quantity. To address this problem, we introduce a redesigned cost function that explicitly accounts for the feedback-induced shift of the potential. We then derive the corresponding optimal feedback law and obtain an analytic expression for the minimum achievable steady-state
phonon occupation number. The redesigned LQG control achieves a lower occupation number than low-pass-filter (LPF) feedback formulated for the same cooling objective. While this improvement is minor at detection efficiencies currently attainable in experiments—indicating that LPF feedback already delivers near-optimal cooling performance—the advantage becomes pronounced as the detection efficiency approaches unity. In this regime, the redesigned LQG control provides an increasing advantage for reaching the motional ground state at a finite measurement strength. We clarify that the conventional and redesigned cost functions represent distinct control objectives rather than different implementations of the same optimization problem.
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High Energy Astrophysical Phenomena
RadioAstron space-VLBI imaging of the jet in M87: II. The parsec-scale structure at 4.8 GHz
Evgeniya V. Kravchenko, Tuomas Savolainen, Alexey S. Nikonov et al. (+9 more)
We present RadioAstron observations of the M87 jet obtained on 2014 February 4-5 at 4.8 GHz ($\lambda=6.2$ cm). The correlated signals between the 10-m space
antenna and ground-based
radio telescopes were detected up to projected baselines of $\thicksim3$\,Earth diameters (0.65~G$\lambda$). The orientation of the jet downstream of the core shifts northward, consistent with the long-term oscillating trend reported in other studies. An elliptical body mode of the Kelvin-Helmholtz instability can create the observed helical shape of the jet. The estimated wavelength of this instability mode suggests that its origin may be related to some processes in the
accretion disc. We present 1.7 - 4.8 GHz and 4.8 - 15.4 GHz spectral index maps showing flattening of the spectrum along the outer streamlines and along the jet spine. Simulations and analysis show that this spectral flattening is partially artificial and is a common systematic effect of the CLEAN procedure of VLBI imaging. The spectral index of the M87 jet is consistent with the optically thin emission, while its steepening can be produced by the propagation of the instability modes causing higher pressure regions near the jet boundary and in its interior.
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All authors Evgeniya V. Kravchenko, Tuomas Savolainen, Alexey S. Nikonov, Ilya N. Pashchenko, Elena E. Nokhrina, Petr A. Voitsik, Leonid I. Gurvits, Yuri Y. Kovalev, Jae-Young Kim, Mikhail M. Lisakov, Andrei P. Lobanov, Kirill V. Sokolovsky
Other Condensed Matter
Chern Insulators on a Twisted Klein Bottle
Rong Xiao and Y. X. Zhao
Recently, momentum-space nonsymmorphic
symmetries have attracted considerable
attention. However, their realizations typically rely on fine-tuning hopping phases to satisfy the required projective
symmetry algebras. Here, we show that such
symmetry algebras arise naturally on bipartite
lattices through the interplay of crystalline and sublattice
symmetries. Unlike previously studied cases, these
symmetry operators can anticommute with the
Hamiltonian and are therefore referred to as momentum-space nonsymmorphic
chiral symmetries. Although the free actions of these
symmetries reduce the Brillouin
torus to more elementary
manifolds, the resulting
manifolds are twisted in the Atiyah–Segal formalism. In particular,
chiral glide reflection (screw rotation) gives rise to a twisted Klein bottle (dicosm) in two (three) dimensions, and this twisting dramatically alters the topological classification. Unlike the untwisted Klein bottle, whose nonorientability forces the Chern number to vanish, the twisted Klein bottle can host nonzero Chern numbers, corresponding to even Chern numbers on the
torus. At open boundaries, the corresponding topological invariant manifests itself through
chiral edge states exhibiting a glide-reflection structure in energy–momentum space. Our results establish momentum-space nonsymmorphic
chiral symmetry as a new organizing principle for discovering and engineering topological phases beyond conventional crystalline classifications.
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Computational Physics
Van der Waals interactions in supercritical water under Earth's mantle conditions
Jiajia Huang, Rui Hou and Ding Pan
The properties of water under high pressure and high temperature (HP-HT) are critical in multiple geochemical processes in deep Earth. Ab initio molecular dynamics (AIMD) is a promising approach to study water under extreme conditions without any empirical parameters. However, the accuracy of AIMD simulations is determined by the exchange-correlation (XC) functional including the dispersion correction used in density functional theory calculations. While van der Waals (vdW) interactions are well known to be critically important for water under ambient conditions, the influence of the dispersion correction on the properties of HP-HT water as found in Earth's mantle remains largely unexplored. To address this, we carried out AIMD simulations for supercritical water at 1, 5, and 10 GPa, and 1000 K. We compared PBE, PBE-D3, RPBE-D3, and SCAN functionals, where D3 means Grimme's D3 dispersion correction. We compared the structural,
diffusion, and vibrational properties of water as computed with these XC functionals. Overall, the discrepancies between the functionals are reduced under extreme P-T conditions relative to ambient conditions. PBE and PBE-D3 exhibit higher
proton-transfer rates than RPBE-D3 and SCAN, suggesting that while vdW interactions do not significantly affect the water structure under extreme conditions, the oxygen-hydrogen bond strength does influence
proton transfer. Our results provide molecular-level insight into water in Earth's mantle and offer valuable guidance for selecting appropriate XC functionals in AIMD simulations of aqueous solutions under extreme conditions.
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Astrophysics of Galaxies
Galaxy-Galaxy Strong Lensing simulation with the GPU acceleration across surveys and multi-bands
Fucheng Zhong, Ruibiao Luo, Nicola R.Napolitano et al. (+3 more)
We present a GPU-accelerated, PyTorch tensor-based simulation framework designed to generate high-fidelity
galaxy-
galaxy strong
lensing images. By integrating synthetic Spectral Energy Distribution (SEDs), the pipeline accurately models the
redshift-dependent photometric properties of lens and source
galaxies, ensuring physical consistency across multi-band observations. The framework incorporates key observational parameters, including Point Spread Functions (PSF), magnitude limits, and zero points, to replicate specific survey conditions, thereby enabling robust cross-survey joint analyses. As an application, we simulate multi-band images for KiDS, LSST, and Euclid using identical lens model parameters, and employ a deep learning network to evaluate image deblending performance. In particular, the simulation leverages PyTorch to ensure full auto-differentiability and GPU acceleration, making it a highly efficient tool for advanced deep learning
algorithms that require gradient-based optimization beyond standard model training. Our framework achieves a speedup of approximately $\mathcal{O}(10^3)$ over traditional CPU-based pipelines, demonstrating the potential feasibility of joint gradient-based lens modeling across next-generation surveys.
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All authors Fucheng Zhong, Ruibiao Luo, Nicola R.Napolitano, Crescenzo Tortora, Valerio Busillo, Rui Li
Pattern Formation and Solitons
Two-Parameter Family of Nonlinear Dirac Equations With Scalar-Scalar plus Vector-Vector Interactions
Avinash Khare, Fred Cooper, John F. Dawson et al. (+1 more)
We obtain exact solutions of the nonlinear Dirac equation in $1+1$ dimensions of the form $\psi(x,t) = e^{-i\omega t} \psi(x)$ for scalar-scalar (SS) plus vector-vector (VV) interaction with interaction Lagrangian given by $$L_{I} = \frac{g^2}{\kappa+1}[(\bar{\psi} \psi)^{\kappa+1} +\frac{1}{p} (\bar{\psi} \gamma_\mu \psi \bar{\psi} \gamma^{\mu} \psi)^{\kappa+1}]$$ where $p > 0$ but arbitrary otherwise. We look for solutions with $0 < \omega < m$ where $\omega, m$ are frequency and mass, respectively. We find solutions for all values of $\omega$ in this range. We compute the charge $Q$ and the energy $E$ for each of the solitary wave solutions and explore the region in the ($p, \kappa$) parameter space in which solitary wave bound states exist (i.e., for which $E/Q < m$). We show that for all the cases while both $E$ and $Q$ depend on the coupling constant $g$, their ratio $E/Q$ is independent of $g$. We further find that in case $p\kappa \le 1$, the charge density for all the solitary waves have only single hump while for $p \kappa > 1$ there is a transition from double to single hump and we determine it as a function of $\omega/m$. We notice that for all $p$ there is a transition at $\kappa=2$ in the behavior of $E/Q$ as a function of $\omega$ which we speculate is related to the onset of instability of the solutions at $\kappa=2$. We obtain the nonrelativistic reduction of the two-parameter family to a non-relativistic modified nonlinear Schrödinger equation (NLSE) and discuss the stability of the single hump olitary waves in the domain of validity of the modified NLSE.
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All authors Avinash Khare, Fred Cooper, John F. Dawson, Avadh Saxena
Cosmology and Nongalactic Astrophysics
Constraints from big bang nucleosynthesis and cosmological observations on varying Higgs vacuum expectation value
Hongrui Feng, Yudong Luo, Toshitaka Kajino et al. (+2 more)
The
Higgs vacuum expectation value (VEV) alters both the electroweak and strong interaction rates. We study both effects on big bang nucleosynthesis (BBN) and seek concordance between observed
primordial abundances of light elements and cosmological constraints from CMB fluctuations and anisotropies. We find a strong negative correlation between
primordial 4He abundance and the
Higgs VEV. Consequently, using a 1.58% uplift of the
Higgs VEV during BBN from the current value, an agreement can be achieved among the new
primordial 4He abundance, observed by the EMPRESS group, Deuterium abundance determined from absorption lines in the Lyman-alpha forest along the line-of-sight of high-
redshift quasars, and the lithium abundance on the Spite plateau. This agreement requires a
baryon-to-
photon ratio different from the CMB determination, indicating the need for nonstandard cosmological
evolution between BBN and recombination epochs. We also demonstrate that a 0.2% uplift in the
Higgs VEV can partially alleviate the "
cosmic Li problem," keeping consistency with the CMB with remaining discrepancy potentially accounted for by
stellar depletion mechanisms.
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All authors Hongrui Feng, Yudong Luo, Toshitaka Kajino, Bao-Hua Sun, Tatsushi Shima
Astrophysics of Galaxies
A Detailed GASKAP-HI View of Shells and Loops in the Magellanic Bridge
Shin-Jeong Kim, Antoine Marchal, N. M. McClure-Griffiths et al. (+19 more)
We present 8 pc-scale GASKAP-HI observations of an HI shell (diameter \sim130 pc) associated with the H\alpha shell DEM171 in the Magellanic Bridge. The Bridge's diffuse, HI-dominated environment, with minimal
galactic shearing and fewer overlapping
star-forming regions, provides an ideal environment to study cold gas formation driven by
stellar feedback. To investigate the HI multi-phase structure and kinematics of the shell, we perform Gaussian decomposition of HI line profiles. We identify cold HI components with velocity dispersions \sigma < 2.5 km/s located within the shell. Complementary Herschel far-infrared (FIR) 250\micron and H\alpha maps show that while the central cavity is ionized, the shell walls contain cold HI, molecular gas, and
dust, suggesting that
stellar feedback has promoted cold gas formation or swept pre-existing cold gas into the shell walls. We also identify cold HI clumps outside the shell tracing a larger-scale structure, MB-Loop I. To investigate the large-scale context, we apply a
Fourier transform method to HI emission-line profiles to map the lower limit of cold-gas column densities across a section of the Bridge, revealing structures from large loops to smaller shells. The association between MB-Loop I and the HI shell suggests that cold HI gas may pre-exist before shell expansion. Finally, the shell exhibits asymmetric expansion, with a preferred orientation roughly perpendicular to the arc along MB-Loop I. Our results show that cold HI gas exists across a wide range of spatial scales in the Magellanic Bridge, highlighting the dynamic interplay that shapes the surrounding interstellar medium.
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All authors Shin-Jeong Kim, Antoine Marchal, N. M. McClure-Griffiths, J. R. Dawson, James Dempsey, Helga Dénes, John M. Dickey, Steven J. Gibson, Katie Jameson, Ian Kemp, Bumhyun Lee, Min-Young Lee, Adam K. Leroy, Callum Lynn, Yik Ki Ma, Marc-Antoine Miville-Deschênes, Eric G. M. Muller, Claire Murray, Hiep Nguyen, Nickolas Pingel, Hye-Jin Park, Jacco Th. van Loon
Optics
Wavelength-Multiplexed Nonlinear Computing with a Single-Layer Diffractive Optical Processor
Yongkang Cheng, Che-Yung Shen, Yuntian Wang et al. (+2 more)
Diffractive optical processors provide a promising platform for high-throughput, low-latency analog computing by exploiting engineered wave propagation to transform optical fields. However, implementing nonlinear mappings in optical hardware remains challenging. Here, we introduce a wavelength-multiplexed encoding-and-decoding (E+D) diffractive processor that exploits multiple illumination wavelengths to enhance the nonlinear function-approximation capability of a compact single-layer diffractive architecture, without cascading multiple diffractive layers or increasing the trainable degrees of freedom. Under sequential wavelength scanning, each wavelength-detector channel implements a distinct nonlinear function at the output of the diffractive processor. Numerical simulations using 100 wavelength channels and 10,000 spatial detector regions at the output of the diffractive processor demonstrate the implementation of one million distinct nonlinear functions through wavelength multiplexing. We also demonstrate a simultaneous multiwavelength illumination configuration in which the E+D diffractive processor performs wavelength-division multiplexing and nonlinear function approximation concurrently. This multiwavelength illumination configuration is experimentally validated by optically implementing 64 distinct nonlinear functions under simultaneous illumination at eight wavelengths from 495 to 635 nm. Through numerical simulations and visible-light experimental demonstrations, our results indicate that this wavelength-multiplexed nonlinear function approximation framework provides a scalable route toward compact, high-capacity diffractive processors for large-scale analog optical computing and optical information processing.
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All authors Yongkang Cheng, Che-Yung Shen, Yuntian Wang, Shiqi Chen, Aydogan Ozcan
General Relativity and Quantum Cosmology
Horizon–orbit scale competition underlying chaos bound violation for spinning particles
Deyou Chen, Lifang Li, Chuang Yang et al. (+1 more)
In this paper, we investigate the chaos bound through the local radial instability of charged spinning test particles on unstable circular orbits in the black-bounce–Kerr–Newman spacetime. Our results show that violation of the bound is governed by the competition between the local orbital-instability scale and the surface
gravity scale, with variations of the black hole background and the particle dynamics providing two complementary routes to the same threshold crossing. Background variations affect both scales and can drive the system into the bound-violating regime when the surface
gravity is suppressed more strongly than the orbital instability. At fixed background, by contrast, the surface
gravity remains unchanged, and the transition across the threshold is driven by changes in the unstable orbit dynamics induced by the particle parameters. The background-controlled and probe-dynamics-controlled routes therefore represent two realizations of a unified horizon–orbit scale competition rather than independent mechanisms.
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All authors Deyou Chen, Lifang Li, Chuang Yang, Kangqiao Liu
Physics and Society
Overlap and topology shape synergy in collective knowledge integration
Daeseong Kim and Masato S. Abe
Collective discovery often requires the integration of partially overlapping knowledge, yet the beneficial level of overlap and the role of background
topology remain unclear. We model individual knowledge as connected subnetworks of a common knowledge space and distinguish internal synergy, in which integration shortens paths between concepts, from external synergy, in which an unknown concept connects to the shared and all individual-specific regions. Internal synergy peaked at intermediate overlap across random, scale-free, modular, and small-world backgrounds, reflecting a balance between complementarity and common ground. External synergy was strongly
topology dependent and was most pronounced when small-world structure maintained overlapping local boundaries. Rewiring separated the total supply of synergistic nodes from their concentration at the accessible boundary; moderate rewiring could increase structural opportunities while dispersing them among more external alternatives and reducing their discovery. Group-size effects on internal synergy depended on
topology, whereas strict higher-order external synergy declined as its all-region criterion became more restrictive. Collective discovery therefore depends jointly on knowledge overlap and on how complementary knowledge regions are organized within the surrounding knowledge space.
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Mesoscale and Nanoscale Physics
Landscape geometry of Majorana zero modes in inhomogeneous superconductors
Guo-Jian Qiao, Zhi-Lei Zhang, Kang Xu et al. (+1 more)
Spatial inhomogeneity breaks translational
symmetry and prevents conventional Bloch-band topological invariants from directly answering a practical question: do Majorana zero modes survive in a given inhomogeneous superconducting device? In this Letter, we develop a real-space landscape approach to address this question. Rather than solving the zero-energy equation as a boundary-value problem, we treat the spatial coordinate as an
evolution parameter and recast the equation as a first-order dynamical system. A Majorana zero mode is then identified with a stable trajectory that satisfies the physical boundary condition and approaches the origin at large distance. We show that the landscape geometry fixes the dimensions of the stable and unstable subspaces, while the intersection of the stable subspace with the physical boundary subspace determines the number of Majorana zero modes. In the homogeneous limit, the topological phase transition is manifested as a
geometric transition of the landscape. Applied to one-dimensional spinless $p$-wave
superconductors and nanowire–
superconductor systems, the approach yields sufficient bounds on both the amplitude and spatial gradient of the inhomogeneity, providing quantitative criteria for the design of Majorana devices.
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All authors Guo-Jian Qiao, Zhi-Lei Zhang, Kang Xu, C. P. Sun
Accelerator Physics
Ultralow Mean Transverse Energy and High Quantum Efficiency Cryogenic Bialkali Photocathode for MHz-Repetition-Rate Electron Sources
D. Wang, S. Liu, J. Liu et al. (+15 more)
Simultaneously achieving high
quantum efficiency (QE), ultralow mean transverse energy (MTE), and robust long-term operation under conditions relevant to continuous-wave (CW) X-ray free-electron
lasers (XFELs) remains a central challenge for
semiconductor photocathodes. This challenge arises from the trade-off between QE and MTE, as well as the difficulty of maintaining stable operation in high-field CW electron guns. Here we demonstrate a cryogenic K2CsSb photocathode that simultaneously achieves high QE, ultralow MTE, and robust long-term operation in a CW gun under XFEL-relevant operating conditions. Under cryogenic operation, the photocathode achieves an MTE of 50 meV while sustaining a QE of 5.4%. Milliampere-level CW current, including operation at 5 mA, was demonstrated together with an approximately 20-day operational history. The observations are consistent with improved carrier survival and/or surface escape in photocathodes prepared using the optimized recipe. These results show that the practical QE-MTE trade-off can be substantially mitigated in cryogenic bialkali photocathodes and provide a practical pathway toward high-brightness electron sources for CW XFELs and energy-recovery linacs.
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All authors D. Wang, S. Liu, J. Liu, Y. Dai, Z. Hong, J. Wang, Y. Shi, M. Tai, L. Feng, H. Xu, L. Lin, F. Wang, F. Zhu, J. Hao, S. Quan, K. Liu, H. Xie, S. Huang
Materials Science
Nitrogen based electride superconductor Nb5Ir3N under pressure: multifunctional physical properties from DFT based first-principles investigation
M. Abdul Hadi Shah, J.H. Abir and S.H. Naqib
Discovery and study of superconducting electrides have opened new avenues in condensed matter physics, driven by their intriguing multifunctional features spanning ambient and high-pressure regimes. This work investigates the ternary nitride
superconductor Nb5Ir3N under pressure ranging from 0 to 20 GPa via density functional theory based simulations. Estimated structural parameters agree well with the available data, confirming their reliability and supporting the validity of this analysis. Negative formation enthalpy, together with evaluated elastic constants and
phonon spectra, confirm the structural, thermodynamic, mechanical, and dynamical stability of Nb5Ir3N over the entire pressure range. Pressure dependent elastic constants and polycrystalline elastic
moduli are investigated. The compound is categorized as ductile in light of estimated mechanical indices. Elastic anisotropy factors indicate that Nb5Ir3N remains anisotropic, with the degree of anisotropy gradually decreasing as pressure increases. Electronic band structure and density of states are calculated with and without
spin orbit coupling to investigate its influence on the electronic structure. Calculated optical response reveals substantial intraband contributions in the low energy region, intense ultraviolet absorption, and strong reflectivity. The spectra exhibit optical anisotropy and a broadening at higher pressures. Pressure induced superconducting features are also discussed qualitatively.
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Computational Physics
Fully differentiable framework for inverse identification of geometry and material parameters with application to determining stress-free configuration of soft tissues
Hyunoh Bae, Tianyi Hu, Adrian Buganza Tepole et al. (+1 more)
Medical images of soft tissues typically depict loaded configurations rather than true unloaded (stress-free) states, which can bias biomechanical simulations and inverse material identification. A gradient-based inverse finite element framework is presented that jointly reconstructs an effective unloaded reference geometry and estimates hyperelastic material parameters from two or more observed deformed configurations. The formulation is fully differentiable and leverages exact end-to-end gradients to enable unified, simultaneous optimization of geometry and constitutive parameters. The objective function combines a nodal-position misfit with a deformation-gradient-based mismatch term, improving robustness under large deformations.
Benchmark studies quantify the influence of loading diversity and observation count and demonstrate reduced sensitivity to poor material initialization. Finally, application to an MRI-derived breast model shows accurate recovery of the unloaded configuration and constitutive parameters from multiple
gravity-loaded states. The framework provides a unified and scalable tool for inverse biomechanics with potential applications in personalized modeling, elastography, and
surgical planning.
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All authors Hyunoh Bae, Tianyi Hu, Adrian Buganza Tepole, Hector Gomez
General Relativity and Quantum Cosmology
Symmetry preservation in black hole quasinormal mode spectra
Han-Wen Hu, Chen Lan, Zong-Kuan Guo et al. (+1 more)
We establish a general relation between
symmetries of gravitational theories and black hole (BH) quasinormal mode (QNM) spectra. We show that a
symmetry implies isospectrality when it induces a bijection between the corresponding QNM boundary value problems. However, conformally related BHs have been reported to exhibit both conformal factor dependent and independent QNM spectra. To resolve this issue, we develop a reduction scheme for higher order perturbation equations. Applied to pure Weyl
gravity, it yields the complete axial spectrum of Schwarzschild, including Regge-Wheeler and
spin-1 branches. Our results show that these seemingly contradictory conclusions result from differences in the perturbation dynamics or in the boundary conditions.
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All authors Han-Wen Hu, Chen Lan, Zong-Kuan Guo, Rong-Gen Cai
High Energy Physics (Phenomenology)
Cat's cradle diagrams for substructure studies
Peter Skands
We propose Cat's Cradle diagrams as a framework to analyse the perturbative accuracy of gauge
quantum field theories across different kinematic regions, interpolating between the power countings of fixed-order perturbation theory and soft-collinear resummation. We propose a simple intermediate counting aimed at quantifying parametric accuracy for resolved jet substructure, nested so that $N^nLO \subset N^nLJ \subset N^{n+1}LL$. We show that the resolved jet-substructure power counting, $N^nLJ$, emphasises contributions that are important for resolved substructure but which are lumped together with less dominant terms in both of the two other countings. It may therefore furnish a complementary quantification of relative parametric accuracy in a kinematic region "midway" between the hard (fixed-order) and soft-collinear (resummation) regimes. We discuss practical applications to parton showers, in the context of a hard process with a characteristic hard scale of order 200 GeV.
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Computational Physics
Improved lattice Boltzmann method for conjugate magnetohydrodynamic simulations
Jun Li, Wai Hong Ronald Chan and Kun Ting Eddie Chua
In the simulation of conjugate magnetohydrodynamic (MHD) flows, where a moving conducting fluid dynamically interacts with bounding conducting walls under the influence of an externally imposed
magnetic field, resolving the electrical conductivity transition across the fluid-solid interface introduces significant numerical challenges. In problems with high
magnetic Reynolds numbers, it is required to solve the full
magnetic induction formulation that has a curl-of-curl term for the
magnetic diffusion, which is simplified to a divergence term in the original vector-valued
lattice Boltzmann method (LBM). The resulting LBM scheme is valid for simulating fluid domains with a constant conductivity where its bounding solid walls are modelled using appropriate boundary conditions. The current study shows that this scheme is also valid for two-dimensional conjugate MHD simulations where the
magnetic field component with non-zero gradients is perpendicular to the conductivity gradient. For general conjugate MHD simulations, we improve the LBM scheme by considering the difference between the curl-of-curl term and the simplified divergence form, which is treated as a source term in the LBM
evolution algorithm and computed using an efficient LBM discretisation scheme. The improved LBM scheme automatically satisfies the required conjugate constraints at the fluid-solid interface as a volume integral inside two adjacent boundary layers. The accuracy of the improved LBM scheme is verified by piecewise analytical solutions in
benchmark problems with an abrupt conductivity jump across the fluid-solid interface.
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Atmospheric and Oceanic Physics
Tropospheric Ozone Formation Potential and Related Design Considerations for Radiative Coolers
Jyothis Anand, Piero Di Carlo, Eleonora Aruffo et al. (+2 more)
Recently, radiative coolers have been widely explored for reducing cooling loads or lowering temperatures in buildings, and at urban scales as a heat-mitigation measure. However, the potential impacts of radiative cooler deployment on the chemical composition of the atmosphere remain largely unexplored. A defining feature of recently-designed radiative coolers is their high ultraviolet (UV) reflectance, which is required for sub-ambient cooling under strong sunlight. Yet, wide adoption of such UV-reflective radiative coolers could substantially increase the UV actinic flux in the atmosphere above. This, in turn, may affect tropospheric ozone concentrations, particularly in urban atmospheres with high NOx concentrations. Here, as a case study, we use a 0-dimensional photochemical box model, constrained by field measurements of meteorological conditions and chemical concentrations in the urban environment of Houston, Texas, to explore the potential impact of the widespread use of UV-reflective radiative coolers on ozone concentrations. Our calculations show that complete deployment of radiative coolers may increase tropospheric ozone levels by as much as 30% during specific meteorological conditions in Houston. Informed by the wavelength-dependent modelling results, we propose specific designs, namely pigmented radiative coolers with different UV reflectances, and UV-absorptive visible-reemitting fluorescent radiative coolers, that could minimize negative ozone formation while retaining appreciable cooling performance. Our results motivate further study on the effects of widespread deployment of radiative cooling designs like superwhite roof paints on air quality, and materials that simultaneously minimize adverse photochemical impact and maximize cooling performance.
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All authors Jyothis Anand, Piero Di Carlo, Eleonora Aruffo, Paul E. Ohno, Jyotirmoy Mandal
Statistical Mechanics
Phillip M. Rauscher
We present a general method for estimating
entropy differences between arbitrary probability distributions using
stochastic interpolants. The marginal distributions which bridge the base and target obey a continuity equation, which allows a straightforward calculation of the
entropy difference in terms of an inner product of the probability flow velocity and score fields. This formulation has several advantages: (i) no computationally expensive divergence calculations of either field are required, (ii) the score field need not even be learned directly if model transferability is not required, and (iii) on-the-fly estimates are produced nearly for free during training. When tractable base distributions are chosen (e.g. Gaussian chain, ideal gas, etc.), statistical thermodynamic
entropies are then immediately recovered. Notably, the analysis relies only on the definition of the Gibbs-Shannon
entropy, rather than any particular statistical mechanical ensemble, so that generalized non-
equilibrium entropies may be computed. The method is demonstrated on several systems of increasing complexity: (i) a 40-dimensional Gaussian mixture model, (ii) the classical XY model of N
spins arranged in one dimension, (iii) the 13-atom Lennard-Jones cluster, and (iv) an active Brownian
polymer.
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Instrumentation and Methods for Astrophysics
Transitioning from ADS to SciX to Serve 21st Century Astronomy
Jennifer Lynn Bartlett, Suze Kundu, Alberto Accomazzi et al. (+1 more)
For decades, the NASA Astrophysics Data System (ADS) has been the foundational digital library for astronomy. As ADS becomes the Science Explorer (SciX), the team prioritizes preserving this trusted experience while increasing their support for space and Earth sciences broadly, without diluting its commitment to astrophysics.
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All authors Jennifer Lynn Bartlett, Suze Kundu, Alberto Accomazzi, Michael J. Kurtz
Mesoscale and Nanoscale Physics
Takumi Funato and Takeo Kato
We develop a microscopic theory of
spin-torque
ferromagnetic resonance (ST-FMR) in nonmagnetic-metal/
ferromagnetic-metal
heterostructures. Tracing out the conduction-electron degrees of freedom in the FM, we derive an effective interfacial exchange coupling between the localized
spins and the conduction electron
spins in the adjacent electron system. Based on this interaction, we calculate the current-induced driving torque, resonance-frequency shift, damping modulation, and resulting dc voltage. As a concrete example, we apply the formulation to a disordered Rashba two-dimensional electron gas and demonstrate that the ST-FMR spectrum reflects the dynamical
spin responses of the adjacent electron system. Our formulation applies to a broad class of
heterostructures and establishes a unified microscopic framework connecting ST-FMR spectra directly to the electronic
spin responses of adjacent systems.
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High Energy Astrophysical Phenomena
FRB 20250607A: Weirder Than Fiction
J. C. F. Balzan, A. Bera, C. W. James et al. (+4 more)
We present a detailed analysis of FRB 20250607A, a two-component FRB detected by the CRAFT survey which exhibits several unusual component-dependent properties, including apparent differential DM, circular polarisation, and time-resolved RM, together with a polarisation-angle (PA) swing that persists through the scattering tail. The scattering timescale and scintillation bandwidth are inconsistent with a single thin-screen origin, placing the dominant scattering screen within $\lesssim61$ kpc of the FRB source. The lack of PA flattening in the scattering tail is a behaviour not previously reported in an FRB or
pulsar and difficult to reconcile with a simple propagation origin. We find no statistically significant differential DM between the two components despite an apparent, and visually obvious, difference in their dispersion, indicating that current uncertainties may be overly conservative. If this apparent differential DM is true, it implies a substantial difference in electron column density between the component sightlines. Two further CRAFT FRBs, FRB 20190611B and FRB 20210407E, show similarly large component-dependent electron-column differences, corresponding to electron-density contrasts consistent with
plasma local to a
neutron-
star magnetosphere. We find no evidence for generalised Faraday rotation, and FRB 20210407E shows component-dependent PA structure. Taken together, these results suggest that the observed DM, circular polarisation, and PA behaviour may arise from differing sightlines through an inhomogeneous or evolving magnetosphere rather than from independent phenomena. Multi-component FRBs therefore provide a sensitive probe of
plasma structure local to their progenitors.
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All authors J. C. F. Balzan, A. Bera, C. W. James, B. W. Meyers, A. T. Deller, R. M. Shannon, Z. Wang
Computational Physics
A consistent and conservative Phase-Field method for compressible multiphase flows with the six-equation model
Ziyang Huang
In the present study, the consistent and conservative Phase-Field method is extended to the six-equation model for compressible multiphase flows. Based solely on the conservation laws and the second law of thermodynamics, the six-equation model with the Phase-Field mechanism is first derived. In addition to satisfying Galilean invariance and consistency of reduction, the model is general to admit an arbitrary number of phases with different formulations of the Phase-Field mechanism. The isobaric closure by the pressure relaxation and the incompressible limit of the proposed model are analyzed. The derivation and analysis identify additional terms arising from the Phase-Field mechanism, which are absent from previous studies. The consistent and conservative numerical approach is adapted to the proposed six-equation model with moderate modifications, retaining the interfacial
equilibrium condition, conservation, and flexibility and robustness of incorporating different formulations of the Phase-Field mechanism with bound preservation. As the new component of solving the six-equation model, both the pressure and pressure-temperature relaxations are theoretically analyzed in a general multiphase setup, with a proof of the existence and uniqueness of a thermodynamically admissible solution for these two relaxations. Various two-phase compressible flow
benchmarks are performed to demonstrate the method, and good agreement with exact solutions is achieved.
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Quantum Physics
Remote Adiabatic Controlled-Z Gate between Distant Superconducting Qubits
Si-Yu Xu, Yi-Rong Jin, Wen-Gang Zhang et al. (+1 more)
Direct entangling gates between spatially separated
qubits are a key capability for modular
quantum computing. They enable nonlocal
quantum circuits to be executed across different processor modules, thereby alleviating single-chip scaling constraints and expanding the effective connectivity of the system. Here, we propose and numerically investigate a remote adiabatic controlled-Z gate between two frequency-tunable superconducting
qubits connected by a multi-mode coaxial cable. The cable-mediated interaction enables the gate to be implemented without additional tunable couplers, preserving a simple
circuit architecture. For a 30-cm cable, simulations incorporating ten standing-wave modes yield an optimized gate infidelity of $4.71\times10^{-7}$ with a duration of 376.7 ns in the absence of decoherence. The gate maintains high fidelity under
qubit-frequency fluctuations and millimeter-scale cable-length variations. Calculations for 50- and 100-cm cable situations demonstrate its potential for even larger cryogenic systems. These results provide a promising approach to extending high-fidelity
quantum operations beyond individual chips and toward scalable, interconnected superconducting
quantum processors.
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All authors Si-Yu Xu, Yi-Rong Jin, Wen-Gang Zhang, Hai-Feng Yu
Instrumentation and Methods for Astrophysics
David R. Gozzard, Fiona H. Panther and Andrew G. White
Classically, the angular resolution of a
telescope is limited by its diffraction limit: the ratio of its observing wavelength to its diameter. Developments in
quantum information theory over the past decade have uncovered
quantum-optimal measurement methods that enable super-resolution imaging beyond the diffraction limit, and many laboratory-scale demonstrations of these methods have been performed over the past decade, culminating in the recent first on-sky demonstration of
quantum-enhanced astronomical imaging. In this Review, we detail the current progress and achievements of these theoretical and experimental results, discuss the astronomical science cases motivating the development of higher resolution
telescopes, summarise the technological challenges facing the practical application of
quantum imaging technologies to astronomy, and present a
vision for the realization of
quantum telescopes with imaging resolutions orders of magnitude better than current observatories.
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Classical Physics
Harmonic Vector Fields and Betti Numbers in Bounded Three-Dimensional Electromagnetic Domains
Wei Jiang and Jie Liu
The
topology of a bounded three-dimensional domain can strongly affect electromagnetic fields. In a topologically complex domain, a curl-free field may not have a globally single-valued scalar potential and a divergence-free field may also fail to have a global vector potential. These topological effects lead naturally to harmonic vector fields in the Helmholtz decomposition. This paper gives a
geometric and constructive study of such fields using vector analysis, circulation integrals, cutting surfaces, scalar Laplace problems, Stokes'
theorem, and Green's identity. The first Betti number is interpreted through independent handle-type circulations, whereas the second Betti number counts enclosed voids. Direct proofs are given for the dimensions of the Neumann and Dirichlet harmonic-field spaces. The analysis is also extended to anisotropic lossless media. The results provide a simple topological interpretation of harmonic fields and physical DC modes in bounded electromagnetic resonators.
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High Energy Physics (Theory)
Vacuum Structure of Maximally Supersymmetric Two-Dimensional Gauge Theories
Richard Eager
We study the
vacuum structure of maximally supersymmetric Yang–Mills theory in two dimensions. At low energies, the theory decomposes into superselection sectors consisting of orbifold conformal field theories and massive
vacua. The sectors are indexed by the cuspidal data appearing in Lusztig's generalized Springer correspondence. This suggests an enhancement of the correspondence to holomorphic factorization
algebras.
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Materials Science
Disentangling Strain and Ti3+ Contributions to the Anomalous Hall Effect in Epitaxial RuO2 Films
S. G. Jeong, A. Santhosh, S. Lee et al. (+7 more)
The anomalous
Hall effect (AHE) reported in epitaxial RuO2/TiO2 has been attributed to a strain-stabilized
magnetic state, but strain can be entangled with Ru-Ti intermixing and interfacial charge redistribution, which can produce Ti3+ and potentially localized moments. Here, we disentangle these contributions using Ti-alloyed RuO2
heterostructures in which abundant Ti3+ states are retained while epitaxial strain is independently changed. The strained and relaxed films have nearly identical Ti/Ru compositions and comparable Ti3+ fractions, yet a pronounced nonlinear AHE appears only in the coherently strained film, while the relaxed
heterostructure exhibits an almost linear
Hall response. Spectroscopic ellipsometry further shows that the AHE-active strained state is accompanied by a reconstruction of the itinerant electronic response, including enhanced
metallicity and longer carrier relaxation times. These results show that Ti3+ formation alone is insufficient to generate the anomalous
Hall state and identify epitaxial strain, through its modification of the itinerant RuO2 electronic structure, as the dominant control parameter.
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All authors S. G. Jeong, A. Santhosh, S. Lee, S. Sheikh, U. M. Jayathilake, T. -L. Lee, T. Low, A. X. Gray, S. A. Chambers, B. Jalan